NUCLEAR DIFFERENCES IN ALLIUM CEPA ROOT TISSUES AS REVEALED THROUGH INDUCTION OF MITOSIS WITH INDOLEACETIC ACID

Abstract

Treatment with the growth substance indoleacetic acid was used to stimulate mitosis in differentiated tissues of Allium cepa roots in order to establish whether nuclear differences, specifically in chromosome number, exist normally and are merely revealed by treatments, or whether these nuclear differences are produced by the treatment. With the concentrations of indoleacetic acid and durations of treatment used, evidence was obtained that: chromosome number differences exist in the differentiated tissues of onion root prior to any treatment and that the appearance of these differences after treatment is a matter of revelation and not of causation. The evidence obtained in these investigations comes indirectly from observations of nuclear size and structure and directly from rare spontaneous mitoses in untreated roots, and in the treated roots (i) from the absence of nuclear abnormalities which might explain otherwise the origin of polyploid cells, (ii) from the uniform occurrence of certain chromosome numbers in specific root tissues, (iii) from proportions of diploid and polyploid divisions during mitotic induction, and (iv) from the lack of relationship between total mitotic activity and number of polyploid mitoses. A gradient of endomitotic polyploidization exits in certain tissues along the longitudinal axis of the onion root.