He-Ne laser pre-exposure alleviates salinity stress through physio-biochemical regulation and enhanced withanolide production in Withania somnifera (L.) Dunal

Helium-Neon (He-Ne) lasers have been widely used for their photo-modulatory responses on plant growth and development. Recent studies have shown the significant effects of lasers on mitigating abiotic stress in plants; however, these effects vary with laser type and plant species used under different abiotic stress conditions. Therefore, we explored the role of He-Ne laser priming in improving salinity stress tolerance in Withania somnifera (Ashwagandha), an important medicinal plant. Here, we used different laser doses (0 as unirradiated control, 20 and 25 J/cm²) for seed priming and sodium chloride (NaCl) (0 as control, 25 and 50 mM) for salinity stress induction. After laser irradiation, the seeds were sown inside pots containing the soil mixture under greenhouse conditions, after which the NaCl treatment was induced for 30 days. The results revealed reverse retardation of morphological traits due to laser irradiation compared with unirradiated control under NaCl stress. The photosynthetic features were significantly highest at 50 mM NaCl (P ≤ 0.001) in 25 J, and there was an insignificant increase in pigment content. The proline and malondialdehyde (MDA) contents were significantly lower at the 50 mM NaCl (P ≤ 0.05) in 25 J group. The soil EC was significantly increased at 25 and 50 mM NaCl (P ≤ 0.001) groups. The antioxidant enzyme activities were significantly enhanced in 20 J (P ≤ 0.01) group than in unirradiated control group. Furthermore, withanolides from shoots and roots were significantly enhanced at 25 mM NaCl (P ≤ 0.001) in 25 and 20 J groups. In conclusion, the He-Ne laser seed pre-illumination demonstrated salinity stress tolerance by regulating physio-biochemical activities and increasing withanolides. Therefore, this technique can be advanced to assist in abiotic stress tolerance in crop plants under changing climatic conditions, also, for large-scale production of withanolides for pharmaceutical and herbal industries.