Absorption of ethyl ester of chlorimuron by excised velvetleaf root tissue was investigated. Chlorimuron uptake increased rapidly, reaching a maximum after 2 h. After 4 h, however, a portion of the previously absorbed herbicide was lost to the external solution. The temperature coefficient (Q10) for chlorimuron absorption between 15 and 25 C was 1.9. The herbicide uptake was severely inhibited by metabolic inhibitors, DNP and KCN, and by anaerobic conditions (anoxia). Results of permeation experiments indicated that chlorimuron did not accumulate in the root tissue against a concentration gradient, and Ci/Co reached 1.0 after a 2-h permeation period. Chlorimuron efflux was continuous and after 2 h of washing the tissue in a herbicide-free solution, 90% of the previously absorbed herbicide was removed, suggesting that its accumulation in the tissue was reversible.

Long-term absorption of 14C-atrazine [2-chloro-4 - (ethylamino) - 6 - (isopropylamino) - s - triazine] by excised velvetleaf (Abutilon theophrasti Medic.) roots was investigated. A rapid, initial phase of absorption was followed by a long-term, linear phase of absorption, which resulted in atrazine accumulation in the tissue to concentrations above the external solution. This accumulation did not result from metabolism of the atrazine. Aging of the excised tissue appeared to be responsible for the accumulation. Dinitrophenol, but not cyanide, inhibited accumulation. Atrazine accumulation decreased as the temperature during absorption was decreased. The Q10 the absorption rate was ca. 2.5 between 15 and 25 C. Efflux of atrazine from the tissue occurred in two phases. At 25 C, loss of 80% of the atrazine occurred in 20 min. At 4C, the rate of this efflux was slower and the phase lasted longer. At both 4 and 25 C a second, slower phase of efflux occurred through at least 6 h and resulted in loss of equal amounts of atrazine at the two temperatures. These experiments show that, in addition to rapid absorption of atrazine to a passive equilibrium, excised velvetleaf roots accumulate atrazine by a metabolically dependent process over long periods of time.

Chlorsulfuron {2-chloro-N-[[(4-methoxy–6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} uptake from different pH solutions by leaves and excised root segments of velvetleaf (Abutilon theophrasti Medik. # ABUTH) was examined. In buffer solutions more 14C-chlorsulfuron penetrated intact leaves at lower pH levels (2.4, 3.4, and 4.4) than at pH 5.6. Initial chlorsulfuron absorption by 1-cm segments cut from the apical 5 cm of roots was rapid in the first 10 min for all pH levels. During the first 10 min, roots absorbed more chlorsulfuron from acidic (pH 2.4 and 3.4) than from higher pH solutions (pH 4.4 and 5.6). Chlorsulfuron efflux occurred in two phases for all pH levels. The first phase was a rapid loss through approximately 10 min, and the second a slow loss through 240 min. In the first 10 min, the efflux of chlorsulfuron was faster from roots incubated in pH 2.4 than in higher pH solutions. Efflux from the other pH levels was similar.

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 theophrasti Medik. # 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.