The effect of abscisic acid and K+ on xylem exudation from excised roots of Lupinus luteus |
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Authors: | Reinhard F M Van Steveninck Margaret E Van Steveninck André Läuchli |
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Institution: | School of Agriculture, La Trobe Univ., Bundoora, Victoria 3083, Australia;M. E. Van Steveninck, Botany Dept, La Trobe Univ., Bundoora, Victoria 3083, Australia;A. Läuchli, Dept of Land, Air and Water Resources, Univ. of California, Davis, CA 95616, USA. |
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Abstract: | External application of abscisic acid (ABA) induces a relatively high rate of xylem exudation in excised roots of Lupinus luteus L. cv. Weiko III. The response is relatively slow with a lag period of ca 1 h. It is also slowly, but reversibly, abolished by application of 3.6 or 36 μ M cycloheximide (CHX). Contrary to expectation, K+ is not a significant factor in maintaining flow rates in lupin roots as no response was measured after adding K+ to root systems, from which K+ had been withheld for periods ranging from 3 h to several days. In fact, excised roots obtained from seedlings raised in the absence of K+ failed to respond to added K+. Total depletion of K+ is difficult to achieve, because of initial seed reserves, and prolonged exudation in lupins can be maintained utilising only a small proportion of the K+ originally present in the root tissue. Nevertheless, the data cast doubt on the general applicability of the concept that volume flow is maintained by an osmotic gradient with K+ as the principal mineral ion. |
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Keywords: | Abscisic acid cycloheximide hydraulic conductivity Lupinus luteus osmotic gradient potassium depletion solute flux volume flow xylem exudation |
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