Chloride transport and photosynthesis in cells of Griffithsia

Abstract

1. A convenient and sensitive method for making oxygen measurements on single giant algal cells is described. 2. Fluxes of Cl − and rates of apparent photosynthetic oxygen evolution and respiratory oxygen consumption have been measured in cells of the marine algae Griffithsia monile and Griffithsia flabelliformis. The Cl − influx was active and light-stimulated, but there was no compulsory linkage between photosynthetic electron flow and Cl − influx. The energy required to support the light-dependent Cl − influx in Griffithsia is estimated at approx. 0.3% of that generated in photosynthesis. 3. The metabolic linkages of the light-stimulated and dark components of Cl − influx have been investigated in G. monile by studying the effects of O 2 and N 2, and of the metabolic inhibitors 3(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), carbonyl cyanide m-chlorophenylhydrazone (CCCP) and phlorizin on the Cl − influx. The effects on carbon fixation, apparent rates of photosynthetic oxygen evolution, respiratory oxygen consumption, and membrane electrical properties were also determined. 4. The results suggest that the light-dependent component of Cl − influx in G. monile is associated with the rate of non-cyclic photophosphorylation. The dark component of the Cl − influx, which may be part of a Cl − exchange-diffusion system and not active transport, may be associated with mitochondrial respiration.