Effects of solute gradients on the osmotic potential of potato tubers stored at two temperatures

Tubers of the potato (Solanum tuberosum L.) cv. Pentland Crown were stored at either 2°C or 16°C in the dark. The concentrations of the major osmotica were measured at three positions along the tuber, together with parallel cryoscopic measurements of osmotic potential. Positive gradients of concentration of potassium and organic acids, from the base to the apex of the tuber, were approximately balanced in their osmotic effect by negative gradients of soluble sugars. Tubers stored at 16°C showed a small net negative gradient of osmotic potential, and those at 2°C a slightly larger positive gradient. This difference was attributed to the steeper gradient of soluble sugars in tubers stored at 2°EC. There were no significant differences in the gradients of potassium, magnesium and organic acids between the two temperature treatments, nor were there any detectable changes in these gradients with time in storage.