GIBBERELLIC-ACID DECOMPOSITION AND ITS LOSS OF BIOLOGICAL-ACTIVITY INAQUEOUS-SOLUTIONS

In addition to gibberellic acid (GA(3)), significant amounts of iso-GA (3), an isomer of GA(3), accumulated in cultures media of the fungus G ibberella fujikuroi. It has been reported that iso-GA(3) is an interme diate in the decomposition of GA(3) to gibberellenic acid, a dicarboxy lic acid lacking the gamma-lactone ring. In this work, we studied the decomposition of GA(3) in buffered aqueous solutions at pH 5 and 7, bo th by spectrophotometry, measuring the appearance of gibberellenic aci d at 254 nm, and using a bioassay by measuring the induction of alpha- amylase in barley endosperm. Results indicate that at both pH values, biological inactivation of GA(3) is more rapid than the appearance of gibberellenic acid, suggesting that inactivation is largely due to con version to the intermediate, iso-GA(3). Furtheremore, no induction of alpha-amylase activity in barley endosperm was obtained in bioassays w ith iso-GA(3).