Effect of cadmium stress on gill tissues of Magallana gigas after adaptation to different light conditions

Cadmium (Cd) is a highly soluble pollutant in aquatic ecosystems that poses a significant threat to mollusks. In this study, a solar simulator with a filter was used to establish two light conditions (with and without the ultraviolet [UV] spectrum) for a light-adaptation period (120 d) in Magallana gigas. Following adaptation, Cd was introduced into seawater containing M. gigas. Comprehensive bioaccumulation, physiological, and transcriptomic analyses were conducted to assess the responses of M. gigas gill tissues to Cd exposure following adaptation to simulated light. The results demonstrated that Cd exposure under both light conditions increased activities of catalase, superoxide dismutase, and glutathione S-transferase, and altered glutathione content, indicating that Cd consistently induced oxidative stress in M. gigas gill tissues. Transmission electron microscopy analysis revealed more severe cellular structural damage and a reduction in mitochondria under Cd exposure with photosynthetically active radiation (PAR) than under UV radiation, suggesting a more pronounced stress response under PAR. This may lead to lipid peroxidation and mitochondrial dysfunction in gill tissues. Additionally, co-exposure to Cd and UV radiation upregulated genes related to carbohydrate and lipid metabolism in the gill tissue, indicating increased energy demand. This high-energy state may have reduced the stress induced by Cd in the gill tissue. These findings highlight the importance of exploring different response strategies among mollusks with varied environmental adaptabilities, while underscoring the significance of considering their environmental acclimation history when investigating the toxicological mechanisms of heavy metal exposure in marine species.