Can exogenous methyl jasmonate mitigate salt stress in radish plants?

Salt stress is a major factor limiting plant growth and productivity, especially under the threat of climate change. Therefore, it is important to develop strategies that aim to ensure food production even under saline conditions. The exogenous application of methyl jasmonate (MJ) to mitigate stress in plants has shown promising results. In this study, we evaluated the effects of different MJ concentrations on radish (Raphanus sativus L.) growth and morphology under salt-stress conditions. Plants were irrigated with saline (120 mM NaCl, 12.25 dS m(-1)) and tap water (control, 0.31 dS m(-1)) and sprayed weekly with MJ solutions (5 mu M, 50 mu M, 500 mu M, and 5 mM) and distilled water. The experimental period started seven days after sowing (DAS) and lasted until 30 DAS. In salt-stressed plants, photosynthetic capacity was reduced and radish growth decreased by 50%; however, the chlorophyll and carotenoid concentration, electrolyte leakage, and dark respiration rate increased. Our results showed that none of the MJ concentrations mitigated growth inhibition caused by salt stress; independent of salt stress, the highest MJ concentration (5 mM) restricted the formation of fleshy storage root. In contrast, 5 mu M MJ mitigated the negative effects of salt stress on carbon assimilation rate, transpiration, stomatal conductance, and dark respiration. Moreover, the growth inhibition induced by salt stress and 5 mM MJ positively correlated with the reduction in the fluorescence signal, mainly during the photochemical rise. Therefore, MJ does not mitigate salt stress in radish, and can inhibit plant growth at high concentration.