An Experimental Study on the Structure of Living Nuclei in the Resting Stage

Abstract

1) The treatments of various plant and animal cell nuclei with hypo- and hypertonic solutions show that the healthy or intact nuclei can be classified into four types according to the behaviour of the morphological components of the nucleus towards hydration or dehydration. In all these nuclei the essential components are the chromonemata which assume a loosely winding form giving the reticulate appearance to the general view of the nucleus or a compactly coiled form appearing as the net-knots or chromocenters, and the karyolymph. The optical homogeneity of the intact nuclei is due to the lack of differente in the refractive index between the two components, the chromonemata and the karyolymph.2) The salivary gland nuelei of the Chironomus larvae are found to belong to Type 3 of our classification. When they are observed in the medium of liquid paraffin, several giant chromosomes which are of a banded structure are observed. When treated with a hypotonic solution, the chromosomes swell markedly and the chromatic bands are transformed into a necklace structure or rows of granules which disappear by further hydration. When these swollen nuclei are dehydrated, the chromatic bands reappear in the original positions in the chromosomes.3) The hydration and dehydration experiments made with the guard cell nuclei of stomata in several plants show that these nuclei undergo marked changes in appearance responding to the osmotic pressures of the solutions applied. The saure changes can be observed also in the natural state in close connection with the functional changes taking place in the guard cells.4) The net-knots or the chromocenters which in some plants and animals are observable in the living nucleus can be experimentally transformed into a Loose mass of uncoiled chromonemata. They may, therefore, be regarded as representing the parts of chromosomes in heteropycnosis or complete chromosomes in the same condition, or aggregates of these, in all of which the chromonemata remain more or less tightly coiled, instead of being in the loosely and irregularly coiled state.It is a great pleasure to the writer to Lake this opportunity of expressing his sintere gratitude to Prof. Y. KUWADA under whose kind guidance and direction the present investigation was carried out.