Polyploidy in the Differentiation and Function of Tissues and Cells in Plants

Open Access
Publisher Website
Google Scholar
Abstract
The actually available data on the occurrence of polyploidy in plant tissues and cells have been critically reviewed. The incidence of polyploidy in the plant body, the cytological mechanisms by which the polyploid condition is produced, the physiological and general significance of polyploidy in the « soma » of plant organisms and related questions have been considered. The most common mechanism of polyploidization acting in plant tissues and cells appears to be supernumerary chromosome reproduction. This is responsible for polysomaty in root and shoot meristems as well as for polyploidy in any type of differentiated tissues and for nuclear growth in general. During the development of ephemeral tissues, such as the anther tapetum, supernumerary chromosome reproduction has been sometimes found to occur intermingled with monochromosome mitoses and/or typical endomitosis of the Gerris-type. Abortive mitoses due to spindle disturbances and chromosome stickiness or both are a very common polyploidization mechanism in ephemeral tissues, such as the anther tapetum and the endosperm. The reasons for believing that a tetraploid (or polyploid) cell with a single nucleus is similar to a coenocyte of the same valence of « ploidy » are presented. The problem of the applicability of experimental mitosis stimulation as a tool for cytological studies of differentiated tissues is discussed, also in connection with the actually available methods of DNA determination in the same tissues. Some cases of histological differentiation in a diploid condition and the typical chimerical constitution of the plant body are finally considered. The present paper was already in the press when the study of K. HOLZER (« Untersuchungen zur karyologischen Anatomie der Wurzel ». Oster. Bot. Zeitsch., 99: 118–155; 1952) was published. Following heteroauxin treatment, mitosis Stimulation could be induced in the differentiated root tissues in 27 out of 49 species of Angiosperms. In 15 of them, both diploid and polyploid (4n, 8n and 16n) divisions could be observed, the 4n and 8n mitoses being always characterized by « pairs » and « groups of four » respectively: a condition clearly indicating their origin through « endomitotic » doublings (« endomitotische Vorgänge »). In the remaining 12 species, on the contrary, all induced mitoses were found to be diploid. No evidence of chromosome breakage during mitosis in the differentiated root tissues investigated was observed by HOLZER. The author expresses, therefore, the view that the chromosome aberrations reported by D'AMATO & AVANZI (1948) and by LEVAN & LOFTY (1949) in Allium Cepa following treatment with 2,4-D and naphftalene acetic acid respectively, might be due to that « zur Teilungsauslösung Stoffe verwendet wurden, die nicht in der Natur auftreten und aus diesem Grunde eine Giftwirkung ausüben'können » (1. c. pag. 151). It seems, however, to the present writer that the lines of evidence supporting the spontaneous occurrence of chromosome changes in the differentiated root tissues of the onion are so numerous and convincing that HOLZER's view is obviously untenable.