Disruption of organization of mitotic microtubules in root meristem cells of Allium cepa induced by chloral hydrate

Data are presented on the effect of chlorahydrate on microtubule organization in the root meristem of Allium cepa. Our studies show that an incomplete preprophase band commonly appears during G2-prophase transition, yet the major effect is the lack of perinuclear microtubules, leading to inhibition of the prophase spindle formation and transition to C-mitosis. Upon chloralhydrate treatment of metaphase cells, we found cells with chromosomes regularly aligned within the metaphase plate and differently disorganized mitotic spindles. Concurrently, C-metaphase cells with remnants of kinetochore fibers were present. In addition, normal bipolar and abnormal irregular types of chromosome segregation were detected, this representing multipolar and diffuse anaphases. The major difference between them is the presence of polar microtubules during multipolar anaphase, and their lacking during diffuse anaphase. Alternatively, microtubule clusters between segregated groups of chromosomes are typical for cells with diffuse anaphase. During bipolar anaphase, excessive aster-like microtubules emanate from the spindle poles, and in telophase accessory phragmoplasts are observed at the cell periphery. The formation of incomplete phragmoplasts was observed after normal bipolar and abnormal chromosome segregation. We conclude that chloralhydrate may affect the nuclear surface capability to initiate the growth of perinuclear microtubules, thus blocking the prophase spindle formation. It also disturbs the spatial interaction between microtubules, which is crucial for the formation and functioning of various microtubular systems (preprophase band, spindle and phragmoplast).