Effects of DCMU and Antimycin A on Photoassimilation of Glucose in Chlorella

Abstract

Two basically different systems have been described by which chloroplast preparations are able to synthesize ATP in the light: cyclic and noncyclic photophosphorylation (2, 3). Other systems producing ATP in the Jight, e.g. pseudocyclic (or aerobic) and oxidative photophosphorylations might only be variations of the 2 basic types (26, 27). A main feature of true cyclic photophosphorylation in chloroplasts is its resistance to DCMU3 and CMU (16), inhibitors of photosynthetic 0 production (5, 29). According to the concept of 2 light reactions in photosynthesis (8, 11, 15, 32) this DCMU resistance means that cyclic photophosphorylation should be driven only by the first light reaction and not depend oln the second onie, which is responsible for the splitting of water. Such evidence has been obtained by Tagawa et al. (22) for ferredoxincatalyzed cyclic photophosphorylation in chloroplast preparations. In spite of a vast literature on photophosphorylation in vitro, much less is known about photophosphorylation in vivo. The best evidence for photophosphorylation in vivo has been obtained by following glucose assimilation of Chlorella (13,14) and of leaf discs (.18), acetate assimilation of Chlamydobotrys (19, 31), .inhibition of photoreduction by glucose in AnkistrodesZnus (6), and light-enhanced p32 incorpo-ratioi -in Helodea dentsa (20). In the following paper the question was investigated whether cyclic photophosphorylation of the type observed in chloroplasts also occurs in vivo. The influence of DCMU and antimycin A on light dependent glucose assimila-