Mitochondrial proline oxidation is affected by hyperosmotic stress in durum wheat seedlings

Comparison of the oxygen uptake rate in the course of proline oxidation, with that of the malate plus glutamate substrate pair and that of succinate showed that an early inhibition of proline oxidation occurs under stress. The drop of the proline-dependent oxygen uptake rate was as a result of a heavy inhibition of proline dehydrogenase (ProDH); on the other hand, malate plus glutamate-dependent and succinate-dependent oxidations were less inhibited, being the maintenance of oxygen uptake rate not dependent on alternative oxidase (AOX) pathway; in fact, DWM-AOX activity did not show any increase under our experimental stress conditions. The selective inhibition of proline oxidation should be considered a mitochondrial adaptation to stress rather than damage to mitochondrial oxidative properties. This result was achieved by means of a novel approach based on the comparison between oxygen uptake rates of washed and purified organelles.