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

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, free proline, relative water content (RWC), electrolyte leakage in the leaves, and the concentrations of Na+ and K+ in 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 roots and 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 shoots and 3.8 folds in roots) significantly increased. However, silicon (particularly at 3 mM) ameliorated the deleterious effects of NaCl. Compared to exclusively salt-stressed plants, the fresh and dry weights were increased by 20.3% and 66%, respectively. Also, the content of total chlorophyll (21%), RWC (83%), and K+ (21% in shoots and 90% in roots) augmented, but electrolyte leakage (38%) and the content of Na+ decreased (39.7% in shoots and 27.8% in roots). Generally, current data suggested that 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 apparatus under salinity.