The 2012 ASHS Annual Conference

Exogenous abscisic acid (ABA) induces leaf chlorosis in various vegetable and ornamental crops, causing a potential problem for its commercial use. In muskmelon seedlings, we have shown that chlorophyll loss increased linearly with increasing ABA concentration by up to 33% (7.57 mM-ABA). One mechanism generally proposed for ABA-induced chlorosis is senescence by stimulated ethylene production. We examined the effect of exogenous ABA (0, 0.1, and 1 mM) on chlorosis and ethylene production in intact Arabidopsis (Arabidopsis thaliana) leaves. Chlorosis occurred only in the oldest leaf treated with 1 mM-ABA; leaf chlorosis index (SPAD reading) decreased by 39% within 24 hours of treatment and by up to 69% thereafter. As opposed to our assumption, ethylene production was suppressed by ABA in the youngest (6–7th) and oldest leaves. The magnitude of reduction was similar in the two leaves at both ABA concentrations (up to 62% to 81%), while the ethylene level in the largest (4–5th) leaf was maintained relatively low and unaffected by ABA. These results suggest that ABA-induced chlorosis is leaf age-dependent, and that it can occur independently of ethylene.