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

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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.