ASGSB 1999 Annual Meeting Abstracts

MEASUREMENT OF SURFACE POTENTIAL CHANGES IN PHOTOTROPICALLY STIMULATED CORN COLEOPTILES USING A MULTI-TIP SCANNING BIO-KELVIN PROBE. D.M. Porterfield¹ and I.D. Baikie². ¹Department of Biological Sciences, University of Missouri-Rolla, ²Marine Biological Laboratory, Woods Hole, MA.

The Kelvin probe is a non-invasive vibrating capacitor technique that can measure changes in surface potential (V), between a conducting tip and a partially conductive specimen.   A multi-tipped scanning Bio-Kelvin probe system was constructed and used to measure changes in surface potential in phototropically responding corn coleoptiles. In addition to surface potential measurements, the system also monitored movement of the coleoptile shoot using a novel tracking and dithering feedback routine used to maintain probe positioning with respect to the specimen.  The four orthogonal arranged probes allowed us to measure and compare both displacement and surface potential changes across (laterally), and down (longitudinally) the coleoptile, in real time.  Seeds were allowed to imbibe and germinate for 4-7 days before being transplanted to an agar-based medium.  Plants were transferred in the dark to the probe system, and were allowed to stand for 2-4 hours before being phototropically stimulated using a blue LED light source. The light was situated behind probe 1 and unilaterally stimulated the top 3 mm of the coleoptile. Longitudinal scans showed that most of the bending occurred in the top 15 mm of the coleoptile and the initial displacement velocity towards the coleoptile was linear with time. A positive wave of voltage moved down the shoot at a rate of 2.4±0.5 cm/h which correlates well with estimates of auxin movement. Surface potentials averaged 65±5 mV but values as high as 100mV were recorded. Lateral scans focused on a region 10 mm down from the tip.  These scans showed that movement correlated with the voltage changes and both displacement and voltage changes were greatest in the plane of stimulation than perpendicular.  To the best of our knowledge this is the first time non-invasive differential voltage measurements have been made while measuring displacement of tropically stimulated plants.

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