BIOSYNTHETIC ORIGIN OF GIBBERELLIN-A3 AND GIBBERELLIN-A7 IN CELL-FREE PREPARATIONS FROM SEEDS OF MARAH-MACROCARPUS AND MALUS-DOMESTICA

Cell-free preparations from seeds of Marah macrocarpus L. and Malus domestics L. catalyzed the conversion of gibberellin A9 (GA9) and 2,3-dehydroGA9 to GA7; GA9 was also metabolized to GA4 in a branch pathway. The preparation from Marah seeds also metabolized GA5 to GA3 in high yield; GA6 was a minor product and was not metabolized to GA3. Using substrates stereospecifically labeled with deuterium, it was shown that the metabolism of GA5 to GA3 and of 2,3-dehydroGA9 to GA7 occurs with the loss of the 1β-hydrogen. In cultures of Gibberella fujikuroi, mutant B1-41a, [1β,2β-2H2]GA4, was metabolized to [1,2-2H2]GA3 with the loss of the 1α- and 2α-hydrogens. These results provide further evidence that the biosynthetic origin of GA3 and GA7 in higher plants is different from that in the fungus Gibberella fujikuroi.