Ultrastructural Changes in Potato Tuber Pith Cells during Brown Center Development.

Electron microscopy revealed that subjecting ;Russet Burbank' potato (Solanum tuberosum L.) plants to 2 days of cool temperature growing conditions (18 degrees C days/10 degrees C nights) did not produce visible damage or changes in tuber pith tissue when compared to warm-grown tubers (23 degrees C days/18 degrees C nights). However, damage to some tuber pith cells was observed after 5 days of cool treatment. Eight days of cool treatment produced extensive alterations in cell structure. The cytoplasm of the cool-treated tuber pith cells had become highly vesiculated and there was evidence of complete destruction of amyloplast membranes and tonoplasts. In many cases the starch grains appeared to be undergoing hydrolysis suggesting total disruption of normal cell function. Sixteen days of cool treatment were sufficient to produce visible brown center development in all cool-grown tubers examined. Electron microscopy of these tissues revealed that, although some organelles were still present, the cytoplasm had become extremely vesiculated and lacked any resemblance to that of tissue from warm-grown tubers. Gross, irregular thickening of cell walls was also detected.