The Effect of Sodium Nutrition on the Pool Sizes of Intermediates of the C Photosynthetic Pathway

Abstract

Changes in C₄ pathway intermediates in response to sodium nutrition, consistent with the hypothesis that there is a limitation in the conversion of pyruvate to phosphoenolpyruvate (PEP) in the mesophyll cells in sodium-deficiency, were observed in the C₄ species, Kochia childsii, Chloris gayana, Amaranthus edulis, Amaranthus tricolor and Atriplex spongiosa. In the C₃ species Lycopersicon esculentum (tomato), no differences were observed when grown with or without added sodium.

Of the group 1 elements, only sodium, irrespective of the salt supplied to deficient cultures, effected these changes in the C₄ species.

In the light, concentrations of aspartate, PEP and 3-phosphoglycerate (3-PGA) were lower and those of pyruvate and alanine were greater in sodium-deficient than normal plants. In the dark, concentrations of aspartate, pyruvate, alanine, PEP and 3-PGA were similar in sodium-deficient and normal plants.

In the C₄ species Atriplex spongiosa, the concentration of sodium required to bring about these changes corresponded to that required for growth responses.

Rapid increases in the concentrations of malate, PEP and 3-PGA and decreases in pyruvate and alanine were observed following the direct application of sodium to leaves.