Exogenous proline and glycinebetaine enhance glutathione-dependent defense mechanisms and mitigate cadmium toxicity in cultured tobacco cells

Abstract

Abstract : Plants exposed to heavy metal stress, including cadmium (Cd), accumulate reactive oxygen species (ROS) and methylglyoxal(MG) that can cause cellular damage, leading to cell death. Efficient antioxidant defense and glyoxalase systems offered by proline and betaine might protect plants against Cd-induced damage. To elucidate the protection mechanisms of proline and betaine against Cd stress, we investigated the effects of exogenous proline and betaine on intracellular superoxide (02~) level, contents of MG, carbonyl and phytochelatins (PCs), and activity of glutathione peroxidase (GPX), glyoxalase I and glyoxalsase II in cultured tobacco Bright Yellow-2 (BY-2) cells exposed to Cd stress. Intracellular 02~ level, and MG, carbonyl, PC2 and PC3 contents were higher in Cd-stressed cells than non-stressed cells, whereas a decrease in PC, contents was observed in Cd-stressed cells. Cadmium stress caused significantly decrease in GPX, glyoxalase I and glyoxalase II activities in BY-2 cells. Exogenous application of proline or betaine to the Cd-stressed cells resulted in a decrease in 0,~ level, and MG and carbonyl contents but an increase in PC, and PC3 contents. In Cd-stressed cells, exogenously applied proline or betaine led to an increase in GPX and glyoxalase I activities that are involved in the detoxification of H202 and MG, respectively. These results suggest that both proline and betaine provide protections against Cd toxicity by reducing carbonyl contents, and increment of the chelation with Cd and antioxidant defense and MG detoxification systems. The present study also demonstrates that betaine may contribute to the further protection against Cd toxicity due to a higher PC formation and GPX activity.