Loss of photosystem II induced by a nitrate deficiency in photoorganotrophically grown Anabaena variabilis

When photoorganotrophically trained cells of Anabaena variabiliswere grown in nitrate-free medium, they lost the activity ofphotosynthetic oxygen evolution and became devoid of phycobilinpigments. These cells (H cells) lacked the fluorescence emissioncharacteristic of photosystem II chlorophyll, and their lamellarfragments failed to photoreduce DPIP even in the presence ofdiphenylcarbazide as the electron donor, suggesting that theloss of photosynthetic oxygen evolution in H cells is primarilydue to degeneration of an integral part of photosystem II. These characteristics of H cells closely resembled those ofheterocysts differentiated from normal, vegetative cells in[i] the deficiency of phycobilin pigments, [ii] the loss ofphotosystem II activity, [iii] the photoorganotrophic mode ofcell growth, depending upon the organic substances furnishedexternally or provided from neighboring vegetative cells, and[iv] the manner of transformation from normal cells, both typesof cells being induced in the absence of nitrate. In spite ofsuch similarity, light and electron microscopic observationsrevealed that H cells differed significantly from heterocysts.Furthermore, the readiness with which H cells resumed photosystemII activity and the independence of this resumption from cellgrowth exclude the possibility that the nutritional enrichmentof heterocysts was responsible for the loss of photosyntheticactivity. ¹Present address: Ocean Research Institute, University of Tokyo,Nakano, Tokyo 164. (Received May 14, 1975; )