The effects of nitrogen topdressing stage on photosynthesis, translocation and distribution of14C assimilate and NR activity of wheat Study on Nitrate Reductase of Winter Jujube(Ziziphus jujuba var.inermis) STUDIES ON THE RELATIONSHIP BETWEEN GRAIN PROTEIN CONTENT AND THE NR ACTIVITY FREE AMINO ACID AND CRUDE PROTEIN CONTENT OF LEAF BLADE IN WHEAT The Effects of Sulfur Nutrition on Some Physiological Parameters in Relation to Carbon and Nitrogen Metabolism in Wheat and Maize