Effects of oxidative stress caused by NaCl or Na2SO4 excess on lipoic acid and tocopherols in Genovese and Fine basil (Ocimum basilicum)

With this investigation, we aimed to study more deeply the antioxidative response to moderate doses of NaCl or Na2SO4 in two cultivars of basil differentially sensitive to salinity. Tolerance to salinity was previously evaluated by the extent of growth inhibition whereas the antioxidant response was assessed studying the changes in the activities of superoxide dismutase (SOD) and catalase as well as in the amounts of tocopherols and lipoic acid. To make possible the comparison of the responses of basil cv. Genovese and cv. Fine to different salts, the experiment was carried out with equimolar concentrations of Na+. The results showed that changes caused by salinity were dependent on cultivar and exposure time. In particular, cv. Genovese was more sensitive to Na2SO4 excess than cv. Fine whereas both of them had higher SOD activity under NaCl salinity. Generally, Fine basil withstood salinity better than Genovese, being endowed with higher constitutive levels of reduced lipoic acid [dihydrolipoic acid (DHLA)] as well as of - and -tocopherols. Moreover, cv. Fine showed the ability to utilise DHLA and to synthesise tocopherols during stressful conditions. Thus, more than one mechanism was involved in basil in the detoxification of reactive oxygen species during salt stress. In fact, when lipoic acid did not participate in the regeneration of reduced ascorbate and glutathione form, high amounts of tocopherols were present, likely protecting cell membranes from oxidative damage and making basil tolerant to moderate salinity.