Close association of centrosomes to the distal ends of the microbody during its growth, division and partitioning in the green alga Klebsormidium flaccidum

Abstract

Division and partitioning of microbodies (peroxisomes) of the green alga Klebsormidium flaccidum, whose cells contain a single microbody, were investigated by electron microscopy. In interphase, the rod-shaped microbody is present between the nucleus and the single chloroplast, oriented perpendicular to the pole-to-pole direction of the future spindle. A centriole pair associates with one distal end of the microbody. In prophase, the microbody changes not only in shape, from a rodlike to a branched form, but also in orientation, from perpendicular to parallel to the future pole-to-pole direction. Duplicated centriole pairs are localized in close proximity to both distal ends of the microbody. In metaphase, the elongated microbody flanks the open spindle, with both distal ends close to the centriole pair at either spindle pole. The microbody further elongates in telophase and divides after septum formation (cytokinesis) has started. The association between the centrioles and both distal ends of the microbody is maintained throughout mitosis, resulting in the distal ends of the elongated microbody being fixed at the cellular poles. This configuration of the microbody may be favorable for faithful transmission of the organelle during cell division. After cytokinesis is completed, the microbody reverts to the perpendicular orientation by changing its shape. Microtubules radiating from the centrosomes flank the side of the microbody throughout mitosis. The close association of centrosomes and microtubules with the microbody is discussed in respect to the partitioning of the microbody in this alga.