Information

20.1: Prelude to Plant Reproduction - Biology

20.1: Prelude to Plant Reproduction - Biology



We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

Plants have evolved different reproductive strategies for the continuation of their species. Some plants reproduce sexually, and others asexually, in contrast to animal species, which rely almost exclusively on sexual reproduction. Plant sexual reproduction usually depends on pollinating agents, while asexual reproduction is independent of these agents. Flowers are often the showiest or most strongly scented part of plants. With their bright colors, fragrances, and interesting shapes and sizes, flowers attract insects, birds, and animals to serve their pollination needs. Other plants pollinate via wind or water; still others self-pollinate.


IGCSE & GCSE Biology by D. G. Mackean

Here you will find the answers to the 'in-text' questions which occur in IGCSE Biology (2nd edition) and GCSE Biology (3rd edition) by D. G. Mackean, published by Hodder Education, London, UK.

Chapter 1. Cells and tissues

1. a Cytoplasm, nucleus, cell membrane
b Chloroplasts
2. The cell membrane controls substances entering or leaving the cell
3. The red cell has no nucleus
4. The cell membrane is formed from living cytoplasm the cell wall is formed from non-living cellulose
5. The section must have been taken above the nucleus
6. a The magnification in Figure 1.1 is x 60, so presumably x100 would be effective
b The wide part of the cell is 7mm. This is 700 times larger than the real cell, so the cell would measure 7 /700 i.e. 0.01 mm
7. Count the nuclei

1. (i) animal cells d, a
(ii) plant cells d, a, b, c
2. (a) In the midrib and veins (sieve tubes)
(b) Palisade cells, epidermis, guard cell, (a vessel is formed by many cells)

1. Lungs (organ), root hair (cell), mesophyll (tissue), multipolar neurone (cell)
2. (Fig.36.13) Bone and muscle, (Fig. 19.9) muscle, nerve tissue, bone
3. a (Organs) The definition on p.7 says an organ is &lsquoa structure with a special function&rsquo so all the labelled structures in Fig. 11.5 could be organs. The exceptions might be the mouth, the pyloric sphincter, the rectum and the anus
b (System) The digestive system


Famous Marine Biologists and a gist of their Contributions

Adolf Appellöf (1857-1921)

Jakob Johan Adolf Appellöf was a Swedish marine zoologist. In 1877, Adolf Appellöf graduated from the famous University of Uppsala, earned his doctorate in zoology, and took up a temporary position as a lecturer in zoology at the same university. Later on, he took up a position of a conservator at the Museum of Bergen, Norway.

With the help of a Bunsow, a sawmill magnate, Adolf Appellöf founded Klubban Biological Station of University of Uppsala. This institute specialized in the study of marine biology and was situated on the western coast of Sweden. He was the member of both the Royal Swedish Academy and the Royal Society of Sciences in Uppsala. His research on cephalopods (mollusks) was a significant contribution to the field of marine biology.

Samuel Stillman Berry (1887-1984)

Would you like to write for us? Well, we're looking for good writers who want to spread the word. Get in touch with us and we'll talk.

He was a U.S. marine zoologist. Samuel Stillman Berry graduated from the University of Stanford (1909) and then pursued M.S. from Harvard. He specialized in the study of cephalopods and received his doctorate on the same subject from the Stanford in the year 1913.

For the next five years he worked as a research assistant at the Scripps Institution for Biological Research, California. Later, he continued his research in malacology, as an independent researcher. The aspirants of marine biology currently use his research work as a basis and/or reference for their studies. He has written over 200 articles on malacology, and has discovered 401 mollusc taxa. His works provide insight into various features of chitons, cephalopods, and snails.

Carl Chun (1852-1914)

He was a renowned German marine biologist. He graduated in zoology from the University of Leipzig. In 1892, he was appointed as a professor in the same university. Carl Chun initiated and headed the German deep-sea expedition on August 1, 1898. He, along with his team members, explored the seas around the continent of Antarctica, and also, the Bouvetøya and the Kerguelen islands. His research subjects were cephalopods and plankton. Carl Chun discovered, and also named, a species of squid, the Vampire Squid.

Jacques-Yves Cousteau (1910-1997)

He was a French researcher and ecologist who studied the lives of underwater animals and plants. He was basically a French naval officer, who was also a popular filmmaker, author and researcher. He is popularly known as Captain Cousteau or Jacques Cousteau. He, along with Emily Gagnan (French engineer), developed the first open-circuit scuba diving equipment known as “Aqua-Lung”

He was a pioneer of marine conservation and a member of L’Academie francaise. Captain Cousteau founded the Underseas Research Group, at Toulon, and the French office of Underseas Research, at Marseille. He was also the director of the Oceanographic Museum of Monaco.

Anton Dohrn (1840-1909)

He was a German marine biologist. He had mastered not only medicine but also zoology. He received his doctorate in 1865. In 1874, he founded “Stazione Zoologica” in Naples. He was the director of this organization until his death. A thesis which proposed the theory of the origin of vertebrates, known as Der Ursprung der Wirbelthiere und das Princip des Functionswechsels: Genealogische Skizzen, was submitted by him in 1875.

Sylvia Earle (1935-present)

She is an American oceanographer and a renowned marine biologist. Sylvia graduated from the University of Florida in 1955 and went on to achieve her master’s degree from the same university. She received her doctorate from Duke University in 1966. She was a curator of phycology at the Academy of sciences, California, a research associate at University of Berkeley, Harvard University, and also a Radcliffe Institute scholar.

In 1970, she headed the first women’s team of aquanauts for a project known as the Tektite Project. She was the chief scientist for National Oceanic and Atmospheric Administration, US. Currently, she is a deep sea explorer-in-residence of National Geographic channel. Sylvia Earle has authored over 125 books on marine science including “Exploring the Deep Frontier”, “The Atlas of the Ocean”, and so on.

Bruno Hofer (1861-1916)

He was a German marine scientist and an environmentalist, who was born in East Prussia. He completed his studies in Natural Sciences in Königsberg, and worked as a lecturer in the Zoological Institute of Munich. He carried out research and studies in limnology. Bruno studied the different fish types and their habitation. During his lifetime, he was the director of the Royal Bavarian Research Station for Fisheries. Hofer also served as the vice-president of the Bavarian Association of Fishermen, and as the editor of the magazine “Allgemeine Fischereizeitung”. Hofer specialized in fish parasitology and pathology.

William Leach (1790-1836)

He was an English marine biologist and a renowned zoologist. He was a qualified medical practitioner who was passionate about marine life and zoology. He worked as a research assistant and a librarian in the Zoological Department at the British Museum. During his tenure at the British Museum, he was in charge of the natural history department.

William Leach researched widely on crustaceans and mollusks. Insects, birds, and mammals also comprised his field of study. “Zoological Miscellany”, “Synopsis of Mollusca of Great Britain”, and a systematic catalog of the “Specimens of the Indigenous Mammalia and Birds”, that are preserved at the British Museum, are some of his popular works.

Nicholas Miklouho-Maclay (1846-1888)

He was a notable Russian anthropologist, ethnologist, and marine biologist, who graduated from St. Petersburg University. In Italy, he met Anton Dohrn, who instilled the idea of starting a research station. Maklai shifted his base from Russia to Australia. With the help of the Linnean Society, he founded a zoological center, known as the Marine Biological Station, in Watsons Bay, Sydney. This was the first marine biological research institute in Australia.

John Murray (1841-1914)

He was a famous Scottish-Canadian oceanographer and marine biologist. He graduated from the University of Edinburgh. He is known as the “Father of Modern Oceanography”. Murray coined the term oceanography. John Murray first brought to light the existence of the mid-Atlantic ridge and oceanic trenches. One of his major contributions to marine biology was the “Bathymetric” survey of 562 freshwater lochs of Scotland. During his lifetime, he wrote many articles and journals on oceanography.

Harald Rosenthal (1937-present)

He is a noted German hydrobiologist. Rosenthal completed his education from Freie Universitat, Berlin. He later studied hydrobiology and fishery in Hamburg. Rosenthal presented a thesis on mass rearing of larval herring. He is acknowledged for his research in fish farming and ecology. Harald Rosenthal focused on aquaculture and ballast water. He is the founder and president of the World Sturgeon Conservation Society, and is also, an active member of the Royal Swedish Academy of Sciences.

Ruth Turner (1915-2000)

She was a renowned marine biologist who researched widely on “Teredo”, a genus of mollusks, that wreaks havoc on docks and boats. She graduated from Bridgewater State College, and went on to earn a doctorate from Harvard. Ruth has published over 200 scientific articles, and a book. Turner specialized in shipworm research. Ruth Turner was the first female marine biologist to make use of Alvin, a deep ocean research submarine.

Charles Thompson (1830-1882)

He was a Scottish marine biologist, who was the chief scientist on the Challenger Expedition. Charles Thompson specialized in the field of deep sea biological conditions. His interest in crinoids prompted him to persuade the Royal Navy to allow him the usage of HMS Lightning and HMS Porcupine, for deep sea dredging.

Charles threw light on such facts as the existence of marine life (vertebrates and invertebrates) at 1200 m below the ocean surface. Another fact brought to light was the considerable variability of deep-sea temperature. The book, “The Depths of the Sea”, was written by Charles Thompson. He was closely associated with John Murray, the oceanographer.

Alister Hardy (1896-1985)

He was a marine biologist, who was an expert on marine ecosystems and zooplankton. Alister Hardy was one of the chief scientists on the RRS Discovery, as part of the Discovery Investigations. He specialized in the study of marine mammals such as whales. He designed and built the “Continuous Plankton Recorder” (CPR), to collect plankton samples. His research of plankton is continued by an organization called the Sir Alister Hardy Foundation for Ocean Science (SAHFOS).

Joseph Ayers (1947-present)

He is a marine biologist who specializes in neurophysiology of the marine life. He graduated from the University of California, Riverside, and pursued his doctorate at the University of California, Santa Cruz. Later, he went on to pursue his postdoctoral degree in neurophysiology from Centre National de la Recherche Scientifique, Marseilles, France and from the University of California, San Diego.

Currently, Joseph Ayers is associated with Biomimetic, an underwater robot program. “Neurotechnology for Biomimetic Robots”, “Biomechanisms of Swimming and Flying”, “Dr. Ayers Cooks with Cognac”, and “The C Around Nahant” are some of the research books authored by him.

Leanne Armand (1968-present)

She is an Australian marine scientist, who is an expert in thew field of diatoms and their distributtion in the Southern ocean. She specialized in micropaleontology for her doctoral degree, at the Australian National University and the University of Bordeaux, France. She went on to pursue post-doctoral research on the dynamics of sea ice with regards to those of the Southern Ocean.

Her research has provided valuable data and insight as to how sea ice helps drive the circulation of the ocean. Also, climatic and fishery models based on this data, can help determine the effect of sea ice on the fishery industry, marine food web, and the interaction and relationship between sea surface and terrestrial climate. She is currently engaged in studying the role of diatoms in the carbon transport cycle in the ocean (surface to ocean floor).

Rachel Carson (1907-1964)

She was an American marine biologist, conservationist, and environmentalist. She had a master’s degree in zoology, and had studied the embryonic development of the pronephros in fish, for her masters dissertation. She was, initially, an aquatic biologist in the U.S. Bureau of Fisheries, but later went on to become a nature writer. She has written numerous books, advancing the cause of marine exploration and conservation.

Her published works have inspired many movements for environmental protection and conservation, and also led to the creation of the U.S. Environmental Protection Agency. Some of theses books include “The Edge of the Sea”, “Under the Sea Wind”, “Silent Spring”, etc. She was posthumously awarded the Presidential Medal of Freedom by Jimmy Carter.

Henry Bigelow (1879-1967)

He was an American oceanographer and marine biologist, who worked the famous ichthyologist Alexander Agassiz, after graduating from Harvard. he later worked at the Museum of Comparative Zoology in 1905 and joined Harvard’s faculty in 1906. He helped found the Woods Hole Oceanographic Institution in 1930. During his lifetime, he published over a hundred research papers along with several scientific books.

He was a world-renown expert on coelenterates and elasmobranchs. His research and publications, earned him the Daniel Giraud Elliot Medal from the National Academy of Sciences, in 1948. His book, “Fishes of the Gulf of Maine”, is still used by students as an exhaustive reference. 26 species and 2 genera of organisms have been named after him, to honor his contributions to the field of marine biology.

Eugenie Clark (1922-2015)

She was an American ichthyologist, famous for her research on poisonous fish and sharks. She is sometimes referred to as “The Shark Lady”. She carried out her graduate studies regarding fish populations, at the Scripps Institute of Oceanography in La Jolla, at the American Museum of Natural History in New York, at the Marine Biological Laboratory in Woods Hole, Massachusetts, and at the Lerner Marine Laboratory in Bimini. Her research formed the subject of her first book, titled “Lady With a Spear”.

For her doctoral studies, she studied the reproduction of platys and swordtail fish. Later, she earned a Fullbright Scholarship, that allowed her to carry out ichthyological research at the Marine Biological Station in Hurghada, Egypt. She helped found the former Cape Haze Marine Laboratory, now known as the Mote Marine Laboratory in Sarasota, Florida. She was awarded the Medal of Excellence by the American Society of Oceanographers, in 1994. She has been honored by having several species of fish named after her.

Paul Dayton (1941-present)

He is an oceanographer and marine biologist, well-known for his research on kelp forest ecology. His research focuses on gaining an understanding of the marine ecosystems.He is the only person to be awarded the George Mercer Award (1974) and the W.S. Cooper Award (2000) from the Ecological Society of America. he has also documented various environmental issues such as the detrimental effects on the environment of overfishing, the phenomenon of El Niño and its effect on coastal ecology, etc. He has published several articles in the premier scientific journal, “Science”. His papers, are also, few of the most cited ecological references.

Hans Hass (1919-2013)

He was an Austrian biologist and a pioneer in the field of diving and underwater filming. He is responsible for the redevelopment of the aqualung, to produce the rebreather, which allows recycling of the user’s exhaled breath. He is also famed for his behavioral research of fish, which led to the proposal of his theory of energon. the theory/hypothesis claims that all biological life-forms on the planet possess behavior that have emerged from a common origin. During his lifetime he tried to fuse together the various concepts from the fields of behavioral science, marine biology, and management science.

A few other famous marine biologists are Jean Bouillon, Malcolm Clarke, Ernst Haeckel, Gotthilf Hempel, Johan Hjort, Stephen Hillenburg, Martin Johnson, Otto Kinne, Nancy Knowlton, Syed Zahoor Qasim, Jack Rudloe, and Takasi Tokioka.

Related Posts

In this article, we will take a look at some of the famous names in the field of genetic research.

Plant growth is the process by which the plant grows in size. A matured plant has a strong stem and healthy leaves. The growth process is enhanced by the nutrients&hellip


RESULTS

Identification of the C. neoformans G-protein β subunit GPB1.

Previous studies revealed that the Gα protein GPA1 (54) regulates mating and virulence in C. neoformans (2). To further address the role of G proteins in mating and physiology, we identified a heterotrimeric G-protein β subunit from C. neoformans.

Oligonucleotides were designed against conserved regions of Gβ subunits and used as primers in low-stringency PCRs with a C. neoformans cDNA library or C. neoformans genomic DNA as a template. Primers encompassing two conserved peptides, IYALHW and AGYDDY, amplified a partial Gβ cDNA homolog from the serotype D strain B-3501. This cDNA clone was sequenced and then used to probe a Southern blot of genomic DNA isolated from the serotype A MATα strain H99 and from the congenic serotype D strains JEC20 (MATa) and JEC21 (MATα). The GPB1 gene was present in a single copy in both mating types and serotypes (data not shown).

The complete GPB1 genomic locus was cloned from a size-selected genomic library. Sequence analysis revealed an open reading frame of 1,059 nucleotides encoding a 352-amino-acid protein (GenBank accession no. <"type":"entrez-nucleotide","attrs":<"text":"AF091120","term_id":"4138840","term_text":"AF091120">> AF091120). Four introns were identified by sequence comparison with a cDNA clone from strain H99. The predicted GPB1 protein shares marked identity with G-protein β subunits from other organisms, including Gβ subunits from humans (68%), Drosophila melanogaster (67%), C. parasitica (70%), Schizosaccharomyces pombe (40%), and S. cerevisiae (38%) (Fig. ​ (Fig.1). 1 ).

C. neoformans GPB1 exhibits identity to G-protein β subunits. The sequences of Gβ subunits from humans (12), D. melanogaster (D.m.) (66), Cryphonectria parasitica (C.p.) (21), Schizosaccharomyces pombe (S.p.) (23), and S. cerevisiae (S.c.) (59) were aligned with that of the C. neoformans (C.n.) GPB1 protein. Identical amino acids are boxed and darkly shaded conservative amino acid substitutions are boxed and lightly shaded.

Disruption of the C. neoformans GPB1 gene.

The GPB1 gene was disrupted by inserting the ADE2 gene into the GPB1 open reading frame, and the resulting gpb1::ADE2 disruption allele was introduced into the ade2 strain M049 by biolistic DNA transformation and homologous recombination. Genomic DNA was extracted from candidate gpb1::ADE2 strains (18). PCRs with primers flanking the ADE2 gene insertion were used to identify gpb1 mutations and generate a 550-bp product from the GPB1 allele and a 3,450-bp product from the gpb1::ADE2 allele.

In total, six gpb1::ADE2 mutant strains were identified from 306 adenine-prototrophic transformants by PCR analysis. In subsequent analyses, independent gpb1 mutations conferred the same phenotypes. Southern blot analysis confirmed that the GPB1 gene had been replaced by the gpb1::ADE2 disruption allele by homologous recombination at the GPB1 locus in all six mutant strains (Fig. ​ (Fig.2). 2 ). The wild-type GPB1 gene is located on a 4.9-kb HindIII fragment and a 1.6-kb NotI-XbaI fragment. In the gpb1::ADE2 mutant, the wild-type 4.9-kb HindIII fragment is replaced by 2.9- and 5.0-kb HindIII fragments (Fig. ​ (Fig.2). 2 ). In addition, the 1.6-kb NotI-XbaI wild-type GPB1 locus is missing from the gpb1::ADE2 mutant, having been replaced by 4.5- and 5.1-kb NotI-XbaI fragments (Fig. ​ (Fig.2). 2 ).

Disruption of the C. neoformans GPB1 gene. (A) A schematic illustration of the GPB1 gene replacement (B) Southern analysis of the wild type and the gpb1 mutant. The ADE2 gene was inserted at an ApaI site in the GPB1 coding domain, and the gpb1::ADE2 disruption allele was used to biolistically transform the Δade2 strain M049 to adenine prototrophy. Genomic DNAs from the isogenic GPB1 wild-type strain H99 and the gpb1::ADE2 disruption mutant were isolated, cleaved with HindIII (H) or with NotI (N) and XbaI (X), separated by 1% agarose gel electrophoresis, transferred to a nylon membrane, and probed with the 32 P-labeled GPB1 open reading frame (indicated by an arrow labeled “probe”). Sizes of DNA fragments resulting from gene disruption are indicated by horizontal arrows. The positions of DNA molecular size standards are indicated on the left.

GPB1 is required for mating in C. neoformans.

We tested whether GPB1 regulates mating in C. neoformans. MATα and MATa strains of C. neoformans mate when cocultured on nutrient-limiting medium (25). Mating consists of conjugation tube formation, cell fusion, and filamentation (1). Subsequent nuclear migration results in the formation of dikaryotic filaments that differentiate to form terminal basidia, in which nuclear fusion, meiosis, and sporulation occur. When one or both parents are sterile, few or no filaments or spores are produced.

The wild-type GPB1 MATα serotype A strain (H99) yielded abundant filaments and basidiospores when crossed with the MATa serotype D strain JEC20 (Fig. ​ (Fig.3). 3 ). In contrast, no filaments or spores were ever observed when any of the independent gpb1 mutant MATα strains were mated with their MATa mating partners (Fig. ​ (Fig.3). 3 ). Reintroduction of the wild-type GPB1 gene into the gpb1 mutant strain restored filamentation and spore production to the wild-type level (Fig. ​ (Fig.3). 3 ).

The C. neoformans G-protein β subunit GPB1 is required for mating. The isogenic C. neoformans wild-type MATα strain H99 (GPB1 GPA1) and the gpb1::ADE2 (gpb1) and gpa1::ADE2 (gpa1) MATα mutant strains were mated with the MATa strain JEC20 on V8 agar medium (upper panels) and V8 agar medium supplemented with 2 or 10 mM cAMP as indicated (lower panels). The wild-type GPB1 gene was reintroduced into the gpb1 mutant strain as described in Materials and Methods (gpb1+GPB1). Mating was at 22ଌ for 7 days. Magnification, 휥.

GPB1 and the Gα subunit GPA1 play different roles in mating.

Several findings suggest that the Gα protein GPA1 and the Gβ protein GPB1 function in distinct pathways to regulate mating. First, the gpb1 mutation confers an absolute mating defect, whereas, following prolonged incubation, gpa1 mutants eventually mate to a limited extent with a wild-type mating partner, forming filaments, basidia, and recombinant basidiospores (Fig. ​ (Fig.3) 3 ) (2). Second, cAMP suppresses the mating defect of gpa1 mutants, but not that of gpb1 mutants (Fig. ​ (Fig.3) 3 ) (2). Third, no interaction between GPA1 and GPB1 was detected in the two-hybrid system (data not shown) (see Materials and Methods).

Several additional findings indicate the Gα subunit GPA1 is not required for pheromone sensing. First, in confrontation assays, the congenic MATα strain JEC21 and the MATa strain JEC20 both produced conjugation tubes in response to pheromone secreted by their mating partners (Fig. ​ (Fig.4A). 4 A). Most importantly, when the wild-type MATα strain JEC21 was grown in confrontation with a gpa1 MATa mutant strain (BAC20), both the gpa1 mutant and the wild-type strain produced conjugation tubes (Fig. ​ (Fig.4A). 4 A). Second, when a plasmid expressing the MF㬑 pheromone was introduced into wild-type and gpa1 mutant MATa strains, both produced conjugation tubes (Fig. ​ (Fig.4B). 4 B). The response of gpa1 mutants to pheromones was somewhat reduced from that of the wild type, but taken together these findings indicate that GPA1 is not required for pheromone sensing. In an assay that detects cell fusion during mating (MATα ura5 strains were coincubated with MATa lys1 strain JEC30 on V8 agar, and prototrophic self-filamenting heterokaryons were detected by replica plating to YNB medium), the gpb1 mutation prevented cell fusion whereas the gpa1 mutation reduced but did not block fusion (data not shown). In a mating assay in which recombinant basidiospores were quantified (MATα prototrophic strains were mated with MATa ura5 lys1 strain JEC53 on V8 agar, and LYS1 ura5 recombinants were selected on 5-fluoroorotic acid–lysine medium), no recombinant basidiospores were produced by the gpb1 mutant whereas the gpa1 mutant produced a reduced number of basidiospores.

The Gα subunit GPA1 is not required for responses to pheromones. (A) Cells of the wild-type MATα serotype D strain JEC21 were grown in confrontation with the isogenic MATa GPA1 wild-type strain JEC20 (upper panel) or the gpa1 mutant strain BAC20 (lower panel), with incubation for 3 days at 24ଌ on filament agar, and conjugation tubes were photographed. Magnification, 휥. (B) A ura5 derivative of the GPA1 wild-type strain JEC20 (MATa ura5) and the isogenic gpa1 mutant strain BAC20 (MATa gpa1::ADE2 ura5) were transformed with plasmid pCnTel1 lacking or expressing the MF㬑 pheromone gene, grown on filament agar for 2 days at 24ଌ, and photographed. Magnification, 흐.

GPB1 is not required for melanin or capsule production or virulence.

The Gα protein GPA1 regulates the production of the virulence factors melanin and capsule in response to nutrient limitation (2). To determine whether the functions of GPB1 and GPA1 are distinct, we tested whether the gpb1 mutation alters virulence factors or virulence.

C. neoformans produces melanin when grown in the presence of diphenolic precursors under carbohydrate-limiting conditions. Melanin is required for virulence and may protect cells from nitrogen- and oxygen-derived radicals produced by host immune cells (56, 57). When cultured on a medium containing niger seed extract as a source of diphenolic compounds, gpa1 mutants did not produce melanin (Fig. ​ (Fig.5A) 5 A) (2). In contrast, gpb1 mutant strains produced melanin to the same extent as the GPB1 wild-type strain (Fig. ​ (Fig.5A). 5 A). By a quantitative spectrophotometric assay, it was determined that gpb1 mutant and GPB1 wild-type cells produced similar levels of laccase activity (data not shown) (63).

GPB1 is not required for virulence factors or virulence in C. neoformans. (A) The isogenic GPB1 GPA1 wild-type strain H99 and the gpb1::ADE2 (gpb1) and gpa1::ADE2 (gpa1) mutant strains were grown on niger seed agar for 72 h at 37ଌ. Strains that produce melanin (GPB1 GPA1, gpb1) form brown colonies on this medium, whereas strains that do not produce melanin (gpa1) are white. (B) Cells of the wild-type strain H99 (GPB1 GPA1) and the gpb1::ADE2 (gpb1) and gpa1::ADE2 (gpa1) mutant strains were grown in low-iron medium plus EDDHA at 30ଌ for 48 h to induce capsule synthesis. The polysaccharide capsule was identified by India ink staining and photographed. Magnification, 󗈀. (C) The GPB1 wild-type (H99) and gpb1 mutant strains were inoculated intracisternally into immunosuppressed rabbits. CSF was withdrawn on days 4, 7, 10, and 14 postinfection, and the numbers of surviving yeast cells were determined by plating serial dilutions of CSF on YPD medium. The mean cell count for each strain was plotted with the standard error of the mean.

C. neoformans is distinguished from many pathogenic yeast by its polysaccharide capsule, which inhibits phagocytosis by host cells and is required for virulence (3). Formation of the capsule is induced during infection or in response to low-iron or elevated-CO2 conditions in vitro (16, 55). To assess capsule production, the wild-type strain H99 and the gpa1 and gpb1 mutant strains were grown in liquid iron-limiting medium. Capsule production in wild-type cells was readily observed by staining with India ink, and the capsule size was decreased in gpa1 mutant cells (Fig. ​ (Fig.5B) 5 B) (2). In contrast, gpb1 mutant cells produced capsules similar to those of wild-type cells (Fig. ​ (Fig.5 5 B).

We next tested whether the gpb1 mutation alters virulence. An animal model of cryptococcal meningitis was employed in which glucocorticoid-immunosuppressed rabbits were inoculated intrathecally with C. neoformans strains and survival in the central nervous system was determined by removing CSF and quantifying yeast cells by serial dilution and culture (2, 45). As shown in Fig. ​ Fig.5C, 5 C, virulence of the gpb1 mutant was similar to that of the GPB1 wild-type strain H99. Both wild-type and gpb1 mutant cells persisted for up to 14 days in the CSF, and they were recovered in similar quantities, although cell counts for the gpb1 mutant were slightly reduced on days 4 and 7. Similar results were obtained with a second gpb1 mutant, as well as when the inoculum size was reduced 10-fold. gpb1 mutant cells recovered from infected animals still exhibited a mating defect in vitro. In summary, in contrast to GPA1, GPB1 is not required for melanin or capsule production and is not a major virulence determinant.

GPB1 regulates mating upstream of a MAP kinase cascade.

Our findings suggested that the Gβ subunit GPB1 activates a signaling pathway that regulates mating in parallel with the GPA1-cAMP-regulated nutrient-sensing pathway. We tested whether the Gβ protein GPB1 regulates a MAP kinase cascade during mating in C. neoformans.

In addition to the G-protein β subunit, two other MAP kinase cascade components have been identified in C. neoformans: a MAP kinase homolog, CPK1 (R. Davidson and J. Heitman, unpublished data), and a homolog of the STE12 transcription factor (61, 67). We tested whether CPK1 or STE12α functions downstream of GPB1 by epistasis, using cloned genes under the control of the C. neoformans GAL7 promoter, which is induced by galactose and repressed by glucose (62).

When the gpb1 mutant strain was transformed with the GAL7-CPK1 gene fusion, mating with a MATa strain was restored on galactose filament agar but not on glucose (Fig. ​ (Fig.6A). 6 A). Thus, expression of the CPK1 MAP kinase suppresses the gpb1 mating defect, providing evidence that GPB1 functions upstream of this MAP kinase. The GAL7-CPK1 gene fusion did not restore mating in gpa1 mutants (data not shown), indicating that CPK1 functions downstream of GPB1 but not of GPA1.

GPB1 activates a MAP kinase cascade involving the CPK1 kinase. (A) The CPK1 gene expressed from the C. neoformans GAL7 promoter in the URA5 plasmid pCnTel1 was introduced into a gpb1 ura5 mutant strain (see Materials and Methods) by biolistic transformation. The isogenic MATα wild-type strain H99 (GPB1 GPA1), the gpb1 mutant strain, and the gpb1 mutant strain transformed with the GAL7-CPK1 gene fusion (gpb1 GAL7-CPK1) were cocultured with a MATa mating partner (JEC20). Mating was for 21 days at 22ଌ on filament agar containing 0.5% galactose (shown here) or 0.5% glucose (data not shown). Magnification, 휥. (B) The congenic serotype D MATa ura5 strain JEC34 and the MATα ura5 strain JEC43 were transformed with the GAL7-GPB1 gene fusion linked to the URA5 gene and grown for 72 h at 24ଌ on filament agar with glucose or galactose. Conjugation tubes emanating from cell patches were photographed. Magnification, 휥.

In contrast to the effects of CPK1, the GAL7-STE12α gene fusion did not restore mating of the gpb1 mutant strain on glucose or galactose filament agar (data not shown). The functions of STE12α likely involve haploid fruiting and not mating, because STE12α overexpression stimulates haploid fruiting (61) whereas ste12α mutations block haploid fruiting but not mating (67).

GPB1 stimulates conjugation tube formation in MATα and MATa cells.

We next tested whether GPB1 plays an active signaling role upstream of the MAP kinase cascade, analogous to that of the Gβγ complex in S. cerevisiae (50). During mating in C. neoformans, the mating partners secrete pheromones that trigger the formation of conjugation tubes in the opposite cell type (1, 41 R. Davidson and J. Heitman, unpublished data). We tested whether GPB1 overexpression stimulates conjugation tube formation in cells not exposed to pheromones.

The GAL7 promoter was fused upstream of the GPB1 gene, and the GAL7-GPB1 gene fusion was introduced into congenic MATα and MATa serotype D strains. Growth on galactose filament agar induced the formation of conjugation tubes in both MATa and MATα strains (Fig. ​ (Fig.6B). 6 B). Conjugation tubes produced in response to GPB1 overexpression were similar to those observed in confrontation assays or in MATa cells in response to expressed or synthetic MF㬑 pheromone (1, 41) (Fig. ​ (Fig.4). 4 ). MATa cells produced more conjugation tubes than did MATα cells, suggesting that the mating responses of the two cell types differ (Fig. ​ (Fig.6 6 B).

GPB1 and MATa cells regulate monokaryotic fruiting.

Mating of MATa and MATα cells of C. neoformans is regulated by both pheromones and nitrogen starvation. In contrast, in response to nitrogen starvation alone, MATα haploid strains differentiate, forming monokaryotic filaments, basidia, and spores by haploid fruiting (62). This filamentous differentiation shares some features with pseudohyphal growth in S. cerevisiae (15). Components of the mating pheromone response pathway are required for pseudohyphal growth, whereas mating pheromones, pheromone receptors, and the coupled heterotrimeric G protein are not (35). We therefore hypothesized that the Gβ protein GPB1 would not be required for haploid fruiting in C. neoformans.

To our surprise, we found that GPB1 is required for haploid fruiting in C. neoformans. Similar to the many lab strains of S. cerevisiae which do not undergo pseudohyphal growth, C. neoformans strains also differ in their ability to form filaments in response to nitrogen starvation. The serotype A strain H99 does not exhibit haploid fruiting under a variety of conditions. Introduction of a dominant active RAS1 mutant (Ras1 Q67L) does stimulate haploid fruiting of strain H99 (Fig. ​ (Fig.7A) 7 A) (J.𠂚. Alspaugh and J. Heitman, unpublished data). However, the dominant active Ras1 Q67L mutant protein did not stimulate haploid fruiting in the gpb1 mutant strain (Fig. ​ (Fig.7A). 7 A). Reintroduction of the wild-type GPB1 gene restored haploid fruiting of the gpb1 mutant (Fig. ​ (Fig.7A). 7 A). The GAL7-STE12α gene fusion (Fig. ​ (Fig.7A) 7 A) and the GAL7-CPK1 gene fusion (data not shown) suppressed the haploid fruiting defect of gpb1 mutants on galactose filament agar. Thus, GPB1 is required for monokaryotic fruiting and functions upstream of CPK1 and STE12α.

GPB1 and MATa cells regulate haploid fruiting. (A) The isogenic GPB1 wild-type strain H99 (far-left panel), the gpb1::ADE2 mutant strain (second panel from left), and the gpb1::ADE2 mutant strain reconstituted with the GPB1 wild-type gene (third panel from left) were transformed with the dominant active Ras1 Q67L mutant gene, grown on glucose filament agar medium for 7 days at 24ଌ, and photographed. The gpb1 mutant strain was also transformed with plasmid pCGS-1 expressing the GAL7-STE12 fusion gene and grown on galactose filament agar (far-right panel) for 7 days at 24ଌ. Magnification, 휥. (B) Cells of the serotype D MATα strain JEC21 were grown in confrontation with themselves (middle panel) or with congenic cells of the opposite (MATa) mating type (strain JEC20) (lower panel). As a control, the MATa strain JEC20 was grown in confrontation with itself (upper panel). Cells were incubated for 10 days at 24ଌ on filament agar and photographed. Magnification, 휥.

We next addressed why the pheromone-sensing Gβ protein is required for haploid fruiting if this process normally occurs in response to nitrogen limitation. We found that when MATα cells are grown in confrontation with MATa cells, monokaryotic fruiting of the MATα cells is dramatically stimulated and abundant filaments, basidia, and basidiospores are produced (Fig. ​ (Fig.7B). 7 B). In contrast, a much lower level of monokaryotic fruiting is observed when MATα cells are grown in isolation or when MATα cells are grown in confrontation with MATα cells (Fig. ​ (Fig.7B). 7 B). The response of MATα cells to confronting MATa cells does not require cell-cell or cell-filament contact, and it occurs before any of the projecting filaments touch the confronting cells. Moreover, monokaryotic fruiting was still observed when a dialysis membrane with a molecular mass cutoff of 3,800 Da was interposed between MATα and MATa cells (data not shown). The C. neoformans mating pheromones are predicted to diffuse through this membrane.

By microscopic observation and nuclear staining with the DNA-specific dye DAPI (4′,6′-diamidino-2-phenylindole), it was determined that the filament cells are linked by unfused clamp connections and are monokaryotic, hallmarks of monokaryotic fruiting. In addition, micromanipulation and mating type tests confirmed that basidiospores produced by MATα cells in response to confronting MATa cells are all MATα and are thus products of asexual monokaryotic fruiting (data not shown). Our findings indicate that monokaryotic fruiting of MATα cells is stimulated by MATa cells, possibly in response to MATa pheromones sensed by a receptor coupled to GPB1.


IV. Growth, photosynthetic and primary metabolite responses

Root herbivory affects patterns of growth, photosynthesis and primary metabolism in a distinct manner. Figure 1 summarises these and other salient differences. Root herbivory can (1) decrease water and nutrient uptake via decreased root biomass or disruption of water and nutrient hydraulics, (2) deplete resources that the plant is storing belowground, (3) impose water deficits that reduce rates of photosynthesis and (4) cause photoassimilates to be diverted belowground for root regrowth and repair. Tolerance to herbivory depends on compensatory growth, a critical way in which plants can endure attack. Compensatory growth in response to root herbivory usually occurs via lateral root proliferation (Brown & Gange, 1990 ), akin to increased levels of branching following stem herbivory (Stephens & Westoby, 2015 ). That said, plants find it harder to compensate, much less overcompensate, for root damage (17% of cases Zvereva & Kozlov, 2012 ) compared with shoot herbivory (35–44% of cases Hawkes & Sullivan, 2001 ). Root and leaf turnover rates are not dissimilar, so it would appear that plants at least have the capacity to compensate for root attack, but can't realise it. This is possibly because root herbivory reduces rates of photosynthesis in plants, by c. 11.7% across plant species, in contrast to shoot herbivory, which generally stimulates it (Zvereva & Kozlov, 2012 ).

Photoassimilates are often translocated to the roots for storage, particularly after episodes of shoot herbivory (Schultz et al., 2013 ) do plants move primary metabolites in the reverse direction in response to root herbivory? Evidence is limited, but Robert et al. ( 2014 ) showed that maize plants infested with root herbivores allocated carbon to the stems as a prelude to root regrowth. Similarly, nitrogen was allocated away from roots to the shoots in knapweed (Newingham et al., 2007 ) and the stems in milkweed (Tao & Hunter, 2013 ) following root attack. However, root herbivores may also manipulate their hosts to allocate primary metabolites, including carbon (Pierre et al., 2012 Robert et al., 2012 ) and phosphorus (Johnson et al., 2013b ) belowground to improve host plant quality (Erb et al., 2013 ).


DNA Markers and Plant Breeding Programs

On a worldwide basis, plant breeding has been one of the most successful technologies developed in modern agriculture: its methods are opportunistic and adaptable to myriad production schemes, they require relatively inexpensive input, and their products have pervasive social benefits. DNA markers have become established as another tool for many phases of crop improvement, but the utility of this technology varies considerably with the application and context of the crop and culture. The world of DNA technology is changing rapidly, whereas plant breeding methodology has remained relatively stagnant. An awareness of genetic diversity and management of crop genetic resources have been important components of plant improvement programs. This chapter attempts to survey the status of selected applications of DNA fingerprinting for activities of common interest to plant breeding programs. There are a number of ways in which DNA markers could improve the management of plant genetic resources for the benefit of plant breeding programs and, ultimately, crop improvement. DNA markers have provided unprecedented opportunities for genetic resolution, and their use will expand, not as a panacea, but as a complement to the existing methods and their inherent limitations. The chapter presents data from several crops to illustrate the use of maps to reveal the features of crop genomes with implications for crop improvement. .


Blog Archive

  • ►� (2)
    • ►㺅/19 - 05/26 (1)
    • ►㺃/03 - 03/10 (1)
    • ►� (35)
      • ►㺉/23 - 09/30 (1)
      • ►㺉/16 - 09/23 (2)
      • ►㺉/09 - 09/16 (3)
      • ►㺈/19 - 08/26 (2)
      • ►㺈/12 - 08/19 (3)
      • ►㺈/05 - 08/12 (1)
      • ►㺇/15 - 07/22 (2)
      • ►㺇/08 - 07/15 (4)
      • ►㺇/01 - 07/08 (1)
      • ►㺆/24 - 07/01 (1)
      • ►㺆/17 - 06/24 (2)
      • ►㺆/03 - 06/10 (1)
      • ►㺅/20 - 05/27 (1)
      • ►㺅/13 - 05/20 (1)
      • ►㺅/06 - 05/13 (2)
      • ►㺄/08 - 04/15 (2)
      • ►㺄/01 - 04/08 (1)
      • ►㺃/25 - 04/01 (3)
      • ►㺁/15 - 01/22 (2)
      • ►� (30)
        • ►㺊/02 - 10/09 (1)
        • ►㺈/21 - 08/28 (1)
        • ►㺈/07 - 08/14 (1)
        • ►㺇/17 - 07/24 (2)
        • ►㺆/19 - 06/26 (1)
        • ►㺅/22 - 05/29 (3)
        • ►㺅/08 - 05/15 (1)
        • ►㺄/10 - 04/17 (2)
        • ►㺃/27 - 04/03 (1)
        • ►㺂/27 - 03/06 (4)
        • ►㺂/20 - 02/27 (1)
        • ►㺂/13 - 02/20 (1)
        • ►㺁/30 - 02/06 (1)
        • ►㺁/16 - 01/23 (4)
        • ►㺁/09 - 01/16 (2)
        • ►㺁/02 - 01/09 (4)
        • ►� (88)
          • ►㺌/26 - 01/02 (2)
          • ►㺋/14 - 11/21 (1)
          • ►㺋/07 - 11/14 (1)
          • ►㺊/24 - 10/31 (3)
          • ►㺊/17 - 10/24 (1)
          • ►㺊/10 - 10/17 (1)
          • ►㺊/03 - 10/10 (3)
          • ►㺉/26 - 10/03 (2)
          • ►㺉/19 - 09/26 (2)
          • ►㺉/12 - 09/19 (2)
          • ►㺉/05 - 09/12 (2)
          • ►㺈/22 - 08/29 (4)
          • ►㺈/15 - 08/22 (1)
          • ►㺇/25 - 08/01 (3)
          • ►㺇/18 - 07/25 (2)
          • ►㺅/23 - 05/30 (1)
          • ►㺅/16 - 05/23 (3)
          • ►㺅/02 - 05/09 (1)
          • ►㺄/25 - 05/02 (1)
          • ►㺄/18 - 04/25 (2)
          • ►㺄/11 - 04/18 (1)
          • ►㺄/04 - 04/11 (3)
          • ►㺃/28 - 04/04 (1)
          • ►㺃/21 - 03/28 (2)
          • ►㺃/14 - 03/21 (4)
          • ►㺃/07 - 03/14 (2)
          • ►㺂/28 - 03/07 (3)
          • ►㺂/14 - 02/21 (8)
          • ►㺂/07 - 02/14 (5)
          • ►㺁/31 - 02/07 (3)
          • ►㺁/24 - 01/31 (1)
          • ►㺁/17 - 01/24 (8)
          • ►㺁/10 - 01/17 (6)
          • ►㺁/03 - 01/10 (3)
          • ▼� (154)
            • ►㺌/27 - 01/03 (2)
            • ►㺌/13 - 12/20 (2)
            • ►㺋/22 - 11/29 (1)
            • ►㺋/15 - 11/22 (1)
            • ►㺋/08 - 11/15 (4)
            • ►㺊/25 - 11/01 (4)
            • ►㺊/18 - 10/25 (2)
            • ►㺊/11 - 10/18 (1)
            • ►㺊/04 - 10/11 (1)
            • ►㺉/27 - 10/04 (5)
            • ►㺉/20 - 09/27 (3)
            • ►㺉/13 - 09/20 (3)
            • ►㺉/06 - 09/13 (1)
            • ►㺈/30 - 09/06 (9)
            • ►㺈/23 - 08/30 (2)
            • ▼㺈/16 - 08/23 (8)
            • ►㺈/02 - 08/09 (8)
            • ►㺇/19 - 07/26 (6)
            • ►㺇/12 - 07/19 (7)
            • ►㺇/05 - 07/12 (3)
            • ►㺆/21 - 06/28 (3)
            • ►㺆/14 - 06/21 (2)
            • ►㺆/07 - 06/14 (1)
            • ►㺅/31 - 06/07 (5)
            • ►㺅/24 - 05/31 (2)
            • ►㺅/17 - 05/24 (2)
            • ►㺅/10 - 05/17 (3)
            • ►㺅/03 - 05/10 (2)
            • ►㺄/26 - 05/03 (3)
            • ►㺄/12 - 04/19 (4)
            • ►㺄/05 - 04/12 (1)
            • ►㺃/29 - 04/05 (1)
            • ►㺃/22 - 03/29 (3)
            • ►㺃/15 - 03/22 (1)
            • ►㺃/08 - 03/15 (4)
            • ►㺃/01 - 03/08 (4)
            • ►㺂/15 - 02/22 (10)
            • ►㺂/08 - 02/15 (6)
            • ►㺂/01 - 02/08 (5)
            • ►㺁/25 - 02/01 (2)
            • ►㺁/18 - 01/25 (3)
            • ►㺁/11 - 01/18 (10)
            • ►㺁/04 - 01/11 (4)
            • ►� (118)
              • ►㺌/14 - 12/21 (2)
              • ►㺋/16 - 11/23 (1)
              • ►㺋/09 - 11/16 (2)
              • ►㺋/02 - 11/09 (1)
              • ►㺊/26 - 11/02 (4)
              • ►㺊/19 - 10/26 (1)
              • ►㺊/12 - 10/19 (5)
              • ►㺊/05 - 10/12 (3)
              • ►㺉/28 - 10/05 (1)
              • ►㺉/21 - 09/28 (3)
              • ►㺉/14 - 09/21 (4)
              • ►㺉/07 - 09/14 (2)
              • ►㺈/31 - 09/07 (2)
              • ►㺈/24 - 08/31 (2)
              • ►㺈/17 - 08/24 (1)
              • ►㺈/10 - 08/17 (2)
              • ►㺇/20 - 07/27 (2)
              • ►㺇/13 - 07/20 (1)
              • ►㺆/22 - 06/29 (1)
              • ►㺆/08 - 06/15 (1)
              • ►㺆/01 - 06/08 (4)
              • ►㺅/18 - 05/25 (6)
              • ►㺅/11 - 05/18 (2)
              • ►㺅/04 - 05/11 (2)
              • ►㺄/27 - 05/04 (1)
              • ►㺄/20 - 04/27 (1)
              • ►㺄/06 - 04/13 (2)
              • ►㺃/30 - 04/06 (3)
              • ►㺃/23 - 03/30 (2)
              • ►㺃/16 - 03/23 (1)
              • ►㺃/09 - 03/16 (6)
              • ►㺃/02 - 03/09 (3)
              • ►㺂/24 - 03/02 (7)
              • ►㺂/17 - 02/24 (2)
              • ►㺂/10 - 02/17 (2)
              • ►㺂/03 - 02/10 (10)
              • ►㺁/27 - 02/03 (7)
              • ►㺁/20 - 01/27 (7)
              • ►㺁/13 - 01/20 (2)
              • ►㺁/06 - 01/13 (7)
              • ►� (83)
                • ►㺌/23 - 12/30 (1)
                • ►㺌/16 - 12/23 (5)
                • ►㺌/09 - 12/16 (2)
                • ►㺌/02 - 12/09 (1)
                • ►㺋/18 - 11/25 (2)
                • ►㺋/11 - 11/18 (2)
                • ►㺋/04 - 11/11 (4)
                • ►㺊/28 - 11/04 (1)
                • ►㺊/07 - 10/14 (1)
                • ►㺉/30 - 10/07 (1)
                • ►㺉/23 - 09/30 (3)
                • ►㺉/16 - 09/23 (5)
                • ►㺉/09 - 09/16 (1)
                • ►㺉/02 - 09/09 (1)
                • ►㺈/26 - 09/02 (2)
                • ►㺇/29 - 08/05 (1)
                • ►㺇/22 - 07/29 (4)
                • ►㺇/08 - 07/15 (2)
                • ►㺇/01 - 07/08 (2)
                • ►㺆/24 - 07/01 (3)
                • ►㺅/20 - 05/27 (2)
                • ►㺅/13 - 05/20 (2)
                • ►㺅/06 - 05/13 (2)
                • ►㺄/22 - 04/29 (2)
                • ►㺄/15 - 04/22 (2)
                • ►㺄/01 - 04/08 (2)
                • ►㺃/25 - 04/01 (6)
                • ►㺃/18 - 03/25 (2)
                • ►㺃/11 - 03/18 (2)
                • ►㺃/04 - 03/11 (3)
                • ►㺂/25 - 03/04 (1)
                • ►㺂/11 - 02/18 (1)
                • ►㺂/04 - 02/11 (1)
                • ►㺁/28 - 02/04 (3)
                • ►㺁/21 - 01/28 (5)
                • ►㺁/14 - 01/21 (2)
                • ►㺁/07 - 01/14 (1)
                • ►� (109)
                  • ►㺌/31 - 01/07 (1)
                  • ►㺌/17 - 12/24 (1)
                  • ►㺌/10 - 12/17 (1)
                  • ►㺌/03 - 12/10 (4)
                  • ►㺋/26 - 12/03 (2)
                  • ►㺋/19 - 11/26 (5)
                  • ►㺋/12 - 11/19 (1)
                  • ►㺋/05 - 11/12 (1)
                  • ►㺊/29 - 11/05 (1)
                  • ►㺊/22 - 10/29 (2)
                  • ►㺊/15 - 10/22 (1)
                  • ►㺊/08 - 10/15 (3)
                  • ►㺊/01 - 10/08 (2)
                  • ►㺉/24 - 10/01 (2)
                  • ►㺉/17 - 09/24 (4)
                  • ►㺉/10 - 09/17 (3)
                  • ►㺉/03 - 09/10 (3)
                  • ►㺈/27 - 09/03 (2)
                  • ►㺈/20 - 08/27 (4)
                  • ►㺈/06 - 08/13 (1)
                  • ►㺇/30 - 08/06 (5)
                  • ►㺇/23 - 07/30 (1)
                  • ►㺇/16 - 07/23 (3)
                  • ►㺇/09 - 07/16 (2)
                  • ►㺇/02 - 07/09 (1)
                  • ►㺆/25 - 07/02 (1)
                  • ►㺆/18 - 06/25 (2)
                  • ►㺆/11 - 06/18 (3)
                  • ►㺅/28 - 06/04 (4)
                  • ►㺅/21 - 05/28 (1)
                  • ►㺅/14 - 05/21 (5)
                  • ►㺅/07 - 05/14 (3)
                  • ►㺄/30 - 05/07 (5)
                  • ►㺄/23 - 04/30 (5)
                  • ►㺄/16 - 04/23 (6)
                  • ►㺄/09 - 04/16 (18)

                  Seed Types and Dispersal Mechanisms

                  Plants have the ability to use and establish new lands for resources by various seed dispersal and rapid colonization traits. When a mature seed is in unfavorable conditions, it can undergo dormancy (a resting state) until surroundings are right. The particular structure of a plant species’ body, fruit, and seed dictate the means of dispersal. Some of these adaptations include the following: nutritious fruits to attract wildlife, buoyant thick-shelled nuts that float thousands of miles, dust-like seeds produced in the millions, winged or plumed seeds, and explosive fruits that can toss their seeds several feet. Seeds can be packaged in cones (pine trees), pods (honey locust), capsules (willow), nuts (chestnut, oak), with wings (ash, elm, maple) or with varying fleshiness of fruit coverings (raspberry, cherry, apple).2 The Hawaiian flora and fauna are representative of long distance dispersal for plants. The plant colonizers that survived the long journey across the Pacific had seeds that were tolerant to salt water or small enough to be carried in the wind or by birds.3

                  Seeds can cross oceans via birds (digestive tract or attachment), by wind (air currents), or by waves (rafting in ocean currents). Seeds of the Australian pine (Casuarina) survive immersion in salt water indefinitely but are not buoyant. These plant seeds are believed to cross oceans by rafting, particularly on floating volcanic pumice upon which they have been seen germinating.4

                  This protective outer layer helps protect the internal plant embryo from injury or from drying out. Seed coats are important in the longevity of the seed. Seed longevity is an ecological characteristic of a plant as well as a physical and a chemical one. The growth form of plant species, their type of seed dispersal, is adapted to the habitat in which they are commonly found. A thin seed coat provides no barrier to water, but allows light to quickly penetrate, triggering the end of seed dormancy.5 Some plants are primary pioneers. They ordinarily grow on tough sites where soil is scarce or poor. How do plants revegetate a burned area as promptly and abundantly as they do? Simply because they have programmed, durable, heat-resistant, and long-lived seeds. Intense heat from a fire can break seed dormancy in some plants (Acacia). The chemical barrier on their seed coats is disrupted, thereby triggering extensive seed germination.6

                  When Herod the Great's palace was excavated in Israel (1963), researchers discovered date palm seeds preserved in an ancient jar. The University of Zurich confirmed the seeds dated from between 155 BC to AD 64. After an additional 40 years, the seeds were pretreated in fertilizers and a hormone-rich solution, and then planted (2005). What grew is one of the oldest known tree seeds successfully germinated, and the only living Judean date palm, a tree thought extinct for over 1,800 years. The plant is called “Methuselah,” named for the oldest person recorded in the Bible.7 , 8 Ancient hazelnut-sized Manchurian seeds were found in a peat layer in a dry lake bed in China. The seeds have very thick protective seedcoats. Several germination tests were done, and most all of the seeds grew. On several seeds, age tests suggested they were between 830 and 1,250 years old.9

                  Tropical drift seedpods and fruit nuts are extraordinary because they can survive months or even years at sea. They are very buoyant with thick protective shells that are impenetrable to salt water. In some drift fruits, such as the coconut, the seed embryo and fleshy white “meat” (endosperm) is enclosed within a hard layer (endocarp) surrounded by a thick husk. Other drift seeds have thick woody coats and internal air cavities that make them buoyant. During their long voyages, these seeds often cross entire oceans (table 1).10 Because many animals died in the Flood, their carcasses could have floated on the surface of the waters, holding and protecting seeds in their bodies. Early experiments by Darwin found that many kinds of seeds in the crops of floating birds can retain their ability to germinate up to 30 days.11

                  Did you know fish can act as a mechanism for seed dispersal? Cattle, sheep, horses, deer, bear, rabbits, birds, and fish are also known to pass viable seeds. The technical term for this is endozoochory. During the Flood of Noah’s day, freshwater and marine fish could have survived in water suited to them, in spite of being temporarily displaced from their normal habitats. The gamitana fish (Colossoma macropomum), of Peru, eats mostly fruit and can transport seeds down the Amazon River up to three miles. Researchers examined 230 fish and found nearly 700,000 intact seeds from 22 plant species, representing 21 percent of the species that fruit during the flood season. The relationship between these fish and plants is based on the seasonal rains, which can flood areas for up to nine months with water 19 feet deep for nearly five months. During the rainy season, these fish spend 90 percent of their time in the flooded habitats, waiting for fruit to fall into the water12

                  Table 1. Drift seeds and fruits collected on three-hour walk on the island of St. John.
                  Beach bean (Canavalia maritima) Asian swamp lily (likely Crinum asiaticum)
                  Coin plant (likely Dalbergia monetaria) Dog almond (Andira inermis)
                  Hog plum (Spondias mombin) Grenade pod (Sacoglottis amazonica)
                  Mammee apple (Mammea americana) Beach morning-glory (Ipomoea pes-caprae)
                  Manchineel tree (Hippomane mancinella) Yellow nickernut (Caesalpinia ciliata or C.major)
                  Mango (Mangifera indica) Oak acorn (Quercus sp.)
                  Nothing nut (Cassine xylocarpa) Sea bean (Mucuna urens)
                  Sandbox tree (Hura crepitans) Pod (possibly Sterculia sp.)
                  Sea coconut (Manicaria saccifera) Sea heart (Entada gigas)
                  Seaside hibiscus (Thespesia populnea) Gray nickernut (Caesalpinia bonduc)
                  Sugar apple (Annona squamosa) Red mangrove (Rhizophora mangle)
                  Tamanu (Calophyllum inophyllum) Coconut endocarp (Cocos nucifera)
                  Tropical almond (Terminalia catappa) Calabash (Crescentia cujete)
                  West Indian locust (Hymenaea courbaril) Box fruit (Barringtonia asiatica)

                  There are two methods of plant reproduction: sexual (seed) and asexual (vegetative). Seed production by flowers or cones requires the transfer of pollen: a sharing of genetic material between two plants. In nature this results in offspring that differ from each other and from their parents. Vegetative propagation is designated “clonal” by scientists: young progeny are genetic copies of the parent plant.

                  Seed germination requires oxygen and water. Following pollination, the development of viable seeds may or may not occur a great deal depends upon environmental conditions. A severe freeze, snow, or rain event at the time of blooming can eliminate the seed cycle for that year. Even if viable seeds are produced and expelled, they may be forced to wait to germinate until some later year when conditions are more favorable. The most reasonable view, widely held by plant experts, is that seed dormancy is not only associated with the absence of germination, but it is also a seed characteristic that determines the conditions required for germination.13

                  Many plants have alternative methods of reproduction, the most common being through vegetative rhizomes. Rhizomes are creeping, underground, root-like stems that run out from a plant with the ability to send up a new shoot, i.e., new clone-like plant. A single rhizome plant can occupy an area of several feet with its roots growing in an interconnecting system. This plant feature is an adaptation to fill an area rapidly.


                  SH designed and performed the experiments, conducted the data analyses, and wrote the manuscript. EK performed Fusarium oxysporum f. sp. fragariae disease assessment experiments. AR contributed to designing the experiments and conducting preliminary experiments. RL conducted the volatile analysis experiments. BP contributed to annotating non-polar metabolites. LH contributed to access high-end computing for network generation and visualization, and programing to generate microbial and metabolite networks. DR contributed to insightful discussions on designing the project, metabolite analyses, data analyses, network generation, and manuscript writing. MM supervised the entire project including microbiome analyses experiments, data analyses, interpretation of the findings, and writing of the manuscript. All authors read and revised the manuscript.

                  This work was completed through funding support provided by the USDA-NIFA Award No. 2016-51102-25815.


                  Forward to the past: the outlook for archaeogenetics in domestic animals

                  During the past decade progress in archaeogenetics has been driven by spectacular technology developments in genomics and other fields. This has led to the establishment of paleogenomics “factories” for studying recent human evolution, migration and admixture at increasingly high resolution [240]. There have also been significant developments in other areas of biomolecular archaeology, some of which we outline below in the context of understanding the genetic history and recent evolution of domestic animals.

                  Ancient DNA may also be readily extracted from a wide range of museum specimens containing biological material from domestic animals [241,242,243]. However, it is important that minimally or non-destructive sampling methods are employed for these items, many of which are literally irreplaceable [244, 245]. Novel sources of aDNA such as avian eggshells and feathers [246], animal glues [247] and parchment made from processed livestock skins [248, 249] will likely have a major impact on archaeogenetics studies of domestic animals. Written documents made from parchment have been carefully maintained and curated for many centuries and therefore represent a valuable repository of genomic information that could illuminate livestock agriculture, breeding and trade stretching back to the early Middle Ages [249].

                  The expansion of livestock paleogenomics studies to encompass wide spatio-temporal surveys of archaeological material will provide new information concerning the development of secondary animal products and resources such as milk, wool, traction and transport that can be repeatedly exploited throughout an animal’s lifespan [250, 251]. Over the coming years it is likely that high-resolution paleogenomics will shed light on human-mediated selection and the phenotypic changes in livestock that underpinned the “Secondary Products Revolution” in early agricultural societies [252]. Another major area of growth during the coming decade will be identifying and analyzing microbial pathogen genomes using archaeological material from domestic animals and wild congeners [253, 254]. This approach will provide new information for infectious disease research in livestock and companion animals, particularly for diseases such as bovine tuberculosis caused by Mycobacterium bovis, which may have emerged as livestock population densities increased during the Neolithic period [255].

                  The introduction of aDNA and particularly paleogenomics to archaeology has not been universally welcomed [256]. In this regard, some commentators have proposed a “new archaeology”, which suggests that the role of archaeologists in population paleogenomics should be to ensure geneticists are fully informed about the complexities of human actions, interactions and population movements during the past [257]. Accordingly, this multidisciplinary approach would fully encompass existing scholarship on human history and prehistory, thereby facilitating accurate interpretations of paleogenomics data from ancient peoples and their animal companions [258,259,260]. Going forward, therefore, it will be important to ensure that archaeologists and historians are actively involved in large-scale paleogenomics studies of livestock and other domestic animals, and that these experts are considered to be more than just passive “sample providers” [256, 261].

                  It is important to finish this review by emphasizing that there will be myriad practical applications for systematically exploring and cataloguing domestic animal genome diversity using high resolution population genomics of extant and extinct domestic animal populations and their wild ancestors. For example, the Functional Annotation of Animal Genomes (FAANG) initiative that aims to identify all functional elements in animal genomes [262] will directly benefit from understanding how genomic regulatory networks have been shaped by domestication, migration and adaptive introgression from wild populations, as well as ancient and more recent human-mediated selection. Finally, identifying and tracking functionally important genomic variation in livestock across space and time will provide novel information for enhancement of welfare, health and production traits using new breeding technologies that are underpinned by genome editing [263].


                  Watch the video: ΓΗΣ ΜΑΔΙΑΜ ΓΑΡΔΕΝΙΑ (August 2022).