Electropotential in Excised Pea Epicotyls

In contrast to intact etiolated pea seedling tissue (Pisum sativum L.), excised segments immersed in a complete nutrient solution show marked increases in ion content, largely of K(+) and NO(3) (-), over a 72-hour period. During this time there is increase in cell electropotential difference, PD. During the initial 6 to 8 hours there is a lag in ion uptake; cell PD, however, increases rapidly from approximately -50 to -100 mv then increases more slowly. The increase in PD precedes and thus may be a prerequisite for the rapid ion accumulation phase. Cell PD increases in either water or nutrient solution but eventually reaches higher levels in the latter. Following water pretreatment of sufficient duration K(+) accumulation shows no lag period. The lag phase noted here appears dissimilar to that of storage tissues.