Use of Potassium and Sucrose by Onion Guard Cells during a Daily Cycle of Osmoregulation |
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Authors: | Amodeo Gabriela; Talbott Lawrence D; Zeiger Eduardo |
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Institution: | 1INGEBI, Vuelta de Obligado 1428 Buenos Aires, Argentina
2Department of Biology and Laboratory of Biomedical and Environmental Sciences, University of California Los Angeles, CA 90024, U.S.A. |
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Abstract: | Solute content of stomata from intact onion cotyledons grownunder either greenhouse or growth chamber conditions was followedover the course of a daily light cycle to determine patternsof osmoregulation. Initial opening of stomata was well correlatedwith guard cell potassium accumulation under both growth conditions.Subsequently, however, there was a consistent decrease in guardcell potassium content despite constant or increasing aperture.Although a secondary increase in potassium was sometimes observedduring the second half of the light cycle, guard cell potassiumcontent was poorly correlated with aperture. Sucrose levelsin guard cells increased 60% during the period of decliningpotassium content, suggesting its use as an alternate osmoticum.Guard cells are postulated to use multiple pathways for theproduction of osmotica over the course of a complete daily cycleof stomatal movements. (Received December 5, 1995; Accepted April 9, 1996) |
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