Glycolaldehyde Inhibition of Photosynthetic Carbon Assimilation by Isolated Chloroplasts and Protoplasts

Abstract

Inhibitors of photosynthetic carbon assimilation by isolated chloroplasts are divided into two categories depending upon the site(s) of action (Bamberger and Avron, 1975). Uncouplers and electron transport inhibitors effect the so-called “light” reactions, whereas the second group effects the activity of chloroplast enzymes, either directly or indirectly. D,L-Glyceraldehyde is a widely used inhibitor of photosynthesis that blocks the conversion of triosephosphate to RuBP (Stokes and Walker, 1970). Complete inhibition of CO2-dependent O2 evolution by intact spinach chloroplasts requires 0.02 M D,L-glyceraldehyde, suggesting that this compound may not freely penetrate the chloroplast envelope. This report describes a new photosynthetic inhibitor, glycolaldehyde, that has properties similar to D,L-glyceraldehyde. This new compound fully inhibits carbon assimilation by intact, spinach chloroplasts at concentrations of 2 × 10−3 M and unlike D,L-glyceraldehyde, also abolishes photosynthesis by isolated mesophyll protoplasts.