J. Plant Physiol. 160. 1157 – 1164 (2003)  Urban & Fischer Verlag http://www.urbanfischer.de/journals/jpp Exogenous silicon (Si) increases antioxidant enzyme activity and reduces lipid peroxidation in roots of salt-stressed barley (Hordeum vulgare L.) Yongchao Liang 1 *, Qin Chen 2 , Qian Liu 1 , Wenhua Zhang 2 , Ruixing Ding 1 1 Department of Plant Nutrition, College of Natural Resources and Environmental Sciences, NanjingAgricultural University, Nanjing, 210095, P.R. China 2 Agricultural College, NanjingAgricultural University, Nanjing, 210095, P.R. China Received January 27, 2003 · Accepted March 18, 2003 Summary Two contrasting barley (Hordeum vulgare L.) cultivars, i.e. Kepin No. 7 (salt sensitive) and Jian 4 (salt tolerant), were grown hydroponically to study the effect of exogenous silicon (Si) on time dependent changes of the activities of major antioxidant enzymes and of lipid peroxidation in roots under salt stress. Enzymes included: superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and gluta- thione reductase (GR). Three treatments with three replicates were investigated consisting of a control (basal nutrients with neither NaCl nor Si added), 120mmol/L –1 NaCl, and 120 mmol/L –1 NaCl +1.0 mmol/ L –1 Si. Plant roots were harvested 2, 4 and 6 days after treatment and assayed for activities of the antiox- idant enzymes and the concentrations of reduced glutathione (GSH) and malondialdehyde (MDA), and electrolytic leakage percentage (ELP). The activities of SOD, POD and CAT in roots of salt-stressed plants were significantly stimulated at Day 2 compared to control plants, but considerably decreased at Day 4 and onward. GR activity in roots of salt-stressed plants remained unchanged at Day 2, but signifi- cantly decreased at Day 4 and onward. However, exogenous Si significantly enhanced these enzyme activities in roots of salt-stressed plants compared to Si-deprived salt treatments. This Si effect was time-dependent and became stronger as the experiments continued. The tendency of change in the activities of antioxidant enzymes and the concentration of GSH coincided with the concentration of MDA, the end product of lipid peroxidation, and the ELP. Higher activities of antioxidant enzymes, and higher concentration of GSH, but lower concentration of MDA and lower ELP were noted in cultivar Jian 4 compared to Kepin No.7, implying genotypic differences with Jian 4 being less susceptible to stress- dependent membrane lipid peroxidation. The effects of Si-enhanced salt tolerance are discussed with respect to cell membrane integrity, stability and function in barley. Key words: Antioxidant enzymes – barley (Hordeum vulgare L.) – lipid peroxidation – salt stress – silicon Abbreviations: Absorb = absorbance. – AOS = active oxygen species. – BSA = bovine serum albu- min. – CAT = catalase. – ELP = electrolytic leakage percentage. – GR = glutathione reductase. – GSH = reduced glutathione. – GSSG = oxidized glutathione. – MDA = malondialdehyde. – NBT = ρ-nitro blue tetrazolium chloride. – POD = peroxidase. – PVP = polyvynilpyrrolidone. – SOD = superoxide dis- mutase. – TBA = 2-thiobarbituric acid. – TCA = trichloroacetic acid * E-mail corresponding author: ycliang@njau.edu.cn 0176-1617/03/160/10-1157 $ 15.00/0