Abstract
Barley endosperm halves release acid phosphatase in response to several gibberellins and gibberellin precursors. Seed halves incubated with 10(-7)m GA(3) at 29 degrees begin to release phosphatase after 11 hr and release it for another 26 hr in response to GA(3). After 37 hr, the rate of release slows to that of seed halves incubated without GA(3). GA(3) is active at 10(-10)m and maximally active at 10(-7)m. Comparative activity of 12 gibberellins and gibberellin precursors is GA(1) = GA(3) > GA(2) > GA(4) = GA(7) > GA(5) = GA(13) > GA(14) > GA(8) = GA(9) > (-)kaurenoic acid > (-)-kaurene. These compounds show the same order of activity and approximately the same relative activity in inducing reducing sugar release as in inducing phosphatase activity. The activity of each compound increases with its presumed position in a biosynthetic pathway leading from kaurene to GA(3). This correlation suggests that activity may be a reflection of the efficiency of conversion to an active form within the seed half.The ease of measuring the acid phosphatase response and the sensitivity of the seed halves to low concentrations of many gibberellins and gibberellin precursors makes this a useful bioassay for gibberellin-like substances.