Stress-induced changes in ubiquinone concentration and alternative oxidase in plant mitochondria

We have investigated the influence of stress conditions such as incubation at 4degreesC and incubation in hyperoxygen atmosphere, on plant tissues. The ubiquinone (Q) content and respiratory activity of purified mitochondria was studied. The rate of respiration of mitochondria isolated from cold-treated green bell peppers (Capsicum annuum L) exceeds that of controls, but this is not so for mitochondria isolated from cold-treated cauliflower (Brassica oleracea L). Treatment with high oxygen does not alter respiration rates of cauliflower mitochondria. Analysis of kinetic data relating oxygen uptake with Q reduction in mitochondria isolated from tissue incubated at 4degreesC (bell peppers and cauliflowers) and at high oxygen levels (cauliflowers) reveals an increase in the total amount of Q and in the percentage of inoxidizable QH(2). The effects are not invariably accompanied by an induction of the alternative oxidase (AOX). in those mitochondria where the AOX is induced (cold-treated bell popper and cauliflower treated with high oxygen) superoxide production is lower than in the control. The role of reduced Q accumulation and AOX induction in the defense against oxidative damage is discussed.