The increase ofα-amylase activity in embryoless rice endosperm induced by the addition of gibberellin A3was examined under various conditions with an aim to establish a bioassay method for gibberellins.Sterilized embryoless rice endosperms were incubated in a test tube containing 0.2–1.0 ml of test solution for 4 days at 30°.α-Amylase activity in the endosperm was determined by measuring digestion of added starch. The increase of amylase activity during the incubation was not affected by the addition of various vitamins, amino acids, organic acids, protease, sucrose, indoleacetic acid or kinetin. Helminthosporol, helminthosporic acid and sclerin (1–10μg/ml) had weak promoting effects. Under appropriate conditions, 10−5μg/ml of gibberellin A3could be detected. In double logarithmic plot, the increase in the enzyme activity was proportional to the gibberellin A3concentration in the range from 10−5
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