Figure 5.

Influence of varying plant Zn status on ZNT1 expression in T. caerulescens and T. arvense. T. caerulescens (Tc) and T. arvense (Ta) were grown for 14 days in a modified Johnson's solution containing 0, 1, or 10 μM Zn (for T. arvense) and 50 μM Zn (for T. caerulescens). (A) Total RNA was isolated from roots and shoots. The Northern blot, equally loaded with 20 μg of total RNA per lane, is shown probed with ZNT1 from T. caerulescens or the ZNT1 homolog from T. arvense. (B) Radiotracer studies of unidirectional ⁶⁵Zn²⁺ influx in roots of T. caerulescens and T. arvense grown under the different Zn concentrations were performed. The K_m and V_max values were determined for saturable Zn²⁺ uptake from the resulting concentration-dependent kinetics [after subtraction of the nonsaturating uptake component that we previously had shown to be root cell-wall-bound ⁶⁵Zn that remained after desorption of radiolabel (10)]. The units for K_m and V_max are μM and pmol of Zn absorbed per 10⁶ cells per min, respectively.