Shoot Apices Of Plants Research Articles

Duration of cell cycles in the shoot apex of Chrysanthemum segetum L.

Summary The rate of cell division in the shoot apices of young Chrysanthemum segetum plants is determined by accumulating metaphases after colchicine treatment. On an average, the cells of the lateral zone divide every 48 hours, while those of the axial zone divide three times slower (T = 130 hours). The rib meristem cells have an intermediate cycle length (T = 70 hours). A practically constant duration of mitosis (2.9 to 3.3 hours) and a parallel development of the mitotic index and the proliferation rate show that the mitotic index is a characteristic parameter of the proliferative state in the shoot apex of Chrysanthemum segetum.

Histochemical investigation of dehydrogenases in shoot apices of wheat plants at different ontogenetic stages

The activity and localization of alcohol (AD), lactic (LD), malic (MD), isocitric (ICD) and succinic (SD) dehydrogenase, resp. was histochemically determined in shoot apices of plants in the vegetative condition during transition to flowering and at the reproductive state. The enzymes were determined in freehand sections, as well as in shoot apices incubatedin toto according toNachlaset al. (1958) using Nitro-BT. The characteristic localization of the enzymes depending on the ontogenic stage of the shoot apex is described. Different parts, layers and cell groups of the apex showed differences in enzyme activity. SD could not be detected in shoot apices. The histochemical findings are discussed in relation to former results obtained from a biochemical investigation of respiration in the same material.

Selective histochemical localization of alcohol dehydrogenase in bud primordia cells of wheat shoot apices

During the histochemical investigation of dehydrogenases in the developing shoot apex of wheat plants it was found that the morphologically similar cells of the peripheral meristem may be differentiated according to the differential activity of alcohol dehydrogenase. While the enzyme was not present or exhibited a very small activity only in the tissue of leaf primordia it was highly active in the cells of bud primordia irrespective of the degree of their development and their differential physiological determination.

THE ANATOMY OF THE SHOOT APEX OF ROTALA ROTUNDIFOLIA (ROXB.) KOEHNE (LYTHRACEAE)

SUMMARY The structure of the shoot apex of Rotala rotundifolia is described with special attention to the initiation of leaf and axil bud primordia. A comparison is drawn between the vegetative shoot apex in aquatic and terrestrial plants and the apex of the inflorescence. The histogenesis of the apex is consistent with the tunica corpus hypothesis of Schmidt (1924). The zonation in the apex is clearly defined, easy to delineate, and stable. The number of apical initial cells is low. A quiescent zone has not been observed. All types of leaf are initiated in the second layer of the two-layered tunica, very close to the centre of the apex. Corpus cells do not participate in the formation of the leaves. Buds in leaf-axils are formed by derivatives of corpus-cells surrounded by a two-layered tunica. An axial procambial cylinder, provided with a pith, appears above the entry of the youngest leaf-traces. It is concluded that the three types of apex in Rotala rotundifolia (the vegetative apex in terrestrial and submerged plants and the inflorescence apex) are built up in the same manner.

Ontogenetical and experimental studies of the floral apex of Portulaca grandiflora. 2. Bisection of the meristem in successive stages

Floral apices at the stages of sepals, petals, stamens, upright carpels, and elevated carpels were bisected by microscalpels, and the regeneration of the meristem halves, their grafting together, and the production of new appendages were studied. At the sepal stage the two halves regenerated into twin flowers, producing petals, stamens, and carpels above the cut surfaces which grafted together. Cusick's finding that, for a particular organ to be formed alongside a wound, the incision must be made before organs of this kind have appeared in their normal positions, was supported. At the stage of petals, however, the twin flowers produced petals as the first new appendages above the cut surfaces. At the stage of stamens, the first appendages produced above the cut surfaces were carpels, again supporting Cusick. Sometimes the new carpels so formed constituted separate adjacent whorls on the twin flowers. At both stages of carpels, the rest of the floral apex (receptacle) showed no regeneration except rapidly grafting together. The reunited receptacle was then used as in normal ontogeny, in formation of carpel margins on which ovules would later have been borne. Generally, cells beneath wound surfaces showed few divisions, compared with the vigorous responses of bisected shoot apices of other plants. Grafting, which did not occur in the terminal regions of bisected shoot apices, readily occurred at cut surfaces of halved floral apices, and this latter response became progressively more rapid in later stages of floral ontogeny. This grafting, along with progressive loss of potential for production of new lateral appendages, are interpreted as manifestations of aging in this determinate meristem, and support the hypothesis that differentiation is concomitant with loss in capacity for growth.

Directional Cell Division in Shoot Apices

Comparative cytohistological studies were made of shoot tips of Equisetum hyemale, Picea abies, and Prunus Persica, as examples from three major taxonomic groups of plants: lower vascular plants, gymnosperms, and angiosperms. The purpose of this study was to find out more specifically what factors determine the formation of apical histogenic layers. Obviously the plane of mitotic division in the cells at the upper surface of shoot apices determines the presence or absence of apical cell-layer formation. The hypothesis proposed is that the plane of mitotic division-positioning of metaphase chromosome plates-in cells in the surface region in shoot apices is determined by: 1) size of cells relative to shape and size of apical dome; 2) size of cells and space in cells relative to size of their nuclei and the freedom of their nuclei from wall pressure; and 3) location of cells and their shape and availability of space across a particular plane in cells in which metaphase plates can be accommodated. The hypothesis would explain the general predominance, or presence, of histogenic layers in shoot apices of angiosperms and relative paucity or lack of them in shoot apices of gymnosperms and lower plants.

Development of Vegetative and Reproductive Apices of Cauliflower, Brassica oleraceae var. Botrytis

The development of shoot apices of cauliflower plants grown under inductive and non-inductive temperatures for flowering was studied. Two cultivars were used, Snowball M and February-Early-March. Neither cultivar flowers without a period of growth at 42 F. February-Early-March requires a cold treatment for curd formation. During the first 5 weeks of growth, shoot apices of vegetative Snowball M plants have five distinct zones: a mantle, central-mother cells, cambial-like cells, peripheral cells, and rib meristem. Curd initiation is marked by a wide shoot apex, lack of cambial-like cell zone, and the initiation of bracts and branch primordia. Under non-inductive conditions for flowering, apices of February-Early-March are similar in their zonation to those of Snowball M before curd initiation. During growth at 42 F, apices of both cultivars have large nuclei and nucleoli and dense cytoplasm. Curd initiation occurs during or following the cold treatment in Snowball M, while in February-Early-...

THE EFFECTS ON CHRONIC GAMMA RADIATION ON THE INTERNAL APICAL CONFIGURATIONS OF THE VEGETATIVE SHOOT APEX OF COLEUS BLUMEI

Clonal plants of a bushy variety ‘Trailing Queen’ of Coleus blumei Benth. were exposed to 600–700 R per day for 28 days. Shoot apices of control and irradiated plants were studied microscopically. The normal vegetative shoot apex has two tunica layers and a corpus which is partly layered and partly composed of randomly divided cells. Five cytohistological zones were observed, including a cup‐shaped zone, imposed upon the tunica‐corpus relationships. Response to gamma radiation resulted in abnormal internal apical configurations. All irradiated shoots was found to have the same internal configurations. Only a single tunica layer broken by occasional periclinal divisions was observed. The cytohistological organization of irradiated apices was different from that seen in the normal shoot tips in that two zones were found. Evidence of a radiosensitivity gradient within the vegetative shoot apex was also observed. The possible significance of the results is discussed.

The Effects on Chronic Gamma Radiation on the Internal Configurations of the Vegetative Shoot Apex of Coleus blumei

Clonal plants of a bushy variety ‘Trailing Queen’ of Coleus blumei Benth. were exposed to 600–700 R per day for 28 days. Shoot apices of control and irradiated plants were studied microscopically. The normal vegetative shoot apex has two tunica layers and a corpus which is partly layered and partly composed of randomly divided cells. Five cytohistological zones were observed, including a cup-shaped zone, imposed upon the tunica-corpus relationships. Response to gamma radiation resulted in abnormal internal apical configurations. All irradiated shoots was found to have the same internal configurations. Only a single tunica layer broken by occasional periclinal divisions was observed. The cytohistological organization of irradiated apices was different from that seen in the normal shoot tips in that two zones were found. Evidence of a radiosensitivity gradient within the vegetative shoot apex was also observed. The possible significance of the results is discussed.

The Relative Biological Efficiency of Gamma Rays and Fission Neutrons in Plant Species with Different Nuclear and Chromosome Volumes

Young seedlings of five plant species (Vicia faba, Pisum sativum, Helianthus annuus, Raphanus sativus, Arabidopsis thaliana) with widely different nuclear and interphase chromosome volumes (ICV) were acutely irradiated with various doses of60 Co gamma rays and fission neutrons. Meristematic shoot apices of control plants were fixed at the time of irradiation, and interphase nuclear and chromosome volumes were calculated from measurements of nuclear diameters. The relation between nuclear or chromosome volume and radiosensitivity as well as the possible influence of differences in these volumes on RBE has been studied. Radiation injury was evaluated on the basis of plant survival, plant dry weight, plant height, and pollen abortion. Dose-effect curves were obtained from the two kinds of radiations; the doses necessary to produce a 50% effect were calculated for each species and each end point used. The doses required for a 50% effect were highest for survival, lowest (and about the same) for dry weight and...

HISTOCHEMICAL CHANGES IN THE SHOOT TIP OF CAULIFLOWER DURING FLORAL INDUCTION

Cauliflower plants were induced to flower after being grown at 42 °F for varying periods of time, depending on the cultivar. Some of the histochemical changes in the shoot apex at the beginning of, during, and after floral induction were studied. During floral induction there is about a 20-fold increase in the volume of nucleoli and about a 3-fold increase in volume of nuclei. Apices of vegetative plants stained with bromophenol blue at pH 2.3, show small and dense nucleoli, dense and granular nuclei, and a small amount of weakly staining cytoplasm. In contrast, cells of apices of induced plants stained with bromophenol blue at pH 2.3, show large and dense nucleoli, large and weakly staining nuclei; however, these cells contain more and denser cytoplasm. Sections of vegetative and induced apices stained with alkaline fast green stained differently from those stained with bromophenol blue. Nucleoli did not stain and cytoplasm stained faintly with fast green while chromosomes stained strongly. Deoxyribonucleic acid (DNA) content of vegetative and induced apices are similar. Shoot apices of vegetative plants contained little or no starch. However, shoot apices of plants grown at 42 °F accumulate large amounts of starch. Floral primordia which develop into functional flowers are glutted with starch, while floral primordia which abort are void of starch.

Inflorescence Initiation in Lolium Temulentum L. XI. Early Increases in the Incorporation of 32p and 35s by Shoot Apices During Induction

There is an increase in the incorporation of 35S, presumably into protein, as well as an increased incorporation of 32p into nucleic acids, in shoot apices of Lolium temulentum plants on the morning after their exposure to 1 long day.

Inflorescence Initiation In Lolium Temulentum l. VIII. Histochemical Changes At the Shoot Apex During Induction

Shoot apices of Lotium temulentum plants exposed to 1 long day were harvested at the beginning of the long day, and on each of the five following days. Longitudinal sections were stained for DNA (Feulgen), DNA and RNA (methyl greenpyronin or acridine orange fluorescence), or basic nuclear proteins (ammoniacal silver nitrate, fast green, or bromophenol blue, with or without acetylation or deamination).

The anatomy of the shoot apex ofHyoscyamus niger L. reversed from the generative to the vegetative state

A study was made of the anatomical structure of the shoot apices ofHyoscyamus niger L. in plants which were transferred from a long-day to a short-day regime after the initiation of the inflorescence. After a certain time these plants are reverted to the vegetative stage with the inhibition of the development of further flower buds and the renewed production of rosette leaves. The inflorescence apex consisted of a few superficial layers of cells and a corpus composed of slightly elongated cells. The anatomical structure of the apices which were reverted into the vegetative state resembled that of shoot apices in the intermediate stage. The apex had several layers of small cells, under which there was a group of small but irregularly arranged cells which passed into the rib meristem.The shoot apices of plants transferred from a long to a short-day regime at different time intervals after fulfilling the requirements of minimal photoperiodic induction thus, on the short day, display morphological and anatomical characteristics of various degrees of transition from generative to vegetative stage.

EXPERIMENTAL CONTROL OF THE SHOOT SYSTEM IN SPORELINGS OF PTERIDIUM AQUILINUM

The shoot system of Pteridium develops from a simple, upright sporeling type through a rhizomatous leaf‐bearing form, into a complex system with rapidly growing, leafless long shoots and slowly growing, leafy lateral branches or short shoots. Transitional stages axe available in sporeling material and ontogeny may be controlled by specific carbohydrate levels. At concentrations of sucrose below 2% a rhizomatous sporeling plant may be maintained indefinitely in the leaf‐bearing state. At 2–8% sucrose, the short shoot habit becomes established, and at 4–8% it may be reliably stabilized. If concentrations up to 5 mg/liter of kinetin are added to cultures of intact plants or to excised short and long shoot apices of plants, the long shoots expand slowly into determined (no further growth possible even on transfer back to basal medium) club‐shaped tips. The short shoot apices, by contrast, quickly proliferate into callus‐like masses and will re‐form organized meristems over the entire lobulate surface on transfer to medium lacking kinetin. The morphogenetic significance of these findings is discussed.

Experimental Control of the Shoot System in Sporelings of Pteridium Aquilinum

The shoot system of Pteridium develops from a simple, upright sporeling type through a rhizomatous leaf-bearing form, into a complex system with rapidly growing, leafless long shoots and slowly growing, leafy lateral branches or short shoots. Transitional stages axe available in sporeling material and ontogeny may be controlled by specific carbohydrate levels. At concentrations of sucrose below 2% a rhizomatous sporeling plant may be maintained indefinitely in the leaf-bearing state. At 2–8% sucrose, the short shoot habit becomes established, and at 4–8% it may be reliably stabilized. If concentrations up to 5 mg/liter of kinetin are added to cultures of intact plants or to excised short and long shoot apices of plants, the long shoots expand slowly into determined (no further growth possible even on transfer back to basal medium) club-shaped tips. The short shoot apices, by contrast, quickly proliferate into callus-like masses and will re-form organized meristems over the entire lobulate surface on transfer to medium lacking kinetin. The morphogenetic significance of these findings is discussed.

On the Organization and Reactivity of the Shoot Apex in Vascular Plants

On the Organization and Reactivity of the Shoot Apex in Vascular Plants

The Distribution of C14 in the Root and Shoot Apices of Young Corn Plants

Concentration of P32 in the meristematic regions of plants has been reported by a number of investigators (3, 5, 6). Rabideau and Burr (5) have given evidence for a gradient in concentration of C13-labeled compounds in the stem tips of bean plants. Belkengren (2) showed rapid movement of carbon-13-labeled materials to bean root tips after exposure of the leaves to C1302 and light. Gustafsson et al. (4) demonstrated accumulation of P32 in the meristematic regions of barley roots. These findings and other considerations have emphasized the desirability of having more information concerning the movement of carbon from leaf-fed carbon dioxide into the meristematic regions of both shoots and roots. In relation to many questions pertaining to growth and development it would be desirable to have information not only with respect to the concentration of carbon in meristematic regions but also with respect to the incorporation of labeled carbon into specific compounds and the distribution of these compounds in the growing regions. The present study was designed to yield information on the concentration of C14 in meristematic regions, the nature of the C14-labeled fractions, and the distribution of these fractions in root and shoot apices of young corn plants. Seedlings of an inbred line of corn, University of Texas number 859, were grown in sand in a greenhouse until they were three to five inches tall (8 to 10 days). They were then transferred to a black lucite disk which served as a plant holder (fig. 1). This holder was perforated with 15 holes in which two-inch lengths of glass tubing were cemented to serve as plant supports. The plants were held in these glass tube supports with a cotton plug in the lower part of the tube. The holder was placed over a desiccator bottom so that the roots of the seedlings dipped into a Shive nutrient solution. This solution was aerated continuously and black cloth was tied around the desiccator as a light screen. The plants were grown in this container for five days. At the end of the fifth day the plants were sealed in the glass tube holders by pouring melted beeswax on top of each cotton plug. When poured at 50? C, this wax caused no detectable damage to the plants. A bell jar of 10 liters volume was placed over the leaves of the plants and sealed to the lucite plant holder with grease. It was held tightly against the lucite disk with several steel springs.