Kinetics of Zinc Uptake in Sorghum (Sorghum bicolor L., Moench) Roots Infected with Arbuscular Mycorrhizal Fungus, Glomus macrocarpum

The kinetics of Zn uptake was studied in arbuscular mycorrhizal (Glomus macrocarpum) and non-mycorrhizal roots of sorghum (Sorghum bicolor L. Moench). Within Zn concentration range, 10 mu mol to 100 mmol m super(-3), five concentration dependent phases of Zn absorption were identified. Phase 0 (0.05-0.1 mmol m super(-3)) was linear but the other four subsequent phases (0.1 mmol to 0.1 mol m super(-3)) conformed to Michaelis-Menten kinetics. At extremely lower concentrations (below 0.05 mmol m super(-3)), Zn absorption followed a linear pattern. Mycorrhizal roots invariably maintained higher Zn absorption rate than non-mycorrhizal root. Higher Zn absorption rate of mycorrhizal roots appeared to be related to higher maximal uptake rate (V sub(max)) for phase 1, 3 and 4 and greater specificity (lower km) for phase 2 (1 to 5 mmol m super(-3)).