Photosystem-I-driven inorganic carbon transport in the cyanobacterium, Anacystis nidulans

Abstract

Anacystis nidulans grown at air levels of CO 2 accumulates high concentrations of inorganic carbon within the cells, which effluxes as CO 2 after a light period. The effect of inhibitors and electron acceptors of photosynthesis on the postillumination CO 2 burst was studied to identify the photosynthetic reaction(s) involved in the inorganic carbon transport. The following results were obtained. (i) In the presence of iodoacetamide, an inhibitor of CO 2 fixation, the CO 2 burst was greater and was insensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea. The inorganic carbon accumulation in the presence of iodoacetamide showed an action spectrum of Photosystem (PS) I reaction. The results demonstrate that a PS-I-mediated cyclic electron flow is involved in the inorganic carbon transport. (ii) Draining of electrons to 2,5-dimethyl- p-benzoquinone (DMQ), p-nitrosodimethylaniline (PNDA), O 2 or nitrite and phenazinemethosulfate (PMS)-bypassed cyclic electron flow inhibited the CO 2 burst. This is ascribed to the inhibition of the cyclic electron flow involved in the inorganic carbon transport. (iii) The electron flow to DMQ and PNDA or PMS-bypassed cyclic electron flow produced ATP actively. Thus, the inorganic carbon transport does not proceed by ATP supply only. (iv) Uncouplers and inhibitors of ATP synthesis had a strong inhibitory effect on the CO 2 burst. From these results, we concluded that both PS-I-cyclic electron flow and ATP are required to drive the inorganic carbon transport.