Production of reactive oxygen species, impairment of photosynthetic function and dynamic changes in mitochondria are early events in cadmium-induced cell death in Arabidopsis thaliana

Background information. Cadmium (Cd) is a highly toxic heavy metal that causes changes in plant metabolism through inhibiting photosynthesis and respiration. The effects of Cd on the morphology and function of the chloroplast and mitochondria, as well as on the production and localization of ROS (reactive oxygen species), were studied at the single-cell level in Arabidopsis. Results. The present study showed that the morphology of chloroplasts changed after Cd treatment, and the photochemical efficiency dramatically declined prior to obvious morphological distortion in the chloroplasts. A quick burst of ROS was detected after Cd treatment. The ROS appeared first in the mitochondria and subsequently in the chloroplast. Simultaneously, the mitochondria clumped irregularly around the chloroplasts or aggregated in the cytoplasm, and the movement of mitochondria was concomitantly blocked. Furthermore, the production of ROS was decreased after pre-treatment with ascorbic acid or catalase, which prevented inhibition of photosynthesis, organelle changes and subsequent protoplast death. Our results suggest that the distribution and mobility of mitochondria, the morphology of chloroplasts and the accumulation of ROS play important roles in Cd-induced cell death. The results are in good agreement with previous reports of many types of apoptotic-like cell death. Conclusion. The changes in the distribution and mobility of mitochondria, and morphology of chloroplasts, as well as the accumulation of ROS, play important roles in Cd-induced cell death.