Growth responses of two tall fescue cultivars to Pb stress and their metal accumulation characteristics.

Tall fescue (Festuca arundinacea), a widely planted cool-season turfgrass and forage, is tolerant to heavy metals. However, previous investigation demonstrated that different accessions varied in Pb tolerance. In present study, hydroponic system was used to study the effects of Pb on two tall fescue cultivars, Pb tolerant 'Silverado' and Pb sensitive 'AST7001', respectively. The results indicated that Pb concentration was 14 times lower in shoots of 'Silverado' (1.34 mg g(-1) dry weight) versus 'AST7001' (19.92 mg g(-1) dry weight), although it was higher in roots of 'Silverado' (68.28 mg g(-1) dry weight) versus 'AST7001' (48.7 mg g(-1) dry weight), when subjected to 1,000 mg L(-1) Pb. In both cultivars, Pb caused an induction in malondialdehyde (MDA) content, to a less increase in 'Silerado' than 'AST7001'. Pb treatment decreased significantly soluble protein content in 'AST7001'. By contrast, soluble protein content was increased progressively, and the ratio of variable to maximal chlorophyll fluorescence was not affected in 'Silverado'. Pb treated tall fescue leaves had a greater level of superoxide dismutase (SOD) and guaiacol peroxidase (POD) activity in both cultivars, however, increase was sharp in 'Silverado' plants. The results of Q-PCR analysis for genes encoding antioxidant enzyme were in accordance with that of enzyme activities. The higher Pb tolerance of 'Silverado' might be attributed to lower shoot Pb concentration and MDA content. Meantime, the amount of soluble protein, activity of SOD and POD, as well as the level of up regulation of Cyt Cu/ZnSOD was all higher in 'Silverado' than in 'AST7001'.