Immediate disruption of spindle poles and induction of additional microtubule-organizing centres by a phenylcarbamate, during plant mitosis

Abstract

Summary. The herbicide carbetamide [(R)-l-(ethylcarbamoyl) ethylphenylcarbamate], in the 0.4 to 0.8 mM range, efficiently induced multipolar mitoses in Allium cepa L. The frequency of multipolar anaphases rose earlier and reached higher values when both concentration and time of treatment increased, up to a maximum of 90% after 1 h of treatment. To identify the physiological target, the kinetics of induction of multipolar mitoses were followed during recovery from very short treatments (5, 10, and 15 min). Tubulin immunodetection showed that phenylcmbamate immediately disrupts the cohesion between the different bundles of microtubule minus ends which converge at the pole. The spindle was rendered multipolar about three times more efficiently in metaphase than in anaphase. The observations do not support any effect of the herbicide on the tubulin polymerization-depolymerization cycle, and suggest that the minus ends of the microtubules remained stabilized in carbetamide. Thus, the density of kinetochore microtubnles and their lengths were unmodified in the individual chromosomes which became detached from both spindle poles in response to the herbicide. Extra microtubule-organizing centres for the assembly of both preprophase band and phragmoplast (the tubulin arrays which characterize the microtubular cycle responsible for cytokinesis in plant cells) were also rapidly induced.

Cytogenetic and microtubule array effects of the zineb-containing commercial fungicide formulation Azzurro® on meristematic root cells of Allium cepa L.

“…The method used provided a sensitive bioassay for detecting damage at the cellular level. These observations verify previous reports showing that microtubule structure anomalies are a reliable tool in genotoxicity and cytotoxicity studies in animal [11,[36][37][38][39][40][41][42][43] or plant cells [44][45][46][47].…”

Formation of division spindles in higher plant meiosis

“…It is noteworthy that in abnormal meiosis in Paspalum, described above, the second cytokinesis occurs in prophase II (Pagliarini et al, 1998). And, finally, the rapid transformation of fully formed bipolar metaphase spindles into multipolar ones under phenylcarbamate action described in Allium root meristem (Gimenez-Abian et al, 1998) also could be the result of activation of ''chaotisation'' process by this agent.…”