Pollen dimorphism in relation to pollen plant formation

Induction of haploid plants from pollen grains on culture of anthers has been possible in a number of angiosperms but it is not yet understood why only a fraction of pollen responds to form haploids. Noteworthy in this connection are the recent experiments on anther culture of barley, tobacco and wheat, where it has been pointed out that pollen populations are basically dimorphic. Pollen capable of forming haploids occur in a low frequency, arc smaller, and different from the majority of pollen destined to form gametes. Particularly in tobacco it has been possible to increase the frequency of pollen capable of forming embryos by subjecting plants to low temperature prior to flowering, and to achieve differentiation of embryogenic pollen by subjecting young buds from such plants to a prolonged cold treatment. On selective isolation, from the rest of the pollen, the embryogenic pollen from such buds readily form embryos at high frequency on a simple mineral-sucrose medium. The embryogenic pollen are repressed for gametophytic differentiation and in culture they differentiate to produce embryos. These experiments provide evidence that only certain pollen are capable of forming haploids.