The Alleviation of the Adverse Effects of Salinity Stress in the Tomato (Solanum lycopersicum L. cv. Mobin) by Application of Ascorbic Acid

Salinity stress is one of the major environmental factor limiting plant growth and productivity. The adverse influence of salinity stress is evaluated on all plant levels. Ascorbic acid is a small, water-soluble antioxidant molecule that acts as a primary substrate in the pathway for detoxification and neutralization of superoxide radicals and singlet oxygen. Ascorbic acid has been shown to play multiple roles in plant growth, such as in cell division, cell wall expansion, and other developmental processes. The objective of the present experiment was to investigate the effects of the exogenous application of ascorbic acid on the growth parameters and photosynthesis attributes of tomato plants.

The experiment was conducted as a factorial in a completely random design with three replications in greenhouse conditions. Salinity stress was applied by 0, 25, 50, 100 mM NaCl in modified Hoagland solution. Ascorbic acid treatments (0, 2.5 and 5 mM) were sprayed on the leaves every three days until the end of experiment. Leaf, stem, and root fresh and dry weight, total fresh and dry weight, yield per plant, net photosynthesis, Stomata conductance, transpiration, internal CO2 concentration, chlorophyll a, b and total chlorophyll, proline and total soluble sugar content were evaluated.

In the present experiment, salinity stress sharply reduced the leaf, stem, root and total fresh and dry weight, yield per plant, net photosynthesis, stomata conductance, transpiration, internal CO2 concentration, chlorophyll a, b and total chlorophyll content whereas the exogenous treatment of AsA appreciably delayed the loss of all studied traits. Foliar application of ascorbic acid under both stress and non-stress conditions improved the growth parameters and photosynthesis attributes. Salinity stress also increased total soluble sugar content and proline accumulation in the leaf of the tomato plant. Application of ascorbic acid under both non-stress and salinity stress conditions decreased total soluble sugar content and proline accumulation and reduced the effects of salinity stress.

This experiment showed that treating the tomato (Solanum lycopersicum L. cv. Mobin) with 5 mM ascorbic acid substantially influences several metabolic processes, leading to the increased growth. The protection of the plant against salinity stress by using of ascorbic acid was possibly to be caused indirectly as a result of increasing amount of chlorophyll which plays an essential role in photosynthesis process and then formation of carbohydrates. Thus, it might be concluded that exogenously applied ascorbic acid has low external osmotic potential and ion toxicity and it might be effective in amelioration of the adverse effects of salt stress.