Physiology of genotypic differences in zinc and copper uptake in rice and tomato
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Excised roots of rice (Oryzae sativa L.) cv IR26 absorbed both Zn2+ and Cu2+ from 0.01 mM to 0.50 mM external solutions at rates twice those of cv M101 over a 30-min period. However, the latter have a two-fold greater affinity (1/Km) for Zn2+ and Cu2+ than do those of the former. Zinc2+ and Cu2+ mutually and competitively inhibited uptake of each other, indicating that both micronutrient cations are absorbed through the same uptake mechanism or carrier sites. Further, these differences in uptake rates are restricted to roots but they cannot be explained by variations in root surface areas.
Excised roots of tomato (Lycopersicon esculentum L.) cv Kewalo absorbed Zn2+ and Cu2+ much more rapidly than did cv Sel 7625-2. Uptake of each cation was competitively and reciprocally inhibited by the other, so Zn2+ and Cu2+ are seemingly accumulated through the same uptake system in tomato also. Tomato cultivars Kewalo and Sel 7625-2 did not differ with regard to affinities of the root apices for Zn2+ and Cu2+; however. Vmax values for Zn2+ and Cu2+ uptake by roots of cv Kewalo were three-fold greater than those for cv Sel 7625-2.
Key wordsCopper Genotypes Rice Tomato Zinc
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