Some Physical Properties of the Nuclear Membrane

Abstract

During the last 50 years several investigators have described processes which bring into evidence such physical properties of nuclear membranes as resistance to deformation, extensibility, elasticity, etc. (Albrecht, Mottier, Kite, Chambers, Nemec). Our observations made on resting nuclei of the embryonic region of the onion root tip, centrifuged at 30,000 g., (35,000 r.p.m., radius: 22 mm.) are a contribution to the stock of facts already accumulated by these authors. The root tips, cut off at a length of 18 mm. were fastened by their cut end in a brass tube 15 mm. long and slightly wider than the roots; their free ends were in the centrifugal direction. The tubes were fixed firmly to the rotor of a Sharpies electric super-centrifuge. The rotor contained some Knop's plant medium in order to keep the roots steadily immersed. The centrifugation lasted from 10 minutes to 2 hours. The roots were then fixed in Flemming's fluid; and stained either with Heidenhain's iron haematoxylin or Flemming's triple stain. After a short centrifugation, the nuclear content is concentrated at the bottom of the nuclei and a clearer space appears at the top. Then the whole nuclei are thrown to the bottom of the cells. (Fig. 1 A.) So far these results are the same as those obtained by previous investigators working with a much lower centrifugal force. After a longer centrifugation the nucleus flattens against the floor of the cell, taking a more or less hemispheric shape, eventually forming an angle of less than 90° between the horizontal diameter of the hemisphere and the vertical portion of the nuclear membrane (Fig. 1B). The diametric line is perfectly straight and shows no evidence of any folding or shrinking. At the top of these hemispheric nuclei one can almost always observe an elevated portion of the membrane which encloses a transparent region and reminds one of a blister.