Effect of salicylic acid on tobacco (Nicotiana rustica) plant under drought conditions

Drought stress impact photosynthesis and stomatal conductance, and may reduce the overall production capacity of plants. Since exogenous application of salicylic acid (SA) can partially alleviatebe increased the negative effects tolerance of drought stress by improve the metabolism pathways and increase the net photosynthesison plant photosynthesis and metabolism, the main objective of this study was to clarify the roles of SA in enhancing 28 days tobacco (Nicotiana rustica Basmas) tolerance to drought stress (50% FC). The results indicated that foliar application of SA (0.5 mM) influenced negatively net CO2 assimilation rate and stomatal conductance and led to reduction of shoot and root dry masses. In contrast, the stress did not reduce significantly the maximal quantum yield of photosystem II (PSII). This that can be explained by enhancement of efficiency for dissipation of excess photon energy in the PSII antenna, determined as non-photochemical quenching, and consequently further protection of PSII from photodamage. Thus, under more drought stress, the reduction of photosynthesis of tobacco plants was due mainly to reduction of stomatal conductance. Under water-deficient conditions, plants showed an increase in chlorophyll a and amino acids concentrations in the leaves when treated with SA while this change for net photosynthesis was negligible. Our results indicated showed that the foliar application of SA had no ameliorative effect on tobacco growth under drought stress, because its effect on elevation of transpiration rate did not increase net photosynthesis under drought condition.