Effects of elevated centrifugal field on the Nitella cell and postcentrifugation patterns of its cytoplasmic streaming and chloroplast files.

Abstract

Listen

Translate article

Two stage centrifugation (250 × g and 6, 000 × g) was used to sediment organelles in layers in Nitella "leaf" cells. The earliest noticeable recovery of cytoplasmic streaming was minute and localized in the endoplasm adjacent to the chloroplast layer. This flow gradually expanded; within a few hours it covered the entire cellular space and showed an abnormal streaming pattern. At that time, chloroplasts still remained packed at the centrifugal end of the cell, and bundles of microfilaments were aligned along the direction of flow in the chloroplast-free area. The abnormal patterns observed were whirls, loops or flow perpendicular to the direction of normal streaming. Analysis of the angular velocities in the whirls indicated that each was an independent piece of rotating endoplasm, as reported by Kamitsubo (8, 9).Approximately one week later, chloroplasts began to reappear in the stripped area, and within 1 to 2 weeks the entire cell was covered with chloro-plasts exactly aligned along the direction of the reconstituted, abnormal flow. This suggests that chloroplast alignment can be governed by the direction of streaming. Cells with abnormal streaming pattrens survived for more than 3 months with no change in pattern. New cells initiated from the centrifuged cells, however, had normal streaming patterns and chloroplast alignments.