Millenaar FF, Benschop JJ, Wagner AM, Lambers H
Department of Plant Ecology and Evolutionary Biology, Utrecht University Graduate School of Experimental Plant Science, Sorbonnelaan 16, 3584 CA Utrecht, The Netherlands (F.F.M., J.J.B., H. L.).
Plant Physiol. 1998 Oct;118(2):599-607. doi: 10.1104/pp.118.2.599.
A possible function for the alternative (nonphosphorylating) pathway is to stabilize the reduction state of the ubiquinone pool (Qr/Qt), thereby avoiding an increase in free radical production. If the Qr/Qt were stabilized by the alternative pathway, then Qr/Qt should be less stable when the alternative pathway is blocked. Qr/Qt increased when we exposed roots of Poa annua (L.) to increasing concentrations of KCN (an inhibitor of the cytochrome pathway). However, when salicylhydroxamic acid, an inhibitor of the alternative pathway, was added at the same time, Qr/Qt increased significantly more. Therefore, we conclude that the alternative pathway stabilizes Qr/Qt. Salicylhydroxamic acid increasingly inhibited respiration with increasing concentrations of KCN. In the experiments described here the alternative oxidase protein was invariably in its reduced (high-activity) state. Therefore, changes in the reduction state of the alternative oxidase cannot account for an increase in activity of the alternative pathway upon titration with KCN. The pyruvate concentration in intact roots increased only after the alternative pathway was blocked or the cytochrome pathway was severely inhibited. The significance of the pyruvate concentration and Qr/Qt on the activity of the alternative pathway in intact roots is discussed.
交替（非磷酸化）途径的一个可能功能是稳定泛醌池的还原状态（Qr/Qt），从而避免自由基产生增加。如果Qr/Qt通过交替途径得以稳定，那么当交替途径被阻断时，Qr/Qt应该稳定性降低。当我们将一年生早熟禾（Poa annua (L.)）的根暴露于浓度不断增加的KCN（细胞色素途径抑制剂）中时，Qr/Qt增加。然而，当同时添加交替途径抑制剂水杨羟肟酸时，Qr/Qt的增加幅度显著更大。因此，我们得出结论，交替途径可稳定Qr/Qt。随着KCN浓度增加，水杨羟肟酸对呼吸作用的抑制作用增强。在本文所述实验中，交替氧化酶蛋白始终处于还原（高活性）状态。因此，交替氧化酶还原状态的变化无法解释在用KCN滴定后交替途径活性的增加。只有在交替途径被阻断或细胞色素途径受到严重抑制后，完整根中的丙酮酸浓度才会增加。本文讨论了丙酮酸浓度和Qr/Qt对完整根中交替途径活性的意义。
