Relationships between Nitrate Reductase Activity, Plant Weight and Nitrogen Content in Seedlings of Triticum, Aegilops and Triticale

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Abstract
Seedlings of 12 genotypes were grown in pots and watered with nutrient solutions providing 0, 1, 6 and 20 mg equivalents of nitrate per I. Increasing the external nitrate supply brought about increases in plant weight, nitrate, reduced nitrogen concentrations and in vivo nitrate reductase activity. When given solution containing 6 mg equivalents of nitrate per litre, the plants contained approximately 0.1 per cent nitrate, a concentrationsimilar to that found in field-grown plantsat thesamestage of growth. At the 6 mg equivalent level nitrate supply, nitrate reductase activity was strongly positively correlated with the concentrations of nitrate and reduced nitrogen and negatively correlated with plant weight. Similar, though weaker, correlations were found at the lower and higher levels of nitrate supply. The two Triticale genotypes however, had higher than average plant weights and nitrate reductase activities, while plants of the two Aegilops species weighed much less, especially at the higher levels of nitrate supply, than the average of all 12 genotypes and generally had correspondingly greater nitrate and reduced nitrogen concentrations and nitrate reductase activities. For individual genotypes, plant weight at a given level of nitrate supply was strongly correlated with weight at all other levels. In a second experiment seedlings of 150 genotypes were grown in compost watered with 10 mM Ca(NO3)2 Nitrate and reduced nitrogen concentrations were negatively correlated with plant weight but there was no significant correlation between nitrate reductaseactivity and either plant weight, nitrate or reduced nitrogen concentration. The results are taken to indicate that genetic factors, other than those determining the supply of reduced nitrogen, were limiting growth and that as a consequence small plants accumulated nitrate and reduced nitrogen compounds in greater concentrations than large ones. The greater nitrate concentrations in small plants may have induced the increased nitrate reductase activity found in these, as compared with larger plants. Because plant weight varied more than did reduced nitrogen concentration, variation in reduced nitrogen per plant was more highly correlated with plant weight than with per cent reduced nitrogen.

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