Effect of Carbonic Anhydrase Inhibition on Photosynthesis by Leaf Pieces of C₃ and C₄ Plants

Abstract

The role of carbonic anhydrase (CA) in the photosynthesis of C₃ and C₄ plants was investigated by use of the effects of the CA inhibitor ethoxyzolamide on peeled and vacuum infiltrated leaf pieces. Two C₄(Zea mays and Amaranthus edulis) and three C₃ (Spinacea oleracea, Nicotiana rustica and Hordeum vulgare) species were studied. The results clearly showed that photosynthesis at limiting inorganic carbon was more severely inhibited in the C₄ species compared with the C₃ species. However, the degree of inhibition in the C₄ species was less than might have been expected based on the rate limitation which the conversion of CO₂ to HCO₃^- would impose on the provision of substrate to PEP carboxylase. The reasons for this lower than expected inhibition is discussed in terms of the lack of penetration of ethoxyzolamide, the diffusion of HCO₃^- through plasmodesmata and the possible existence of a plasma membrane CA activity.