Université Pierre et Marie Curie, Laboratoire de Géologie dynamique, 75230 PARIS Cedex 05, France.
Plant Physiol. 1982 Apr;69(4):880-4. doi: 10.1104/pp.69.4.880.
Nitrogen isotope fractionation by Pearl Millet (Pennisetum americanum L. and P. mollissimum L.) grown on nitrate was associated with nitrate reductase activity. Fractionation was evidenced at the step of nitrate reduction when the substrate-to-enzyme ratio was high (possibly saturating for the active sites of the nitrate reductase enzyme), for instance in young seedlings having a low nitrate reductase activity or in seedlings grown on high nitrate concentration.When the substrate concentration was low (and, hence, the active sites of the enzyme were possibly not saturated), the isotopic discrimination could only be associated with the uptake of nitrate into the cell. In that case, isotopic fractionation was null. It is concluded that the uptake of nitrate does not discriminate among nitrogen isotopes.
珍珠粟(Pennisetum americanum L. 和 P. mollissimum L.)在硝酸盐上生长时,其氮同位素分馏与硝酸还原酶活性有关。当基质与酶的比例较高(可能使硝酸还原酶的活性位点饱和)时,例如在硝酸还原酶活性较低的幼苗或在高硝酸盐浓度下生长的幼苗中,在硝酸盐还原的步骤中就可以观察到分馏。当基质浓度较低(因此,酶的活性位点可能不饱和)时,同位素的选择性只能与硝酸盐进入细胞的吸收有关。在这种情况下,同位素分馏为零。结论是,硝酸盐的吸收不会对氮同位素进行区分。