The effects of nitrate, nitrite, and ammonia on photosynthetic carbon metabolism of Acetabularia chloroplast preparations compared with spinach chloroplasts and whole cells of Acetabularia and Dunaliella

Abstract

Nitrogen was supplied in the form of nitrate, nitrite, or ammonium ions to whole cells of Dunaliella tertiolecta, to whole cells and chloroplast preparations of Acetabularia mediterranea, and to spinach chloroplasts, while they were photosynthesizing in 14CO2. The 14C labeling patterns in these experiments provide information on several aspects of the photosynthesis, nitrogen metabolism, and physical properties of these systems. The rates and products of photosynthesis are affected in different ways by different ions, depending on the penetration of each ion, its toxicity, and on the ability of the system under test to synthesize amino acids. Thus the ions that penetrate spinach chloroplasts, while they may inhibit photosynthesis, do not affect the distribution of 14C among photosynthetic products because no amino acids are formed. The large differences in behavior between Acetabularia whole cells and chloroplast preparations from these cells suggest that the membrane structure surrounding cytoplasmic droplets in the latter may be tonoplast rather than plasmalemma in origin.