Effects of silicon in alleviating salt stress in flue cured tobacco (Nicotiana tabacum l.)

Abstract

Silicon (Si) is the second most abundant mineral element in the soil and the ability of Si to alleviate the adverse effects of sodium chloride (NaCl) on plant growth is well documented. The response of tobacco to Si and NaCl was evaluated in the incubator, the outdoor float tray system and the greenhouse. The effects of salinity and supplemental silicon on germination, seedling development and early performance of transplanted tobacco (Nicotiana tabacum L.) were investigated in a complete randomised block design with a 3 x 3 factorial treatment structure. The first factor was NaCl, with three levels (0 mM, 25 mM and 50mM), and the second factor was Si, with three levels (0 mM, 2 mM, 4 mM; for the first and second experiments and 0 g Si / 50 g soil, 0.4 g Si / 50 g soil and 0.8 g Si / 50 g soil; for the third experiment). Silicon was applied as sodium silicate in the first two experiments and as diatomaceous earth (78 % Si) in the greenhouse experiment. Germination and plant growth parameters, potassium (K+) and sodium (Na+) accumulation, total protein content (TPC), ascorbic acid content in plant tissue, electrolyte leakage (EL), electric conductivity (EC) in growth media and relative water content (RWC) of leaves, were analysed in the experiment . Application of silicon had no effect on germination percentage and rate of germination (R). The highest root dry weight of 4.044 g / plot was observed in the 25 mM NaCl / 4 mM Si treatment. Silicon application (4 mM) recorded a 49.2 % increase in TPC at 50 mM NaCl treatment as compared to the control. Sodium chloride supply greatly increased EL in leaves, however the silicon amendments significantly (p < 0.001) reduced the EL of leaves under salt stress. Silicon resulted in a significant (p < 0.001) increase in ascorbic acid content, with the 4 mM Si treatment recording the highest ascorbic acid content. The accumulation of Na+ in seedling tissues was enhanced by NaCl, however the application of Si significantly (p = 0.001) reduced the Na+ content in leaves, with the 4 mM Si treatment recording the lowest Na+ content. Present findings suggested that silicon has a key role in the enhancement of salt tolerance in tobacco seedlings. There is need to perform further studies, in tobacco seedlings, on the effect of silicon supply on activity of anti-oxidant enzymes under salt stress conditions.