Effect of nitrogen, phosphorus or potassium on the photosynthetic rate and ribulose-1,5-bisphosphate carboxylase content in rice leaves during expansion

Effect of the supply of nitrogen, phosphorus and potassium on the photosynthetic rate and the ribulose-1,5-bisphosphate (RuBP) carboxylase content was examined in the expanding 12th leaf blade of rice. The photosynthetic rate was determined using an open infrared gas analysis system. The amount of RuBP carboxylase was measured by rocket immuno-electrophoresis. The rate of leaf photosynthesis was promoted by the increase in nitrogen content. On the other hand, the supply of phosphorus or potassium had no effect on photosynthesis in the expanding leaf when the contents exceeded 0.2 and 1.3% on a dry weight basis, respectively. The RuBP carboxylase content of the leaf was closely correlated with the nitrogen content. However, the relationship between the carboxylase and phosphorus or potassium contents was not positive. Thus, the supply of nitrogen determined the content of RuBP carboxylase protein in the leaf and consequently the rate of photosynthesis. Phosphorus and potassium were not the nutrients which directly affect the content of RuBP carboxylase.