Cadmium is a potent inducer of programmed cell death (PCD) in plants but the morphological changes in cells exposed to cadmium are poorly characterized. Using light and transmission electron microscopy (TEM) we have investigated the changes in ultrastructure of tobacco BY-2 cells treated with 50 µM CdSO4. The cadmium-induced alterations in cell morphology occurred gradually over a period of 3-4 days and the first stages of the response resembled vacuolar type of cell death. The initial formation of numerous small cytoplasmic vacuoles and dilation of endoplasmic reticulum was followed first by fusion of smaller vacuoles with each other and with big vacuoles, and then by the appearance of autophagic vacuoles containing autophagic bodies. The final stages of cell death were accompanied by necrotic features including loss of plasmalemma integrity, shrinkage of the protoplast and unprocessed cellular components. In addition, we observed a gradual degradation of nuclear material. Our results demonstrate that cadmium-induced plant cell death is a slow process featuring elements of vacuolar cell death and terminating with necrosis.

Faculty of Science Department of Experimental Plant Biology Charles University Prague Vinicna 5 12844 Prague Czech Republic

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