PHYSIOLOGIA PLANTARUM 115: 393–400. 2002 Copyright C Physiologia Plantarum 2002 Printed in Denmark – all rights reserved ISSN 0031-9317 Salt stress induces up-regulation of an efficient chloroplast antioxidant system in the salt-tolerant wild tomato species Lycopersicon pennellii but not in the cultivated species Valentina Mittova a , Moshe Tal b , Micha Volokita a and Micha Guy a,* a The Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus 84990, Israel b Department of Life Science, Ben-Gurion University of the Negev, PO Box 653, Beer Sheva 84105, Israel *Corresponding author, e-mail: michagu/bgumail.bgu.ac.il Received 2 July 2001; revised 4 February 2001 The response of the chloroplastic antioxidant system of the cultivated tomato Lycopersicon esculentum (Lem) and its wild salt-tolerant related species L. pennellii (Lpa) to NaCl stress was studied. An increase in H 2 O 2 level and membrane lipid peroxidation was observed in chloroplasts of salt- stressed Lem. In contrast, a decrease in these indicators of oxidative stress characterized chloroplasts of salt-stressed Lpa plants. This differential response of Lem and Lpa to salinity, correlates with the activities of the antioxidative enzymes in their chloroplasts. Increased activities of total superoxide dismutase (SOD), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), glutathione-S- transferase (GST), phospholipid hydroperoxide glutathione peroxidase (PHGPX) and several isoforms of non-specific peroxidases (POD) were found in chloroplasts of salt- treated Lpa plants. In these chloroplasts, in contrast, activ- Introduction The production of activated oxygen species (AOS), which can damage DNA, proteins, chlorophyll and membrane function (Alscher et al. 1997), is a by-product of oxidative metabolism in chloroplasts (Asada 1996), mitochondria (Levine 1999) and peroxisomes (del Rio et al. 1992). AOS production is further enhanced in re- sponse to various abiotic stresses, such as drought (Smir- noff 1993, Yu and Rengel 1999), salt (Herna ´ndez et al. 1995, Yu and Rengel 1999), extreme temperatures (Pras- ard et al. 1994), and herbicides (Bowler et al. 1992). Nu- merous studies show that the level of antioxidative en- zymes increases when plants are exposed to biotic or abi- otic stresses (for review see Polle 1997, Levine 1999). A bbreviations – APX, ascorbate peroxidase; DHAR, dehydroascorbate reductase; GR, glutathione reductase; GSH, reduced glutathione; GST, glutathi- one-S-transferase; LOX, lipoxygenase; MDHAR, monodehydroascorbate reductase; PHGPX, phospholipid hydroperoxide glutathione peroxidase; POD, non-specific peroxidase; SOD, superoxide dismutase. Physiol. Plant. 115, 2002 393 ity of lipoxygenase (LOX) decreased while in those of salt- stressed Lem it increased. Although total SOD activity slightly increased in chloroplasts of salt-treated Lem plants, differentiation between SOD types revealed that only stromal Cu/ZnSOD activity increased. In contrast, in chloroplasts of salt-treated Lpa plants FeSOD activity in- creased while Cu/ZnSOD activity remained unchanged. These data indicate that salt-dependent oxidative stress and damage, suffered by Lem chloroplasts, was effectively allevi- ated in Lpa chloroplasts by the selective up-regulation of a set of antioxidative enzymes. Further support for the above idea was supplied by leaf discs experiments in which pre- exposure of Lpa plants to salt-treatment conferred cross- tolerance to paraquat-induced oxidative stress while in- creased oxidative damage by paraquat-treatment was found in salt-stressed Lem plants. Comparison of the responses of cultivars and/or re- lated species, exhibiting differential sensitivity to salt stress, showed a correlation between salt tolerance and increased activity of the antioxidant system. For in- stance, Gossett et al. (1994, 1996) found a strong re- lationship between antioxidant capacity and NaCl tol- erance in cotton. Meneguzzo et al. (1999) attributed the better salt tolerance of one wheat line over the other line to the induction of ascorbate synthesis. Gue- ta-Dahan et al. (1997) showed enhanced activities of superoxide dismutase (SOD; EC 1.15.1.1), ascorbate peroxidase (APX; EC 1.11.1.11). The importance of enzymes involved in detoxification of membrane lipid