The effect of salicylic acid under drought stress on some physiological and biochemical traits of Portulaca oleracea L.

Considering the increasing trend of drought development and lack of desirable land for agriculture in the world, the use of drought resistant species or the use of compounds that reduce the effects of drought stress and induction of resistance to stress in plants is very important. In the present study, the effects of salicylic acid (SA) foliar spray (0, 0.5 and 1 mM) on physiological and biochemical responses of purslane (Portulaca oleracea L.) as a medicinal plant under drought stress (90, 60 and 30% of field capacity (FC)) were examined in a factorial experiment based on a completely randomized design with four replications in Islamshahr Branch, Islamic Azad University, Islamshahr, Iran. The results showed that 60 and 30% FC reduced the height (18.5 and 45%, respectively) and total dry weight (43.1 and 58.6%) of the plant compared to the control treatment. Drought stress, especially 30% FC, reduced photosynthetic pigments, relative water content, membrane stability and induced oxidative stress (increased levels of methylglyoxal and malondialdehyde). However, foliar application of SA by regulating chlorophyll metabolism (activity of chlorophyllase and delta-aminolevulinic acid dehydratase) and improving proline metabolism (activity of proline dehydrogenase and delta-1-proline-5-carboxylate synthetase 1) increased the contents of chlorophylls and proline and, consequently, improved photosynthetic apparatus efficiency and relative water content under drought stress. SA also improved plant tolerance to drought stress by increasing the activity of enzymes involved in the glyoxalase system and improving the redox state of the ascorbic acid-glutathione cycle. Therefore, SA under drought stress can play an effective role in reducing and modulating the negative effects of stress.