SUMMARYThe 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...

https://www.tandfonline.com/doi/pdf/10.1080/00087114.1952.10797544

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

Nucleoli and related nuclear structures

THE GENUS Lilium has been investigated by numerous workers and all species are reported as having a somatic number of twenty-four (Sato, 1932; Sansome and LaCour, 1934; Mather, 1935; Beal, 1942; and Stewart, 1943) with the exceptions of the triploid species L. tigrinum .(Takenaka and Nagamatsu, 1930) and several species in which aneuploids are found (Sansome and LaCour, 1934; Mather, 1935; Beal, 1942; and Stewart, 1943). Thus, species relationships cannot be clarified by evidence of chromosome number. A similar situation obtains in many other genera and in these cases useful information can be obtained from a comparative study of the chromosome morphology of the members of the group. The earlier reports of clhroinosome number in Liliunm were based on observations of sectioned material. The limitations of this method for a study of clhromosome morphology on material with very long chromosomes such as Lilium are obvious. Cooper (1935, 1936) utilized pollen grain divisions in L. IIenr,yi and L. regale, but his illustrations show neitlher primary nor secondary constrictions. In recent investigations utilization of the propriono or aceto carnmine smear technique and excised pretreatment with colchicine (Stewart and Bamford, 1943; Emsweller and Stewart, 1944) has given clear flat figures of the very long chromosomes of Lilium and allow a critical study of their morphology. This is a report of such a study to serve as a base for more extensive investigations of the phylogeny of the genus. MIATERIALS AND METHODS.-Root tips were used exclusively and these were taken from bulbs obtained fro6m commercial dealers in the United States and fromii collections of native species and garden escapes in the vicinity of College Park. None of the planits used in previous studies survived the interval and plants reported here represent additional data on the occurrence of aneuploids in Lilium (Stewart, 1943). Identification has been checked witlh Elwes (1880), Wilson (1925), Woodcock and Coutts (1935), Slate (1939), and various articles in the Royal Horticultural Society Lily Yearbooks. Root tips were fixed in 3:1 absolute alcoholglacial acetic acid for 24 hours, then rinsed and stored in 80 per cent alcohol until used. Smears were made by the propriono-carmine technique. The oiiiission of acid hydrolysis and the use of glass tools throughout to eliminate any trace of iron in the stain resulted in the nucleoli staining a bright red color from 24 to 48 hours after the preparation of the slide. The roots prepared in this way showed cells at the critical stages of mitosis for the classification of constrictions as shown in fig. 49 and 51. 1 Received for publication July 16, 1946. Scienitific Paper No. A-135. Contribution No. 2024 of the Maryland Agricultural Experiment Station (Departm ant of R3otany). The morphology of the chromosomes at somatic metaphase was determined from divisions in root tips given excised pretreatment for 30 minutes in a 0.2 per cent aqueous solution of colchicine followed by washing in water for 90 minutes. This is a slight modification of previous methods (Burrell, 1939; O'Mara, 1939; Stewart and Bamford, 1943; Stewart, 1943; Emsweller and Stewart, 1944). Buds and mature pollen have been collected and preserved for future work. Observations were made with the aid of 43x and 90x apochromatic oil immersion objectives and 15x compensating oculars. Camera lucida drawings at table level (approximately 2000X) were made of all the metaphase clhromosomes separately in from one to three cells of each plant of a species or variety. These were cut out and for each cell arranged in pairs on the basis of total length, position of primary constriction, and number and position of secondary constrictions. The idiograms (fig. 1-48) are these drawings of a haploid set from a typical cell which was the least distorted in preparation and traced so that the primary constrictions appear on a horizontal line. The order from left to right in each case is of increasing arm length ratio (long/ short) rising from approximate unity. Letters are assigned to the chromosomes according to their order in this scheme. Both chromosomies of pairs which are heteromorphic in the position of the secondary constrictions are shown and designated by a letter and its prime. The centric fragments and extra chromosomes which are not duplications of one of the normal complement are placed on the right regardless of the length of its short arm and are designated by the letter MI. In addition to the camera lucida idiograms a series of photoidiograms of representatives of the divisions of the genus Lilium are presented (fig. 52). These are constructed in exactly the same way as the other idiograms except that photomicrographs are used in place of camera lucida drawings. RESULTS.-The results are presented almost completely by the idiograms (fig. 1-48). There are nio large variations in chromosome morphology in the genus, all species having two long pairs of chromosomes with submedian centromeres and ten pairs with subterminal centromeres. The 2n number of all species reported here is 24 and although individuals were found in L. auratum, L. tsingtauense, L. Sargentiae, and L. pumilum with 2n 25 and one plant in L. Henryi with 2n 26, the additional chromosomes are, with two exceptions, centric fragments and in all cases are unlike any of the normal complement. However, the variations in the length of the chromosomes and the variation in position and function of the constrictions differentiate the species into two groups. The following is a detailed classification of the

/pdf/the-morphology-of-somatic-chromosomes-in-lilium-23iga2mdj7.pdf

The morphology of somatic chromosomes in lilium

1.

The composition of microsporocyte nucleoli of maize with different chromosomal constitutions was studied by the analysis of absorption spectra obtained from an ultraviolet microspectrophotometer.




2.

The presence of ribonucleic acids (RNA) and proteins in the nucleolus was confirmed by the presence of two broad and overlapping absorption peaks around 2637 A and 2800 A. The former peak was removable by treatment of the tissue sections with cold perchloric acid.




3.

The amount of RNA per nucleolus was determined by measuring the absorbance and the diameter and thickness of nucleolus sections at 2637 A. Non-specific light loss and absorption due to proteins were corrected for by the use of blank slides which were subjected to cold perchloric acid extraction.




4.

By means of the above technique, the amount of RNA per nucleolus was found to be significantly different in the various strains of maize studied.




5.

The size of and amount of RNA in the nucleolus were found to increase until mid-pachynema and then diminish and finally disappear at late diakinesis. The increase in volume was found to lag behind that in the RNA content. This observation, together with the observation that the RNA/protein ratio went down during the same period, was interpreted as indicating that during the growth of the nucleolus the RNA content increases faster than does the protein content, and that the synthesis or incorporation of proteins into the nucleolus is dependent upon RNA. The RNA content of the nucleolus was found to have doubled at some time between mid-leptonema and zygonema, an increase which was thought to be the result of the reduplication of the nucleolar, organizer during leptonema.




6.

A linear relation was established between the RNA content of the nucleolus and the number of extra nucleolar organizers present on supernumerary B6 chromosomes. The extra organizers did not change the RNA/protein ratio of the nucleolus. Extra heterochromatin in the supernumerary B chromosomes was found to increase the RNA content of the nucleolus only very slightly.




7.

Extra euchromatin was believed to have no appreciable effect on nucleolar composition since the RNA content of nucleoli from triploid plants, like that of nucleoli from plants trisomic for the nucleolar chromosome, was only three-halves as much as in their respective normal diploid siblings.




8.

The entire nucleolar chromosome is probably involved in nucleolus formation since changes in the RNA content, though not in the RNA/protein ratio, were found in plants carrying a translocation involving the nucleolar chromosome.

Chromosomal control of nuclear composition in maize.

Chinese hamster cell strains in the early passages in culture display wide variation in number of nucleolus-like bodies per cell, though such strains are characteristically euploid. A variety of criteria indicate that the nucleolus-like bodies are true nucleoli. Their Azure B- and fast green-staining properties indicate the presence of RNA and protein; they have typical nucleolar fine structure, including both fibrous and granular components; radioautography reveals that their patterns of uptake of uridine-(3)H into RNA are similar to those reported for nucleoli of other cell types; actinomycin D, at a level which selectively inhibits ribosomal RNA synthesis, greatly reduces their RNA synthesis and also causes segregation of fibrous and granular nucleolar components. Colchicine was used to experimentally fragment the nuclei of these cells into a number of separate karyomeres, each presumably containing some, or only one, of the chromosomes of the complement. Almost all the karyomeres contain nucleolus-like bodies which, by the same criteria applied to the multiple nucleolus-like bodies of uninuclear cells, appear to be true nucleoli. The nucleoli of individual karyomeres of the same cell often differ from each other in fine structure while the multiple nucleoli of a uninuclear cell generally resemble each other. The evidence presented in this study indicates that Chinese hamster cells contain many nucleolus-producing sites scattered through the genome.

https://rupress.org/jcb/article-pdf/40/1/248/1068988/248.pdf

K. T. Jacob

Papers

Chromosome numbers and the relationship between satellites and nucleoli in Cassia and certain other Leguminosae.