Responses of wheat to zinc sulfate fertilizer and plant growth-promoting rhizobacteria under cadmium stress in soil

Cadmium (Cd) is a major pollutant in soils as a result of extensive use of fertilizers, mining and industrial discharges. Zinc (Zn) and certain bacterial species have been known to alleviate Cd toxicity in plants. In this study, the individual and combined effects of the application of Zn and Pseudomonas species with the aim of reducing Cd stress in wheat cultivars were investigated. Plants (durum wheat and bread wheat) were exposed to different concentrations of Cd and Zn, and either P. putida or P. fluorescens in a growth chamber. Concentrations of Zn, Cd, chlorophyll (Chl), carotenoid, hydrogen peroxide (H2O2), and malondialdehyde (MDA), as well as antioxidant enzyme activities were assayed. The addition of Zn in soils reduced the toxicity of Cd in durum wheat more than in bread wheat even though there was more uptake of Zn in bread wheat. Analysis of variance showed that by using Zn fertilizer and Pseudomonas species the amounts of peroxidase (POD), polyphenoloxidase (PPO), MDA, and H2O2 were reduced at three growth stages. Surprisingly, with increasing Zn concentration, Cd concentration in plant tissue was slightly increased, which suggests that adding Zn to soil could facilitate Cd desorption from soil particles. Application of Pseudomonas and Zn could be a promising solution to reduce detrimental effects of Cd, especially in durum wheat.