Promotion of Growth and Invertase Activity by Gibberellic Acid in Developing Avena Internodes 1

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RESUMO

Gibberellic acid (GA3) induces invertase activity within 6 hours in Avena stem segments that are incubated in the dark at 23°. 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 × 10−5 μm GA3. The increase in invertase activity elicited by GA3 between 3 × 10−5 μm and 300 μm 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 hours of incubation, then decays slowly between 12 and 48 hours. In GA3-treated segments, the invertase activity also rises during the first 6 hours, parallel to that in control segments and continues to rise during the next 42 hours. These changes in invertase activity during 48-hour incubation periods do not parallel the changes in growth that occur in control and GA3-treated segments. Cycloheximide at 10 μg/ml abolishes all GA3-promoted growth and invertase activity in these segments. Actinomycin D at 40 and 80 μg/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.

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