The Role of Cytoplasm in Cytokinesis of Plant Cells

Abstract

To elucidate the role of cytoplasmic structures in determination of the position of new cell wall, relatively mild centrifugal forces (3550 g or less, 15 minutes) were exerted on the stamen hair cells of Tradescantia reflexa. Observations were made all in vivo. Cinematographic technique was employed in some cases.
After centrifugation, the spindle returns to the center of the cell with simultaneously proceeding elongation of the spindle itself and poleward separation of the daughter chromosomes. The process of recovery from the effects of centrifugation is almost the same without regard to strength and direction of the centrifugal force and whether the cell is centrifuged once, twice or three times successively to opposite directions.
The cytoplasm in a dividing cell is considered to be specially differentiated to maintain the shape and function of the spindle and to determine the mitotic axis and the cytokinetic plane. The spindle is considered to be held at its right position in the cell by the following manner that it is enveloped with a cytoplasmic layer (spindle envelope), which is connected to some differentiated pattern in the cell cortex by the polar plasmic strands, the phragmosome and other cytoplasmic strands. The returning movement of the spindle after centrifugation is considered to be brought about by movements of this cytoplasmic system.
Abnormal partition walls were formed in some few cases after repeated centrifugation. These abnormalities seem due to general enervation of the cells by accidental damages in the buds during centrifugation, rather than due to the direct effect of centrifugal forces.
By treatment of cold-ethanol-fixed pollen mother cells of Lilium longiflorum with hydrogen peroxide and detergent, the cytoplasmic envelope of the spindle can be distinctly visualized.