ELECTRON MICROPROBE ANALYSIS OF SILICA IN EPIDERMAL CELLS OF EQUISETUM

Patterns of silica deposition on the outer epidermal cell walls of Equisclum arvense and E. hycmalc var. affine were examined by means of electron microprobe analysis. Silica is deposited primarily in discrete knobs and rosettes on the epidermal surface in E. arvense and essentially in a uniform pattern on and in the entire outer epidermal cell walls of E. hyemale var. affine. This markedly contrasts with patterns of silica deposition in internodal epidermal cells of Avena saliva (Gramineae) where silica is deposited primarily in cell walls and cell lumina, and to a much lesser extent, on the outer epidermal surface. Semi-quantitative analysis with the electron microprobe shows that in intercalary meristematic cells of E. aruense, silicon is not present in any cells, but that in mature epidermal cells above the intercalary meristem it is present in significant quantities. The study thus suggests that silica deposition must be a very rapid process in Equisclum and Avena.     

ELECTRON PROBE MICROANALYSIS OF SILICON DEPOSITION IN THE INFLORESCENCE BRACTS OF THE RICE PLANT (ORYZA SATIVA)

The deposition of silicon in tissues of the inflorescence bracts of rice has been studied with the electron probe microanalyzer. Tissues for analysis were prepared by means of peels, frozen transverse and longitudinal sections, chromations and macerations. The microanalysis shows the heaviest deposition in a layer external to the abaxial (outer) epidermis. The cells of this epidermis are only sparsely silicified, but the’ imprints of these cells are left on the outer silica layer. In the inner tissues of the bracts, silicon deposition is mostly associated with the cell walls.     

Silica deposition in relation to ageing of leaf tissues in Sasa veitchii (Carriere) Rehder (Poaceae: Bambusoideae)

BACKGROUND AND AIMS: Silica deposition is one of the important characteristics of plants in the family Poaceae. There have been many investigations into the distribution, deposition and physiological functions of silica in this family. Two hypotheses on silica deposition have been proposed based on these studies. First, that silica deposition occurs passively as a result of water uptake by plants, and second, that silica deposition is controlled positively by plants. To test these two apparently contradictory hypotheses, silica deposition in relation to the ageing of leaf tissues in Sasa veitchii was investigated. METHODS: Tissues were examined using a light microscope and a scanning electron microscope equipped with an energy dispersive X-ray microanalyser. KEY RESULTS: The deposition process differed depending on cell type. In mesophyll tissue, fusoid cells deposited large amounts of silica depending on leaf age after maturation, while chlorenchyma cells deposited little. In epidermal tissue, comprised of eight cell types, only silica cells deposited large amounts of silica during the leaf's developmental process and none after maturation. Bulliform cells, micro-hairs and prickle hairs deposited silica densely and continuously after leaf maturation. Cork cells, guard cells, long cells and subsidiary cells deposited silica at low levels. CONCLUSIONS: The significance of these observations is discussed in relation to the two hypotheses proposed for silica deposition in Poaceae. The results of the present study clearly indicate that both hypotheses are compatible with each other dependent on cell types.     

TRICHOMES OF CANNABIS SATIVA L. (CANNABACEAE)

The diversity of non-glandular and glandular hairs of Cannabis sativa L. (marihuana) are described by scanning electron microscopy. The non-glandular hairs are of two major types, as distinguished by size differences and locations, and all of them are highly silicified. The presence of silica as well as cystoliths of calcium carbonate help in the identification of marihuana even in its ash residues. X-ray microanalyses of Cannabis hairs are compared with those of Humulus lupulus and Lantana camera, whose hairs have been considered to resemble those of marihuana. Glandular hairs are found to be of two major categories. One group consists of glands whose heads are generally made up of eight cells and the other group whose heads are generally made up of two cells but never more than four cells. All glands of both categories are stalked. Some glands of the first category are massively stalked and these are restricted solely to anthers and bracts of staminate and pistillate plants. The massive stalk is considered to be made up of epidermal and hypodermal cells that have grown in response to some stimulation during anthesis. Fine details of the shoot system of Cannabis, such as cuticular ridges on epidermal cells, warty protuberances on non-glandular hairs, and surface views of glands in developing stages are also reported. Glandular hairs on the bracts of Humulus lupulus resemble those of Cannabis.     

Scanning Electron Microscopy of Silica Deposits in the Culms, Floral Bracts and Awns of Barley (Hordeum sativum Jess.)

Deposits of silica in the culm internodes, floral bracts andawns of Hordeum sativum Jess (cv Deba Abed) have been investigatedusing the scanning electron microscope The deposits were isolatedfrom all organic matter by digestion with nitric and perchloricacids Two basic types of deposits were recognized, lumen andwall silicification, the latter with or without lumen infillings In the culm internodes, lumen deposits are derived from idioblasts(‘hats’), sclerenchyma and xylem vessels In thefloral bracts they are derived from idioblasts (‘hats’and astenform opals), epidermal long cells (dendriform opals),sclerenchyma and xylem vessels The shape of these deposits doesnot generally resemble the outline of the cell itself, but depositsderived from cell walls do closely resemble the infact cell.In the culm, the walls of stomatal cells, trichomes and, largelythe outer tangential walls of mature long epidermal cells, becomesilicified, together with some cork cells In the floral bracts,silica is found in most epidermal cell walls but is confinedto the trichomes, scutiform cells and costal epidermal cellsearly in their development At maturity concentrations of silicaare much higher in the floral bracts and awns than in the culmsand leaves The results are discussed in relation to the pattern of depositionand its possible functions. Hordeum sativum Jess, barley, silica deposits, opals, scanning electron microscopy     

Silica deposition in abaxial epidermis before the opening of leaf blades of Pleioblastus chino (Poaceae, Bambusoideae)

BACKGROUND AND AIMS Silica deposition is one of the important characteristics of the family Poaceae. The distribution, deposition process and physiology of silica in this family have been extensively investigated. Bamboos among members of Poaceae have leaves with a fairly long life span, and the leaves continuously accumulate silica in their tissues throughout their life, not only during the course of leaf opening, but also after opening. It has been revealed that the silica deposition process in relation to ageing of the bamboo leaf after opening differed depending on the cell types comprising the tissues. However, silica deposition has never been examined during the development and maturation periods of bamboo leaves. Hence, to clarify the silica deposition process in a developmental stage of the bamboo leaf, distribution of silica was observed in the abaxial epidermis before the opening of the leaf blades of Pleioblastus chino. METHODS: Abaxial epidermal tissues of leaves were examined using a scanning electron microscope equipped with an energy dispersive X-ray microanalyser. KEY RESULTS: Among seven cell types comprising the abaxial epidermis, three types of cells, guard cells, prickle hairs and silica cells, deposited silica conspicuously, and another four types, cork cells, long cells, micro hairs and subsidiary cells, deposited only a little silica. Among the former group of cell types, silica cells and guard cells deposited silica over their entire surfaces, while prickle hairs deposited silica only in the point-tips. Silica deposition was detected firstly in prickle hairs, and then in silica cells and guard cells. Only silica cells were assumed to deposit silica conspicuously before leaf opening but not conspicuously after opening. CONCLUSIONS: Cell types in leaf epidermis of bamboo are classified into three groups according to the silica deposition pattern. Silica deposition in silica cells may be positive as a part of the physiological activities of leaves.     

Distribution of Silicified Cells in the Leaf Blades of Pleioblastus chino(Franchet et Savatier) Makino (Bambusoideae)

Distribution of silicified cells in the leaf blades of Pleioblastuschino was investigated using a light microscope and a scanningelectron microscope equipped with an energy dispersive X-raymicroanalyser. The most dense accumulation of silica was foundin epidermal tissues. Little silica was deposited in vascularbundles and chlorenchyma, while more was deposited in bundlesheath and fusoid cells. In the epidermis, silica density andfrequency of silicified cells differed depending on cell type,although silica deposition was observed in most cell types.Heavy deposition was found in silica cells, bulliform cells,micro hairs and prickle hairs. Silica cells were the cell typemost frequently silicified (96.9–99.7%) in the adaxialand abaxial epidermis. Silica may be deposited as leaf tissuesage.Copyright 2000 Annals of Botany Company Pleioblastus chino(Franchet et Savatier) Makino, bamboo, silicified cells, leaf blade, epidermis, chlorenchyma, silica, clearing method, freeze-fracturing, freeze-drying, light microscopy, scanning electron microscopy, X-ray microanalysis     

Electron-probe microanalysis of silicon in the epidermis of rice (Oryza sativa L.) internodes

Summary Electron-probe X-ray microanalysis showed that significant amounts of silicon are accumulated in the entire epidermal system of the rice internode except in the stomatal apparatuses. Thus, there is a lack of specific sites for Si deposition from levels just above the base to the tip of the rice internode. In the intercalary meristem region, 1 cm above the base of the internode, point-count data indicate more Si accumulation in the dumb-bell shaped silica cells than in the long epidermal cells. Above this region, Si is accumulated essentially in a uniform pattern in all epidermal cells. Such a pattern for Si accumulation in rice internodes markedly contrasts with that for Avena internodes and may explain, in part, why rice plants have a higher percentage Si (dry weight basis) in their shoots. The adaptive significance of this silicification pattern in rice is discussed.     

Heterogeneity of silica and glycan-epitope distribution in epidermal idioblast cell walls in Adiantum raddianum laminae

Laminae of Adiantum raddianum Presl., a fern belonging to the family Pteridaceae, are characterised by the presence of epidermal fibre-like cells under the vascular bundles. These cells were thought to contain silica bodies, but their thickened walls leave no space for intracellular silica suggesting it may actually be deposited within their walls. Using advanced electron microscopy in conjunction with energy dispersive X-ray microanalysis we showed the presence of silica in the cell walls of the fibre-like idioblasts. However, it was specifically localised to the outer layers of the periclinal wall facing the leaf surface, with the thick secondary wall being devoid of silica. Immunocytochemical experiments were performed to ascertain the respective localisation of silica deposition and glycan polymers. Epitopes characteristic for pectic homogalacturonan and the hemicelluloses xyloglucan and mannan were detected in most epidermal walls, including the silica-rich cell wall layers. The monoclonal antibody, LM6, raised against pectic arabinan, labelled the silica-rich primary wall of the epidermal fibre-like cells and the guard cell walls, which were also shown to contain silica. We hypothesise that the silicified outer wall layers of the epidermal fibre-like cells support the lamina during cell expansion prior to secondary wall formation. This implies that silicification does not impede cell elongation. Although our results suggest that pectic arabinan may be implicated in silica deposition, further detailed analyses are needed to confirm this. The combinatorial approach presented here, which allows correlative screening and in situ localisation of silicon and cell wall polysaccharide distribution, shows great potential for future studies.     

MORPHOGENESIS OF CAPITATE GLANDULAR HAIRS OF CANNABIS SATIVA (CANNABACEAE)

The glandular secretory system in Cannabis sativa L. (marihuana) consists of three types of capitate glandular hairs (termed bulbous, capitate-sessile, and capitate-stalked) distinguishable by their morphology, development, and physiology. These gland types occur together in greatest abundance and developmental complexity on the abaxial surface of bracts which ensheath the developing ovary. Bulbous and capitate-sessile glands are initiated on very young bract primordia and attain maturity during early stages of bract growth. Capitate-stalked glands are initiated later in bract growth and undergo development and maturation on medium, to full sized bracts. Glands are epidermal in origin and derived, with one exception, from a single epidermal initial. The capitate-stalked gland is the exception and is of special interest because it possesses a multicellular stalk secondarily derived from surrounding epidermal and subepidermal cells. Glands differentiate early in development into an upper secretory portion and a subtending auxiliary portion. The secretory portion, depending on gland type, may range from a few cells to a large, flattened multicellular disc of secretory cells. The secretory portion produces a membrane-bound resinous product which caps the secretory cells. Capitate-stalked glands are considered to be of particular evolutionary significance because they may represent a gland type secondarily derived from existing capitate-sessile glands.     

Silica Distribution in the Caryopsis and Inflorescence Bracts of Foxtail Millet [Setaria italica (L.) Beauv.] and its Possible Significance in Carcinogenesis

Silicon deposits in the caryopsis and inflorescence bracts offoxtail millet [Setaria italica (L.) Beauv.] were investigatedusing light microscopy, scanning electron microscopy and electronprobe microanalysis. The samples were obtained from Lin Xian,Henan province, northern China and CSIRO, Australia. High concentrations of silicon were observed in the papillaeon the external surfaces of the inflorescence bracts, and inthe epidermal cells. In the caryopsis silicon was depositedin the aleurone layer. Silicification was heavier in the LinXian samples. The heavy accumulation of silica in the foxtail millet and thepossibility that fragments of plant silica may be implicatedin the aetiology of oesophageal cancer in the Lin Xian regionare discussed. Setaria italica (L.), Beauv, foxtail millet, caryopsis, silica distribution, scanning electron microscopy     

不同色彩珙桐叶片和苞片解剖结构及色素含量比较研究

以生长于同一生境下的粉红珙桐(粉红色叶片、苞片)与普通珙桐(绿色叶片、白色苞片)为试材,对比两种色彩珙桐叶片/苞片解剖结构和色素含量的差异,以揭示珙桐色彩转变的规律。结果显示：(1)两种珙桐叶片均属于异面叶类型,栅栏组织由一层长柱形细胞整齐排列而成,海绵组织排列疏松,部分粉红叶片的上表皮细胞向外凸起,绿叶无此现象;粉红叶片的总厚度及其表皮角质层、栅栏组织和海绵组织厚度都高于绿叶,而表皮较薄。(2)两种珙桐苞片均无栅栏组织和海绵组织的分化,粉红苞片上表皮细胞明显隆起,上表皮角质层增厚,而下表皮变薄。(3)粉红叶片的类黄酮、花色苷含量分别是绿色叶片的1.52倍、3.67倍,两者的光合色素含量无显著差异,但粉红叶片的叶绿素a/b值比绿色叶低很多;粉红苞片花色苷含量显著高于白色苞片,而两者类黄酮含量差异不大。研究表明,花色苷是珙桐叶片和苞片色彩转红的直接因素,类黄酮有助于叶片呈红色;粉红珙桐叶片/苞片的解剖结构发生了一定变化,对光能的利用效率更高,对阴湿环境的适应性增强。     

Function of silica bodies in the epidermal system of rice (Oryza sativa L.): testing the window hypothesis

Silicon has been considered to be important for normal growthand development of the rice plant (Oryza sativa L.). To investigatethe physiological function of deposited silica in rice leaves,the hypothesis that silica bodies in the leaf epidermal systemmight act as a ‘window’ to facilitate the transmissionof light to photosynthetic mesophyll tissue was tested. Thesilica content of leaves increased with supplied silicon andwas closely correlated with the number of silica bodies perunit leaf area in the epidermal system. There was a significantdifference in silica deposition and formation of silica bodiesbetween Si-treated and non-treated leaves; silicon was polymerizedinside the silica cells and bulliform cells of the epidermis,in Si-treated leaves. Although the ‘windows’ wereonly formed in leaves with applied silicon, optical propertiesof leaf transmittance, reflectance and absorptance spectra inSi-treated and non-treated leaves were almost equal. Furthermore,light energy use efficiency and quantum yield of Si-treatedleaves were less than in leaves not containing silica bodies.Thus, silica bodies, at least based on the data, do not functionas windows in rice leaves. Key words: Silicon, window hypothesis, rice, optical property, quantum yield     

Function of silica bodies in the epidermal system of rice (Oryza sativa L.): testing the window hypothesis

Silicon has been considered to be important for normal growth and development of the rice plant (Oryza sativa L.). To investigate the physiological function of deposited silica in rice leaves, the hypothesis that silica bodies in the leaf epidermal system might act as a 'window' to facilitate the transmission of light to photosynthetic mesophyll tissue was tested. The silica content of leaves increased with supplied silicon and was closely correlated with the number of silica bodies per unit leaf area in the epidermal system. There was a significant difference in silica deposition and formation of silica bodies between Si-treated and non-treated leaves; silicon was polymerized inside the silica cells and bulliform cells of the epidermis, in Si-treated leaves. Although the 'windows' were only formed in leaves with applied silicon, optical properties of leaf transmittance, reflectance and absorptance spectra in Si-treated and non-treated leaves were almost equal. Furthermore, light energy use efficiency and quantum yield of Si-treated leaves were less than in leaves not containing silica bodies. Thus, silica bodies, at least based on the data, do not function as windows in rice leaves.     

ELECTRON PROBE ANALYSIS OF SILICON AND OTHER ELEMENTS IN LEAF EPIDERMAL CELLS OF THE RICE PLANT (ORYZA SATIVA L.)

By means of electron probe analysis, the effects of significant amounts of accumulation of silicon on the accumulation of calcium, potassium, magnesium, manganese, phosphorous, iron, and sodium in the silica cells of rice leaves are described. The silica cells of both the surfaces of the leaf blade and leaf sheath were studied. Silicon accumulation in the silica cells appears to decrease the amount of accumulation of potassium on both the surfaces of the leaf blade and sheath. The effect of significant amounts of silicon accumulation on the accumulation of other elements in a particular cell varies in different organs or on different surfaces of the organ of the same plant. Magnesium, manganese, iron, and phosphorus could not be detected in the adaxial epidermis of the leaf sheath and magnesium and iron in the adaxial epidermis of the leaf blade. Manganese, magnesium, and phosphorus were not detected in the abaxial epidermis of the leaf blade nor iron in the abaxial epidermis of the leaf sheath. Sodium was not revealed in either surface of the leaf blade and leaf sheath. Possible mechanisms for the effects of silicon accumulation on the accumulation of these elements in rice leaf epidermal cells are discussed.     

ULTRASTRUCTURE OF A CHAIN-FORMING DIATOM PHAEODACTYLUM TRICORNUTUM1

The ultrastructure of a chain-forming clone of the polymorphic diatom Phaeodactylum tricornutum Bohlin has been studied by scanning and transmission electron microscopy. Both fusiform and tri-radiate cells are capable of forming chains. The cells, lacking any silica shell, are attached to each other at the central region of the theca, leaving the arms free. Neither homogenization nor sonication completely disrupts the chains. The attachment is due to fusion of the cell wall in the central region of the cell during cell wall deposition. This fusion results from failure of the cytoplasmic cleavage furrow to separate the plasma membranes of the two daughter cells sufficiently so that a single wall is deposited instead of two separate walls. Possible explanations for this are discussed.     

DEVELOPMENTAL MORPHOLOGY OF COTTON FLOWERS AND SEED AS SEEN WITH THE SCANNING ELECTRON MICROSCOPE

This report assembles and pictorially presents observations on the timing of relatively uniform and well-defined developmental events in the cotton flower and its component parts. The first floral bud occurs on the 7–9th node approximately 35–40 days postemergence; 20–25 additional days elapse until anthesis. Floral parts are morphologically well defined by two weeks preanthesis. In about 85 % of the flowers the basal, abaxial surface of two of the three bracts contains an outer involucral nectary; occasionally, none, one, or three nectaries are found. The maximum rate of increase in floral bud length occurs during the 24 hrs preceding anthesis. Flower opening occurs at about daylight, although light is not required. Multipored pollen grains germinate in about ½ hr after deposition on the stigmatic hairs. Fertilization is accomplished, for most ovules, by the end of the first day postanthesis. Stomata are abundant, particularly at the chalazal ends of ovules. Fiber initials (epidermal cells of the ovule) begin their elongation phase on the morning of anthesis and are bounded by a thin primary wall. Areas of contrast (spots) observed through the scanning electron microscope are speculated to be organelles “seen through” the relatively amorphous fiber wall, which lacks extensive fibrillar orientation of cellulose. Fiber elongation ceases by about 24–28 days postanthesis, and by 50–70 days postanthesis fibers are mature and exhibit a thickened secondary wall and spiral twisting. Concomitant with the time of fiber maturity, the ovary wall splits and opens along locular suture lines.     

A Developmental Study of Silicification in the Trichomes and Associated Epidermal Structures of the Inflorescence Bracts of the Grass, Phalaris canariensis L

Silicon accumulation is greatest in the abaxial epidermis ofthe inflorescence bracts of Phalaris canariensis L. It occursinitially in glumes 1 week before emergence, at low levels inthe trichomes and long cells, but at high levels in the papillae.Accumulation in long cells remains low throughout, althoughit increases with time. Papillae and prickle hair silicon countsconsiderably exceed values for other epidermal structures. Siliconis also deposited in glume macrohairs before emergence, andat maturity reaches intermediate levels. Little silicon is present in the macrohairs and long cells ofthe abaxial epidermis of the fertile lemma prior to emergence.After emergence, however, silicon is rapidly accumulated inthese structures, and at maturity they have the highest siliconlevels of all the mature bract tissues. Silicon accumulation in the lemma lags behind that of the glumeuntil emergence, when it increases more rapidly, and by maturityexceeds that of the glume in macrohairs and long cells. Thesignificance of the results is discussed in relation to wallthickening, bract anatomy and panicle emergence. Phalaris canariensis, L, canary grass, inflorescence bracts, silicification, trichome, glume, lemma     

Structure and Function of Silica Bodies in the Epidermal System of Grass Shoots

Silica (SiO₂.nH₂O) is deposited in large quantities in the shootsystems of grasses. In the leaf epidermal system, it is incorporatedinto the cell wall matrix, primarily of outer epidermal walls,and within the lumena of some types of epidermal cells. This biogenic silica can be stained specifically with methylred, crystal violet lactone, and silver amine chromate. At theultrastructural level, the silica in lumens of silica cells,bulliform cells and long epidermal cells is made up of rodsabout 2.5 µm in length and 0.4µm in width. Ultimateparticles in the rods range from 1 to 2 nm in diameter. In contrast,silica in the cell wall matrix of trichomes and outer wallsof long epidermal cells is not rod-shaped, but rather, formsroughly spherical masses. Detailed analyses are presented on the frequencies of occurrenceof the different types of epidermal cells that contain silicain the leaves of representative C₃ and C₄ grasses. The C₄ grasseshave higher frequencies of bulliform cell clusters, silica cells,and long epidermal cells, whereas the C₃ grasses have higherfrequencies of trichomes. No correlation was found in the frequencyof occurrence of silica bodies in bulliform cells for C₃ grassesas compared with C₄ grasses. Of all the grasses examined, Coix,Oryza, and Eleusine had the highest densities of such bodies,and some taxa had no silica bodies apparent in their bulliformcells. The idea that silica bodies in bulliform cells and silica cellsmight act as "windows’ and trichomes might function as‘light pipes’ to facilitate light transmission throughthe epidermal system to photosynthetic mesophyll tissue belowwas tested. The experimental data presented do not support eitherof these hypotheses. C₂ and C₄ grasses, biogenic silica, light pipes, window hypothesis, silica staining, silica ultrastructure     

ELECTRON MICROSCOPE STUDIES ON THE ACTIVE ACCUMULATION OF SR++ BY RAT-LIVER MITOCHONDRIA

Electron-opaque granules are deposited in isolated rat-liver mitochondria concomitant with the energy-linked accumulation of Sr⁺⁺ by these organelles. High temperature microincineration (600°C) of thin sections of mitochondria containing different amounts of Sr⁺⁺ shows that a clear qualitative correlation exists between the number of inorganic residues remaining after incineration and the amount of Sr⁺⁺ translocated into the mitochondria. By loading the mitochondria with consecutive pulses of small amounts of Sr⁺⁺ ("multiple-pulse" loading), very early stages of granule formation can be detected; the first detectable deposits are seen closely associated with the cristae. The evidence presented supports the hypothesis that mineral deposition following or during the in vitro accumulation of ions by mitochondria occurs, at least initially, at sites on these membranes and not as nonspecific precipitates in the mitochondrial matrix. The large number of electron-opaque deposits (100 to 200) seen in single thin sections of individual mitochondria having accumulated intermediate levels of Sr⁺⁺ clearly exceeds the number of normal dense granules in rat-liver mitochondria, indicating that the normal matrix granules per se do not constitute sites essential for deposition. At the highest levels of Sr⁺⁺ uptake studied in the multiple-pulse loading experiments, needlelike deposits are seen, a result which suggests that the structural form ("crystallinity") of the mineral deposits may be determined by the rate of accumulation.