INTERMEDIATES OF PEROXISOMAL METABOLISM UNDER CONDITIONS OF OXYGEN DEFICIT AND CARBON-DIOXIDE EXCESS

We investigated activity of NADH- and NADPH-dependent glyoxylate reductases, NADH-hydroxypyruvate reductase, and glycolate oxidase in leaves of pea and rice seedlings in the process of incubation in the dark in an atmosphere of helium or CO2. Glyoxylate reductase activity increased two- to threefold in comparison with the control (air), this effect being long-term in rice, but observed only on the first day in pea. Glycolate oxidase and hydroxypyruvate reductase were activated to a lesser extent and for a shorter time: Their activity declined to the control level on the 3rd day of incubation in rice and to a value considerably below the control level in pea. Activation of the enzymes occurred at the level of transcription. Decarboxylation of C-14-glycine and glycolate by pea leaves was slowed fourfold after 24 h of CO2 anoxia and twofold in an atmosphere of helium, whereas this effect was not expressed in rice. It is concluded that intermediates of peroxisomal metabolism-glyoxylate, hydroxypyruvate, and oxalate-under conditions of CO2 excess and O2 deficit become acceptors of electrons from NAD(P)H, which plays an important role in blocking of the mitochondrial ETC under conditions of anoxia, these adaptive changes being longer-lasting in the anoxia-resistant plant rice than in pea.