Roots of Vicia faba were treated with a 0.02% solution of colchicine for 2 hours. Some roots were also treated, 22 hours later, with 10-6 M IAA for I day. All beans were grown on for a further 6 days and the total growth of primary and lateral roots was determined.
Primary roots treated with colchicine and then IAA showed significantly greater growth than roots treated only with colchicine. Lateral roots produced by the treated primary roots showed significantly less growth when treated with colchicine and IAA than when treated only with colchicine. Primary- roots treated with colchicine and IAA had fewer polyploid cells, in division, than roots treated only with colchicine, indicating that recovery of the diploid condition is related to the rate of root growth.
IAA treatment does not produce an immediate stimulation of growth; no effect was seen for 3 days. Its effect appears to be one of facilitating the normal mechanisms by which an apical meristem recovers from a colchicine treatment. The stimulation of root growth by concentrations of IAA that are normally inhibitory leads us to conclude that one result of a treatment with colchicine is a reduction in the level of natural auxin in a root.