Departments of Botany and Agronomy, University of Illinois, Urbana, Illinois 61801.
Plant Physiol. 1976 Oct;58(4):505-9. doi: 10.1104/pp.58.4.505.
Experiments were conducted to determine whether the nitrate flux to the leaves or the nitrate content of the leaves regulated the nitrate reductase activity (NRA) in leaves of intact maize (Zea mays L.) seedlings having low water potentials (psi(w)) when other environmental and endogenous factors were constant. In seedlings that were desiccated slowly, the nitrate flux, leaf nitrate content, and NRA decreased as psi(w) decreased. The decrease in nitrate flux was caused by a decrease in both the rate of transpiration and the rate of nitrate delivery to the transpiration stream. Upon rewatering, the recovery in NRA was correlated with the nitrate flux but not the leaf nitrate content.Recovery depended on protein synthesis, since recovery could be prevented in excised leaves if an inhibitor of protein synthesis was present. However, it also depended on a high nitrate flux, since recovery could be prevented if there was no nitrate flux, despite a relatively high, constant leaf nitrate content, a high psi(w), and the absence of an inhibitor of protein synthesis.The synthesis of NRA could be increased at low psi(w) if seedlings were desiccated in the presence of additional nitrate, which increased the nitrate flux to the leaves. Since the decrease in NRA at low psi(w) could be relieved by increasing the nitrate flux and recovery also depended on nitrate flux, the inhibition of NRA at low psi(3) was not controlled by a direct effect of psi(w) on protein synthesis nor by alterations in the leaf nitrate content, but rather by a decrease in the nitrate flux that in turn regulated the synthesis of the enzyme.
进行了实验以确定在其他环境和内源性因素保持不变的情况下，当完整的玉米（Zea mays L.）幼苗具有低水势（psi(w)）时，是叶片中的硝酸盐通量还是叶片中的硝酸盐含量调节硝酸盐还原酶活性（NRA）。在缓慢干燥的幼苗中，随着 psi(w)的降低，硝酸盐通量、叶片硝酸盐含量和 NRA 都降低。硝酸盐通量的降低是由蒸腾速率和硝酸盐向蒸腾流输送速率的降低共同引起的。重新浇水后，NRA 的恢复与硝酸盐通量相关，但与叶片硝酸盐含量无关。恢复取决于蛋白质合成，因为如果存在蛋白质合成抑制剂，离体叶片中的恢复就会受到抑制。然而，它也取决于高硝酸盐通量，因为如果没有硝酸盐通量，尽管叶片硝酸盐含量相对较高且恒定、psi(w)较高且没有蛋白质合成抑制剂，恢复也会受到抑制。如果幼苗在额外硝酸盐的存在下干燥，NRA 的合成可以在低 psi(w)下增加，这增加了叶片中的硝酸盐通量。由于在低 psi(w)下 NRA 的减少可以通过增加硝酸盐通量来缓解，并且恢复也取决于硝酸盐通量，因此低 psi(w)下 NRA 的抑制不是由 psi(w)直接影响蛋白质合成或叶片硝酸盐含量的改变来控制的，而是由硝酸盐通量的降低来调节，而硝酸盐通量反过来又调节酶的合成。
