Warner R L, Huffaker R C
Department of Agronomy and Soils, Washington State University, Pullman 99164-6420, USA.
Plant Physiol. 1989;91(3):947-53. doi: 10.1104/pp.91.3.947.
Barley (Hordeum vulgare L.) has NADH-specific and NAD(P)H-bispecific nitrate reductase isozymes. Four isogenic lines with different nitrate reductase isozyme combinations were used to determine the role of NADH and NAD(P)H nitrate reductases on nitrate transport and assimilation in barley seedlings. Both nitrate reductase isozymes were induced by nitrate and were required for maximum nitrate assimilation in barley seedlings. Genotypes lacking the NADH isozyme (Az12) or the NAD(P)H isozyme (Az70) assimilated 65 or 85%, respectively, as much nitrate as the wild type. Nitrate assimilation by genotype (Az12;Az70) which is deficient in both nitrate reductases, was only 13% of the wild type indicating that the NADH and NAD(P)H nitrate reductase isozymes are responsible for most of the nitrate reduction in barley seedlings. For all genotypes, nitrate assimilation rates in the dark were about 55% of the rates in light. Hypotheses that nitrate reductase has direct or indirect roles in nitrate uptake were not supported by this study. Induction of nitrate transporters and the kinetics of net nitrate uptake were the same for all four genotypes indicating that neither nitrate reductase isozyme has a direct role in nitrate uptake in barley seedlings.
大麦（Hordeum vulgare L.）具有NADH特异性和NAD(P)H双特异性硝酸还原酶同工酶。利用四种具有不同硝酸还原酶同工酶组合的近等基因系，来确定NADH和NAD(P)H硝酸还原酶在大麦幼苗硝酸盐转运和同化中的作用。两种硝酸还原酶同工酶均由硝酸盐诱导产生，且是大麦幼苗最大程度硝酸盐同化所必需的。缺乏NADH同工酶（Az12）或NAD(P)H同工酶（Az70）的基因型分别同化了野生型65%或85%的硝酸盐。两种硝酸还原酶均缺乏的基因型（Az12;Az70）的硝酸盐同化量仅为野生型的13%，这表明NADH和NAD(P)H硝酸还原酶同工酶负责大麦幼苗中大部分的硝酸盐还原。对于所有基因型，黑暗中的硝酸盐同化速率约为光照下的55%。本研究不支持硝酸还原酶在硝酸盐吸收中具有直接或间接作用的假设。所有四种基因型的硝酸盐转运蛋白诱导情况和净硝酸盐吸收动力学相同，这表明两种硝酸还原酶同工酶在大麦幼苗硝酸盐吸收中均无直接作用。
