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.