Growth Regulators for Pollen Embryogenesis - In Solanaceous plants, pollen embryogenesis does not require any growth regulators, but low levels of auxins, cytokinins and even GA3 appear beneficial; 0.1 mg/l IAA gave the best results. In Hyoscyamus niger an auxin, e.g., 2 mg/l 2, 4-D, enhanced the frequency of responding calli but had no effect on the number of embryogenic pollen grains.
In contrast, cytokinins (0.01-10 mg/l) reduced the number of pollen grains producing embryos most likely by interfering with cell division in induced pollen grains. In species where callus is formed, e.g., cereals, auxins and cytokinins are almost invariably used either in combination or in sequence, but the role played by them is not known. It seems that different GRs may be required for best results with different plant species.