GA(4) DOES NOT REQUIRE CONVERSION INTO GA(1) TO DELAY SENESCENCE OF ALSTROEMERIA-HYBRIDA LEAVES

The biological activity and metabolism of applied GA(1) and GA(4) were studied in leaves of alstroemeria (Alstroemeria hybrida). It appeared that GA(4) was 2 orders of magnitude more active in delaying leaf sen escence than GA(1). GA(3)-13-OMe, a GA analog that cannot be hydroxyla ted on the 13-C position, also retarded chlorophyll loss, although les s efficiently. Tritiated and deuterated GA(1), GA(4), and GA(9) were a pplied to leaves, and their metabolites were analyzed. According to hi gh performance liquid chromatography and gas chromatography-mass spect rometry analyses, GA(9) was converted into GA(4) and GA(3)4, and GA(4) was converted into GA(3)4 and more polar components. No evidence was found for the conversion of both GA(9) and GA(4) into GA(1), even at t he relatively high concentrations that were taken up by the leaf. The results strongly suggest that GA(4) is recognized directly by a recept or involved in regulation of leaf senescence in alstroemeria.