Aluminum tolerances of two wheat genotypes related to nitrate reductase activities

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Abstract
Acid soil (A1) tolerance in certain wheat (Triticum aestivum L.) genotypes has been associated with high protein levels in the grain. Superior Al tolerance in some wheat genotypes is also characterized by the ability to use NO‐ 3‐N in the presence of NH+ 4‐N and to increase the pH of the growth medium. Such evidence suggests that nitrogen metabolism is involved in differential A1 tolerance. In the absence of mineral stress, UC 44–111 wheat is significantly higher in nitrate reductase (NR) activity than Anza wheat. Our objectives were to test the hypothesis that differential NR activities in these two genotypes are associated with differential Al tolerance and to determine the specific effects of Al on their NR systems. The high NR UC 44–111 genotype was significantly more tolerant to an Al‐toxic Tatum soil at pH 4.5 and 4.9 and to Al in nutrient cultures than was the low NR Anza. The UC 44–111 also induced a higher pH in nutrient solution than did Anza when both were under Al stress. Greater sensitivity of Anza to the acid soil was associated with a chlorosis which seemed to be due to Al‐induced interference in the uptake and/or use of Fe, Cu and K. Under Al stress in nutrient solutions the Al‐sensitive Anza was characterized by chlorosis, decreased Fe concentrations in tops, decreased Ca and Mg in both tops and roots, a tendency toward accumulation of P, A1 and Fe in roots, and reduced Mn in tops. UC 44–111 was significantly higher in NR activity than Anza in the presence or absence of A1 in nutrient solutions. Aluminum stress significantly reduced NR activity in the tops of Anza but had no effect on that in UC 44–111 cops. The postulated relationship among acid soil tolerance, A1 tolerance, and NR activity was confirmed for the two genotypes. Hence, possible relationships between acid soil tolerance and N efficiency warrant further study.