K+-stimulated phenanthrene uptake by wheat roots. The uptake of phenanthrene was performed at 25°C for 4 h in modified Hoagland nutrient solutions (i.e., potassium ions were replaced with sodium ions in nutrient solution, pH 5.5) with 5.62 μM phenanthrene. Data points represent mean and SD values of triplicates. Error bars do not extend outside all data points. fr wt, Fresh weight.