THE REGULATION OF NITROGEN ACCUMULATION IN THE GRAIN OF WHEAT PLANTS (TRITICUM-AESTIVUM)

Nitrogen accumulation in the ear of wheat plants (Triticum aestivum L. cv. Klein Chamaco) during ear growth was studied under 4 experimental conditions. Plants were grown in pots with Perlite or soil, and fertilized with nutrient solutions. In one experiment the plants were grown in a greenhouse and supplied with high (16 mM) or low (1.6 mM) N in the nutrient solutions until anthesis, and then with or without nitrogen supply until ripening. In a second experiment the plants were grown with high N supply until anthesis, and then for half of the plants light intensity was decreased by 50%, and at the same time, N supply was terminated for half of the plants within each fight treatment. A third experiment was similar to the previous one, but was carried out in a growth cabinet under 20% of the maximal irradiance in the greenhouse. In a fourth experiment half the ear was excised at anthesis in half of the plants, and these plants were then supplied with nutrient solutions with or without nitrogen. In all experiments there was a linear relation between the rate of N accumulation and the rate of ear growth. A wide range of final individual grain weights and N concentrations was observed among the experiments. The same maximum N concentration was observed for all grain sizes, although the N concentration could be different between grains of the same size. The grain N concentration correlated with the rate of N accumulation per unit of ear weight increase during ear growth. It is suggested that in wheat plants there is a dependence of nitrogen transport on carbon transport to the ear, and that the final grain N concentration is determined by the N/C ratio exported from the vegetative tissues.