Selenium nanoparticles mitigates drought stress in E. purpurea by enhancing morpho-physiological characteristics and gene expression related to the phenylpropanoid pathway

This study investigates the impact of selenium nanoparticles foliar application in alleviating the adverse effects of drought stress on the Rose Carmine cultivar of Echinacea purpurea . The experiment was conducted in a split-plot design, with main plots arranged as a completely randomized design, with three replications at the Agricultural Research Field of the Faculty of Agriculture, Urmia University, Iran. Drought stress, as the main treatment, was implemented at four levels (20, 40, 60, and 100 % of field capacity) by monitoring soil moisture at root depth using a TDR device. Alongside varying drought stress levels, foliar application of selenium nanoparticles (SeNPs) was conducted as a sub-treatment at four concentrations (0, 5, 10, and 20 mg/L) every two weeks over a three-months period. The plants treated with 5 mg/L SeNPs exhibited higher chlorophyll (9.67 mg/g fresh weight) and carotenoid content (3.8 mg/g fresh weight) in the 60 and 40 % of FC, respectively. The peak phenylalanine ammonia-lyase enzyme activity (20.43 nmol/mg) was found in the 20 % FC treatment with a 10 mg/L selenium application. The highest relative expression level of the phenylalanine ammonia-lyase ( PAL ) gene was observed in the 20 % FC with a 10 mg/L SeNPs application, while in the case of cinnamic acid 4-hydroxylase ( C4H ) and hydroxycinnamoyl transferase ( HCT ) genes, the maximum relative expression level was observed in the 60 % FC treatment with 20 mg/L SeNPs application. These findings suggest that SeNPs, due to their antioxidant properties, positively affect the expression of key genes involved in production of pigments and enzymes in Echinacea purpurea under drought stress conditions and effectively mitigate the adverse effects of drought stress by modifying the plant resilience, productivity, and vegetative growth related traits, in direct or indirect manner. • Drought stress affects the whole structure of Echinacea pupurea . • Selenium has positive effects in alleviating the adverse effects of drought stress. • The amount of selenium solution used as well as the drought stress intensity are very effective in the efficacy. • Alter in PAL , C4H and HCT relative expression by SeNPs protect E. purpurea against ROS via phenolics enhancement.