GA4 does not require conversion into GA1 to delay senescence of Alstroemeria hybrida leaves

The biological activity and metabolism of applied GA1 and GA4 were studied in leaves of alstroemeria (Alstroemeria hybrida). It appeared that GA4 was 2 orders of magnitude more active in delaying leaf senescence than GA1. GA3-13-OMe, a GA analog that cannot be hydroxylated on the 13-C position, also retarded chlorophyll loss, although less efficiently. Tritiated and deuterated GA1, GA4, and GA9 were applied to leaves, and their metabolites were analyzed. According to high performance liquid chromatography and gas chromatography-mass spectrometry analyses, GA9 was converted into GA4 and GA34, and GA4 was converted into GA34 and more polar components. No evidence was found for the conversion of both GA9 and GA4 into GA1, even at the relatively high concentrations that were taken up by the leaf. The results strongly suggest that GA4 is recognized directly by a receptor involved in regulation of leaf senescence in alstroemeria