Enhancement of salt tolerance in black bean variety (Phaseolus vulgaris L.) by silicon nutrition

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In order to study the effect of silicon nutrition to increase salt tolerance in black bean variety of Phaseolus vulgaris, 12-day-old seedlings were treated with NaCl (0 and 50 mM) and NaCl (50 mM) + silicon (0.5 or 3 mM) in the green house for four weeks. The analyzed parameters were fresh and dry weights, total chlorophyll and free proline concentrations, relative water content (RWC) and electrolyte leakage in the leaves, and the concentrations of Na+ and K+ in the shoots and roots. Salt stress decreased the values of fresh (39.3%) and dry weight (48.4%), total chlorophyll (20.9%), K+ (60.6% in the roots; 20.3% in the shoots) and RWC (50%). Moreover, the level of free proline (19%), electrolyte leakage (2.4 folds) and Na+ concentration (4.6 folds in the shoots; 3.8 folds in the roots) significantly increased. However, silicon (particularly at 3 mM) ameliorated the deleterious effects of NaCl. At this case and compared to exclusively salt stress, the fresh and dry weights were increased by 20.3 and 66%. Also, the content of total chlorophyll (21%), RWC (83%) and K+ (21% in the shoots, 90% in the roots) augmented, but electrolyte leakage (38%) and the content of Na+ decreased (39.7% in the shoots, 27.8% in the roots). Generally, current data suggested silicon enhanced salt tolerance in black bean plants by reducing the entrance of Na+ and maintaining the level of K+ in the salinized tissues. Besides, it improved the water status, membrane integrity and function of photosynthetic machinery under salinity.