Uptake of 2,4-dichlorophenoxyacetic acid by suspension-cultured maize cells

The uptake of 2,4-D-[1-14C] by maize cells was studied in relation to 2,4-D concentration, density of suspension, growth phase of subculture and pH of the medium. The uptake was estimated by the equilibrium 2,4-D content in the cells Csub(t) and by the relative rate of the approach of cell 2,4-D content to Csub(t)(k) which was shown to be constant during the uptake. An increase in suspension density caused a decrease in Csub(t) and an enhancement of k. The exponential phase cells (4th day of subculture) took up 2,4-D more actively than the stationary phase cells just transferred to the fresh medium. This activation of uptake can only partly be conditioned by the acidification of the medium during the subculture. An increase in 2,4-D concentration in the medium from 1 mg/l to 5-10 mg/l caused an enhancement of k in the initial culture and its decrease in the 4th day culture. Only part of absorbed 2,4-D could be washed out by three successive 1 h incubations of the cells with the medium without 2,4-D. The non-removed (or very slowly removed) 2,4-D was equal near to 70% of total absorbed 2,4-D in the cells of the 4th day culture and 20% in the cells of the initial culture. (author)