Antioxidative Systems and Stress Tolerance: Insight from Wild and Cultivated Tomato Species

The role of antioxidative systems of the salt-sensitive cultivated tomato, L. esculentum (Lem) and its wild salt-tolerant relative L. pennellii (Lpa) in salt tolerance was studied. For this, leaf and root cell organelles (chloroplasts/plastids, mitochondria, and peroxisomes) isolated from control and salt-treated Lem and Lpa plants were characterized and compared. In general, the inherent organellar antioxidative systems of the two tomato species were highly similar. The activities of SOD and the ascorbate–glutathione cycle isozymes, in the various cell organelles, were separated into soluble and membrane-bound fractions. Latency and solubilization assays were used to map the in situ suborganellar localization of the ascorbate–glutathione cycle isozymes. These activities were localized to both faces of the organellar membranes and in the lumens of various suborganellar compartments and were modeled for peroxisomes, chloroplasts, and mitochondria. Differences between the inherent antioxidative systems of Lem and Lpa were found. These included different ratios of the soluble to membrane-bound activities and different SOD-type inventories. In Lem organelles, stress-induced downregulation of antioxidative isozymes, and oxidants, was correlated with increased oxidative damage, in contrast, in Lpa organelles a stress-induced upregulation of the antioxidative isozymes, and oxidants, was correlated with alleviation of oxidative stress. Similarly, cross-tolerance to imposed oxidative stress by SHAM and 3-AT was found only in Lpa plants grown in salinity and was dependent, at least in part, upon the capacity for de novo GSH synthesis. The failure of Lem to upregulate its antioxidative systems is discussed.