Effects of colchicine and high hydrostatic pressure on the nuclear position in onion root-tip cells

Abstract

The root-tip cell possesses a mechanism by which the position of the nucleus is actively controlled. Our preliminary observations demonstrated that the cell is capable of restoring the nucleus to its original position when it has been displaced by centrifugal force. The aim of the present study is to approach the problem of the nuclear position in meristematic cells by examining its normal position in cells from cut roots, its displacement in centrifuged roots, and the return to normal position in the course of recovery with or without various treatments. Immediately after centrifugation (1 300 g for 30 min) more than 95% of the cell nuclei were observed to be clearly displaced. The study of recovery in tap water shows that after 2 h, 90% of the cells had their nuclei once more in the central position. Incubation of centrifuged roots in colchicine (0.1% and 0.5%) demonstrated that this drug does not alter the rate of recovery of the nuclear position. On the other hand, high hydrostatic pressure (12000 psi) inhibited completely the mechanism by which the nuclear position was restored. The recovery in water of the centrifuged roots subjected to a 2 h treatment at 12 000 psi showed that the inhibitive effect of the hydrostatic pressure was rapidly reversible. We therefore suggest that the mechanism which regulates the position of the nucleus is based essentially on cytoplasmic streaming which is not dependent on microtubules.