The ultrastructure of the diffuse kinetochore in Luzula nivea

Abstract

Material of Luzula nivea was fixed and processed in the normal way for sectioning and use of the transmission electron microscope. In addition, irradiated as well as control material was employed. Irradiation is known to produce chromosome breaks which rejoin. Apparent side-by-side adherence at metaphase of the chromosomes of Luzula nivea in control material disappeared at the earliest moment of anaphase and because of the high visibility of the kinetochores of this species, one pair of sister kinetochores could be readily associated with one pair of chromatids. Rejoining of chromosome breaks which does not disappear at anaphase, could not be distinguished at metaphase from the above described adherence. Chromatids also were apparently adherent at metaphase and it is pointed out that this is commonly seen in most organisms sectioned for the electron microscope. The apparent adherence is regarded as an artifact of fixation and subsequent processing. The authors do not agree with the interpretation of the chromosomes of Luzula as polycentric. From serial sections it has been established that in Luzula nivea a single diffuse kinetochore extends along most of the length of the chromosome, but does not occupy the whole width.