Fig. 2. Induction of apoptosis and necrosis by cadmium exposure in oyster hemocytes. (A) Representative dot plots for annexin V-FITC and propidium iodide (PI) staining in hemocytes exposed to vehicle (control) or varying concentrations of cadmium for 72 h. Live cells appear in the bottom left quadrant of the dot plot and have low FITC and PI fluorescence. Apoptotic cells in the bottom right quadrant are characterized by low PI fluorescence, indicating integrity of the plasma membrane, but high FITC fluorescence due to the translocation of phosphatidylserine into the outer leaflet of the plasma membrane. Necrotic cells have high PI and FITC fluorescence and are found in the upper right quadrant of the dot plot. (B,C) Quantitative graph of the data shown in A indicating the changes in the proportion of apoptotic (B) and necrotic (C) cells in the hemocyte population after 72 h of exposure to different cadmium concentrations. Vertical bars represent S.E.M. Filled circles correspond to the values that were significantly different from the respective control (0 µmol l^-1 Cd²⁺; P<0.05; N=5-8). The levels of apoptosis and necrosis in control hemocytes after 72 h of culture were not significantly different from those in freshly isolated oyster blood cells (12.0±1.70 and 0.9±0.34% of apoptosis and necrosis, respectively, N=10, P>0.05), indicating that culture conditions used in these experiments supported normal viability of oyster hemocytes.