Uptake kinetics of arsenic by lettuce cultivars under hydroponics

Abstract

Arsenic (As) uptake ability based on kinetic parameters by two lettuce cultivars; Sijibaiye (SJBY) and Texuanyanlingsun (TXYLS) was investigated in nutrient solution containing eight levels of arsenic (As). Depletion of As from solution was monitored over a period of 24 h at regular time to estimate As uptake kinetics of the plants. K_m and V_max values were evaluated with the aid of the Lineweaver - Burk plot (that is the double reciprocal plot of initial velocity (1/v) versus substrate concentration (1/[s]). Both cultivars were capable to assimilate As(V), although with different kinetic parameters. The values obtained for K_m and V_max varied with plant cultivars. Using Lineweaver- Burk, values of K_m and V_max were found to be much lower in SJBY (26.721 mg L^-1 and 0.7737 mgAsg^-1 shoot d.wt.hr^-1) than that of TXYLS (81.922 mg L^-1 and 1.8488 mgAsg^-1 shoot d.wt.hr^-1), indicating SJBY had the lowest uptake ability than TXYLS plants. Furthermore, TXYLS had the highest K_m value than SJBY, confirming that uptake in the plant cell plasma membrane of TXYLS had a higher affinity for As than SJBY plants. The time (24 h) affects the depletion of As in both cultivars. It can be concluded that among the cultivars, SJBY could be finally identified as the most suitable cultivar to be grown in polluted farmland. Therefore, it has been suggested that there is possibility to lower the As concentration in lettuce by selecting and breeding cultivars with less As concentration that can be safely grown in contaminated soils with slight levels of As for safe consumption.

Key words: Arsenic (V), cultivars variation, kinetic parameters, Lineweaver Burk, uptake rate.