EFFECT OF CENTRIFUGATION ON THE DEVELOPMENT AND TIMING OF PREMITOTIC POSITIONING OF THE NUCLEUS IN ADIANTUM PROTONEMATA.

When single-celled protonemata of Adiantum capillus-veneris L. were centrifuged immediately before transferring to darkness from continuous irradiation with red light, their nuclei were displaced basipetally. Both filamentous and branched protonemata were obtained. The stronger the centrifugal acceleration, the more frequently the branched protonemata were induced. The effect of centrifugation at 1,300 x g for 15 min on nuclear displacement was different at different stages of the cell cycle. In early G phase, the nucleus was easily displaced by centrifugation, but quickly returned to the original position after centrifugation. In late G phase, the nucleus was displaced, but after centrifugation it never came back to the original position. In late G and M phases, the nucleus was no longer displaced by the centrifugation. Premitotic positioning of the nucleus in cytokinesis took place about 5 hr before cell plate formation in all centrifugal treatments described above.