REGULATION OF K-STRESS AND ABSCISIC-ACID( CHANNELS IN MAIZE ROOTS BY WATER)

Root cortical and stelar protoplasts were isolated from maize (Zea may s L.) plants that were either well watered or water stressed, and the patch-clamp technique was used to investigate their plasma membrane K channel activity. In the root cortex water stress did not significant ly affect inward-or outward-rectifying K+ conductances relative to tho se observed in well-watered plants. In contrast, water stress signific antly reduced the magnitude of the outward-rectifying K+ current in th e root stele but had little effect on the inward-rectifying K+ current . Pretreating well-watered plants with abscisic acid also significantl y affected K+ currents in a way that was consistent with abscisic acid mediating, at least in part, the response of roots to water stress. I t is proposed that the K+ channels underlying the K+ currents in the r oot stelar cells represent pathways that allow K+ exchange between the root symplasm and xylem apoplast. It is suggested that the regulation of K+ channel activity in the root in response to water stress could be part of an important adaptation of the plant to survive drying soil s.