Principle of Development of Androgenic Haploids
The basic principle of anther or pollen culture is the production of haploid plants exploiting the totipotancy of micro spore and the occurrence of single set of chromosome (n) in the microspore. In this process, normal development and the function of pollen cell to become a male gamete is stopped and is diverted forcely to a new metabolic pathway for vegetative cell division. For this objective, microspores , either within intact anther or in isolated state , are grown aseptically on the nutrient medium where the developing pollen grain will form callus tissue or embryoids that ultimately gives rise to haploid plantlets.
The principle behind the anther culture is that without disturbing the natural habitat and environment of the enclosed anther, pollen can be grown by culturing the intact anther. In culture condition, the diploid tissue of anther will remain living without proliferation at the selective medium and , at the same time it will encourage the development of pollen by nursing and providing nutrient. The haploid embryoids or the callus tissue can be seen as the anther dehisces in culture. But there is always possibility that the diploid callus or plantlets. To avoid this problem, free pollens isolated from the anther are grown in nutrient medium. Pollens at the uninucleate stage, just before the first mitosis is most suitable for induction of haploids.
Induction of haploids can be enhanced by keeping the anther or flower bud at low temperature. Low temperature causes the dissolution of microtubules, alteration in the first mitosis or maintenance of higher ratio of viable pollen capable of embryogenesis. Cold treatment may also act to help the embryogenesis of the anther which is considered to be inhibitory for the production of haploids.
Nutritional requirement of the excised anther are much similar than those of isolated micro spores. Rich medium should be avoided for anther culture since it proliferate the diploid tissue of anther wall. Incorporation of activated charcoal into medium has stimulated the induction of androgenesis. Iron, potato extract, coconut milk and growth regulators like auxin and cytokinins are used in anther and pollen culture due to their stimulatory effect on androgenesis.