Endogenous Gibberellin-Like Substances in Somatic Embryos of Grape (Vitis vinifera × Vitis rupestris) in Relation to Embryogenesis and the Chilling Requirement for Subsequent Development of Mature Embryos

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Abstract
Endogenous GA-like substances were examined in suspension cultures of somatic embryos of a hybrid grape (V. vinifera .times. V. rupestris) during embryogenesis, and in mature embryos chilled at 4.degree. C, and subsequently incubated at 26.degree. C with and without abscisic acid (ABA). The extract was separated into a nonpolar fraction (would contain GA-precursors); a fraction that would contain free GA; and a highly H2O-soluble fraction (would contain GA glucosyl conjugates and very polar free GA). Quantitation after SiO2 partition chromatography was accomplished by microdrop and immersion dwarf rice bioassays. As embryogenesis developed, the free and highly H2O-soluble GA-like substances, expressed on a dry weight basis, decreased (however, they increased on a per embryo basis). Chilling at 4.degree. C for 1 wk greatly increased activity of free GA-like substances (per g dry weight and per embryo); it then declined over the next 3 wk of chilling. Activity (per g dry weight and per embryo) in the H2O-soluble fraction declined throughout chilling. Activity in the GA-precursor fraction, however, increased steadily with chilling (per g dry weight and per embryo). Incubation at 26.degree. C after chilling enhanced activity in the free GA and H2O-soluble fractions (per g dry weight and per embryo), but activity in GA-precursor fraction dropped dramatically. Incubation at 26.degree. C with (.+-.) ABA after chilling prevented germination and maintained high activity for GA precursors and less polar free GA and low activity in the polar free GA and H2O-soluble fractions. Kaurene and kaurenoic acid were characterized in the GA-precursor fraction of chilled embryos by GLC-mass spectrometry (GLC-MS). The existence of GA4 and GA9 in ABA-treated, chilled embryos was also confirmed by GLC-MS.
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