Zinc Absorption by Wheat Seedlings: I. Inhibition by Macronutrient Ions in Short-Term Experiments and its Relevance to Long-Term Zinc Nutrition
1972
Chaudhry, F. M. | Loneragan, J. F.
Short-term Zn²⁺ absorption by intact wheat seedlings (Triticum aestivum L.) was studied to resolve large discrepancies between Zn²⁺ absorption in short-term experiments with excised roots and in long-term experiments with whole plants. Excision, pretreatment, and age of seedlings had no effect on short-term Zn²⁺ absorption. Zn²⁺ absorption responded to changes in temperatures with Q₁₀ values of 6.1, 1.8, and 1.9 for the temperature ranges 2 to 10, 10 to 20, and 20 to 29C, respectively. Addition of macronutrient salts to 250µM Ca(NO₃)₂ in the absorbing solution decreased Zn²⁺ absorption by about 80%. Micronutrient salts had a small additional effect on Zn²⁺ absorption. Cations rather than anions inhibited Zn²⁺ absorption. Nitrate salts of alkali and alkaline earth cations strongly depressed Zn²⁺ absorption. In the presence of 250µM Ca(NO₃)₂, nitrates of alkali cations at 750µM and of additional Ca²⁺ at 250 and 375µM depressed Zn²⁺ absorption from 1µM ZnCl₂ in the order NH₄⁺ > Rb⁺ > K⁺ > Cs⁺ > Ca²⁺ > Na⁺ > Li⁺. Nitrates of alkaline earth cations at concentrations of 250µM depressed Zn²⁺ absorption in the order Mg²⁺ > Ba²⁺ ≥ Sr²⁺ = Ca²⁺. Replacing NO₃⁻ with Cl⁻, SO₄²⁻, or H₂PO₄⁻, had no effect on Zn²⁺ absorption. The inhibitory effects of alkali and alkaline earth cations appeared to be mutually competitive. Large effects of K⁺ at low concentrations of Ca²⁺ decreased and finally disappeared with increasing concentrations of Ca²⁺. The rates of Zn²⁺ absorption by 6-day-old, intact wheat seedlings closely approximated those reported for long-term experiments over a wide range of solution Zn²⁺ concentrations from 0.05 to 5.0µM when the temperature and the composition of the absorbing solutions were identical. These results suggest that it may be possible to relate short-term studies of Zn²⁺ absorption to long-term studies of Zn nutrition.
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