Genetic Study of Nitrate Transport across the Plasma Membrane of Root Epidermal Cells in Some Crop Plants

培育高效利用植物养分的作物是低投入作物生产的目标之一。本研究测定了几种作物幼苗高亲和性硝酸盐吸收的动力学参数Km和Vmax，以评价硝酸盐吸收基因的表达。结果表明：（1）20个日本大麦品种的Km和Vmax分别为50.9-111.7 μ M和2.24-4.99 μ mol/g/h。然而，这些结果被认为是低估，因为实验程序。2)苗期不同耐水性大麦基因型的Km和Vmax分别为143.0-209.4 μ M和3.37-7.85 μ mol/g/h。动力学参数和耐水性之间没有关系。3)16个水稻品种（包括籼、粳稻）的Km和Vmax分别为75.7-130.3 μ M和4.30-7.17 μ mol/g/h。在Km值相近的籼粳品种中，籼型品种的Vmax值往往低于粳型品种。4)小麦、黑麦和小黑麦的Km和Vmax与大麦和水稻相近。5)在4个影响水稻硝酸盐同化的突变体中，氯酸盐敏感突变体M605的Km值显著高于野生型Norin 8。此外，145个水稻基因型对40 μ M KNO_3和400 μ M KNO_3的吸收能力之比存在差异，表明动力学参数存在变异性。

Breeding of crops with efficient use of plant nutrient is one of the goals for low-input crop production. In this study, two kinetic parameters, Km and Vmax, for high affinity nitrate uptake by young seedlings were determined in several crop plants for evaluating the expression of nitrate uptake gene (s). Summary of the results are shown as follows.1) In twenty Japanese barley cultivars, Km and Vmax were 50.9-111.7 mu M and 2.24-4.99 mu mol/g/h, respectively. IIowever, these results were thought to be underestimated because of experimental procedure. 2) In barley genotypes with different water tolerance at seedling stage, Km and Vmax were 143.0-209.4 mu M and 3.37-7.85 mu mol/g/h, respectively. No relationships between the kinetic parameters and water tolerance was observed. 3) In sixteen rice cultivars including both indica and japonica, Km and Vmax were 75.7-130.3 mu M and 4.30-7.17 mu mol/g/h, respectively. In the cultivars of indica and japonica showing similar level of Km, indica cultivars tended to show lower Vmax than japonica cultivars. 4) Km and Vmax in several genotypes of wheat, rye and Triticale were similar level of those of barley and rice. 5) In four rice mutants affecting nitrate assimilation, M605, a chlorate hypersensitive mutant, showed significantly higher Km than that of the wild type, Norin 8. Furthermore, there was difference in ratio of nitrate uptake ability from 40 mu M KNO_3 to that from 400 mu M KNO_3 in 145 rice genotypes, suggesting variability in the kinetic parameters.