Stimulation of H+ Efflux and Inhibition of Photosynthesis by Esters of Carboxylic Acids

Abstract

Suspensions of mechanically isolated Asparagus sprengeri Regel mesophyll cells were used to investigate the influence of various carboxyester compounds on rates of net H+ efflux in the dark or light and photosynthetic O2 production. Addition of 0.15 to 1.5 mM malathion, .alpha.-naphthyl acetate, phenyl acetate, or p-nitrophenyl acetate stimulated H+ efflux and inhibited photosynthesis within 1 min. In contrast, the more polar esters methyl acetoacetate or ethyl p-aminobenzoate had little or no effect on either of these 2 processes. A 0.15 mM concentration of .alpha.-naphthylacetate stimulated the normal rate of H+ efflux, 0.77 nm H+ per 106 cells per minute by 750% and inhibited photosynthesis by 100%. The 4 active carboxyester compounds also stimulated H+ efflux after the normal rate of H+ efflux was eliminated with 0.01 mg/ml oligomycin or 100% N2. Oligomycin reduced the ATP level by 70%. Incubation of cells with malathion, .alpha.-naphthylacetate, or p-nitrophenyl acetate resulted in the generation of the respective hydrolysis products ethanol, .alpha.-naphthol and p-nitrophenol. Possibly, inhibition of photosynthesis and stimulation of H+ efflux result when nonpolar carboxyester compounds enter the cell and generate acidic carboxyl groups when hydrolyzed by esterase enzymes.