Root morphology and cadmium uptake kinetics of the cadmium-sensitive rice mutant

To understand the physiological mechanism that confers Cd sensitivity, root morphology and Cd uptake kinetics of the Cd-sensitive mutant and wild type rice were investigated. The root length, root surface area, and root number of mutant rice decreased more significantly with increasing Cd concentration in growth media compared with the wild type rice. The uptake kinetics for Cd-109(2+) in roots of both the mutant and wild type rice were characterized by a rapid linear phase during the first 6 h and a slower linear phase during the subsequent period. Concentration-dependent Cd2+ influx in both species could be characterized by the Michaelis-Menten equation, with similar apparent K-m values for mutant and wild type rice (2.54 and 2.37 mu M, respectively). However, the V-max for Cd2+ influx in mutant root cells was nearly 2-fold higher than that for wild type rice, indicating that enhanced absorption into the root is one of the mechanisms involved in Cd sensitivity in mutant rice.