Phenols, phenoloxidase, and photosynthetic activity of chloroplasts isolated from sugar cane and spinach.

Sugar cane chloroplasts isolated in simple media possessed little photochemical activity, but showed rapid O2 uptake, independent of light. A similar rapid consumption of O2 was observed with brei prepared from cane leaves. This was not observed in brei of spinach leaves. Authentic polyphenols and cane leaf extracts stimulated the consumption of O2 by cane preparations and inhibited photosynthesis in chloroplasts isolated from spinach. Chlorogenic acid and caffeic acid were the major o-diphenols in extracts of cane leaves. These compounds inhibited reactions associated with CO2 fixation by the photosynthetic carbon reduction cycle. Assimilation of CO2 due to phosphoenol pyruvate carboxylase activity was less sensitive to inhibition by o-diphenols. Mechanisms are discussed whereby o-diphenols may inhibit cane chloroplasts during their isolation.