Alterações fisiológicas e metabólicas induzidas por primings em diferentes fases do desenvolvimento de plantas de arroz

Abstract

Soil salinity is one of the main abiotic stresses limiting the productivity of rice (Oryza sativa L.), especially in semi-arid regions such as the Brazilian Northeast. Low-cost management strategies, such as priming (prior exposure to a stress inducer), have been investigated to mitigate these effects, but the mechanisms responsible for the influence of the developmental stage at which priming occurs remain poorly understood. This study aimed to investigate the physiological and metabolic responses associated with stress memory induced by priming (treatment with 25 mM NaCl for 7 days) applied at two distinct developmental stages of rice plants (cv. Nipponbare): during germination (GPS) and at the V6 vegetative stage (VPS). After priming, the plants were subjected to salt stress with 50 mM NaCl for 16 days (Experiment I) or 11 days (Experiment II). Growth variables, ion homeostasis (Na⁺ and K⁺), oxidative stress indicators (lipid peroxidation, H₂O₂, ascorbate redox state), gas exchange (net photosynthesis, stomatal conductance, transpiration), and metabolomic profiling by GC-MS in leaves, stems, and roots were analyzed. The results demonstrated that the GPS plants maintained leaf area, total biomass, and tiller number equivalent to the control plants (without NaCl), reduced the Na⁺/K⁺ ratio by 33% compared to isolated salt stress (S), decreased H₂O₂ levels and lipid peroxidation, and preserved net photosynthesis with only an 11% reduction (compared to 24% under salt stress). The GPS group also presented a higher total ascorbate pool and activation of the antioxidant system. In contrast, the VPS treatment aggravated the stress effects, with a 67% reduction in tiller number, a 75% reduction in leaf area, increased H₂O₂ and membrane damage equivalent to or greater than the S group, in addition to the lowest photosynthetic rate among all treatments. Metabolomic analysis made it possible to suggest an organ-dependent response, since in VPS plants, the leaves accumulated amino acids related to protein degradation (serine and alanine), while GPS preserved sugar homeostasis in the stems and a metabolic transition profile between the control and salinity treatments. It is concluded, therefore, that saline priming during germination possibly confers positive memory of salt stress in rice through ionic, antioxidant, and metabolic adjustments, while priming at the V6 vegetative stage (VPS) is ineffective and can induce negative memory.