Reversible inhibition of root growth and cell proliferation by pentavalent arsenic in Allium cepa L.

Abstract The effect of pentavalent arsenic on root growth and cell cycle was studied in Allium cepa L. root meristems. Arsenic inhibited root growth in relation to dose, the inhibition being transient at low concentrations (1 ppm) and irreversible with higher concentrations. Pentavalent arsenic also increased the length of the cell cycle. Cell frequency in the four cell cycle compartments (G 1 , S, G 2 and M) was transiently altered at 2 ppm arsenic, with an increase in the frequency of G 1 and G 2 cells. Simultaneously, there was a partial inhibition of leucine uptake and its incorporation into protein, with no decrease in ATP intracellular concentration. Phosphate prevented the inhibitory action of pentavalent arsenic on root growth and meristem cell proliferation. It is postulated that the transient inhibition of both processes observed at low concentrations of pentavalent arsenic is the result of a change in the phosphate/arsenic levels induced by phosphate influx from the bulb. It is proposed that the increase in the frequency of cells in G 1 and G 2 is a consequence of the partial inhibition of protein synthesis observed and/or a result of arsenolysis of phospho-proteins necessary for the cell cycle transit.