Chromosome and aster dimensions of dividing cells in regenerating tissues of clymenella torouata exposed to sulfhydryl and sulfoxide

Abstract

Previous reports in This Journal from this Insti tute yield the conclusion that the naturally occurring chemical equilibrium composed of the SH group and its partially oxidized derivatives is an important factor in the regulation of cell proliferation. Which processes and which structures are primarily affected has yet to be determined. The most striking structural feature is the increase or decrease in number of nuclear divisions. This is found not only in sections of root-tips and regenerating tissue, but also in amoebae in culture (1, 2). I t does not follow, however, that the influence is exerted directly upon the chromatin. Many themieal and cytological studies must be made before this can be settled. But a beginning must be made somewhere. So I have attempted to measure differences in chromosome length and thickness and in aster spread in the polar and equatorial planes in control material and that grown in the presence of the chemical groups. All measurements were made under oil immersion with a Zeiss binocular microscope carrying a 2 mm. H-90, 1.30 apochromat objective and two K 15 • eyepieces. Dimensions were gotten with a Zeiss eye-piece micrometer scale 0.5 ram. in length divided into 0,01 mm. Constant illumination was obtained with a Bausch and Lomb 'Dayl ight ' lamp carrying a 15 watt tungsten filiament bulb. With this set up valid measurement of chromosome length and aster spread is not difficult. The matter is different when it comes to chromosome thickness. The procedure was to line up a chromosome lengthwise between two of the scale divisions in the eye-piece micrometer and then estimate the space occupied thereby. Long practice is necessary and was taken before such estimates have any degree of reliability. No measurements were recorded until many