Studi sull'agglutinazione cromosomica (“stickiness„) in Allium Cepa L. e altre Monocotiledoni

Abstract

Summary Chromatic agglutination (stickiness) has been found in root tips of Scilla sibirica, Fritillaria imperialis (2n=48+2ff.), Crinum Amoenum and C. rubrum, and in the nucellar and ovarial cells of Tricyrtis hirta. All these plants were living under greenhouse conditions. A thorough study of chromatic agglutination has been carried out in onion bulbs coming from a storehouse where minimum temperature ranging from 0 to —C. were recorded, in onion seedlings and in two plants of Fritillaria imperialis. Untreated material as well as material submitted to different experimental conditions (plants raised from bulbs in the greenhouse, effects of low and high temperature, of inorganic solutions, of water deficiency0-tested only on seedlings-) has been investigated. In the plants which did not survive there was a great increase in stickness and mitotic aberrations, parallel to the dimisnished viability of the individual. Matrix starvation, i. e. diminished production of matrix material and stickiness can occur together. The double effect of low temperatures on spindle function and matrix behavior has been investigated. Increased degree of stickiness and matrix starvation coexist, at least in most experiments. Of special interest is the poor resistance of tetraploid Fritillaria to low temperatures. After 42 hours at—2° C. all roots had lost their turgor and the cells appeared killed by the treatment. Root tips, treated with water at 45°, 55° and 60° C. for 30° and 60° and then fixed and Feulgen stained, were compared with material hydrolysed in N/HCI at 60° C. withouth fixation. The behavior of nucleic acid in this last experiment has been described, as well as the partial fixing effect of N/HCI at 60° C. The cytological effect of 0, lmol solutions of Ni(NO3)2, Th (NO3, UO2(NO3), CrO3 (0,lmol = 1%) and of PlCl1 1% has been studied. All these solutions induce an obvious stickiness, before they effect fixation. The effect of the CrOa solution on chsomesome matrix, chromosome and chormatid breakage, shape and appearence of resting nuclei is described. Mitotic abarrations in onion seedlings have been reinvestigated. Dessiccation experiments point out the connection existing between water deficiency, degree of chromatic agglutination and frequency of chromosome aberrations. The following morphological aspects of chromatic agglutination have been especially investigated: Chromosome structure. Chromosomes are 4-partile at pro-metaphase and 2-partite at ana-telophase. Splitting of chromatids takes place during the resting stage. Course of mitosis until anaphase. “Distorted” metaphases, “prophase” metaphases and metaphases with all the chromosome arms turned upwards were detected in plants showing a poor viability and also in seedlines of the dessiccation experiments. Delayed and disturbed metaphase congression are typical of sticky chromosomes. Anaphase. Tension of chromatids during the anaphasic separation, constitution of three different types of bridges (pseudobridges, bridges for asyminetrical chromatid distension and bridges for sister reunions), lagging of chromosomes have been described. Bridges due to asymmetrical chromatid distension are generally; the consequence of a disturbed metaphase congression. Behavior of the SAT-apparatus. The anomalous distensions of the SAT-thread during meta-anaphase and the morphological appearence of satellites have been studied. The importance of stickiness as a physiological factor in all these phenomena is pointed out. Chromosome morphology. Under-spiralisation and errors in spiralisation have been very frequently met with: the last-mentioned especially under experimental conditions. Occurrence of an accessory constriction in one of the sister chromatids during anaphase has been sometimes observed and its origin ascribed to despiralisation. The meaning of “general starvation” (DARLINGTON and LA COUR 1945) is discussed. Extensibility of the different chromosome regions. The present observations are in general agreement with the conclusions of PINTO-LOPES (1945). Stainability of chromosomes. A survey of stain intensity in different conditions of observation and experiment is given. The importance of chromatic agglutination for a right interpretation of mitotic aberrations is pointed out. Some observations reported by previous workers are critically discussed.