Root tips were collected and placed in an aqueous solution of 8-hydroxyquinoline (2.5 mM) used as the pre-treatment, for 4 h in darkness (2 h at 4 C plus 2 h at 21 C). A solution of Carnoy (absolute ethanol and glacial acetic acid, 31 v/v) was used to fix the tissues for at least 24 h at -20 C. Fixed material was then stored in 70 % ethanol at 4 C pending slide preparation.