Photorespiration rate in spinach leaves under moderate NaCl stress

We analyzed the effect of NaCl stress on photorespiration of spinach leaves by calculating the rate of carboxylation/oxygenation of ribulose-1,5-bisph osphate carboxylase/oxygenase, and by measuring the content of amino acids produced through photorespiration. After 20 d of NaCl stress the carboxylat ion rate was reduced while the oxygenation rate was not affected. The conte nts of serine, glycine, and alanine increased relevantly. The amount of glu tamine also increased after 20 d but the amount of glutamate did not. Hence photorespiration may be stimulated under moderate NaCl stress. A relevant electron transport rate was observed under CO2-free air, which may indicate refixation of photorespiratory CO2. When NaCl accumulation proceeded for m ore than 20 d, photosynthesis was reduced and the content of photorespirato ry amino acids started to decrease, but the oxygenation rate did not change .