Figure 4. TEM of Symbiodinium cells lost from Xenia elongata at temperatures of 28 to 32°C. Most Symbiodinium cells appeared normal at 28°C (A).

Symptoms of cell death become evident at 30°C as organelles move to opposing ends of the cell (B). Symptoms of irreversible late stage apoptosis (C) or necrosis (D) occurred at 32°C within 9 h. Symbols: ab = apoptotic body, chr = chromosome, cl = chloroplast, cw = cell wall, gx = glyoxysome, m = mitochondria, n = nucleus, py = pyrenoid, rcw = ruptured cell wall, sg = starch grain. Scale bar = 500 nm.