CHANGES IN SELECTED PLANT-GROWTH REGULATORS DURING GERMINATION IN SORGHUM

The technique of radioimmunoassay following sample resolution by HPLC was used to assay the amounts of the cytokinins zeatin (Z), zeatin rib oside (ZR) and isopentenyladenine (IPA), the combined amounts of gibbe rellins(1+3) (GA(1+3)), and the amounts of indole acetic acid (IAA) an d abscisic acid (ABA) during germination in grains of sorghum. Concent rations of GA(1+3) were low throughout germination and did not appear to be related to the time of germination. In the mature, non-germinate d grain, the concentration of each of the other plant growth regulator s was much higher in the smaller component comprised of the embryonic axis and scutellum than in the much larger endosperm tissue. During th e germination period studied (64 h), these concentrations declined, wi th a peak in the amount of the cytokinin IPA and a small peak in Z+ZR (24 h) in the embryo following the first visible signs of root protrus ion and coincident with a large enhancement in amylase activity. The h igh concentration of ABA in the embryo tissue prior to germination was noteworthy. It is suggested that the interaction of ABA and the cytok inins IPA and Z+ZR may play a significant role in controlling sorghum germination.