ABSTRACT
This chapter reviews the new findings on the regulation of the alternative pathway and, then, present views on the role of the nonphosphorylating path, in the context of a plant's response to environmental stresses, including attack by pathogens. Environmental stresse often not only increases the metabolic activity in plants, involving an increased respiration, but also induce a change in metabolic routes. However, plant mitochondria also have respiratory electron transport pathways that allow the oxidation of organic acids to proceed without coupling to oxidative phosphorylation. First, plant mitochondria contain a rotenone-insensitive NADH dehydrogenase, a bypass of complex I, that transfers electrons from NADH produced in the tricarboxylic acid cycle to ubiquinone without coupling to proton extrusion. Second, there is a cyanide-resistant, alternative pathway, that transfers electrons from ubiquinol to oxygen by the alternative oxidase without coupling to proton extrusion. Cyanide-resistant mitochondrial respiration is due to a single quinol oxidase: the alternative oxidase.
