Changes in Calcium-ATPase Activity Associated with the Washing (Ageing) of Potato Tuber Discs

ATPase activity in cell wall and microsomal fractions from fresh and washed potato tuber discs was measured. The activity was markedly stimulated by Ca(2+) whereas K(+) and Na(+) had little effect. The Ca(2+)-ATPase increased with washing, particularly in the cell wall fractions and in the low density fractions after discontinuous sucrose gradient centrifugation. The activities of succinic dehydrogenase and cytochrome-c-oxidase also increased with disc washing, although activity was highest in the denser regions of the gradient. A fine structural study of fresh and washed tissues revealed a pronounced increase in the membrane profile concentration of the endoplasmic reticulum and mitochondria after ageing for 24 hours.