The effects of salicylic acid (SA) on ethylene biosynthesis in detached rice leaves were i nvestigated . S A at pH 3 .5 effectively inhibited ethylene production within 2 h of its application . It inhibited the conversion of ACC to ethylene, but did not affect the levels of ACC and conjugated ACC . Thus, the inhibitory effect of SA resulted from the inhibition of both synthesis of ACC and the conversion of ACC to ethylene .
Effects of compounds that influenced calcium uptake and calmodulin inhibitors on the senescence of detached rice leaves were examined. Chelators, ethyleneglycol-bis-03-aminoethyl ether)-N,N,N",W-tetraacetic acid (EGTA) and l,2-bis-(o-aminophenoxy)-ethane-/v",N,7V,A''-tetraacetic acid (BAPTA), significantly promoted senescence of detached rice leaves in the dark and light. The effect of EGTA can be reversed by treating detached rice leaves with calcium. Verapamil, a calcium channel blocker, and lanthanum chloride, a calcium antagonist, promoted dark-induced, and suppressed BA-and light-retarded senescence of detached rice leaves. Calcium ionophore A23187 and ruthenium red, believed to raise cytosolic level of Ca 2+ , were quite effective in retarding dark-induced and ABA-promoted senescence of detached rice leaves. Calmodulin inhibitors, W-7, compound 48/80, chlorpromazine and trifluoperazine, significantly promoted dark-induced, and suppressed BA-and light-retarded senescence of detached rice leaves. It is concluded that cytosolic level of Ca 2+ may regulate senescence of detached rice leaves through a calmodulindependent mechanism.
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