OXYGEN DEPENDENCE OF ELONGATION GROWTH AND OXYGEN-UPTAKE IN MAIZE COLEOPTILES

Auxin-mediated elongation growth of maize coleoptile segments is inhib ited by reducing the O-2 concentration in the incubation medium to les s than or equal to 100 mu mol . l(-1). The half-maximal elongation rat e is reached at 40 mu mol . l(-1) O-2, i.e. about two orders of magnit ude higher than with mitochondrial respiration. O-2 uptake of the segm ents measured under similar conditions with an O-2 electrode shows a v ery similar dependence on O-2 concentration. Auxin increases O-2 uptak e by 5-10% when it induces growth. About 40% of the O-2 uptake is inse nsitive to inhibition by KCN. Auxin has no effect on O-2 uptake in the presence of KCN. The possibility that auxin-mediated elongation growt h depends on a KCN-sensitive oxidative process, other than cytochrome c oxidase-catalyzed respiration, is discussed.