Exogenous application of citric acid mitigates salt-induced oxidative stress in Moringa oleifera seedlings

Abstract

Seeds of Moringa oleifera were planted in sandy and vermicular soil (1/2 w/w) and irrigated with Hoagland solution. Two weeks later, the seedlings were divided into three groups: The first group was irrigated with a control solution (Hoagland solution), the second with a salt solution (10 g/l NaCl) and the third group with a mixed solution (10 g/l NaCl and 100 mM citric acid (CA)). Salinity induced a substantial inhibitory effect on seedling growth of Moringa oleifera. Salt treatment reduced shoot fresh weight (FW), the content of photosynthetic pigments and total soluble proteins (SP). Furthermore, salt treatment resulted in accumulation of total free amino acids, soluble sugars and proline. CA supply in saline solution improved shoot growth, and photosynthetic pigment and soluble proteins levels. The important content of citric acid in leaves was accompanied with a decrease of total free amino acids, soluble sugar and proline contents. More that, exogenous application of citric acid led to a decrease of Malondialdehyde (MDA) and hydrogen peroxide (H2O2) accumulation, reflecting the reduction in the imbalance situation and membrane damage induced by salt stress. Alternatively, citric acid supply in saline conditions reduced the rise of superoxidase dismutase (SOD) and catalase (CAT) activities induced under salinity. Citric acid enhanced the growth rate of salt-treated Moringa oleifera via enhancing antioxidant function. Consequently, citric acid treatment may be a promising method for improving Moringa oleifera plants’ tolerance to salt stress.