Multiphasic zinc uptake system in mycorrhizal and nonmycorrhizal roots of French bean (Phaseolus vulgaris L.)

摘要

Kinetics of Zn uptake by vesicular arbuscular mycorrhizal (Glomus macrocarpum) and nonmycorrhizal roots of French bean (Phaseolus vulgaris L.) were investigated employing ~(65)Zn. Within 10 #mu#mol to 100 mmol Zn m~(-3) solute concentration, five concentration-dependent Zn uptake phases were resolved. Zinc uptake by roots was linear in the range 0.053-0.1 mmol Zn m~(-3) (phase 0). However, at extremely low concentration (below 0.05 mmol m~(-3)), Zn uptake followed a sigmoidal pattern. In the concentration range, 0.1 mmol to 100 mmol m~(-3), four other distinct uptake phases each one following Michaelis-Menten kinetics were observed. Mycorrhizal roots exhibited generally higher Zn absorption rate than the nonmycorrhizal roots; this is attributed to higher maximal uptake rates (V_(max)) for phases 1, 2 and 3. The greater specificity of phase 4 was a result of a lower k_m value.