Cadmium uptake in E lodea canadensis leaves and its interference with extra‐ and intra‐cellular pH

This study investigated cadmium ( C d) uptake in E lodea canadensis shoots under different photosynthetic conditions, and its effects on internal (cytosolic) and external pH . The plants were grown under photosynthetic (light) or non‐photosynthetic (dark or in the presence of a photosynthetic inhibitor) conditions in the presence or absence of C d C l 2 (0.5 μ m ) in a medium with a starting pH of 5.0. The pH ‐sensitive dye BCECF ‐ AM was used to monitor cytosolic pH changes in the leaves. Cadmium uptake in protoplasts and leaves was detected with a C d‐specific fluorescent dye, Leadmium Green AM , and with atomic absorption spectrophotometry. During cultivation for 3 days without C d, shoots of E . canadensis increased the pH of the surrounding water, irrespective of the photosynthetic conditions. This medium alkalisation was higher in the presence of C d C l 2 . Moreover, the presence of C d also increased the cation exchange capacity of the shoots. The total C d uptake by E . canadensis shoots was independent of photosynthetic conditions. Protoplasts from plants exposed to 0.5 μ m C d C l 2 for 3 days did not exhibit significant change in cytosolic [ C d 2+ ] or pH . However, exposure to C d C l 2 for 7 days resulted in increased cytosolic [ C d 2+ ] as well as pH . The results suggest that E . canadensis subjected to a low C d C l 2 concentration initially sequesters C d into the apoplasm, but under prolonged exposure, C d is transported into the cytosol and subsequently alters cytosolic pH . In contrast, addition of 10–50 μ m C d C l 2 directly to protoplasts resulted in immediate uptake of C d into the cytosol.