CHANGES IN PHOTOSYNTHETIC YIELD, AMINO ACIDS, AND ORGANIC ACIDS ARE INDUCED BY AMMONIUM ADDITION TO CELLS OF PHORMIDIUM LAMINOSUM (CYANOPHYCEAE)1

Abstract

ABSTRACTThe effect of NH4+ addition to NO3−‐growing cells of the non‐N2‐fixing cyanobacterium Phormidium laminosum (Agardh) Gomont (strain OH‐1‐pCl1) on photo‐synthetic and respiratory electron transport as well as on the intracellular levels of amino acids and some organic acids was studied. Addition of ammonium to nitrate‐growing cells resulted in substantial increases in the pool size of most amino acids and a transient decrease in the pool size of organic acids. The high demand for organic acids was partially overcome by degradation of stored carbohydrates, more than by newly fixed carbon, as indicated by the large stimulation of the respiration rate upon ammonium addition. Following ammonium addition, the photosynthetic yield of the in vivo noncyclic electron transport decreased, and the sensitivity of photosystem II to photodamage increased. Results indicate that cells balance their photosynthetic and respiratory activities depending on nitrogen availability and point to an important involvement of respiration in providing energy for ammonium assimilation until adaptation of bioenergetic processes to the new nitrogen source is complete.