The effect of salinity stress on tomato defense mechanisms and exogenous application of salicylic acid, abscisic acid, and melatonin to reduce salinity stress

Tomato is one of the most commonly consumed agricultural products, and the stability of its production plays an influential role in the food security of human societies. Therefore, finding solutions to reduce the risk of factors impacting tomato production could greatly help any country's economic development. During recent decades, climate change has caused the spread of salt marshes worldwide, which has affected the production efficiency and the area under tomato cultivation. Consequently, it has made scientists think about finding cheap, suitable, and minimal-risk methods for the environment to reduce the impact of salinity on tomato seedlings. Researchers have conducted several studies on the exogenous use of plant hormones in reducing salinity impact in tomato seedlings, and this study also tried to evaluate the effects of salinity stress on tomato structures (biochemical, physiological, and morphological), as well as the role of abscisic acid, salicylic acid, and melatonin hormones in tomatoes and their exogenous application in reducing salinity stress. According to the present study, the exogenous use of each of the hormones mentioned above under salinity stress conditions increases the resistance of tomato seedlings through the improvement of enzymatic and non-enzymatic animation activities, plant growth indexes, proline content, potassium ion content, K+/Na+ ratio, seed germination, relative water content, photosynthetic performance, phenolic compounds, total soluble sugars, accumulation of mineral osmolytes, protein content, expression of genes related to salt tolerance, ascorbic acid-glutathione cycle, and root architecture, as well as the reduction in ethylene content, reactive oxygen species, electrolyte leakage, sodium ion content, and content of malondialdehyde. The present study also showed that salicylic acid, abscisic acid, and melatonin interact with other internal plant hormones; therefore, their use to reduce the adverse effects of salinity stress should be carefully considered.