Seaweed extract ameliorates salt stress in tomato plants by enhancing the antioxidant system and expression of stress-responsive genes

Biostimulants such as seaweed extracts are widely used to stimulate plant growth and crop productivity under optimal or stressful conditions, constituting a sustainable strategy to mitigate the impacts of abiotic stress on plant performance. In this study, a growth experiment was conducted to evaluate the effects of an aqueous extract from the seaweed Padina gymnospora on the physiological, biochemical, and molecular characteristics of Solanum lycopersicum under salt stress. The experiment included four treatments: 1) control plants, 2) plants irrigated with 300 mM NaCl solution, 3) plants treated with the P. gymnospora extract, and 4) plants treated with the P. gymnospora extract and irrigated with 300 mM NaCl solution. Salt stress increased the activity of antioxidant enzymes (catalase and superoxide dismutase) and resulted in the overaccumulation of the osmolyte proline and flavonoids while enhancing photosynthetic performance and chlorophyll content. In addition, treatment with P. gymnospora extract increased total reducing sugars and phenols in salt-stressed plants, which was correlated with DPPH and ABTS antioxidant activity. The induction of stress-responsive genes, such as SlHB7, SlSOD1, SlRD29, and SlHKT, appears to be a major factor modulating the responses to P. gymnospora extract application in tomato plants. The results of this study demonstrate that the application of P. gymnospora to tomato plants attenuated the damage caused by salt stress. It is essential to continue studying the potential of seaweed extracts to mitigate stress in plants, given the promising agricultural applications of these novel biostimulants.