Mitigation of nickel stress in Abelmoschus esculentus L. through citric acid seed priming

Nickel (Ni) contamination of agricultural soils is an important threat to crop productivity and food safety because of its persistence and phytotoxicity. The present study assessed the possibility of citric acid (CA) seed priming as a strategy to mitigate Ni-induced stress in Abelmoschus esculentus L. A pot trial was conducted under a completely randomized design with four treatments (hydropriming as control, Ni stress, CA priming, and stress + priming). The CA priming significantly improved seed vigor (201.67%), photosynthetic pigments (Chlorophyll a 4.55 mg g-1, total chlorophyll 10.48 mg g-1), and relative water content (59.05%), which resulted in better membrane stability (67.48%) and improved plant growth under Ni stress. These improvements were accompanied by a strong activation of antioxidant defense systems as measured by enhanced activities of peroxidase (40.44 U g-1 FW), catalase (54.38 U g-1 FW), and ascorbate peroxidase (60.37 U mg-1 protein), in addition to higher values of protein content (1.68 mg g-1). Furthermore, gas chromatography mass spectrometry-based metabolomic profiles of leaf tissues showed that CA priming induced an increased accumulation of organic acids, phenolics, fatty acids, sugars, and amino acid derivatives related to metal chelation, osmo-protection, and oxidative stress mitigation. The coordinated regulation of physiological, biochemical, and metabolic responses underscores the efficacy of CA priming in the maintenance of cellular homeostasis and possibly reduced Ni toxicity.