Priming with methyl jasmonate alleviates polyethylene glycol-induced osmotic stress in rice seeds by regulating the seed metabolic profile

The present study was designed to study the effects of priming using 2.5 mM or 5 mM methyl jasmonate (MeJA) on the tolerance of rice (Oryza sativa, L) seedlings to osmotic stress that was simulated by 30 g/L of polyethylene glycol (PEG, 6000). The results showed that seed germination and seed vigor were improved by 2.5 mM MeJA priming as compared with unprimed control. However, the application of 5 mM MeJA reduced the germination and seed vigor. Similarly, the seedlings parameters that were decreased under PEG stress, including root length, shoot length, fresh weight and dry weight, were better improved by 2.5 mM MeJA priming than 5 mM MeJA priming. Priming with 2.5 mM MeJA also improved photosynthetic parameters that were decreased under PEG stress, such as net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO₂ concentration (Ci) and transpiration rate (Tr). In addition, under PEG stress, the chlorophyll content and the photochemical efficiency of PSII (Fv/Fm) were better improved by 2.5 mM MeJA than 5 mM MeJA. MeJA priming improved water potential, water use efficiency (WUE) and relative water content (RWC) under PEG stress condition but worsened electrical conductivity. The Gas Chromatography-Mass Spectrometry (GC–MS) analysis revealed that PEG stress induced changes in the concentration of many metabolites in the root and shoot tissues of both studied cultivars. The proline content was significantly increased under PEG stress indicating plant positively undergoing the PEG stress. Our data showed that priming with 2.5 mM MeJA alleviated the effects of PEG stress on seed germination and seedling growth in rice.