Greenhouse hydroponic experiments were performed to evaluate potential role of H2S on Al toxicity in barley seedlings. Seedlings pretreated with 200 mu M NaHS as a donor of H2S for 24 h and subsequently exposed to 100 mu M AlCl3 for 24 h had significantly longer roots than those without NaHS. The promoted root elongation was correlated with a substantial decrease in Al-induced overproduction of lipid peroxidation, electrolyte leakage and Al accumulation in roots, and a marked increase in Al-induced depress activities of Na+K+-ATPase and W-ATPase. The alleviating role of H2S on Al-induced toxicity was also found in a time- and dose-dependent experiment. Addition of 200 and 400 mu M NaHS to 100 mu M AlCl3 effectively alleviated Al-toxicity, markedly diminished Al-induced MDA accumulation, and increased chlorophyll content, net photosynthetic rate (Pn) and maximal photochemical efficiency (Fv/Fm) compared with Al alone. Exogenous H2S significantly elevated depressed CAT activities, and further improved root POD activity. Moreover, NaHS decreased Al accumulation, but elevated concentrations of S, P, Ca, Mg and Fe in plants. These data suggest that H2S-induced alleviation in Al toxicity is attributed to reduced Al uptake and MDA accumulation, improved uptake of P. Ca, Mg and Fe, and elevated ATPase and photosynthetic performance. (C) 2012 Elsevier B.V. All rights reserved.