Abstract
Phosphate starvation compromises electron flow through the cytochrome pathway of the mitochondrial electron transport chain, and plants commonly respond to phosphate deprivation by increasing flow through the alternative oxidase (AOX). To test whether this response is linked to the increase in nitric oxide (NO) production that also increases under phosphate starvation, Arabidopsis thaliana seedlings were grown for 15 d on media containing either 0 or 1mM inorganic phosphate. The effects of the phosphate supply on growth, the production of NO, respiration, the AOX level and the production of superoxide were compared for wild-type (WT) seedlings and the nitrate reductase double mutant nia. Phosphate deprivation increased NO production in WT roots, and the AOX level and the capacity of the alternative pathway to consume electrons in WT seedlings; whereas the same treatment failed to stimulate NO production and AOX expression in the nia mutant, and the plants had an altered growth phenotype. The NO donor S-nitrosoglutathione rescued the growth phenotype of the nia mutants under phosphate deprivation to some extent, and it also increased the respiratory capacity of AOX. It is concluded that NO is required for the induction of the AOX pathway when seedlings are grown under phosphate-limiting conditions.
Highlights
Phosphorus is an important macronutrient and a shortage of inorganic phosphate (Pi) leads to biochemical, physiological and morphological changes in plants that reduce plant growth and yield (Wissuwa et al, 2005)
Phosphate starvation compromises electron flow through the cytochrome pathway of the mitochondrial electron transport chain, and plants commonly respond to phosphate deprivation by increasing flow through the alternative oxidase (AOX). To test whether this response is linked to the increase in nitric oxide (NO) production that increases under phosphate starvation, Arabidopsis thaliana seedlings were grown for 15 d on media containing either 0 or 1 mM inorganic phosphate
Numerous studies have shown the importance of these pathways under Pi starvation (Rychter and Mikulska, 1990; Wanke et al, 1998), including observations on Phaseolus vulgaris mitochondria, which showed increased AOX activity and decreased cytochrome c oxidase (COX) activity when isolated from plants grown on a Pi-deficient medium (Rychter et al, 1992; Juszczuk et al, 2001)
Summary
Phosphorus is an important macronutrient and a shortage of inorganic phosphate (Pi) leads to biochemical, physiological and morphological changes in plants that reduce plant growth and yield (Wissuwa et al, 2005). Respiratory metabolism undergoes several modifications in response to the reduced availability of Pi, including the increased use of inorganic pyrophosphate to conserve ATP, the reconfiguration of glycolysis and the induction of the alternative pathways of. Similar observations have been made on tobacco (Nicotiana tabacum) cell suspension cultures, where Pi limitation caused a strong increase in AOX protein and the capacity for cyanide-resistant respiration (Parsons et al, 1999; Sieger et al, 2005); while in leaves, growth on low Pi increased the activity of the AOX pathway increased in P. vulgaris and Gliricidia sepium, but not in tobacco (Gonzàlez-Meler et al, 2001)
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