Gibberellin metabolism in excised lettuce hypocotyls: Response to GA9 and the conversion of [3H]GA9 |
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Authors: | Linda J Nash Russell L Jones John L Stoddart |
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Institution: | (1) Department of Botany, University of California, 94720 Berkeley, CA, USA;(2) Welsh Plant Breeding Station, SY23 3EB Aberystwyth, UK;(3) Present address: Department of Botany, University of Glasgow, G12 8QQ Glasgow, UK |
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Abstract: | Elongation growth and gibberellin (GA9) metabolism in excised hypocotyls of lettuce (Lactuca sativa L. cv. Arctic) were investigated. Exogenously supplied GA9 stimulates elongation of hypocotyl sections and this response is intermediate between that elicited by GA1 or GA20 and GA4/7 mixture. Although uptake of radioactivity from 3H]GA9 increases with time, this gibberellin does not accumulate in the tissue but is rapidly converted to a compound with HPLC properties resembling those of 3H]GA20. After 2 h incubation in 3H]GA9, the presumptive GA20 represents 90% of the acidic ethyl acetate-soluble radioactivity in the tissue. Radioactivity is also associated with an acidic butanol-soluble fraction containing two components resolvable by HVE. The major component is similar in electrophoretic properties to a GA-glucosyl ether while the other compares to a GA-glucosyl ester. Conversion of 3H]GA9 to its 3H]GA20-like metabolite is reduced by addition of carrier GA9 or GA4/7 at concentrations as low as 1 M, while GA1, GA3 and L-proline are without effect. Formation of the GA20-like compound can be blocked by the addition of 2,2-dipyridyl, and this inhibitory effect of dipyridyl can be reversed by addition of Fe2+. At 200 M dipyridyl, elongation growth as well as 3H]GA9 metabolism are reduced by 80%. The relationship of the metabolism of GA9 to the growth response is discussed.Abbreviations AB
butanol-soluble
- AE
ethyl-acetate-soluble
- GA
gibberellin
- GA1, GA4
gibberellin A1, gibberellin A4, etc.
- TLC
thin layer chromatography
- HPLC
high performance liquid chromatography
- HVE
high voltage electrophoresis |
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Keywords: | Cell elongation Gibberellins Lactuca |
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