Identification of Gibberellins in Spinach and Effects of Light and Darkness on their Levels

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Abstract
The endogenous gibberellin (GA) content of spinach (Spinacia oleracea) was reinvestigated by combined gas chromatography-mass spectrometry analysis. The 13-hydroxy GAs: GA(53), GA(44), GA(19), GA(17), GA(20), GA(5), GA(1), GA(29), and GA(8); the non-3, 13-hydroxy GAs: GA(12), GA(15), GA(9), and GA(51); and the 3beta-hydroxy GAs: GA(4), GA(7), and GA(34), were identified in spinach extracts by comparing full-scan mass spectra and Kovats retention indices with those of reference GAs. In addition, spinach plants contained GA(7)-isolactone, 16,17-dihydro-17-hydroxy-GA(53), GA(29)-catabolite, 3-epi-GA(1), and 10 uncharacterized GAs with mass spectra indicative of mono- and dihydroxy-GA(12), monohydroxy-GA(25), dihydroxy-GA(24), and dihydroxy-GA(g). The effect of light-dark conditions on the GA levels of the 13-hydroxylation pathway was studied by using labeled internal standards in selected ion monitoring mode. In short day, the GA levels were higher at the end of the light period than at the end of the dark period. Levels of GAs at the end of each short day were relatively constant. During the first supplementary light period of long day treatment, GA(53) and GA(19) declined dramatically, GA(44) and GA(1) decreased slightly, and GA(20) increased. During the subsequent high-intensity light period, the GA(20) level decreased and the levels of GA(53), GA(44), GA(19), and GA(1) increased slightly. Within 7 days after the beginning of long day treatment, similar patterns for GA(53) and GA(19) occurred. Furthermore, when these plants were transferred to darkness, an increase in the levels of GA(53) and GA(19) was observed. These results are compatible with the idea that in spinach, the flow through the GA biosynthetic pathway is much enhanced during the high-intensity light period, although GA turnover occurs also during the supplementary period of long day, both effects being responsible for the increase of GA(20) and GA(1) in long day.