The metabolism of applied gibberellic acid in Pharbitis nil choisy: tentative identification of its sole metabolite as gibberellic acid glucoside and some of its properties

Abstract

Radioactive gibberellic acid ([(14)C]GA3) applied to seedlings of Pharbitis nil strain Violet is converted to one single metabolite (R-[(14)C]GA3), which has been tentatively identified as GA3-glucoside. As with authentic GA3-glucoside, R-[(14)C]GA3 can be hydrolysed to some extent with cellulase and β-glucuronidase, but hardly at all with β-glucosidase. Acid hydrolysis, which is more effective than enzymatic hydrolysis, yielded GA3 as well as a biological inactive compound. The latter represents a degradation product of GA3 due to the sensitivity of GA3 to acidic conditions.The R-[(14)C]GA3, like authentic GA3-glucoside, possesses little or no biological activity. R-[(14)C]GA3 applied to developing seeds is partly hydrolysed during imbibition of the mature seed but is, however, reconverted to R-[(14)C]GA3 during subsequent germination. Applied R-[(14)C]GA3 is strongly accumulated in the cotyledons of Pharbitis seedlings, to a greater extent than [(14)C]GA3. However, unlike [(14)C]GA3 it is not accumulated in the apical regions of the hypocotyl. Furthermore no competition was observed between R-[(14)C]GA3 and [(14)C]GA3, which suggests that they do not compete for the same sites.