Silvana Avanzi

Cytochemical and Autoradiographic Analyses on the Embryo Suspensor Cells of Phaseolus Coccineos

SUMMARYSpecific staining methods (Feulgen, methyl green-pyronin, toluidine blue molybdate, acridine orange), digestion tests (DNase and RNase) and autoradiographic techniques (incorporation of tritiated thymidine, uridine, lysine, tryptophan; DNA detection by means of tritiated actinomycin D) have been used to study the embryo suspensor of Phaseolus coccineus. Most of material studied consisted of developing seeds in which the cotyledons of the embryo occupied one third to one half of the endospermatic cavity. In the typically club-shaped suspensor, both the « handle » portion (which contains cells with low to medium degree of endopolyploidy) and the « knob » portion (which contains polytene chromosome cells) have been analyzed.Indications have been found that the cells with low and medium degree of endopolyploidy undergo extra DNA synthesis (gene amplification) on many heterochromatic chromosome regions during early stages of embryogenesis. Later on, the extra DNA synthesized seems to be released, from t...

Chromosome Breakage by Pyrrolizidine Alkaloids and Modification of the Effect by Cysteine

SUMMARYThe author has studied the cytological effect, in onion root tips, of 6 pyrrolizidine alkaloids already known to be hepatotoxic in mammals and mutagenic in Drosophila.A comparative analysis of the effect of treatments with solutions of identical concentrations (3.2, 1.6 and 0.8 × 10—3M/1) and for identical durations (24-hour treatment followed by one, two and several days of recovery into water) has shown that: 1. - all the alkaloids studied are able to induce chromosomal damage, the most active being lasiocarpine, heliotrine and jacobine;2. - no qualitative difference in action exists between the 6 alkaloids: the aberrations observed are almost exclusively of chromatid type, even in recovery experiments of long duration, in which aberrations due to chromosome breakage in the pre-split phase should occur;3. - a characteristics common to the alkaloids studied is the high relative frequency of chromatid bridges to fragments. Such a high reunion ability of broken ends has not been observed so far in A...

Some Cytological Aspects of the Differentiation of Metaxylem in the Root of Allium Cepa

SUMMARYA cytological study was accomplished on the immature metaxylem of Allium cepa roots in the histological region between 500 and 3000 μ from the tip. Labelling experiments with 3H-thymidine, 3H-uridine and 3H-lysine were also carried out.The results show that in metaxylem maturation four morphologically detectable stages can be distinguished: 1) Cells close to the region of the apical initials undergo a process of chromosome endoreduplication.2) Cells of the histological region between 800 and 1200 μ from the root tip show amplification of the genes of the nucleolar organizing region.3) Cells of the histological region between 1200 and 2000 μ from the root tip show extrusion of the nucleolus from the nucleus (about 30% of cells show the phenomenon). Nucleoli, either extruded or not extruded, incorporate 3H-thymidine in their peripheral area in concomitance with chromatin incorporation. On the contrary, the inner part of the nucleolus is active in DNA synthesis when chromatin is almost inactive.4) Aft...

Sequential development of meristems in the embryo of Triticum durum. A DNA autoradiographic and cytophotometric analysis

DNA labeling with thymidine-3H and DNA cytophotometry have been used to study the sequential development of meristems in the embryo of Triticum durum. It has been found that the embryonic shoot apex completes its development at ca. 63% water content in the seed; at seed maturity, it consists exclusively of cells with 2C (G1) nuclear DNA content. Other meristems—the apices of primary root and of the seminal roots of the first and second pair, primordia of leaves 1, 2, and 3—complete their development at 47–48% seed water content, or lower. At seed maturity, all leaf primordia and most apices of the second pair roots are made of 2C cells only whereas the meristems of the primary root and of the first pair roots contain different proportions of 4C (G2) cells in addition to 2C cells. An analysis of the labeling index and of the mitotic index in the meristems of the embryos has shown that, at late stages of embryo development, DNA synthesis is stopped earlier than mitosis; but the interval between the inhibition of DNA synthesis and the inhibition of mitosis is different in different meristems. Consequently, in some meristems—leaf primordia, apices of most seminal roots of the second pair—mitotic activity lasts long enough to deplete completely the meristem of 4C (G2) cells; in the remaining root meristems, this “depletion phase” is less efficient, the degree of its efficiency decreasing progressively in the succession: roots of second pair → roots of first pair → primary root. The significance of these observations for studies on developmental processes is discussed.

The Shoot Apical Cell of Equisetum Arvense, a Quiescent Cell

SUMMARYA DNA cytophotometric analysis was carried out on 50 shoot apices of Equisetum arvense, 38 belonging to main stems and 12 to branches. No clear difference in the nuclear conditions of the apical cell was found between the two types of shoot. 38 apical cells showed a greater than 4C nuclear DNA content (polyploidy); the remaining gave a DNA content 4C, corresponding to the DNA post-syntesis phase, or G2, of diploid cells. Neither 2C nor 2C-4C intermediate values were found. Only one apical was found in mitosis (diploid).In 21 apices, 30 segment cells were analyzed; in 20 of them a greater than 4C DNA content was estimated. No division was observed in 100 segment cells belonging to the 50 shoot apices, two per apex.The views of previous workers on the organization and mode of functioning of shoot apices with single apical cells are discussed in the light of the present observations. It is concluded that: i) in established shoot apices of Equisetum — and probably other Cryptogams — the shoot apical ce...

New Evidence on the Organization of the Root Apex in Leptosporangiate Ferns

SUMMARYDNA cytophotometry and DNA labelling with 3H-thymidine were used to study the apical cell in lateral root primordia of Marsilea strigosa and in root apices of Marsilea strigosa, Blechnum brasiliense, B. gibbum, Polypodium aureum and Ceratopteris thalictroides.The initial cell of the lateral root in Marsilea makes a series of divisions which lead to a primordium with a tetrahedral apical cell. At different stages of development of the primordium, the apical cell becomes « quiescent »; that is, it divides rarely, if at all, whilst mitotic activity is retained by the mass of cells surrounding the apical. This situation is kept in the apex of adult roots in Marsilea and the other species investigated. Quiescence of the apical cell is due to a permanent, or long-lasting, block in the G2 phase without any interference with further DNA synthesis up to 8–16C intermediate DNA contents. From time to time, the apical cell enters mitosis with either 4C (diploid) or — more rarely — 8C (tetraploid) DNA content. ...

Chromosome Endoreduplication (Endopolyploidy) in Pea Root Meristems Induced by 8-Azaguanine

SUMMARYThe effect of 8-azaguanine (5 × 10−4M) on the root meristems of Pisum sativum has been studied.The immediate effect of 8-azaguanine is an inhibition of interphase (G2) nuclei to enter mitosis ending in the absence of mitosis after a 12-hour treatment. Inhibition of DNA synthesis (H3-thymidine incorporation) starts to appear after 6 hours: 8-azaguanine does not interfere with DNA synthesis once it is initiated, but it inhibits the initiation of DNA synthesis (passage from G1 to S) at least in the majority of cells (data of the DNA cyto-photoinetry).When roots treated with 8-azaguanine for 17 hours recover in water for 24 hours, both diploid (14 monochromosomes) and endotetraploid (14 diplochromosomes = 4-chromatid chromosomes) mitoses are found in the meristem. The proportion of diplochromosome mitoses is still higher when the 24-hour water recovery follows two 8-azaguanine treatments, 17-hours each, separated by a 6-hour root immersion in 5 x 10—4M guanine. A treatment has also been found which ind...

A DNA Cytophotometric Investigation on the Development of the Female Gametophyte of Ginkgo Biloba

SUMMARYDNA cytophotometry has been used to study the development of the female gametophyte of Ginkgo biloba. It has been found that, at the beginning of the cellular stage, a large part of the cell population of the gametophyte is not haploid as to DNA content. Namely, very few nuclei (about 5%) show IC DNA content (i.e. the content of an haploid cell in the presynthetic stage of the mitotic cycle), while about 50% show 2C DNA content, more than 40% 4C and the remaining 8C and higher contents.As to mitoses, 2C and 4C divisions are found to occur simultaneously; the latter are much more numerous. The very active division of the 4C cells is responsible for the gradual decrease of their percentage in the gametophyte while the 2C cell population progressively increases. Nevertheless, in a mature gametophyte, some 4C cells are still present. They are located in the outer region of the gametophyte. Moreover, the cells of the archegonial jacket show a DNA content corresponding to 2C, 2–4C, 4C and 4–8C.The nuclei...

Chromosome Breakage in Vicia Faba by Lasiocarpine and Monocrotaline

SUMMARYThe author has studied the cytological effect of lasiocarpine and monocrotaline in Vicia faba lateral root tips. From the data gathered it may concluded that: 1) There are neither quantitative nor qualitative differences in chromosome breaking activity between the two chemicals.2) Vicia faba is more sensitive than Allium cepa to the cytological effect of monocrotaline; namely the percentage of abnormal anaphases and the frequency of fragments per cell are four times higher in Vicia than in Allium.3) The radiomimetic effect of monocrotaline is clearly temperature dependent, but the temperature does not seem to influence any one aberration in a particular way.

SOLID STEM: A RADIATION INDUCED MUTATION IN TRITICUM DURUM DESF

SUMMARYData are presented on the inheritance and culm anatomy of a solid stem mutant, induced in durum wheat Cappelli by X-irradiation.F1 plants of the cross between the mutant and the mother line Cappelli had intermediate phenotype. Genetic analysis of F2 was particularly complicated as, in addition to parental types, many intermediate phenotypes were present. Completely hollow-stemmed plants reached 23.1% of the whole population, while the remaining individuals had at least the top internode below the spike filled with pith (3:1 segregation: 0.5>P>0.3). Two hypothesis might be considered to explain the data obtained, namely: 1) X-irradiation induced a semidominant mutation;2) X-irradiation neutralized the action of a gene for hollow stem, epistatic, only when homozygous, on one or more genes inducing stem solidness.Considering the cytogenetical information on solid stem in the genus Triticum, the second hypothesis seems most probable.A statistical analysis was carried on two anatomical parameters, namel...