Hybrid Priming with He–Ne Laser and Hydrogen Peroxide Advances Phenolic Composition and Antioxidant Quality of Salvia officinalis Under Saline and Non-Saline Condition

Common sage (Salvia officinalis) is a perennial herb whose health-promoting value greatly depends on its phenolic compounds content. He–Ne laser and H2O2 are considered as potent elicitors to modulate secondary metabolism and stress tolerance in plants but their combined effect is unknown. Therefore, in the current study, we assessed the impact of solo and hybrid priming of seeds with H2O2 (5 mM) and He–Ne laser (6 J/cm2) on the composition of phenolics in S. officinalis under non-saline and saline conditions. Results revealed that salinity (75 mM NaCl) reduced biomass, the content of chlorophyll a, b, and carotenoids, increased electrolyte leakage, enhanced the total phenolic and flavonoid contents, and changed the proportion of phenolic fractions in leaves. Hybrid priming more prominently than individual seed priming with laser and H2O2 improved biomass and content of photosynthetic pigments, reduced electrolyte leakage, up-regulated phenylalanine ammonia-lyase (PAL) transcripts and activity of PAL enzyme, and intensified de novo biosynthesis of phenolic acids and flavonoids. Besides, HPLC analysis showed that hybrid priming further increased the content of ferulic, hesperidin, quercetin, kaempferol, luteolin, apigenin, and particularly rosmarinic acid and more strongly amplified DPPH scavenging capacity in leaves of salt-stressed plants. Overall, our results, via a heat map and principal component analysis, uncovered that hybrid priming with laser and H2O2 improved the salt tolerance and antioxidant value of S. officinalis. Therefore, hybrid priming might be a novel strategy to enhance the antioxidant properties and stress tolerance in medicinal plants.