Cyto-Histological Investigations of Antimitotic Substances and their Effects on Patterns of Differentiation

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Abstract
An attempt has been made to analyze some sources of somatic cell variation, resulting from experimental and natural actions on mitosis, in relation to the ensuing patterns of differentiation. The following three essential antimitotic effects have been considered: 1) Preprophase inhibition (or mitostatic action). The cyto-histological consequences of mitosis suppression in both shoot and root tips and in cambial zones have been analyzed. Mitosis suppression by relatively high doses of growth substances has been regarded as one aspect of the two-phase action of these compounds on mitosis. Consequently, consideration has been given the histogenetic phenomena connected with mitosis stimulation in normally proliferating regions as well as in differentiated tissues (dedifferentiation). 2) Spindle inhibition (C-mitotic action). Polyploidy, aneuploidy, and reduction in chromosome number resulting from suppression, and/or disturbances of spindle and centromere activity have been regarded as the most prominent sources of cell variation per se and in relation to chimeras and mosaicisms. 3) Cytokinesis inhibition. The need for a detailed study of cytokinesis inhibitors is emphasized for any understanding of the significance of polynucleation in short-lived tissues (anther tapetum, endosperm).