Authors: Rainer Stahlberg Robert E Cleland Elizabeth Van Volkenburgh
Publish Date: 2004/09/09
Volume: 220, Issue: 4, Pages: 550-558
Abstract
Slow wave potentials SWPs are transitory depolarizations occurring in response to treatments that result in a pressure increase in the xylem conduits Px Here SWPs are induced by excision of the root under water in 40 to 50cmtall lightgrown sunflower plants in order to determine the effective signal range to a naturally sized pressure signal The induced slow wave depolarization appears to move up the stem while it is progressively decremented ie the amplitude decreases with increasing distance from the point of excision with a rate that appears to rise acropetally from 25 to 55 cm−1 The decline of the SWP signal in both amplitude and range could be experimentally increased i when root excision was carried out in air and ii when the transpiration of the sunflower shoot was minimized by a preceding removal or coating of the leaves A further decline of the SW signal was expected to occur when leaves were included in the measured path However when the most distant apical electrode was attached to an upper leaf it showed a considerably larger depolarization than a neighboring stem position This apparent amplification of the SWP signal is not confined to the leaf blade but includes the petiole as well The amplification disappeared i when the illumination level was lowered to room light ii when the blade was excised either completely or along the remaining midvein and iii when the intact leaf blade was submersed in water These treatments reduce the SWP at the petiole to a small fraction of the signal in the opposite control leaf and specify bright illumination and blademediated transpiration as prerequisites of a signal increase that is confined to young expanding leavesWe thank the Dr William E Bradley Foundation for initiating and financially supporting this project Dr Richard L Walker Dr Edward F Haskins all of the University of Washington and Nicolas R Stephens University of Wisconsin for stimulating and helpful discussions
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