Norflurazon Absorption by Excised Velvetleaf (Abutilon theophrasti) Roots

The absorption of norflurazon [4-chloro-5-(methylamino)-2-(3-(trifluromethyl)phenyl)-3(2H)-pyridazinone] by 1-cm segments cut from the apical 5-cm roots of velvetleaf (Abutilon theophrastiMedik. # ABUTH) was studied. Norflurazon absorption was rapid in the first 10 min but there was very little increase thereafter up to 120 min. Norflurazon also penetrated the entire tissue volume within 30 min after the root segments were placed in absorption solution. Norflurazon did not accumulate to concentrations above the external solution over 120 min, and 90% of the absorbed herbicide diffused freely out of the tissue within 10 min. The metabolic inhibitor KCN did not affect norflurazon uptake, whereas pretreatment of root tissue with DNP increased absorption. Anoxia increased absorption by 60 and 120% above aerated treatment at 10 min and 2 h, respectively. These experiments suggest that norflurazon, which is considered to move primarily in the apoplast, moved into both the apoplast and symplast of velvetleaf root cells by simple diffusion.