The Effects of Grain Nitrogen and Applied Nitrate on Growth, Photosynthesis and Protein Content of the First Leaf of Barley Cultivars

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Abstract
Five cultivars of barley with widely differing grain nitrogen contents were compared. In the absence of exogenous nitrate supply plants grown from high nitrogen grain showed a more rapid leaf emergence, greater leaf size, especially of the first leaf, higher photosynthetic rate and greater total souble protein and Fraction 1 protein content of the first leaf, than plants grown from low nitrogen grain. However, early supply of nitrate to plants grown from low nitrogen grain enabled these to perform as well as those from grain with a high nitrogen content. Regression analysis showed that Fraction 1 content of the first leaf is closely correlated with grain nitrogen which exerts a progressively greater effect on content of this protein as application of exogenous nitrate is delayed. The more rapid photosynthetic rate of plants grown with high nitrogen, and the consequent greater rate of dry matter accumulation, is attributable mainly to effects of nitrogen availability on leaf area and much less to effects on leaf protein.