Nitrate Nutrition and Temperature Effects on Wheat: Soluble Components of Leaves and Carbon Fluxes to Amino Acids and Sucrose

Lawlor, D. W., Boyle, F. A., Young, A. T., Kendall, A. C. and Keys, A. J. 1987. Nitrate nutrition and temperature effects on wheat: Soluble components of leaves and carbon fluxes to amino acids and sucrose.—J. exp. Bot. 38: 1091-1103. Amounts of some metabolites and the incorporation of '*CO2 into photosynthetic products were measured in the third leaf of wheat, grown with two rates of nitrate supply at two temperatures, to analyse the effects of environmental conditions on the fluxes of carbon. Ribulose foisphosphate and 3-phosphoglyceric acid content per unit area were greater under nitrate deficiency and decreased with leafage, but did not differ consistently with temperature. Sucrose content of young leaves was larger in cool than in warm conditions and with low nitrate, and decreased with age to similar values in all treatments. Starch accumulated with leafage, slightly more in cool than warm conditions, and with nitrate deficiency. Glutamate (plus glutamine), aspartate (plus asparagine), glycine and serine content of leaves were greatest with added nitrate in cool temperature; changes with leaf age and conditions are discussed. The C content of assimilation products after exposure to CO2 (for up to 10 min at 20 °C) under steady-state conditions was slightly greater in plants grown in the warm than in the cool temperature and with additional nitrate. Additional nitrate increased the proportion of '*C in, and flux of carbon to, amino acids, particularly serine and glycine, and decreased it in sugar phosphates and sucrose. Cool growth temperatures increased the proportion of C in amino acids (predominantly glycine and serine) and decreased that in sucrose. Changes in the balance of carbon fluxes between amino acids and carbohydrates are discussed in relation to glycolate pathway metabolism and alternative routes of amino acid synthesis. Key words—Wheat, temperature, nitrate supply, carbon flux, sucrose, amino acids. Correspondence to: Physiology and Environmental Physics Department, Rothamsted Experimental Station, Harpenden, Herts. AL5 2JQ, U.K.