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Reproductive system in plants

mode of reproduction in crop plants, mode of pollination

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Reproductive system in plants

  1. 1. Reproductive System In Plants •Breeding procedure depends upon: Mode of reproduction Pollination of crop species
  2. 2. Cell Division • Cell division id of 2 types: 1. Mitosis 2. Meiosis MITOSIS: • Cell increases in number • Mitotic cell division takes place in somatic cells resulting in growth of organism • Two identical daughter cells produced from mother cell. • It has 5 stages: Interphase, Prophase, metaphase, Anaphase, Telophase
  3. 3. It has 5 stages: Interphase, Prophase, metaphase, Anaphase, Telophase
  4. 4. Meiosis • Meiotic cell division occurs in reproductive organs during gamete formation • Reduce the chromosome no. from diploid (2n)  haploid (n) • Two divisions of cytoplasm and one duplication of chromosome occurs • 1st Meiotic division: Reductional Division 2 daughter cells formed with half chromosome number • 2nd meiotic division: Similar to mitotic division
  5. 5. MODE OF REPRODUCTION Asexual Reproduction: •Vegetative reproduction •Apomixis •Adventive embryony Sexual Reproduction: •Autogamy •Allogamy
  6. 6. Asexual Reproduction Vegetative reproduction Vegetative parts: rhizomes, tuber, corn, bulbs Cutting and grafting: Stem, roots Apomixis Parthenogenesis: embryo from egg cell without fertilization Apogamy: embryo from either synergids or antipodal cells Apospory : embryo from egg cell or embryo sac Adventive embryony Embryo directly formed from vegetative cells of ovule like nucleus, chalaza and integuments
  7. 7. Role of apomixes in plant breeding Rapid production of pure lines Maintenance of superior genotypes Conservation of heterosis
  8. 8. Significance of asexual reproduction • It leads to perpetuation of same genotype with great conservation • Large no. of genetically identical genotypes can be obtained irrespective of degree of heterozygosity • Desirable clone can be maintained • Mutation breeding is easy in vegetative produced plants • Polyploidy breeding is also very useful as induced bud can be used as propagule and polyploidy can be maintained
  9. 9. Sexual reproduction Process involves fusion of male and female gametes to form seed and it is also called Amphimixes Flower has special structure for reproduction • Androecium  Stamen • Gynoecium Carpel Sporogenesis: production of microspore and megaspore • Microspores are produced in anthers  Microsporogenesis • Megaspores are produced in ovule  Megasporogenesis
  10. 10. Microsporogenesis • Anther has 4 pollen sacs, with numerous pollen mother cells (PMCs) meiosis • Each PMC-------- 4 haploid cells (microspores)pollen grains(by thickening of cell wall)
  11. 11. Megasporogenesis • Occurs in ovules inside ovary • Each single cell in ovule differentiates into Megaspore Mother cell  undergo meiosis 4haploid megaspores 3 haploid megapores degenerates • One functional megaspore per ovule obtained
  12. 12. Difference between microsporogenesis and megasporogenesis Microsporogenesis Megasporogenesis It is meiotic formation of haploid microspores from diploid microspore mother cell. It is meiotic formation of haploid megaspores from diploid megaspore mother cell. The arrangement of microspores in a tetrad is generally tetrahedral. The arrangement of megaspores in a tetrad is commonly linear. All the four microspores of a spore terad are functional. Only one megaspore of a spore tetrad is functional. Micro sporogenesis is found inside microsporangium. It is found inside a megasporangium. A large number of microspore mother cells are functional in a microsporangium. Generally a single megaspore mother cell is functional in a mega sporangium.
  13. 13. Gametogenesis Production of male and female gametes in microspore and megaspores. Microgametogenesis: production of male gamete/sperm • During pollen maturation, microspore nucleus divides mitotically produce: -> • generative nucleus • Vegetative/tube nucleus • When pollination occurs  pollen germinates • Pollen tube enters the stigma and grows through style • Generative nucleus undergo mitotic division to produce 2 sperms • Pollen tube enters the ovule through micopyle, and discharge 2 sperms into embryo sac
  14. 14. Megagametogenesis : Nucleus of functional megaspore divides mitotically to produce 4 or more nuclei Generally, Megaspore nucleus undergo 3 mitotic divisions to produce 8 nuclei: • 3 moves to one pole and produce a central egg cell and 2 synergid cells, 1 synergid on either side of egg cell • Another 3 migrate to opposite pole, forms antipodal cells • 2 remains in the centre, polar nuclei that fuse to form secondary nucleus. Thus, megaspore develops into a embryo sac /megagametophyte is called megagametogenesis
  15. 15. Fertilization • Fusion of one of the sperm with egg cell produce diploid zygote is fertilization – Zygote divide mitotically to produce a diploid embryo • Fusion of remaining sperm with secondary nucleus to form a triploid primary endosperm nucleus is Triple fusion – Triploid primary endosperm mitotically divide repeatedly to form endosperm – During seed development, endosperm provides nutrition to developing embryo • One male gametes unite with the eggs cell known as syngamy or fertilization and another male gamete fuse with the pollar nuclei known as triple fusion, when these two processes occurs simultaneously known as double fertilization
  16. 16. Mode Of Pollination Depending on nature of pollination plants can be categorized as self and cross pollinated Autogamy/ self fertilization: Transfer pollens from anther to stigma of same plant • Leads to homozygosity • Several mechanism : bisexualiy, homogamy, cleistogamy, chasmogamy Allogamy/ cross fertilization: pollen grains transfer from anther of one plant to stigma of another plant. • Leads to heterozygosity • Several mechanism: monecy, dioecy, dichogarny, heterostyly, herkogamy, self incompetibility, male sterlity
  17. 17. Autogamy/ self pollination Bisexuality • male and female organ on same plant Homogamy • anther and stigma of flower matures at same time Cleistogamy • pollination and fertilization occurs in unopened flower bud • Wheat, oats and barley Chasmogamy • flower opens only after completion of pollination • Wheat, oats, barley and rice
  18. 18. Allogamy / cross pollinated Dicliny/unisexuality • Monecy: Same plant but different male female flowers • Maize, banana, castor and mango • Dioecy: Staminate and pistillate flowers on different plants • Papaya and spinach Dichogamy • Stamen and pistil of hermophrodite plant mature at different times • Protandry: maize and sugarbeat (stamen mature before pistil) • Protogyny: bajra (pistil mature first) Heterostyly • Styles and filament of flower are of different length Herkogamy • Due to physical barrier like hyline membranearound anther
  19. 19. • Inability of fertile pollen to fertilize the same flower • Brassica, radish, rye and nicotiana Self incompatibility • Pollen grains are non functional • Types: Genetic (GMS), Cytoplasmic (CMS), CGMS and Transgenic Male Sterility Allogamy
  20. 20. Autogamous species • Cereals: Rice, wheat, barley, oats • Legumes: chickpea, pea, cowpea, lentils, green gram, black gram soya bean, moth bean • Oilseeds: Sesame, linseed • Vegetables: tomato, okra, brinjal, peanut, chillies Seed propagated • potato Vegetative propagated
  21. 21. Allogamous species • Cereals: maize, pearlmillet, rye • Legumes: alfaalfa, red clover, white clover, sweet clover • Oilseeds: some brassica strains {B. campestris}, sunflower, castor • Vegetables: cabbage, carrot, cauliflower, cucumber, onion, radish, turnip, sewwt potato Seed propagated • Sugarcane, coffee, rubber, grapes, banana Vegetative propagated
  22. 22. Genetic constitution of allogamous species Preserve and promote heterozygosity Show mild  severe inbreeding depression and heterosis Hybrid and synthetic varieties are the aim of breeder
  23. 23. Often Allogamous Species •Cross pollination exceeds 5% to 30% •Sorghum, cotton, triticale, rai, pigeonpea and tobacco, jowar, jute, Seed propagated
  24. 24. Relevance of Mode of Reproduction • It determines: – Genetic constitution – Nature of gene action – The ease in pollen control – Stability of varieties after realease