In vitro Androgenesis
androgenesis is the formation of sporophyte from the male gametophyte on artificial medium. It is most commonly found in family Solanaceae and Poaceae (Graminae). Success of in vitro
androgenesis is based on adjustment of developmental stage of pollen, minerals of culture medium and growth regulators as well as thermal shock or other treatments.
Methods of in vitro
androgenesis is given in Fig. 8.10. Pollen grains are isolated from excised anther and extracted in a beaker. Well collected pollens are washed properly and centrifuged and decanted. They are inoculated in liquid medium, then subcultured in solid MS medium. In culture pollen grains can be induced to produce callus or embryo from which whole plants are regenerated in one month. This technique is most successful in Brassica, Datura, Petunia, etc.
Mainly there are two ways of in vitro
morphogenesis of pollen grains, direct and indirect (Fig. 8.10).
Fig. 8.10. Types of in vitro pollen morphogenesis in Datura (based on Sangwan, 1981)
- Direct androgenesis.
Direct androgenesis is also called pollen derived embryogenesis. Here pollen directly acts as a zygote and, therefore, passes through various embryogenic stages similar to zygotic embryogenesis. When pollen grains has reached globular stage of embryo, wall of pollen is broken and embryo is released. The released embryo develops cotyledons, then the plants. Direct androgenesis is very common in many plants of the family Solanaceae and Brassicaceae (Fig. 8.10) (Prakash and Giles, 1987).
- Indirect androgenesis.
In indirect androgenesis the pollen grains, instead of normal embryogenesis, divide erratically to develop callus (Fig. 8.10). Indirect androgenesis has been found in barley, wheat, Vitis, coffea, etc. Possibility of pollen morphology from the dividing pollen varies. The haploid callus, embryo or plantlets may originate from (i) the continued division of vegetative cells of the pollen (the generative cell soon degenerate), (ii) multiple division of generative cells (non-vegetative cell), and (Hi) division products of both generative and vegetative cells (Sangwan, 1981).