Photoperiod Modification of [C]gibberellin A(12) Aldehyde Metabolism in Shoots of Pea, Line G2

In G2 peas (Pisum sativum L.) apical senescence occurs only in long days (LD), and indeterminate growth is associated with elevated gibberellin (GA) levels in the shoot in short days (SD). Metabolism of GA(12) aldehyde was investigated by feeding shoots grown in SD or LD with [(14)C]GA(12) aldehyde through the cut end of the stem for 0.5 to 6 hours in the light and analyzing the tissue extract by high performance liquid chromatography. More radioactive products were detected than can be accounted for by the two GA metabolic pathways previously known to be present in peas. Three of the major products appear to be GA conjugates, but an additional pathway(s) of GA metabolism may be present. The levels of putative C(20) GAs, [(14)C]GA(53), [(14)C]GA(44), [(14)C]GA(19), and/or [(14)C] GA(17), were all elevated in SD as compared to LD. Putative [(14)C]GA, was slightly higher in LD than in SD. Putative [(14)C]GA(53) was a major metabolite after 30 minutes of treatment in SD but had declined after longer treatment times to be replaced by elevated levels of putative [(14)C] GA(44) and [(14)C]GA(19/17). Metabolism of GA(20) was slow in both photoperiods. Although GA(20) and GA(19) are the major endogenous GAs as determined by gas chromatography-mass spectrometry, putative [(14)C]GA(20) and [(14)C]GA(19) were never major products of [(14)C]GA(12) aldehyde metabolism. Thus, photoperiod acts in G2 peas to change the rate of GA(53) production from GA(12) aldehyde, with the levels of the subsequent GAs on the 13-OH pathway being determined by the amount of GA(53) being produced.