The maintenance of colchicine‐arrested metaphases in plants requires protein synthesis

Abstract

With the aim of finding out factors involved in chromosomal condensation, the kinetics of both metaphase accumulation and the subsequent formation of restitution nuclei in the presence of 1 mM colchicine have been analysed in Allium cepa L. meristems. Restitution nuclei are formed by decondensation of the chromosomes from the c‐mitoses and the reformation of nuclear envelopes around them. The study has been carried out in control conditions as well as in conditions which either inhibit protein synthesis (1 μg/ml cycloheximide) or modify the accuracy of transcription (by near ultraviolet light irradiation under anoxia of cells with bromosubstituted‐DNA). The results suggest that the high condensation of chromosomes observed in colchicine‐arrrested metaphases depends on sustained synthesis of protein, and that the DNA regions coding for such proteins are transcribed not before late prophase. By using cells, the genome of which has been partially bromosubstituted, fed bromodeoxyuridine during different fractions of this S period, it could be inferred that the coding regions for the proteins involved in chromosome condensation are probably multiple since they replicate throughout the whole S period.

Synchronous nuclear-envelope breakdown and anaphase onset in plant multinucleate cells

“…In plant cells, replication and postreplication checkpoints, such as those surveilling the completion of DNA replication and the postreplicative repair of DNA damage in G2 and prophase, are conserved (Del Campo et al 1997, Pelayo et al 2001. The existence of a spindle checkpoint that controls the metaphase-to-anaphase transition was made obvious by observations of colchicine-arrested cells which, after their delay at c-mitosis, reorganize their chromatin and re-form a nuclear envelope around the chromosomal complement (Sans et al 1989).…”

Early and late replicating DNA involved in the G1 to S transition in Allium cepa L meristematic cells

“…Bromosubstitution of portions of genome followed by anoxic UVA irradiation allowed to correlate discrete DNA sequences to G 2 [6,7] prophase [23], and metaphase [22] completion in Allium cepa L meristems. Analogous methods were used to detect replication times of specific .genes in mammalian cells [4,5,26].…”