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Development and Growth Regulation

Effects of Chilling and ABA on [³H]Gibberellin A₄ Metabolism in Somatic Embryos of Grape (Vitis vinifera L. x V. rupestris Scheele) ¹

Plant Physiology Research Group, Department of Biology, University of Calgary, Calgary, Alberta, Canada T2N 1N4, Department of Agronomy and Horticultural Science, The University of Sydney, Sydney, N.S.W. 2006, Australia

Previous work has indicated that changes in gibberellin (GA) metabolism may be involved in chilling-induced release from dormancy in somatic embryos of grape (Vitis vinifera L. x V. rupestris Scheele). We have chilled somatic embryos of grape for 2, 4, or 8 weeks, then incubated them with [³H]GA₄ (of high specific activity, 4.81 x 10¹⁰ becquerel per millimole) for 48 hours at 26°C. Chilling had little effect on the total amount of free [³H]GA-like metabolites formed during incubation at 26°C, but did change the relative proportions of individual metabolites. The amount of highly water-soluble [³H] metabolites formed at 26°C decreased in embryos chilled for 4 or 8 weeks. The concentration of endogenous GA precursors (e.g., GA₁₂ aldehyde-, kaurene-, and kaurenoic acid-like substances) increased in embryos chilled for 4 or 8 weeks. Treatment with abscisic acid (ABA) (known to inhibit germination in grape embryos) concurrent with [³H]GA₄ treatment at 26°C, reduced the uptake of [³H] GA₄ but had little effect on the qualitative spectrum of metabolites. However, in the embryos chilled for 8 weeks and then treated with ABA for 48 hours at 26°C, there was a higher concentration of GA precursors than in untreated control embryos. Chilled embryos thus have an enhanced potential for an increase in free GAs through synthesis from increased amounts of GA precursors, or through a reduced ability to form highly water-soluble GA metabolites (i.e., GA conjugates or polyhydroxylated free GAs).

³ Present address: Phytogen, 101 Waverly Drive, Pasadena, CA 91105, USA.

¹ Supported by Natural Sciences and Engineering Research Council of Canada Grant A-2585 to R. P. P. and a grant from Rural Credits Development Fund, Reserve Bank of Australia, to M. G. M.