A Differential Response to Colchicine of Meristems of Roots of Vicia faba

Abstract

In whole root systems of Vicia faba, including primaries and laterals, the meristems do not respond in a uniform manner to treatment with colchicine. The meristems of the primary and fully emerged lateral roots become mixoploid and these roots show a temporary inhibition of growth. Lateral roots that emerge within 48 hours of treatment show no effects of colchicine; their growth is not inhibited and they contain few or no polyploid cells. The cells of the primordia that produce these laterals appear to be insensitive to colchicine: at the insensitive stage these primordia contain at least 1, 000 cells. Primordia with less than 800 cells are very sensitive to colchicine. They do not recover from treatment and appear to be completely inhibited. The stages of extreme sensitivity and resistance are transient phases in the morphogenesis of a lateral root. The change in sensitivity to colchicine is accompanied by a fall in the mitotic index; this is highest in young primordia, where it is about twice the value found in growing laterals.