Characterization of Rapid Atrazine Absorption by Excised Velvetleaf (Abutilon theophrasti) Roots

Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] uptake from solution by excised velvetleaf (Abutilon theophrasti Medic.) root segments was studied. Initial atrazine absorption by 1-cm segments cut from the apical 5 cm of roots was rapid. Atrazine concentration in the tissue became equal to the external atrazine concentration by 30 min. Atrazine did not accumulate in the root tissue to concentrations above the external solution, and rapid efflux of atrazine occurred when the root segments were washed with atrazine-free solution. Atrazine absorption was linear over a range of external atrazine concentrations. Dinitrophenol and KCN increased atrazine absorption during the first 3 min of exposure to atrazine. Anoxia increased atrazine absorption but decreased K+ uptake. Decreasing temperatures decreased atrazine absorption. Q10 values for atrazine uptake were between 1.3 and 1.4. The response of atrazine absorption by the excised roots to inhibitors, anoxia, external atrazine concentration, and temperature indicated simple diffusion as the mechanism of absorption of atrazine by velvetleaf roots.