Biosynthetic Origin of Gibberellins A(3) and A(7) in Cell-Free Preparations from Seeds of Marah macrocarpus and Malus domestica.

Cell-free preparations from seeds of Marah macrocarpus L. and Malus domestica L. catalyzed the conversion of gibberellin A(9) (GA(9)) and 2,3-dehydroGA(9) to GA(7); GA(9) was also metabolized to GA(4) in a branch pathway. The preparation from Marah seeds also metabolized GA(5) to GA(3) in high yield; GA(6) was a minor product and was not metabolized to GA(3). Using substrates stereospecifically labeled with deuterium, it was shown that the metabolism of GA(5) to GA(3) and of 2,3-dehydroGA(9) to GA(7) occurs with the loss of the 1beta-hydrogen. In cultures of Gibberella fujikuroi, mutant B1-41a, [1beta,2beta-(2)H(2)]GA(4), was metabolized to [1,2-(2)H(2)]GA(3) with the loss of the 1alpha- and 2alpha-hydrogens. These results provide further evidence that the biosynthetic origin of GA(3) and GA(7) in higher plants is different from that in the fungus Gibberella fujikuroi.