The role of electrogenic xylem pumps in K+ absorption from the zylem of Vigna unguiculata: the effects of auxin and fusicoccin |
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Authors: | A H DE BOER K KATOU A MIZUNO H KOJIMA H OKAMOTO |
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Institution: | Biological Institute, Faculty of Science, Nagoya University, Nagoya 464, Japan |
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Abstract: | Abstract We tested the hypothesis that electrogenic ion pumps, working at the parenchyma symplast/xylem interface of pea hypocotyls, provide the driving force for K+ uptake from the xylem. Solutions of known composition were perfused through a hypocotyl segment. The K+ activity of the solution flowing out of the xylem (K+out) increased (i.e. K+ uptake decreased) when aerobic respiration was inhibited by lack of O2, and this was preceded by a decrease in Vpx (electrical potential difference between parenchyma symplast and xylem). Perfusion with auxin (1AA) and fusicoccin (FC) stimulated the electrogenic activity of the ‘xylem pumps’ (111 and 205% respectively) and stimulated uptake of K + from the xylem (with 71% and 29% respectively). The close correlation between xylem pump activity and K+ uptake corroborated the aforementioned hypothesis. Interestingly, inhibition of pump activity by anoxia was incomplete in the presence of FC. It is thought that FC increases the affinity of the ATP-requiring xylem pump for ATP, thus ensuring that ATP production during fermentation is sufficient to fuel the pump in the absence of O2. |
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Keywords: | Vigna unguiculata Leguminosae cow pea auxin electrogenic xylem pumps fusicoccin growth regulation pressurized xylem perfusion |
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