SALT-INDUCED OXIDATIVE STRESS MEDIATED BY ACTIVATED OXYGEN SPECIES INPEA LEAF MITOCHONDRIA

The effect in vivo of salt stress on the activated oxygen metabolism o f mitochondria, was studied in leaves from two NaCl-treated cultivars of Pisum sativum L. with different sensitivity to NaCl. In mitochondri a from NaCl-sensitive plants, salinity brought about a significant dec rease of Mn-SOD (EC 1.15.1.1) Cu,Zn-SOD I (EC 1.15.1.1) and fumarase ( EC 4.2.1.2) activities. Conversely, in salt-tolerant plants NaCl treat ment produced an increase in the mitochondrial Mn-SOD activity and, to a lesser extent, in fumarase activity. In mitochondria from both salt -treated cultivars, the internal H2O2 concentration remained unchanged . The NADH- and succinate-dependent generation of O2.- radicals by sub mitochondrial particles and the lipid peroxidation of mitochondrial me mbranes, increased as a result of salt treatment, and these changes we re higher in NaCl-sensitive than in NaCl-tolerant plants. Accordingly, the enhanced rates of superoxide production by mitochondria from salt -sensitive plants were concomitant with a strong decrease in the mitoc hondrial MnSOD activity, whereas NaCl-tolerant plants appear to have a protection mechanism against salt-induced increased O2.- production b y means of the induction of the mitochondrial Mn-SOD activity. These r esults indicate that in the subcellular toxicity of NaCl in pea plants , at the level of mitochondria, an oxidative stress mechanism mediated by superoxide radicals is involved, and also imply a function for mit ochondrial Mn-SOD in the molecular mechanisms of plant tolerance to Na Cl.