Nitrogen Assimilation in Common Wheats Differing in Potential Nitrate Reductase Activity and Tissue Nitrate Concentrations

Two high-yielding, short-statured spring wheats (L.), ‘Anza’ and UC 44-111, have relatively low grain protein concentration and differ substantially (Anza, low; UC 44-111, high) in in vitro nitrate reductase activity. These genotypes were planted in N-rate field experiments for three seasons in California to study variation in tissue nitrate and in N accumulation in leaves, straw, and grain. In all experiments Anza often had signiticantly higher laminae tissue NO concentrations than UC 44-111. When measured, total N per gram of laminae dry weight was consistently higher in UC 44-111 than in Anza. In two field studies with added N, UC 44-111 accumulated by heading time more total protein per hectare than Anza. Percent grain protein of UC 44-111 was slightly higher, usually significantly, than Anza. This was also true for percent straw protein except where adequate N and moisture were available throughout the life cycle. In an N-rate study UC 44-111 produced more grain protein per hectare per kilogram of N applied than Anza. Anza frequently had higher N translocation efficiency (N harvest index) than UC 44-111. In one experiment, a third genotype ‘Yecora 70’, a high protein cultivar, had significantly higher grain protein concentration than the other two genotypes, apparently due to greater remobilizatinn and translocation of N from straw to grain after anthesis. Data from these and previous studies indicate that growth relationships are related to the differences in N assimilation observed between Anza and UC 44-111: 1) in solution cultures the rate of leaf appearance of UC 44-111, but not of Anza, was regulated by nitrate concentration; 2) in two field experiments, laminae of UC 44-111 showed greater increases in area and dry weight in response to added N than did Anza; and 3) applied soil N resulted in greater increases in light interception at the early boot stage for UC 44-111 than for Anza.