Unraveling the role of chrysin in mitigating cadmium toxicity in pepper by improving antioxidant defense, phytohormone biosynthesis and photosystem II and aquaporins related transcripts☆

Cadmium (Cd) is the most dangerous and prevalent one which has tremendous impacts on global food security. Although chrysin (Chr) has been extensively studied in Cd stressed animal system, the role of this valuable flavonoid in plants is yet to be clarified. Therefore, this study was designed to determine the effects of different doses of Chr (0, 50, 150 and 300 mu M) on some physiological, biochemical and gene expression in pepper grown under Cd stress (0 and 50 mM Cd). Cd stress significantly arrested relative water, proline, essential nutrients and phytohormones content when compared to non-stressed plants. However, Cd stress caused significant enhancement of hydrogen peroxide (H2O2), melondialdehyde (MDA), and tissue electrolyte leakage (EL) and reduction of enzymatic antioxidants like superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and peroxidase (POD), and expression of photosystem II (PSII) and aquaporin (AQPs) related transcripts compared to non-stressed plants. Compared to Cd stress, Chr positively regulated the formation of H2O2, MDA and %EL, antioxidant enzyme activity, as well as accelerated the synthesis of indole-3-acetic acid (IAA), gibberellic acid (GA) and cytokinins (CK) and reduced the level of abscisic acid (ABA), which was significantly increased by Cd stress. In addition, Chr demonstrated enhanced expression of CaPsbB, CaPsbD, CaPsb1 and CaPsb2, CaPIP1-2 and CaTIP5-1 in both root and shoots and when compared to Cd stressed plants. The findings obtained at the end of the study show that Chr is very important for alleviation of Cd toxicity in pepper plants.