Promotion of Growth and Invertase Activity by Gibberellic Acid in Developing Avena Internodes

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Abstract
Gibberellic acid (GA3) induces invertase activity within 6 hr.in Avena stem segments that are incubated in the dark at 23[degree]. The maximum amount of promotion is about 5 times that of invertase activity in untreated segments. GA3 causes significant promotion of invertase activity at concentrations as low as 3 x 10-5 [mu][image] GA3. Theincrease in invertase activity elicited by GA3 between 3 x 10-5 [mu][image] and 300 [mu][image] closely parallels the growth promotion that is caused by GA3 over this concentration range. In control segments, invertase activity rises steeply during the first 6 hr of incubation, then decays slowly between 12 and 48 hr. In GA3 treated segments, the invertase activity also rises during the first 6 hr., parallel to that in control segments and continues to rise during the next 42 hr. These changes in invertase activity during 48-hr incubation periods do not parallel the changes in growth that occur in control and GA3-treated segments. Cycloheximide at 10 [mu]g/ml abolishes all GA3-promoted growth and invertase activity in these segments. Actinomycin D at 40 and 80 [mu]g/ml decreases GA3-promoted growth by 20 % and invertase activity by 38 and 44%, respectively. The data clearly support the idea that protein synthesis is necessary for GA3-promoted growth and invertase activity in Avena stem segments.