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Title: Translocation and metabolism of gibberellins in seedlings of Phaseolus coccineus L.
Author: Nash, Linda Joan
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1976
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The investigations reported here concern the translocation and metabolic relationships of gibberellins (GAs) in light-grown seedlings of Phaseolus coccineus L., in which GA1, GA4, GA5 and GA20 are known to be endogenous components (Bowen et al., 1973). These four GAs were equally effective in promoting subapical elongation of shoot explants when applied exogenously to the apical bud or stem base. The apical buds or stem bases of intact seedlings were treated with [3h] GA1,GA 4, GA5, GA8, GA9, GA12 aldehyde or GA14. The redistribution of radioactivity from apically applied GAs differed considerably from that observed after applications to the stem base. Apically applied GAs were retained by the apical bud and underwent relatively little metabolism in a 24h period, whereas basal application resulted in extensive redistribution of the [3h] GAs and of a high proportion of chromato- graphically distinct radioactive metabolites. No evidence was obtained for the export of [3H] Gas from cotyledons to the remainder of the developing seedling. The identity of the conversion products of applied [3H ] GAs was further investigated by analytical HPLC of extracts previously extensively purified by gel-permeation and charcoal adsorption chromatography and preparative-scale HPLC. Analysis of extracts by analytical HPLC permitted the identification of a number of metabolites by subsequent mass spectrometry. The apparent rates of conversion of [3H] Gas differed considerably, the most rapid disappearance being observed after feeding [3H] GA8, whereas recoveries of [3H] GA5 were high relative to other GAs. Each applied [3H] GA was found to give rise to a characteristic array of products, and there was thus no evidence for the accumulation of a single terminal .metabolite. Mass spectrometric evidence demonstrated conclusively that [3H]GA4 was converted to [3H]GA1, and [3H] GA9 to [3H] GA20, in high yields. [3H] GA1 gave rise to small amounts of a compound with chromatographic properties identical to those of GA8, but there was no significant accumulation of further metabolites of [3h] GA20. There was no observable accumulation of free GA-like metabolites after [3H] GA14 treatment, but complex spectra of meta-bolites were obtained after [3H] GA12 aldehyde feeds. All of the applied GAs and each of their free GA-like metabolites were converted to acidic butanol-soluble conjugates which probably represented glucosyl ethers. In the case of [3H] GA1, [3H] GA5,and [3H] GA20 treatments, these conjugates represented the major meta-bolites recovered. In addition, [3h] GA4, [3H] GA12 aldehyde and [3H] GA14 feeds provided significant quantities of presumptive glucosyl esters of the applied GAs and their acidic ethyl acetatesoluble metabolites. GA metabolism in p. coccineus seedlings was found to differ both quantitatively and qualitatively from that reported for Pisum sativum (Railton et al., 1974; Frydman and MacMillan, 1975), Gibberella fujikuroi (MacMillan, 1974b) and cucurbita maxima endosperm preparations (Graebe and Hedden, 1974). However, some resemblances to the conversions of applied [3H] GAS by developing P. vulgaris seeds (Yamane et al., 1975) were noted. In P. coccineus seedlings, both biosynthetic and catabolic mechanisms appear to be active, with the result that applied GAs are readily metabolised, but the accumulation of products is less marked than in either Gibberella fujikuroi or developing seeds.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available