Abstract
The hypothesis that defoliation might lower seed ABA levels with related changes in the effects of exogenous ABA on photosynthate unloading within seeds was tested. Defoliation of dwarf bean ( Phaseolus vulgaris L. cv. Masterpiece) plants markedly reduced ABA concentrations in seeds although reduction occurred in embryos rather than testas. Results from three experiments examining the effects of ABA on 14 C-photosynthate unloading from excised testas were variable but showed that the promotory effect of ABA was diminished as a result of defoliation pretreatment. The data are consistent with the viewpoint that the variability commonly seen in experiments investigating ABA involvement in photosynthate unloading is caused by fluctuating endogenous ABA levels due, in turn, to the growing conditions of experimental plants.
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