Abstract Saline stress negatively affects the physiological and biochemical functions of plants, inhibiting growth, the ability to perform photosynthesis, interfering with enzymatic activity, and protein and chlorophyll synthesis. Salicylic acid and jasmonic acid are two phytohormones involved in plant defense metabolism and have been used to mitigate the effects of salt stress in plants. In this context, the aim was evaluate whether the foliar application of salicylic acid and jasmonic acid, and their interactions, attenuate the salt stress effects on physiological, biochemical and growth responses of lettuce. An experiment was designed with three salinity levels (0; 36.5 and 76.5 mM) and foliar application of salicylic acid (0 and 500 µM) and jasmonic acid (0 and 100 µM). The fresh and dry masses, gas exchange, chlorophyll content, malondialdehyde content, proline, relative conductivity of membranes, soluble proteins, total and reducing sugars and phenols were evaluated. At the highest salinity (76.6 mM) there was a reduction in the fresh mass of the aerial part and root by 21.84% and 13.80%, respectively, in relation to the control, showing that salinity reduced lettuce growth. Gas exchange decreased with salinity, except for net photosynthesis and total chlorophyll, which remained unchanged. The application of the hormones did not influence the growth and gas exchange of lettuce. In the treatment without saline stress, total leaf sugar decreased with the application of hormones alone, but increased by 74.23% with the combined application of hormones (SA + JA), while in moderate stress, the isolated application increased total leaf sugar compared to the control. Proline increased in the leaf at a salinity of 76.5 mM, but with the application of SA it reduced by 37.92%, showing the attenuation effects of this hormone to saline stress. The exogenous application of salicylic acid and jasmonic acid did not influence growth and gas exchange, but improved biochemical responses under moderate (36.5 mM) and severe (76.5 mM) salinity, suggesting possible defense mechanisms of these phytoregulators in lettuce under salt stress.
Lemos-Neto et al. (Mon,) studied this question.