Salinity and copper-induced oxidative damage and changes in the antioxidative defence systems of Anabaena doliolum Ashish Kumar Srivastava, Poonam Bhargava and Lal Chand Rai* Laboratory of Algal Biology, Center of Advanced Study in Botany, Banaras Hindu University, Varanasi, 221005, India *Author for correspondence: Tel.: +91-542-2307146, Fax: +91-542-2368174, E-mail: lcrai@bhu.ac.in Received 6 October 2004; accepted 16 February 2005 Keywords: Anabaena doliolum, antagonism, antioxidative defence system, copper, homeostasis, oxidative stress, salinity Summary This study provides first-hand information on the salinity and copper-induced oxidative damage and its protection in Anabaena doliolum by the antioxidant defence system. Oxidative damage measured in terms of lipid peroxidation, electrolyte leakage and H 2 O 2 production was induced by different concentrations of NaCl and Cu 2+ . A greater electrolyte leakage by NaCl than Cu 2+ supported the hypothesis of salinity being more injurious than copper. To explore the survival strategies of A. doliolum under NaCl and Cu stress, enzymatic antioxidant activities e.g. superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) and nonenzymatic antioxidant contents such as glutathione reduced (GSH), ascorbate, a-tocopherol, and carotenoid were measured. A general induction in SOD and APX activities as well as ascorbate and a-tocopherol contents was found under NaCl and Cu 2+ stress. In contrast to this, an appreciable decline in GR activity, GSH pool and carotenoid content under Cu 2+ and an increase under NaCl stress were observed. CAT activity was completely inhibited at high doses of NaCl but stimulated following Cu 2+ treatment. The above results suggest the involvement of APX and CAT in the scavenging of H 2 O 2 under Cu 2+ stress. In contrast to this, only APX was involved in H 2 O 2 scavenging under salt stress. Our postulate of Cu 2+ -mediated antagonism of salt stress can be explained by a conceivable reversion of Na + -induced disturbance of cellular homeostasis by redox active Cu 2+ . Introduction For meeting the food demand of an ever-increasing population Indian agriculture has undergone a major revolution. This goal was achieved by the use of high yielding varieties of crops that require frequent irriga- tion and application of fertilizers and pesticides. Accu- mulation of salt and metal in the soil are the two offshoots of the above practice. Current estimates sug- gest that about 20% of the cultivated and 50% of the irrigated lands all over the world are adversely affected by salinity (Zhu 2001). Canal irrigation is one of the foremost causes of soil salinity in India. Irrigation of crops by water from ponds, lakes, and rivers (often contaminated with metal ions) is responsible for accu- mulation of metal ions in soil. Notwithstanding this, copper is an important constituent of frequently used pesticides and algicides such as copper sulphate (blue stone), copper oxychloride, copper hydroxides and fungicides. Anabaena doliolum, an important N 2 -fixing cyanobacterium occurring in paddy fields, is generally challenged by the high levels of salinity and copper present in the soil. Its survival, therefore, depends on the production of such defence tools as antioxidants or stress proteins. Of the two strategies the former consti- tutes the first line of defence for any organism. The oxidative damage in living cells is characterized by the enhanced production of reactive oxygen species viz. superoxide anion (O 2 ) ), and peroxides, including H 2 O 2 , hydroxyl radical (OH  ) and oxygen free radical (O  ). A moderate amount of reactive oxygen species is produced by cells during photosynthesis and respiration. Under normal conditions these reactive oxygen species have several important functions such as lignification of the cell wall of higher plants, defence against pathogen, sensing and adaptation to stress conditions and induc- tion of apoptosis by modulating gene expression (Neill et al. 2002). However, increase in reactive oxygen species content adversely affects the physiological, biochemical and molecular variables of organisms. In order to sur- vive under stress, every cell possesses a complex array of enzymatic and nonenzymatic antioxidant defence sys- tems. Superoxide dismutase (SOD) is the first enzyme of the enzymatic antioxidative pathway to convert super- oxide anion into peroxides, which are scavenged by catalase (CAT), ascorbate peroxidase (APX) and World Journal of Microbiology & Biotechnology (2005) 21: 1291–1298 Ó Springer 2005 DOI 10.1007/s11274-005-2442-2