Effects of Ca2+ and Temperature on Potassium Uptake along Roots of Wheat, Rice and Cucumber

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AbstractThe differences in K+ uptake of different segments of excised roots of two thermophilic plants (rice, Oryza sativa L. cv. Dunghan Shali and cucumber, Cucumis sativus L. cv. Csemege Fürtös) and a non‐thermophilic plant (wheat, Triticum aestivum L. cv. Aurora) were investigated in the presence and absence of Ca2+, at 0 and 25°C, using radiotracer K+(86Rb+) technique. The K+ uptake exhibited different temperature‐ and Ca2+‐dependent distributions along the root axis for the different species studied. In the case of rice and cucumber an extraordinarily large K+ uptake occurred in the apical root portion at 0°C if Ca2+ was omitted. The presence of Ca2+ diminished this anomaly. For wheat normal K+ uptake patterns were observed under similar conditions. At 25°C Ca2+‐stimulated K+ uptake may appear in each root segment, depending upon species and composition of the uptake solution. The results indicate that there may be considerable differences in the compositions of the cell walls and membranes of root cells of thermophilic and non‐thermophilic plants, and in their ion‐exchange properties, especially in the apical region.