Chlorsulfuron inhibition of cell cycle progression and the recovery of G1 arrested cells by Ile and Val

Cultured pea root tips were treated with 14 nM chlorsulfuron (CS) for up to 60 h. The progression of cells from G₁ into S was monitored by measuring³H-thymidine (³H-Thy) incorporation into DNA. Chlorsulfuron treatment decreased the amount of³H-Thy incorporated; however, this amount never reached zero. Short-term labeling experiments indicate that the cells are arrested in a narrow band within G₁. Cell progression recovered from the CS treatment when roots were transferred to either White's medium or White's supplemented with isoleucine (Ile) and valine (Val). Lag time before recovery began in the White's or White's plus Ile and Val medium was 12 and 4 h, respectively. The initial slope of the recovery curves was similar irrespective of the type of recovery media. Increasing the duration of CS treatment did not change the length of the lag or initial slopes of the recovery curves. The level of³H-Thy incorporation decreased with increasing duration of CS treatment for root segments transferred to Ile and Val recovery medium.