Effects of exogenous NO on the growth, mineral nutrient content, antioxidant system, and ATPase activities of Trifolium repens L. plants under cadmium stress

This work investigated the effects of SNP (sodium nitroprusside; an NO donor) on 100 mu M cadmium (Cd) toxicity in 2-week-old Trifolium repens L. plants. Cd accumulated to a greater degree in roots than in shoots and resulted in oxidative stress, as evidenced by increased concentrations of hydrogen peroxide and malondialdehyde. In addition, Cd exposure markedly hindered root and shoot elongation and biomass production, reduced the activities of H+-ATPase in the plasma membranes (PMs) and tonoplasts (V), and inhibited the absorption of mineral nutrition. However, the addition of various SNP doses alleviated the inhibitory effects on plant growth caused by Cd, elevated the activity of the PM H+-ATPase in both shoots and roots, enhanced the activity of V-H+-ATPase in roots, and partially enhanced the uptake of minerals (shoots: Mg and Cu; roots: Ca, Mg, and Fe) in Cd-treated plants. Shoot and root Cd accumulation significantly diminished when plants were subjected to Cd plus SNP treatments, though the level of root Cd accumulation was not dependent on the SNP dosage level. Moreover, the addition of SNP considerably upregulated ascorbate peroxidases (APX), catalases and superoxide dismutase (SOD) activity in shoots under Cd stress, but downregulated APX and SOD activity in roots. The addition of SNP did not influence glutathione reductase (GR) activity in roots, but markedly increased its activity in shoots. Similar to root GR levels, shoot ascorbate content experienced no significant change between Cd plus SNP treatment and Cd treatment alone; however, root ascorbate and glutathione levels decreased in plant tissues in the treatments with Cd and SNP. The results obtained in this work indicate that SNP applied exogenously, particularly at lower doses, can effectively deplete the detrimental effects on white clover growth, likely by reducing oxidative damage, modulating mineral absorption, and re-establishing the levels of ATPases.