: Effect of Plant Growth Promoting Rhizobacteria and Silicon nutrition on growth, physiological and biochemical criteria of in spearmint (Mentha spicata L) Cd stress condition

Recently the contamination of environment is one of the most important matter in human life. Heavy metals are one of the main resources of soil pollutant, the accumulation and uptake of these elements by plants leads to toxicity in plants and health risk in human. Cadmium is one of the most important heavy metals. Recently the use of plant growth promoting rhizobacteria as biofertilizers and nutrition of plants by elements such as silicon has been considered as the main strategies for reduction the toxicity of heavy metals. For evaluation of effect of plant growth promoting rhizobacteria inoculation and silicon nutrition on growth, physiological and biochemical characteristic of spearmint (mentha spicata L) under cadmium stress condition, two separated factorial experiment based on completely randomized design in four replications was conducted in laboratory and Research Greenhouse of Mohaghegh Ardabili University at 2015-2016. Experimental factors included soil contamination by Cdcl2 (0, 50, 100, 2500 mg/kg soil), inoculation with plant growth promoting rhizobacteria and silicon nutrition (0,1mm), In first experiment soil inoculation by Pseudomonas putida strain 10 and strains in 150 and 159 of Pseudomonas fluorescence and control (inoculation with water). In second experiment plants were sprayed with concentration of 1mM silicon and water (as control), then physiological and biochemical growth indexes were measured. The result indicated that concentration of 250 ppm of cadmium caused a significant reduction in all growth criteria, photosynthetic pigments, relation water content, membrane integrity. This concentration of cadmium led to increase the carbohydrates, leaf proline, antioxidant enzyme activity. The higher content of this element accumulation resulted in root and air part but the application of plant growth promoting rhizobacteria and silicon nutrition improve the toxicity of cadmium in plant and accumulation of this metal decrease especially in aireal part of plant.