Journal of Plant Process and Function

Salinity is a complex phenomenon that involves not just an osmotic effect, but also toxic ion effects and nutritional imbalance. In order to evaluate the effects of severity and duration of sodium chloride stress on some biochemical and photosynthesis parameters of tobacco a factorial experiment was conducted using a randomized completely block design with three replication with using a hydroponic culture in Biotech Center of Urmia university. In this study, the effects of 5 salinity levels (0, 50, 100, 150 and 200 mM NaCl) and three time periods (2, 5, and 12 days) were evaluated. The results showed that under sodium chloride stress the dry weight and photosynthetic pigments compared to the control were reduced, while proline content was increased. The results of analysis of variance showed that sodium chloride levels, duration of stress and the interaction of stress and duration of salinity have significant differences on stomatal conductance, transpiration rate, CO₂ concentration and water use efficiency (p≤0.01). The sodium chloride levels and the interaction of stress and duration of sodium chloride stress have significant differences on net photosynthetic rate and mesophilic conductance. The net photosynthesis, stomatal conductance, transpiration rate, intercellular CO₂ concentration and mesophilic conductance in 200 mM sodium chloride at 12 days after stress compared to control 74%, 97%, 90%, 48% and 59% decreased, respectively. These results indicate that stomatal limitations might be the main cause of decrease of photosynthesis in tobacco plant under sodium chloride stress.