The influence of non-cytotoxic concentrations of the herbicide 2,4-dichlorophenoxyacetic acid on the DNA synthesis in cultured vertebrate cells.

The influence of the herbicide 2,4-Dichlorophenoxyacetic acid on the growth of cultured chicken muscle cells was studied by observing morphological changes and by cytophotometric measurement of the DNA content of individual cells. DNA-synthesis curves were derived from the distribution of DNA values. No marked effects were observed at a concentration of 60 mug per liter. In contrast, doses of 600 mug per liter caused a loss in cell differentiation consisting of a partial lack of polar orientation, diminished formation of fibers, and an increase of the N/C ratio. The nuclear matrix of desoxyribonucleoprotein (DNP) changed to a more heteropycnotic structure. Isolated cell necroses were found after 44 hrs of exposure. When compared to the controls, the relative DNA synthesis time was found to be prolonged 1.5-fold. The number of cells in the G2 phase decreased during 44 hrs of exposure. It is concluded from these results that the dosedependent growth inhibition of 2,4-D on vertebrate cells in culture takes effect during DNA synthesis. The morphological changes of the nuclear structure suggests that 2,4-D directly affects the template activity of the DNP matrix.