Effect of Cadmium and Silicon on Growth and Some Physiological Aspects of Red Beet

Cadmium (Cd) as a heavy metal induces some disorders in normal metabolism in plants. Furthermore, Silicon (Si) is able to ameliorate the deleterious effects of some toxic elements like Cd. Keeping this in view, an experiment was conducted to find out the effects of Cd and Si on growth and some physiological aspects of Beta vulgaris L. cv. Dark Red. The experiment was arranged as a factorial scheme based on  randomized complete block design with four replications. Three levels of Cd (0 , 2.5 and 5 mg L-1) from CdSO4 and three levels of Si (0 , 28 and 56 mg L-1) from Na2SiO3 were added to nutrient solution. Perlite was used as growing media and the seeds of red beet were planted in the pots (14 L). The results showed that Cd addition significantly increased Cd concentration in leaves and roots. Application of Cd significantly decreased photosynthesis rate, chlorophyll content, leaf number, leaf area and total soluble solids (TSS) in the roots.  Additionally, increased Cd concentration in the growing media led to increased malondialdehyde (MDA) and hydrogen peroxide (H2O2) concentration in leaves. At 5 mg L-1 Cd, concentrations of H2O2 and MDA in leaves were 2.4  mM/g Fwt and 84.5 nM/g Fwt, respectively. The rate of photosynthesis in 5 mg L-1Cd, control and 56 mg L-1 Si treatments were 7.9, 18.25 and 25.76μ mol CO2 m-2s-1, respectively. Application of Si in nutrient solution significantly increased leaf number, leaf area, photosynthesis, chlorophyll content, total soluble solids (TSS) in roots and dry weight in plants. Increased Si in nutrient solution had no effect on the Cd concentration in leaves and roots of red beet. Nevertheles, malondialdehyde (MDA) and H2O2 concentrations in leaves of red beet were reduced with Si addition to the nutrient solution. In general, it is recommendable to take into consideration the benefits of Si addition to red beet growth media, but more investigations are needed