PLANT PHYSIOLOGY , Vol 102, Issue 4 1157-1162, Copyright © 1993 by American Society of Plant Biologists

ENVIRONMENTAL AND STRESS PHYSIOLOGY

Effect of High Physiological Temperatures on NAD+ Content of Green Leaf Mitochondria (Apparent Inhibition of Glycine Oxidation)

C. Lenne, M. Neuburger and R. Douce
Laboratoire de Physiologie Cellulaire Vegetale (Unite Associee au Centre National de la Recherche Scientifique no. 576), Departement de Biologie Moleculaire et Structurale, Centre d'Etudes Nucleaires, 85 X, F-38041 Grenoble-Cedex, France

We observed a rapid decline in the rate of glycine oxidation by purified pea (Pisum sativum L.) leaf mitochondria preincubated at 40[deg]C for 2 min. In contrast, exogenous NADH and succinate oxidations were not affected by the heat treatment. We first demonstrated that the inhibition of glycine oxidation was not attributable to a direct effect of high temperatures on glycine decarboxylase/serine hydroxymethyltransferase. We observed that (a) addition of NAD+ to the incubation medium resulted in a resumption of glycine-dependent O2 uptake by intact mitochondria, (b) addition of NAD+ to the suspending medium prevented the decline in the rate of glycine-dependent O2 consumption by pea leaf mitochondria incubated at 40[deg]C, (c) NAD+ concentration in the matrix space collapses within only 5 min of warm temperature treatment, and (d) mitochondria treated with the NAD+ analog N-4-azido-2-nitrophenyl-4-aminobutyryl-3[prime]-NAD+ retained high rates of glycine-dependent O2 uptake after preincubation at 40[deg]C. Therefore, we conclude that the massive and rapid efflux of NAD+, leading to the apparent inhibition of glycine oxidation, occurs through the specific NAD+ carrier present in the inner membrane of plant mitochondria. Finally, our data provide further evidence that NAD+ is not firmly bound to the inner membrane.