Effect of salicylic acid on the alternative pathway of yellow lupine respiration

The effects of salicylic acid (SA) on the rate of respiration and the activity of cyanide-resistant sensitive to salicylhydroxamic acid oxidation pathway in detached etiolated cotyledons of yellow lupine (Lupinus luteus L.) and mitochondria isolated from these cotyledons were studied. Cotyledon treatment with 1 mM SA for 12 h increased the rate of oxygen uptake predominantly due to the activation of cyanide-resistant respiration (CRR) and alternative pathway of mitochondrial oxidation. It was established that the lupine genome encodes at least two isoforms of alternative oxidase (AO), LuAOX1 and LuAOX2, with the mol wt of about 35 kD. These proteins are always present in the mitochondria of etiolated lupine cotyledons, but their level increased rapidly after cotyledon treatment with SA, probably by increasing the mRNA content of the corresponding genes. SA-induced expression of Aox genes was correlated with the activation of CRR and an increase in the maximal activity (capacity) of AO in both detached yellow lupine cotyledons and mitochondria isolated from them.