Contents 1 Morphology 2 Seedless vascular plants 3 Gymnosperms 4 Angiosperms 5 Embryogenesis 6 See also 7 References

Morphology[edit] The microspore has three different wall layers. The outer layer is called the perispore, the next is the exospore, and the inner layer is the endospore. The perispore is the thickest of the three layers while the exospore and endospore are relatively equal in width.[4]

Seedless vascular plants[edit] In heterosporous seedless vascular plants, modified leaves called microsporophylls bear microsporangia containing many microsporocytes that undergo meiosis, each producing four microspores. Each microspore may develop into a male gametophyte consisting of a somewhat spherical antheridium within the microspore wall. Either 128 or 256 sperm cells with flagella are produced in each antheridium.[3] The only heterosporous ferns are aquatic or semi-aquatic, including the genera Marsilea,Regnellidium, Pilularia, Salvinia, and Azolla. Heterospory is also known in the lycopod genus Selaginella and in the quillwort genus Isoëtes. Types of seedless vascular plants: Ferns Spikemosses Quillworts

Gymnosperms[edit] In seed plants the microspores develop into pollen grains each containing a reduced, multicellular male gametophyte.[5] The megaspores, in turn, develop into reduced female gametophytes that produce egg cells that, once fertilized, develop into seeds. Pollen cones or microstrobili usually develop toward the tips of the lower branches in clusters up to 50 or more. The microsporangia of gymnosperms develop in pairs toward the bases of the scales, which are therefore called microsporophylls. Each of the microsporocytes in the microsporangia undergoes meiosis, producing four haploid microspores. These develop into pollen grains, each consisting of four cells and a pair of external air sacs. The air sacs give the pollen grains added buoyancy that helps with wind dispersal.[3] Types of Gymnosperms: Conifers Pines Ginkgos Cycads Gnetophytes

Angiosperms[edit] As the anther of a flowering plant develops, four patches of tissue differentiate from the main mass of cells. These patches of tissue contain many diploid microsporocyte cells, each of which undergoes meiosis producing a quartet of microspores. Four chambers (pollen sacs) lined with nutritive tapetal cells are visible by the time the microspores are produced. After meiosis, the haploid microspores undergo several changes: The microspore divides by mitosis producing two cells. The first of the cells (the generative cell) is small and is formed inside the second larger cell (the tube cell). The members of each part of the microspores separate from each other. A double-layered wall then develops around each microspore. These steps occur at relatively the same time and when complete, the microspores have become pollen grains.[3]

Embryogenesis[edit] Although it is not the usual route of a microspore, this process is the most effective way of yielding haploid and double haploid plants through the use of male sex hormones.[6] Under certain stressors such as heat or starvation, plants select for microspore embryogenesis. It was found that over 250 different species of angiosperms responded this way.[6] In the anther, after a microspore undergoes microsporogenesis, it can deviate towards embryogenesis and become star-like microspores. The microspore can then go one of four ways: Become an embryogenic microspore, undergo callogenesis to organogenesis (haploid/double haploid plant), become a pollen-like structure or die.[6][6]

See also[edit] Microsporangium Spore Megaspore

References[edit] ^ Evert, Ray (2013). Biology of Plants. 41 Madison Avenue New York, NY 10010: Peter Marshall. ISBN 978-1-4292-1961-7.  ^ Bateman, R.M.; Dimichele, W.A. (1994). "Heterospory - the most iterative key innovation in the evolutionary history of the plant kingdom". Biological Reviews of the Cambridge Philosophical Society. 69: 315–417.  ^ a b c d Bidlack, James E.; Jansky, Shelley H. (2011). Stern's Introductory Plant Biology. New York, NY: McGraw-Hill. ISBN 0-07-304052-5.  ^ Lang, G (1995). "Quartäre Vegetationsgeschichte Europas". Feddes Repertorium.  ^ Bhatnagar, S.P. (1996). Gymnosperms. New Age International. p. 8. ISBN 8122407927.  ^ a b c d Seguí-Simarro, José M.; Nuez, Fernando (2008-09-01). "How microspores transform into haploid embryos: changes associated with embryogenesis induction and microspore-derived embryogenesis". Physiologia Plantarum. 134 (1): 1–12. doi:10.1111/j.1399-3054.2008.01113.x. ISSN 1399-3054.  v t e Botany History of botany Subdisciplines Plant systematics Ethnobotany Paleobotany Plant anatomy Plant ecology Phytogeography Geobotany Flora Phytochemistry Plant pathology Bryology Phycology Floristics Dendrology Plant groups Algae Archaeplastida Bryophyte Non-vascular plants Vascular plants Spermatophytes Pteridophyte Gymnosperm Angiosperm Plant morphology (glossary) Plant cells Cell wall Phragmoplast Plastid Plasmodesma Vacuole Tissues Meristem Vascular tissue Vascular bundle Ground tissue Mesophyll Cork Wood Storage organs Vegetative Root Rhizoid Bulb Rhizome Shoot Stem Leaf Petiole Cataphyll Bud Sessility Reproductive (Flower) Flower development Inflorescence Umbel Raceme Bract Pedicellate Flower Whorl Floral symmetry Floral diagram Floral formula Receptacle Hypanthium (Floral cup) Perianth Tepal Petal Sepal Sporophyll Gynoecium Ovary Ovule Stigma Archegonium Androecium Stamen Staminode Pollen Tapetum Gynandrium Gametophyte Sporophyte Plant embryo Fruit Fruit anatomy Berry Capsule Seed Seed dispersal Endosperm Surface structures Epicuticular wax Plant cuticle Epidermis Stoma Nectary Trichome Prickle Plant physiology Materials Nutrition Photosynthesis Chlorophyll Plant hormone Transpiration Turgor pressure Bulk flow Aleurone Phytomelanin Sugar Sap Starch Cellulose Plant growth and habit Secondary growth Woody plants Herbaceous plants Habit Vines Lianas Shrubs Subshrubs Trees Succulent plants Reproduction Evolution Ecology Alternation of generations Sporangium Spore Microsporangia Microspore Megasporangium Megaspore Pollination Pollinators Pollen tube Double fertilization Germination Evolutionary development Evolutionary history timeline Hardiness zone Plant taxonomy History of plant systematics Herbarium Biological classification Botanical nomenclature Botanical name Correct name Author citation International Code of Nomenclature for algae, fungi, and plants (ICN) - for Cultivated Plants (ICNCP) Taxonomic rank International Association for Plant Taxonomy (IAPT) Plant taxonomy systems Cultivated plant taxonomy Citrus taxonomy cultigen cultivar Group grex Practice Agronomy Floriculture Forestry Horticulture Lists Related topics Botanical terms Botanists by author abbreviation Botanical expedition Category Portal WikiProject Retrieved from "" Categories: Plant reproduction

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