Physiological effects of gibberellic acid. III. Observations on its mode of action on barley endosperm

Abstract

As a response to increasing amounts of gibberellic acid (GA3) the barley endosperm liberates increasing quantities of reducing sugar and protein. There is, as well, a proportional decrease in the resultant dry weight of the endosperm. This GA3-induced response syndrome can be prevented by preheating the intact grain before treatment with GA3, or by incorporating 1 of several sulfhydryl reacting compounds in the incubation solution. The response syndrome over the 1st 24 hour period is also sensitive to incubation temperature, evidencing a pronounced maximum at 30[degree]C. Q10 values derived from the endosperm responses to GA3 range from 2.6 to 8.7 indicating that enzyme formation or activation is occurring. When the incubation time, at 24[degree]C, is extended to 3 days half the initial dry weight of the endosperm is lost to the ambient solution with a large proportion of this loss being recoverable as reducing sugar and protein. A possible sequence of events leading to these manifestations is discussed, and a tentative hormonal role for gibberellin as an "endosperm mobilizing hormone", in the germination of barley, is suggested.