The existence of the K+ channel in plant mitochondria

In this study, evidence is given that a number of isolated coupled plant mitochondria (from durum wheat, bread wheat, spelt, rye, barley, potato, and spinach) can take up externally added K+ ions. This was observed by following mitochondrial swelling in isotonic KCl solutions and was confirmed by a novel method in which the membrane potential decrease due to externally added K+ is measured fluorimetrically by using safranine. A detailed investigation of K+ uptake by durum wheat mitochondria shows hyperbolic dependence on the ion concentration and specificity. K+ uptake electrogenicity and the non-competitive inhibition due to either ATP or NADH are also shown. In the whole, the experimental findings reported in this paper demonstrate the existence of the mitochondrial K+(ATP) channel in plants (PmitoK(ATP)). Interestingly, Mg2+ and glyburide, which can inhibit mammalian K+ channel, have no effect on PmitoK(ATP). In the presence of the superoxide anion producing system (xanthine plus xanthine oxidase), PmitoK(ATP) activation was found. Moreover, an inverse relationship was found between channel activity and mitochondrial superoxide anion formation, as measured via epinephrine photometric assay. These findings strongly suggest that mitochondrial K+ uptake could be involved in plant defense mechanism against oxidative stress due to reactive oxygen species generation.