Effects of Some Amino Acid Analogues on the Uptake and Transport of K+ and Ca2+ in Wheat and Mung Bean Seedlings: I. CORTICAL CELL FLUXES AND TRANSPORT TO THE STELE IN EXCISED ROOT SEGMENTS, AS AFFECTED BY p-FLUOROPHENYLALANINE |
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Authors: | THORNTON B; MACKLON A E S |
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Abstract: | Effluxes of K+ and Ca2+ from root segments of both wheat, Triticunaestivum L. cv. Capelle and mung bean, Vigna radiata (L.) Wilczek,were measured in the presence or absence of 20 mol m3para-fluorophenylalanine (p-FPA). The results were used to estimatethe compartment contents and transmembrane K+ and Ca2+ fluxesin root cortex cells. Using the Ussing-Teorell flux equationas the criterion, it was concluded that entry of K+ from theoutside solution to the cytoplasm, and from the cytoplasm tothe vacuole were active in both wheat and mung bean. Also, inboth species, Ca2+ entered the cytoplasm passively across theplasmalemma and was actively pumped back to the external solution.However, interpretation of the direction of active transportacross the tonoplast depends upon an assumption about Ca2+ activityin the cytoplasm. The only qualitative effect of p-FPA was to alter the drivingforce for K+ influx, across the plasmalemma in wheat, from anactive to a passive one. Quantitative effects of the analoguewere seen for K+ fluxes in both wheat and mung bean and forCa2+ fluxes in wheat. The p-FPA reduced transport of K+ in bothspecies, while transport of Ca2+ was unaffected. The implicationsof these results for the two pump hypothesis arediscussed. Key words: Triticum aestivum, Vigna radiata, Two pump hypothesis |
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