Modulatory effects of glutamic acid on growth, photosynthetic pigments, and stress responses in olive plants subjected to cadmium stress

Abstract

Cadmium (Cd) is a toxic heavy metal that severely impacts plant growth and photosynthesis and induces oxidative stress. This study investigates the modulatory effects of glutamic acid (GA) on Olea europaea (olive) seedlings subjected to cadmium stress. The experiment included control, Cd-stressed, GA-treated, and combined Cd and GA-treated groups. Cd exposure significantly reduced plant growth, as evidenced by decreased root length (3.5 cm) and shoot length (9 cm) compared to control plants (5 cm and 12 cm, respectively). Additionally, Cd stress led to a reduction in chlorophyll content (16.2 mg/g fresh weight) and elevated oxidative markers like H₂O₂ and MDA. The application of GA significantly improved plant growth and physiological parameters, with statistically significant increases in root length (up to 6.5 cm) and shoot length (up to 14 cm) in the combined treatment group (p ≤ 0.05). Furthermore, GA treatment led to a marked elevation in total chlorophyll content (up to 27.5 mg/g fresh weight), compared to 16.2 mg/g in Cd-stressed plants (p ≤ 0.05), reflecting a significant improvement in photosynthetic efficiency. GA also elevated the antioxidant enzyme activity catalase (CAT) and peroxidase (POD), reducing oxidative stress by decreasing hydrogen peroxide and MDA levels. The findings suggest that glutamic acid effectively mitigates Cd-induced phytotoxicity, enhancing stress resistance and promoting plant growth. This research provides valuable insights into using glutamic acid as a possible approach to mitigate heavy metal stress in plants, offering implications for agriculture and environmental management in Cd-contaminated areas. Specific applications may include its use in phytoremediation practices or as a supplement in agricultural management to improve crop resilience in polluted environments. Further research could explore the molecular mechanisms underlying GA’s protective effects and its potential synergy with other biostimulants to enhance heavy metal tolerance in a broader range of crops.