Sexual Reproduction in Flowering Plants
Special modesapomixis, parthenocarpy, polyembryony
- Apomixis occurs through vegetative propagation and Agamospermy in which vegetative reproduction produces new plant from buds, leaves and stem and there is no requirement of seed.
- Agamospermy is of three types
(i) Recurrent agamospermy
(ii) Adventive embryony
(iii) Non-recurrent agamospermy
- A diploid embryo-sac is formed having diploid egg cell which grows into a diploid embryo, Termed as re-current agamospermy. Eg: Apple, Allium.
- In adventive embryony, one or few extra embryos are formed from diploid cells of nucleus (or) integument but never from egg. Eg. Opuntia, citrus.
- Embryo develops parthenogenetically from haploid egg, synergid, antipodal cells is termed as Non-recurrent agamospermy.
- Diplospory and Apospory are the sub-types of recurrent agamospermy.
- In diplospory, a diploid embryo sac is formed from diploid megaspore mother cell without regular mitotic division.
- Apospory develops embryo from diploid nuclear mother cell.
- The phenomenon of having more than one embryo is called Polyembryony (Eg. group of ground nut, onion etc.) Which is of 2 types (i) simple and (ii) Adventive.
- Polyembryony due to fertilization of more than one egg is termed as simple.
- Formation of extra embryos through sporophytic budding is called as adventive polyembryony.
- The other two types of polyembryony are false and true wherein false type, more than one embryo arise in different embryo sacs in the ovule.
- If more than one embryo is formed in the same embryo sac in the ovule it is termed as true polyembryony.
- Development of fruits without fertilization is parthenocarpy, coined by Noll who also suggested that the parthenocarpic fruits are seedless
Eg. Banana, guava, apple, pineapple.
- Parthenocarpy can be induced artificially by following methods: auxins, gibberellins, delaying pollination, use of powdered pollen grains and extracts.
- Parthenocarpic fruits don’t contain irritant seeds and are used for quicker food processing.
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