Foliar spray of salicylic acid induces physiological and biochemical changes in purslane ( Portulaca oleracea L.) under drought stress

Purslane (Portulaca oleracea L.) is a plant with a long history in cooking and folk medicine that has been distributed worldwide. In the present study, purslane was used as a model plant to investigate the effect of foliar application of salicylic acid (SA) on plant tolerance to drought stress. The effects of SA foliar spray (0, 0.5 and 1 mM) on physiological and biochemical responses of purslane seedlings under drought stress (90, 60 and 30% field capacity) were investigated. The results showed that drought stress decreased the contents of photosynthetic pigments, parameters of gas exchanges, proline, soluble sugars, total phenolic, flavonoids, growth, and biomass production. However, SA improved photosynthetic pigments, gas exchanges, compatible solutes and secondary metabolites and thereby increased purslane growth and biomass production. Drought stress also induced oxidative stress (H2O2 and MDA) in purslane seedlings; however, SA reduced the drought-induced oxidative stress by regulating the activity of antioxidant enzymes. Drought stress increased the content of palmitic and arachidonic acid and decreased unsaturated fatty acids (oleic, linoleic and linolenic acid), stearic and behenic acid in the leaves of purslane. However, SA improved the fatty acids content under drought stress. These results indicate that foliar application of SA improved the adaptation and tolerance of the purslane plant to drought stress by improving gas exchange, increasing the accumulation of secondary metabolites and compatible solutes, improving the antioxidant defence system and regulating the fatty acids profile of membrane lipid.