Sexual Reproduction In Flowering Plants


Sexual Reproduction In Flowering Plants logoSubject: Biology    Exam: AIPMT / NEET-UG

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Important Points

Gametic fusion or Syngamy is also referred to as Amphimixis. Reproduction avoiding gametic fusion is termed apomixis or asexual reproduction. As for instance in Citrus the supernumerary embryos produced by nucellus and finally lodged in the embryo-sac are referred to as apomictic embryos, and even adventive embryos.
Apogamy is development of sporophyte form gametophyte without gametic fusion. Apogamous sporophytes are thus abnormal in being haploid. They are of no consequence in the life cycle of the plant. Apospory, likewise, is formation of gametophte from sporophyte without meiosis. Aposporous gametophytes are thus abnormal in being diploid. Both apogamy and apospory are only of academic significance as they reveal that ploidy of a cell does not seal the developmental destiny of the cell; a diploid cell can develop like a haploid one (in apospory) and hapoid, like a diploid-one. Parthenogenesis which is development of embryo or individual from the gamete without fertilization, is a form of apogamy. Apogamy (preceded by meiosis) is the only example of asexual reproduction producing variation among the progeny.
Formation of diploid embryo-sac (abnormally, without the meiosis), also call diplospory is an example of apospory. Parthenogenesis from diplosporous embryo-sac would produce no variation in progeny (due to lack of meiosis) and amount to cloning.
In case of interspecific and intergeneric hybridizations, the degeneration (or abortion) of hybrid embryo can be averted by retrieving the hybrid embryo and culturing it (embryo rescue or resuscitation).
Product of congenital fusion between stamens and stigma as found in orchids and milkweeds, is called gynostegium or gynostemium. Orchids and milkweeds (=asclepiads) are also characterized in possessing pollinia (fusion product of all pollen of an anther sac) and translator apparatus (to enforced a peculiar mode of insect pollination or entomophily).
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