Plant Reproduction II Lifecycle PDF

Plant Reproduction: The Plant Learning objectives: Lifecycle Be able to: Compare asexual and sexual plant reproduction, including the advantages and disadvantages Describe male and female gametophyte development Describe how the concept of modularity applies to female gameto...

Plant Reproduction: The Plant Learning objectives: Lifecycle Be able to: Compare asexual and sexual plant reproduction, including the advantages and disadvantages Describe male and female gametophyte development Describe how the concept of modularity applies to female gametophyte evolution Identify the parts of the mature male and female gametophytes Describe post-pollination development in flowering plants Identify the parts of the seed Identify the stages of embryo development Plant Life Cycles Life Cycle = the sequence of events that occur as an individual grows, matures, and reproduces. ant Life Cycles: Asexual any mechanism of producing offspring that does not involve the production of and fusion of gametes. Based on mitosis (in Eukaryotes) Offspring have identical copies of the parent genes ant Life Cycles: Asexual Rapid colonization of a new site is possible. All may be adversely affected by even minor changes in habitat Even isolated individuals can reproduce. ant Life Cycles: Asexual Fragmentation one of the most common methods of asexual reproduction. A large vining plant grows to several meters in length. Individual parts become self- sufficient by adventitious roots. If middle portions of the plant die, ends become separated and act as individuals. ant Life Cycles: Sexual the production of offspring that through the production of and fusion of gametes. Requires meiosis (reduces the number of chromosome sets) Offspring genetically different from the parents  some are less adapted than the parents  others are more adapted Isolated individuals can only reproduce through selfing In less stable environments, sexual reproduction can produce progeny that are more fit Plant Life Cycles Many plants reproduce both sexually and asexually. Seeds are produced by sexual reproduction and can be dispersed over long distances. New plants that are produced asexually are usually not capable of long-distance dispersal.  Alternation of Generations Type of sexual life cycle in all land plants Sporic Meiosis = meiosis produces spores 2 multicellular generations Gametophyte haploid produces gametes (sperm and egg) via mitosis Sporophyte diploid produces spores via meiosis  Alternation of Generations Spore a haploid reproductive cell that can grow into an adult without the fusion of another cell Produced by meiosis Gamete a haploid reproductive cell that must fuse with another gamete Produced by mitosis  Alternation of Generations Zygote undergoes mitosis to form a multicellular diploid organism (sporophyte) The diploid organism undergoes meiosis to form spores The spores undergo mitosis to /Syngamy form a multicellular haploid organism (gametophyte) Cells of the haploid organisms undergo mitosis to form gametes Gametes fuse to form a diploid zygote owering Plant Life Cycle The flower is part of the diploid sporophyte In the anther, specialized tissue undergoes meiosis to form microspores Pollen Development anther locule Pollen Development In the anther locule, microspore mother cells (2n) will undergo meiosis to form 4 haploid spores These cells have no cell wall and are instead surrounded by callose Pollen Development After the microspore mother cells undergo meiosis, the four resulting haploid microspores (male tetrad spores) are held together in a tetrad by that callose wall tapetum microspore callose Pollen Development The callose disintegrates, and the tetrad breaks apart releasing ‘free’ microspores. Each of these develops into a pollen grain. The tapetum cells undergo programmed cell death tapetum ‘free’ microspore Pollen Pollen grains have an elaborate cell wall composed of sporopollenin Cell wall Sporopollenin Phenolic polymer with carotenoids and carotenoid esters Impregnates walls of vascular plant spores (including pollen) Prevents desiccation Almost indestructible by microorganisms No enzyme capable of degradation has been identified  Pollen Water is not required for fertilization so fertilization can occur over longer distances To ensure fertilization, many plants produce vast amounts of pollen. The forests of Sweden produce 75,000 tons of pollen each year. Most is lost for fertilization Pollen Development Microspore Male gametophyte Mitosis Tube cell Generative cell The microspore undergoes mitosis to form a two –celled male gametophyte with a tube cell and a generative cell Pollen Development The generative cell will undergo mitosis one more time to form two sperm cells Mature male gametophyte in flowering plants = 3 cells! tube cell Sperm Tube cell sperm cells Pollen Development Male gametophyte Tube cell Generative cell Tube cell Sperm The microspore undergoes mitosis to form a two –celled male gametophyte with a tube cell and a generative cell. The owering Plant Life Cycle Male Gametophyte owering Plant Life Cycle Special cells in the flower undergo meiosis to form four megaspores Three degenerate Ovule wall Manekia (Arias 2007) owering Plant Life Cycle Functional megaspore undergoes mitosis to form megagametophyte Nuclei migrate to new positions in the embryo sac synergids egg Female Gametophyte most typical form is 7 cells, 8 nuclei Retained with in the ovule of the mother plant synergids polar not free living like female gametophytes nuclei of mosses & ferns antipodals emale Gametophyte Diversity rview of Female Gametophyte Development etophytes in Flowering Plants are Highly Reduced Male gametophytes = 3 cells Most typical female gametophyte = 7 cells, 8 nuclei Compare to the relatively large leafy structures in mosses male Gametophyte Evolution Modularity the concept that organisms or metabolic pathways are composed of modules. Duplication of modules = profound changes in structure Duplication can result in new functions for duplicated modules Modularity the concept that organisms or metabolic pathways are composed of modules. Duplication of modules = profound changes in structure Duplication can result in new functions for duplicated modules Modularity Water lilies and other early-diverging angiosperm lineage only have 1 module = 4 cells and 4 nuclei Modularity Duplication led to 8 nuclei, 7 cells Pollination Must get the sperm, produced by the male gametophyte to the egg, produced by the female gametophyte Pollen is transported from the anther to a stigma of a flower = Pollination We will return to pollination he Progamic Phase The stage between pollination and fertilization Pollen After pollen reaches the stigma, it Germination germinates A pollen tube grows out of the grain Pollen Germination Pollen tube wall is made mostly of callose  male Pollen Tube gametophy Growth te female gametoph yte The pollen tube carrying the male gamete grows down the style to reach the female gametophyte = through the Transmitting Tract Pollen Competition As pollen tubes grow through the style they compete with each other. Only the fastest (and presumably most fit) will reach the ovules and pass on their genes to the next generation Pollen Tube Growth The pollen tube is guided by signals from the ovule he Progamic Phase Fertilization The pollen tube enters the nucleus through the  Double Fertilization The pollen tube enters the nucleus through the micropyle The two sperm nuclei are released into the female gametophyte One sperm fuses with the egg to form the zygote One sperm fuses with the 2 fused polar nuclei to form 3n endosperm = DOUBLE FERTILIZATION  Double Fertilization Egg Unique to Sperm Angiosperms nucleus #1 cytoplasm of pollen tube Results in a better nutritive store (endosperm) than that found in gymnosperm seeds Sperm nucleus #2 polar nucleus Fertilization Fertilization results in a seed that represents a new sporophyte phase Seeds Sperm 1 Sperm2 Egg 2-Polar Nuclei n n n n+n Zygote One Cell 2n Mitosis Onecells Many Cell Endosperm Embryo = Many cells Mitosis 3n 2n Seed Smallest In orchids, like Vanilla Seeds http://waynesword.palomar.edu/ww0601.htm#seed Close-up of Seeds  Endosperm Two-thirds of all human calories come from Endosperm Endosperm Flour (oat, wheat, barley, rice) = finely ground endosperm. White flour – just endosperm Whole wheat – endosperm + outer layers Teosinte (wild ancestor of corn) has kernel that are too difficult to eat, but Teosinte can pop. Central Americans were likely popping corn over 9000 years ago  Seed Ontogeny Sperm2 Egg n n Zygote One Cell 2n Mitosis Embryo = Many cells 2n  Asymetrical Initiation of polarity in the environmen tal signal first mitotic division of the zygote Polarization Fixation of polarity cell division Polarity in Fucus (brown algae) Arrowroot Sagittaria (monocot) apical cell = will become embryo proper basal cell = will become suspensor Zygote + Mitosis =Two cell stage Fig 22-3  Beginning of Differentiation The mass of undifferentiated cells begins to differentiate into primary meristems 1. Protoderm 2. Ground Meristem 3. Procambium Fig 22-3 Capsella – globular stage Capsella – torpedo stage cotyledon suspensor Capsella – mature embryo  Endosperm Embryo at Ovule Globular Stage Stalk Cells Suspensor Basal Cell Endosperm Cotyledons *Cotyledons absorb the endosperm before germination Seed Early Development in Monocots: Styles = “silk” Zea Embryo  embryo scutellum coleoptile/coleorhiza plumule/radicle endosperm pericarp + seed coat Zea mays  Pericarp (Fruit Wall) and Seed Coat  Pericarp and Seed Coat Endosperm The endosperm is still present at germination  Pericarp and Seed Coat Endosperm Embryo Scutellum  Plumule (Epicotyl) Scutellum  Plumule (Epicotyl) Scutellum Hypocotyl  Plumule (Epicotyl) Scutellum Hypocotyl Radicle Coleoptile Plumule (Epicotyl) Scutellum Hypocotyl Radicle Coleorhiza  Seeds – Key Processes 1. Dormancy 1. Metabolic processes slow down as the moisture content of the embryo decreases. Cell water content declines from ~ 90% to less than 15% - for long term storage less than 8%  Dormancy and Longevity Sacred lotus seeds have germinated after 1,450 years Date palm germinated germinated after 2,000 years, found in food stores hidden in AD 70 The longest-running test of seed dormancy in soil at Michigan State University 1879: buried 20 bottles containing sand and seeds from 21 common plants 8 sprouted in 1920 3 in 1980 2 in 2000  Dormancy and Longevity Seed Banks Seed banks throughout the world store about 0.6 % of the world's plant diversity Seedbanks in Iraq, Afghanistan & Syria lost or affected by war, Philippines destroyed in 2006 tsunami. “Doomsday Vault” = Svalbard Global Seed Vault in Norway opened in 2008 – Global Crop Diversity Trust (0.5 million varieties)  Seed Conservation Lyon Arboretum – University of Hawai'i at Manoa Hawaiian Rare Plant Program Seed Conservation Lab 10 million seeds banked 550 taxa of native Hawaiian plants (~40% of the flora). Over half are federally listed as threatened or endangered. Provide for both long-term storage – preservation of genetic variation Propagation of plants for restoration efforts.  Seeds – Key Processes 1. Dormancy 1. Metabolic processes slow down as the moisture content of the embryo decreases. Cell water content declines from ~ 90% to less than 15% - for long term storage less than 8% 2. Dispersal 1. Moving away from home. 2. Fruit vs. seed 3. Many modes and mechanisms of dispersal for both bodies. http://news.sciencemag.org/environment/ 2015/10/plant-seeds-look-smell-poop-fooling-dung- beetles-planting-them  Seeds – Key Processes 1. Dormancy 1. Metabolic processes slow down as the moisture content of the embryo decreases. Cell water content declines from ~ 90% to less than 15% - for long term storage less than 8% 2. Dispersal 1. Moving away from home. 2. Fruit vs. seed 3. Many modes and mechanisms of dispersal for both bodies. 3. Germination = Resumption of growth 1. Water (see Dormancy) 2. Temperature 3. Oxygen (needed for aerobic respiration) 4. Environmental cues (light, period of cold) 5. Hormones (-Abscisic Acid, + Gibberellins)  Seed Germination 1. Scarification - breaking seed coat – for water or oxygen a. Digestive tract b. Mechanical cracking c. Fire 2. Leaching off of inhibitors 3. Stratification - winter cold period  Endosperm Pericarp and Seed Coat Coleoptile Plumule (Epicotyl) Scutellum Embryo Hypocotyl Radicle Coleorhiza Corn Grain or Kernel A Monocot