Effect of silicon nutrition on growth, physiology and biochemical of dill (Anethum graveolens L) under Pb stress conditions.

Silicon is one of the beneficial elements for plants, recent studies have shown that this element plays a very important role in plant resistance to environmental stresses, including heavy metal stress. To evaluate the effect of silicon foliar spraying on increasing tolerance to lead contamination in dill (Anethum graveolens L) a factorial experiment based on completely randomized design with four replications was conducted in research greenhouse of Mohaghegh Ardabili University at 2015-2016. Experimental factors included soil contamination by lead (0, 400, 600 and 1000 mg/kg soil) from (Pb(NO3)2 source and silicon( From Na₂SiO₃5H2o source) levels 1 mM and control (spraying with water). During this experiment traits such as plant height, plant dry weight, leaf number, lateral branch number, root dry weight, electrolyte leakage, leaf relative water content, photosynthetic pigments, proline, total carbohydrates and catalase and peroxidase enzymes activity, concentration of lead and calcium concentration in the plant's shoot were measured. The results showed that lead stress had a significant reduction effect on the measured growth parameters of the plat. The highest root dry weight, stem diameter, leaf relative water content was obtained in control plants which  treated  with  spraying by 1 mM silicon. The highest value for  proline and  carbohydrates production, catalase and peroxidase enzymes activity were obtained by combination of  spraying with 1 mM of silicon  at  under 1000 ppm lead contamination. In general the results of this study showed that the foliar application of silicon can be advised for improving growth of dill plants under lead contamination stress conditions.