Internode Length in Pisum: Gene na May Block Gibberellin Synthesis between ent-7alpha-Hydroxykaurenoic Acid and Gibberellin A(12)-Aldehyde

Abstract

The elongation response of the gibberellin (GA) deficient genotypes na, ls, and lh of peas (Pisum sativum L.) to a range of GA-precursors was examined. Plants possessing gene na did not respond to precursors in the GA biosynthetic pathway prior to GA(12)-aldehyde. In contrast, plants possessing lh and ls responded as well as wild-type plants (dwarfed with AMO-1618) to these compounds. The results suggest that GA biosynthesis is blocked prior to ent-kaurene in the lh and ls mutants and between ent-7alpha-hydroxykaurenoic acid and GA(12)-aldehyde in the na mutant. Feeds of ent-[(3)H]kaurenoic acid and [(2)H]GA(12)-aldehyde to a range of genotypes supported the above conclusions. The na line WL1766 was shown by gas chromatography-mass spectrometry (GC-MS) to metabolize [(2)H]GA(12)-aldehyde to a number of[(2)H]C(19)-GAs including GA(1). However, there was no indication in na genotypes for the metabolism of ent-[(3)H]kaurenoic acid to these GAs. In contrast, the expanding shoot tissue of all Na genotypes examined metabolised ent-[(3)H]kaurenoic acid to radioactive compounds that co-chromatographed with GA(1), GA(8), GA(20), and GA(29). However, insufficient material was present for unequivocal identification of the metabolites. The radioactive profiles from HPLC of extracts of the node treated with ent-[(3)H]kaurenoic acid were similar for both Na and na plants and contained ent-16alpha,17-dihydroxykaurenoic acid and ent-6alpha,7alpha,16beta,17-tetrahydroxykaurenoic acid (both characterized by GC-MS), suggesting that the metabolites arose from side branches of the main GA-biosynthetic pathway. Thus, both Na and na plants appear capable of ent-7alpha-hydroxylation.