Absorbance of Feulgen-stained somatic cell nuclei.

Abstract

ANALYSIS of published data on cytophotometric measurements of Feulgen-stained somatic cell nuclei from rat liver and thyroid gland1, untreated and croton oil treated mouse ear epithelial nuclei2 and mouse neuron and liver nuclei3 has shown that a straight line is obtained when the absorbance, E, is plotted against the reciprocal of the squared nuclear diameter. Consequently a and b are constants in the expression : E = a + bD −2 The ways in which the total nuclear deoxyribonucleic acid-content have been calculated4–8 demonstrate that the nuclei have been imagined as being homogeneously absorbing objects, that is, objects in which the absorbing particles are randomly distributed, non-interacting and retaining their shape and number. But according to the equation the mass (=deoxyribonucleic acid-content) must remain constant, no synthesis can therefore take place, and this is contradictory to experimental facts. We can therefore conclude that in spite of the finding that the equation describes the data well, it does not mean that the nuclei are homogeneously absorbing objects. A non-random distribution of the Feulgen-stain was observed by DeSmul and LeComte9, and reconstructions of serially cut human and rodent somatic nuclei in this laboratory10 have shown that the Feulgen-stained material and the nucleoli are distributed in a peripheral zone. We can therefore conclude that the absorbing material, that is, deoxyribonucleic acid, is not randomly distributed and consequently that published data on the total nuclear deoxyribonucleic acid content, calculated from cytophotometric measurements of fixed tissue assuming a random distribution of the absorbing particles, are erroneous. The linear relationship between the nuclear absorbance and the inverse nuclear surface area may simply mean that both the absorbance and the geometrical dimensions are dependent variables of a common variable as, for example, the growth process, thus : A practical consequence of this is, as is also evident from the equation, that a simple measurement of the nuclear geometrical dimensions will yield the same information as that obtained by the far more complicated and costly photometric method.