Nitric oxide induces the alternative oxidase pathway under phosphate deficiency

Abstract

Nitric oxide (NO) is a signal molecule that plays an important role in plant growth, development and stress physiology. In recent years the biosynthesis and action of NO in plant mitochondria has gained increasing attention. The plant mitochondrial electron transport has two pathways for the reduction of oxygen: the cytochrome pathway and the alternative oxidase (AOX) pathway. Both pathways are involved in mitochondrial NO metabolism, and the AOX pathway protects plants against the production of deleterious quantities of reactive oxygen species (ROS). We studied the cytochrome and alternative pathways in Arabidopsis thaliana subjected to phosphate deficiency. WT (cv. Columbia) and nia1,2 (nitrate reductase deficient mutant) seedlings were grown in axenic cultures that contained either 1 mM (+P) or 0 mM (-P) inorganic phosphate. Phosphate starvation increased production of NO in WT, leading to increased capacity in the AOX pathway and decreased superoxide levels. In contrast, the nia1,2 mutant failed to induce NO under phosphate starvation, leading to a lower AOX capacity and increased production of superoxide. As a result, the nia mutants had a lower biomass than WT plants under phosphate starvation. Furthermore the NO donor GSNO restored the nia1,2 phenotype under phosphate starvation, confirming the requirement for NO for stress resistance during phosphate starvation.