Effect of LED priming on growth indices, antioxidant enzymes and total phenolic compounds in basil (Ocimum basilicum) under salinity stress

Priming is the exposure of organisms or cells to a small amount of physically or chemically damaging agents that prepare the organism for subsequent stress exposure through an enhanced response. Accordingly, in this study, the effect of pretreatment of four different LED lights including red LED light, red LED light (70%) + blue light (30%), blue LED light and white LED light in comparison with greenhouse light on two green and purple genotypes of sweet basil was studied under control and salinity stress with a concentration of 150 mmol NaCl. For research, seeds of two genotypes of green and purple sweet basil were planted in pots containing sandy loam soil. After 50 days, 48 pots were transferred to a chamber containing LED lamps and 12 pots were kept in the greenhouse. After 2 weeks, the pots were transferred from the chamber containing LED lamps to the greenhouse and salinity treatment was applied for 2 weeks. The results showed that 150 mM NaCl treatment reduced the fresh and dry weight of shoot and chlorophyll a and increased the amount of hydrogen peroxide, catalase activity and total phenolic compounds in both genotypes under greenhouse light conditions. In light control conditions in both genotypes, red + blue LED light increased the fresh and dry weight of aerial parts, chlorophyll a and total phenolic compounds and decreased the content of hydrogen peroxide compared to other lights. In saline conditions, the results showed that pretreatment with red + blue LED light in green genotype and red LED in purple genotype increased shoot fresh weight (65% and 52%, respectively) and shoot dry weight (2 and 73%, respectively), chlorophyll a (98% and 58%, respectively), total phenolic compounds (2 times and 20%, respectively) and the activity of antioxidant enzymes and reduction of hydrogen peroxide content (33% and 72%, respectively) compared to plants not pre-treated with these lights. According to the results, the use of LED pretreatment (red + blue LED light in green genotype and red LED in purple genotype) by strengthening support mechanisms such as reducing membrane lipid peroxidation, increasing the activity of antioxidant enzymes, phenolic compounds and photosynthetic pigments have played an important role in improving the condition of basil in both control and salinity conditions.