Effects of exogenous nitric oxide on cadmium toxicity in black poplar (Populus nigra): physiological approaches

Abstract

Cadmium (Cd) is a highly toxic metallic contaminant that negatively affects plant metabolism and causes reductions in productivity. Nitric oxide (NO) is a signaling molecule that regulates various physiological processes and is involved in response to biotic/abiotic stresses. This work investigated the effects of exogenous sodium nitroprusside (SNP), a nitric oxide (NO) donor, application on Cd toxicity in black poplar (Populus nigra). Black poplars were exposed to individual/combined CdCl2 and SNP treatments for 21 days by complete randomized design with three replications. Cd concentrations increased in leaves, bark, and roots at Cd treatments, whereas Cd + SNP applications had alleviative effects on Cd exposures, except for leaves. Photosynthetic pigments (chlorophyll a, b, a + b and carotenoids) reduced with Cd treatments in leaves, while they increased in Cd + SNP applications. Similarly, plant biomass was reduced with Cd treatments, but Cd + SNP application prevented these reductions. SNP also alleviated malondialdehyde (MDA) and hydrogen peroxide (H2O2) accumulation in leaves under Cd treatments. Catalase (CAT, EC 1.11.1.6) and ascorbate peroxidase (APX, EC 1.11.1.11) activities were also affected by Cd and Cd + SNP applications. Cd exposure also decreased Zn2+, Fe2+ and Mn2+ levels in leaves, bark and roots, while it increased Cu2+ level in leaves and roots. This study concludes that Cd toxicity caused a reduction of plant growth and mineral nutrition parameters. However, SNP indicates great potentials for improving the growth under Cd toxicity in P. nigra.