Effect of Sodium Nutrition and Light Upon the Concentrations of Alanine in Leaves of C₄ Plants

Abstract

The concentration of alanine in the leaves of representatives of each of the three types of C₄ plants was found to be consistently greater in sodium-deficient than in sodium-sufficient plants. The sodium treatment, however, did not affect the alanine concentration in the leaves of tomato, a C₃ plant or in the roots of Amaranthus tricolor, a C₄ plant. The alanine concentration of leaves of A. tricolor decreased rapidly upon the addition of sodium to cultures of sodium-deficient plants. The concentration of sodium required to give this response was approximately 50 µM, which was similar to that needed for the growth response. When plants that had been previously illuminated were placed in the dark, the alanine concentration increased rapidly, but was lowered again to the original concentration on return to the light. These changes in the alanine concentrations of leaves of C₄ plants in response to sodium and light treatments are discussed in relation to the C₄ photosynthetic system.