Frequency Of Cell Division Research Articles

ONTOGENY IN MONOCOTYLEDONS AS REVEALED BY STUDIES OF THE DEVELOPMENTAL ANATOMY OF PERICLINAL CHLOROPLAST CHIMERAS

The developmental anatomy of apically stable periclinal chloroplast chimeras was studied in a number of monocotyledonous genera. Their ontogeny is basically similar to that of dicotyledons. In both there are three independent apical layers (L‐I, L‐II, and L‐III) whose derivatives can be traced in stem, leaf and flower. The bulk of the stem tissue is derived from L‐III with only the epidermis and one or two hypodermal cell layers from L‐I and L‐II. All three layers participate in formation of the leaf with great flexibility in the amount of tissue from each. There is more instability in growth of most monocotyledonous leaves than in dicotyledonous leaves. As a result there is relatively more tissue derived from L‐I and L‐II and less from L‐III. The same is true in floral development so that a significant number of gametes are of L‐I origin. As in dicotyledons, there is variation in direction, timing, and frequency of cell division. However, an overriding genetic control results in normal size, shape, and structure. The evidence from genetic and cytochimeras in both monocotyledons and dicotyledons has provided direct experimental proof of the functional reality of the apical layers described by Hanstein and Schmidt.

Experiments on anther culture in barley. Influence of culture methods on cell proliferation and organ differentiation

Several experiments have been performed in order to induce cell proliferation and plant differentiation from pollen grains by anther culture in barley. Some modifications of the culture media, pretreatments and transfer of the anthers increased notably the frequency of cell division, but the low proportion of normal green plantlets differentiating from microspores and calluses remains the major obstacle preventing the practical use of anther culture in barley breeding.

Cell Division in the Carapace Epidermis of Daphnia Magna Straus (Cladocera)

Cell division frequency in the carapace epidermis of D. magna declines with increasing animal size. Cell division is not necessarily one of the activities of premolt. During any particular intermolt the dividing cells are larger than those that do not divide but their size is also related to animal size, the cells in small animals dividing at a smaller average size than in larger individuals. Cell abundance following mitosis and prior to ecdysis consequently is not fixed but depends on animal size. The synthesis of an ephippium appears to be accompanied by cell division frequencies much higher than those occurring contemporaneously in other regions of the carapace.

On the Cortex Formation in the Apical Meristems of the Elongating Crown Roots of Rice Plants

The process of cortex formation in the apical meristems of normally elongating crown roots of rice plants was studied by observing cell arrangement and cell divisions. All longitudinal cell files in cortex of a root branched from the endodermal cell file (Fig.2). The branchings mostly occurred within 200 μm of the meristem tip (intersecting point of root axis with cap boundary). Consequently, the number of cortical cell layers decreased toward the meristem tip. Cortical cells dividing transversely were found as far as about twice the root diameter from the meristem tip (Fig. 7). The frequency of transverse cell divisions decreased gradually toward the meristem tip, from the 150 μm level in roots thicker than 600 μm in diameter and from the l00 μm level in thinner roots (Fig. 8). In thicker roots, no transverse division was seen in parts more distal than 50 μm. Periclinal cell divisions occurred only in endodermal cells near the meristem tip where transverse division frequency and layer number of cortical cells decreased (Fig.11). Most endodermal cells dividing periclinally are those from which cortical cell files are branched in a basal direction (Fig. 9). In thicker roots, periclinal divisions occurred in endodermal cells 50 μm-200 μm distant from the meristem tip; and in thinner roots, in those within 150 μm (Fig. 8). The transverse cell divisions in the most distal part of cortex with less number of cell layers are considered to decrease the number of cortical cell layers by sending this part in the basal direction. Thus, thicker roots with less frequency of transverse cell division in distal part of meristematic cortex tend to maintain their layer numbers in comparison with thinner roots. The periclinal cell divisions in endodermal cells act as if they compensate for the decrease in the number of cortical cell layers.

FLEXIBILITY IN ONTOGENY AS SHOWN BY THE CONTRIBUTION OF THE SHOOT APICAL LAYERS TO LEAVES OF PERICLINAL CHIMERAS

The development of leaves on apically stable, periclinal chimeras was studied in a number of dicot genera. The mutant cell layers of the shoot apex and the tissues derived from them were as active developmentally as the normal layers. Ontogeny was the same in these chimeras as in nonchimeras, and growth of their leaves can be outlined as follows. Formation of the buttress, the axis, and the lamina of simple dicot leaves were independent events. In each the first growth included derivatives of the apical layers, usually three in number, found in the apex of the shoot and the lateral buds. Most cell divisions in the outer layers (L‐I and L‐II) were anticlinal relative to the new structures. Therefore, in the proximal regions of the buttress, axis (petiole and midrib), and lamina, the derivative cells of L‐I and L‐II were usually present in single layers. The rest of the internal tissue was from L‐III. As formation of the axis and the lamina proceeded, derivatives of L‐II replaced L‐III internally in the distal and marginal regions leaving cells of L‐III behind. Both the determinate growth of leaves and the pattern of cell divisions at and near the leading edges of growth meant that no cells in the leaf were comparable to the initial cells of the shoot apex. As the lamina extended, there were extensive intercalary cell divisions, both anticlinal and periclinal, so that in any given region of a leaf the layers of internal cells were from either L‐II or L‐III. At any point along the axis, L‐III participated or did not participate in laminar extension. At any given stage in laminar growth either of two sister cells in any internal layer divided either a few times or extensively. The extreme variability in direction and frequency of cell division during leaf development was under an overriding genetic control, which resulted in the normal or typical size, shape and thickness of leaves.

Studies on the Relationships and Evolution of Supraspecific Taxa Utilizing Developmental Data. II. Relationships and Evolution of Oryzopsis hymenoides, O. virescens, O. kingii, O. micrantha, and O. asperifolia

In an attempt to understand better the relationships of critical species of the grass genus Oryzopsis, the floret development and embryology of five species were studied. The floret development and embryology of O. virescens and O. hymenoides are presented elsewhere; the results of studies of O. kingii, O. micrantha, and O. asperifolia are presented here, and these five species are compared with O. miliacea, Stipa richardsonii, S. lemmonii, S. hendersonii, and S. tortilis. Thirty-one characters were taken, standardized into two states, and the coefficient of similarity between all possible species pairs was calculated using a simple matching coefficient. The interrelationships were analyzed by a two-dimensional ordination. Oryzopsis hymenoides is more similar to species of Stipa and hence should be considered as S. hymenoides. Oryzopsis miliacea and O. virescens, members of the section Piptatherium, do not group together. Instead, O. miliacea clusters with O. micrantha, a species that has been placed in the section Oryzopsis. Three species of the section Oryzopsis, O. kinqii, O. asperifolia, and O. micrantha, cluster together, There was no support for the previously erected hypothesis that O. asperifolia is intermediate between the sections Oryzopsis and Piptatherium. Evolution of these species is the result of the accrual of many minor developmental, and hence genetic, differences. Most developmental differences are due to frequency of cell division, and there is no apparent change in the kinds of developmental differences with varying degrees of relationship.

Frequency of mammary cell division in relation to age: its significance in the induction of mammary tumors by carcinogen in rats.

Frequency of mammary cell division in relation to age: its significance in the induction of mammary tumors by carcinogen in rats.

The Cytology of Various Organs in Zinc-deficient Rats with Particular Reference to the Frequency of Cell Division

Deficiency of zinc in the rat was associated with parakeratosis of the oesophageal epithelium, atrophy of the epidermis and degenerative changes in the pancreatic acinar tissue. Many of the degenerating pancreatic acinar cells had the characteristic features of shrinkage necrosis. Lesions were not found in the liver. In deficient rats the mitotic indices of the oesophagus and pancreas were higher than in pair-fed controls; in the epidermis the mitotic index was lower, and in the liver it was not different from control values. When Zn-deficient rats were given a single oral dose of Zn the mitotic index in the oesophagus was reduced; in the epidermis, liver and pancreas it was increased. In the oesophagus, epidermis and liver the effects of colchicine in the Zn-deficient rats were limited to the arrest of mitosis in metaphase, but in the pancreas of Zn-deficient rats injected with colchicine there was mitotic arrest, and in addition a marked increase in the incidence of acinar cells affected by degenerative changes. Colchicine also had marked cytotoxic effects in the pancreas of rats fed on the Zn-deficient diet but given a single oral dose of Zn.

Comparison of N-ethyl-N-nitrosourea Effects in three strains of chlorococcal algae

Three strains of three different species of chlorococcal algae(Chlorella kesslerii Scenedesmus quadricauda andScenedesmus obliquus) were compared in their physiological and genetical responses to N-ethyl-N-nitrosourea (NEU). The mutagen was applied in the basic doses corresponding to their specific tolerance to it. Exponentially-graded doses derived from the basic ones acted for the same period of time and single basic doses acted at linearly-increased periods of time in parallel experiments. The influence of the mutagen on the cell cycle just in progress was characterized by the increase in the frequency of cell divisions which yielded a lower number of autospores. The conditions of the cells during the first three days after treatment were determined according to the average increase of their lag phase. The relative toxicity of the mutagen was expressed as the survival frequencies. The mutation effects were evaluated according to the frequency of permanent changes observed in the growing cell colonies : lethal, morphological and pigmentation. NEU was found to be a relatively suitable mutagen for the chlorococcal algae studied.

Cell population kinetics of excised roots of Pisum sativum.

The cell population kinetics of excised, cultured pea roots was studied with the use of tritiated thymidine and colchicine to determine (1) the influence of excision, (2) the influence of sucrose concentration, (3) the average mitotic cycle duration, and (4) the duration of mitosis and the G(1), S, and G(2) periods of interphase.(1) The results indicate that the process of excision causes a drop in the frequency of mitotic figures when performed either at the beginning of the culture period or after 100 hours in culture. This initial decrease in frequency of cell division is independent of sucrose concentration, but the subsequent rise in frequency of division, after 12 hours in culture, is dependent upon sucrose concentration. Two per cent sucrose maintains the shortest mitotic cycle duration. The use of colchicine indicated an average cycle duration of 20 hours, whereas the use of tritiated thymidine produced an average cycle duration of 17 hours.

On the Effect of Temperature upon the Division and Elongation of Cells in the Root of Rice Plant

Experiments were carried out to investigate the effect of temperature upon the division and elongation of cells in the seminal root of rice plant. The results obtained are as follows : 1) We could find no dividing cells in the root tips of the seedling kept under 40° and 43°C, as results of changes in protoplasm : vacuolation of cytoplasm, deformation of nucleolus and others. Under 25°C treatment, the intensity of cell division was most flourishing. The number of dividing cells decreased in proportion to the decline from 25°C as in Fig. 1. 2) The primary maxima of the frequency of cell division occurred at 10 A.M. and 10 P.M. with the smaller secondary maxima at 4 A.M. and 6 P.M., and this periodicity proceeded in a similar rhythmic fashion without distiniction of difference of temperatures as to be seen in Fig. 2. 3) The degree of the elongation of cortical cells were most conspicuous under 30°C treatment, and those cells were shortened according as temperature rose or fell from that point. Furthermore, we recognized that the effect of temperature on the elongation of the root was almost the same as the results obtained in the elongation of cortical cells above mentioned. 4) As the optimum temperature for cell division differed from that for cell elongation in root tip, it may be considered that in accordance with changes of temperature the inner morphological state of roots became unlike, even if the growth of roots was same.

Structure of the Angiosperm Apex

DURING the past twenty years or so, a considerable amount of research has been carried out, especially in the United States, into the anatomical structure of the vegetative apices of angiosperms. Many of these apices were described in terms of Schmidt's well-known tunica-corpus concept. This concept implied that the apex consists of two zones—the tunica, consisting of one or more layers of cells, where divisions are ordinarily anticlinal, and the corpus, where cell divisions take place in a number of planes. In practice, the application of this concept is an extremely arbitrary procedure. In later years, a number of workers have described zones in the vegetative apex which are distinguished, not by direction of cell division, but by cell size, frequency of cell division and density of cell contents. These workers have distinguished three main zones: (1) the central initiation zone, consisting of comparatively large, lightly staining cells which show few divisions; (2) the flank meristem, consisting of smaller, more deeply staining cells, which show frequent divisions; and (3) the rib or file meristem, where the cells are to be found in well-marked vertical rows.

HISTOLOGICAL EFFECTS OF GROWTH‐REGULATING SUBSTANCES ON SUNFLOWER TISSUE OF CROWN‐GALL ORIGIN GROWN IN VITRO

VARIOUS GROWTH-REGULATING substances, each at progressively increasing concentrations, have shown marked effects on the development of sunflower and tobacco callus in tissue cultures (Hildebrandt and Riker, 1947). The sunflower tissue came from crown-gall but was bacteria free; the tobacco tissue came from a natural gall on a hybrid. Except for the amount of growth produced, no conspicuous macroscopic differences appeared in these tissues. However, the possibility remained that histological differences might be present. The inhibition of growth of plant tissue with a strong concentration of growth substance has been reported (K6gl et al., 1934; Marmer, 1937; Levan, 1939). Kraus et al. (1936) have shown the increased activity and proliferation of cells of bean resulting in the formation of adventitious roots when treated in certain ways with indole-3-acetic acid. Since then, many investigators have descrihed responses made by different types of plant cells following applications of different growth substances (reviewed by Skoog, 1947, who includes other reviews). The microscopic structure of tobacco callus cultured in vitro has been described by White (1939) and by Caplin (1947). White considered the two main requirements for a true tissue culture are an undifferentiated state and the unlimited capacity for growth. The effects of growth-regulating substances on normal and pathological plant tissue growing in vitro have already received some attention. Gautheret (1945, 1947a) for example. in a series of papers has shown the concentration to be a critical factor in callus development and differentiation. Similarly the effects of indole-3-acetic acid, indole-butvric acid and alpha-naphthalene-acetic acids, respectively, on normal plant tissue and bacteria-free tissue of crown-gall origin of sunflower and periwinkle. grown in vitro, was reported by de Ropp (1947). The normal tissues responded at high and low concentrations by proliferation of cells of the cambial zone and by root formation. Tissue of crowngall origin remained unchanged in structure, except at the high concentrations where growth of the tissues was reduced. Gautheret (1947a, 1947b) '-Received for publication December 12, 1948. This work was supported by the Donner Foundation and by the Research Committee of the Graduate School from funds supplied by the Wisconsin Alumni Research Foundation. Published with the approval of the Director of the Wisconsin Agricultural Experiment Station. Valuable suggestions were received from Dr. J. B. Torrie on the statistical analysis and from Prof. Emma L. Fisk on the manuscript. studied normal plant tissue cultures grown in vitro. At a low concentration of indole-3-acetic acid, considerable cell division appeared; whereas cells without the growth substances failed to grow. As the concentration was increased, the frequency of cell division decreased but a swelling of the cells in all directions followed. The present studies were made to determine what, if any, histological changes were induced in the bacteria-free crown-gall tissue of sunflower by the added growth substances. This extends the work already reported by Hildebrandt and Riker (1947). Representative masses of tissues were fixed, sectioned, stained and examined. MATERIALS AND METHODS.-The sunflower used, the cultural procedures, and the amount of growth secured has been described bv Hildebrandt and Riker (1947). Representative tissues from 13,000 individual pieces were selected for examination. They explained that the sunflower tissue was originally isolated in 1941 from a secondary petiolar crown-gall but no longer contained crown-gall bacteria. The weak concentrations of growth-regulating substances on which sunflower tissue cultures examined here were grown, were 1 X 10-11 g./l. for indole-3-acetic acid and for alpha-naphthaleneacetic acid; I X 10-9 g./l. for indole-butyric acid; and 1 X 10-7 g.jl. for parachlorophenoxy-acetic acid. These concentrations were selected because they represented high points on the growth curves already described. The strong concentration for all of the growth substances was 1 X 10-3 g./l. Control cultures on media lacking a growth substance were also examined. After 6 weeks incubation on the media, fragments of the tissue were weighed and then fixed in formalin-aceto-alcohol. The tissue fragments were dehydrated with n-butyl alcohol and embedded in paraffin. Sections 10 , in thickness were cut on a rotary microtome. The stains used were either ironalum hematoxylin and safranin, or fast green and safranin. Microchemical tests (Johansen, 1940) were made for membrane substances. For statistical analysis, the total number of cells and the number of tracheal elements per unit area (approximately 1/4 sq. mm.) were counted. Cells were counted in ten fields in each of five different tissues at each of the concentrations (control, weak and strong) used for the four growth-regulating substances. OBSERVATIONS.-The kinds of cells present and their development were relativelv simple in this

Tests by Tissue Culture Methods on the Nature of Immunity to Transplanted Skin

ABSTRACT The transplantation of skin from one rabbit to another elicits a reaction that conforms in main outline with that of an actively acquired immunity. The experiments described in this paper were designed to test the hypothesis that the regression of such grafts is secured by the action of antibodies demonstrable in vitro. Skin from adult rabbits has therefore been cultivated in the presence of serum and growing mesenchymal tissues derived solely from rabbits heavily and specifically immunized against it. Immune sera and tissues are without effect on the survival, cell-division frequency and migratory activities of explanted skin, and agglutinins for epidermal cell suspensions are not demonstrable in immune sera. With certain stated qualifications, it has therefore been concluded that the occurrence of free antibodies is not a sufficient explanation of the regression of skin homografts in vivo.

The Photodynamic Action of Neutral red on Root Tips of Barley Seedlings. Part I. The Effect on Frequency of Cell Division

The Photodynamic Action of Neutral red on Root Tips of Barley Seedlings. Part I. The Effect on Frequency of Cell Division

Histological Study of the Developing Fruit of the Sour Cherry

1. This paper pictures and discusses the gross development of the fruit of the sour cherry (Prunus cerasus L. var. Montmorency) from 18 days before full bloom to fruit ripening, and the histological changes during the pre-bloom stage, stage I (rapid development for 20 days following full bloom), stage II (retarded development for 16 days), and stage III (rapid development for 21 days to fruit ripening). 2. Three principal tissues compose the ovary wall: inner and outer epidermis, stony pericarp, and fleshy pericarp. The stony pericarp may be divided into an inner and an outer layer, and the fleshy pericarp into an innermost layer of small thin-walled parenchyma, a middle region of large thin-walled parenchyma, and an outer or hypodermal layer of collenchyma. 3. The fleshy and the stony pericarp are derived each from distinct groups of cells which are early separated from one another by characteristic size, shape, and frequency and periodicity of cell division. 4. The inner layer of the stony pericarp is d...