Silicification of bamboo (Phyllostachys heterocycla Mitf.) root and leaf

Bamboo is a silicon accumulating plant. In leaves, the major place of silicon (Si) deposition is the epidermis, with the highest concentration of Si in silica cells. In bamboo roots, the deposition of Si is found only in endodermal cell walls. The silicification of leaves and roots was examined in the economically important bamboo plant Phyllostachys heterocycla, using an environmental scanning electron microscope coupled with X-ray microanalysis, as well as gravimetric quantification. The content of Si on a dry weight basis measured by gravimetric quantification was 7.6% in leaves and 2.4% in roots, respectively. Moreover, quantification of EDX data showed high Si impregnation of the inner tangential endodermal walls. Si content in this part of the root endodermal cell walls was even higher than that in the outer leaf epidermal walls, where conspicuous deposition of Si often occurs in grass plants.     

Silicification in sorghum (Sorghum bicolor) cultivars with different drought tolerance

Sorghum belongs to a group of economically important, silicon accumulating plants. X-ray microanalysis coupled with environmental scanning electron microscopy (ESEM) of fresh root endodermal and leaf epidermal samples confirms histological and cultivar specificity of silicification. In sorghum roots, silicon is accumulated mostly in endodermal cells. Specialized silica aggregates are formed predominantly in a single row in the form of wall outgrowths on the inner tangential endodermal walls. The density of silica aggregates per square mm of inner tangential endodermal cell wall is around 2700 and there is no significant difference in the cultivars with different content of silicon in roots. In the leaf epidermis, silicon deposits were present in the outer walls of all cells, with the highest concentration in specialized idioblasts termed 'silica cells'. These cells are dumb-bell shaped in sorghum. In both the root endodermis and leaf epidermis, silicification was higher in a drought tolerant cultivar Gadambalia compared with drought sensitive cultivar Tabat. Silicon content per dry mass was higher in leaves than in roots in both cultivars. The values for cv. Gadambalia in roots and leaves are 3.5 and 4.1% Si, respectively, and for cv. Tabat 2.2 and 3.3%. However, based on X-ray microanalysis the amount of Si deposited in endodermal cell walls in drought tolerant cultivar (unlike the drought susceptible cultivar) is higher than that deposited in the leaf epidermis. The high root endodermal silicification might be related to a higher drought resistance.     

Cellular re-distribution of flavin-containing polyamine oxidase in differentiating root and mesocotyl of <Emphasis Type="Italic">Zea mays</Emphasis> L. seedlings

Plant polyamine oxidases (PAOs; EC 1.5.3.11) are hydrogen peroxide-producing enzymes supposedly involved in cell-wall differentiation processes and defence responses. Maize (Zea mays L.) PAO (MPAO) is a 53 kDa secretory glycoprotein, abundant in primary and secondary cell walls of several tissues. Using biochemical, histochemical, ultrastructural and immunocytochemical techniques, the distribution and sub-cellular compartmentalisation of MPAO in the primary root and mesocotyl of seedlings at different maturation stages or after growth under varying light conditions were analysed. In apical root tissues, MPAO immunoreactivity was mainly detected in the cytoplasmic compartment, while a lower immunoreactivity was observed in the cell walls. In the more mature, basal part of the root, intense immunogold labelling was found in the primary and secondary walls of protoxylem precursors and vessels, while endodermal cells and living metaxylem precursors were immunopositive both in their walls and in their thin cytoplasmic compartments. A re-distribution of MPAO protein from the cytoplasm toward the primary and secondary walls was also recognised when immunoreactivity of basal root tissues from 3-day-old seedlings was compared with that detected in 11-day-old tissues. Accordingly, biochemical analyses revealed MPAO entrapment in the extracellular matrix of mature tissues. In the mesocotyl, an enrichment of MPAO immunolabelling in the cell wall of protoxylem, metaxylem and epidermal tissues, as a function of light exposure, was observed. Taken together, these data support the hypothesised role of PAOs in cell-wall maturation. Moreover, the relevant intraprotoplasmic MPAO localisation observed mainly in differentiating root tissues suggests an additional role in intracellular production of hydrogen peroxide.Alessandra Cona and Sandra Moreno have contributed equally to this paper.     

X-ray Microanalysis of the Seminal Root of Sorghum bicolor with Particular Reference to Silicon

Sorghum bicolor (L.) Moench. cv. P508.GB plants were grown inwater culture for 1 week, when the seminal roots were harvestedand sampled at five positions starting from the base: 0.0, 0.25,0.50 and 0.75 of the axis length, and a sub-apical position,11 mm behind the tip. Mineral distribution in bulk frozen rootsegments was investigated using SEM and X-ray microanalysis.The elements detected were potassium, chlorine, sulphur, sodium,phosphorus, calcium and silicon. The first four occurred inall root zones. Phosphorus was ubiquitous, but appeared to accumulatein the pericycle protoplasm. Calcium and silicon exhibited themost variation along the seminal axis. Calcium was present inall tissues at the base, but decreased acropetally, being detectedin only the outer cortical and epidermal walls of the subapicalzone. Silicon was present at low levels in protoplasts and wallsof most root tissues, and accumulated in the endodermal protoplastand walls. Deposition in walls is initiated coincident withthe earliest stages of secondary wall thickening. Silicon contentof the inner tangential wall of the endodermis exhibits a decreasingacropetal gradient along the axis length. It is absent frommost cell walls of the sub-apical zone. Silicon pathways inthe root, and silica aggregate formation in relation to thesurrounding ionic environment, are discussed. Sorghum bicolor (L). Moench, seminal root, cryostage, SEM, X-ray microanalysis, ion localization, silicon, endodermis     

Silicon mitigates the Cd toxicity in maize in relation to cadmium translocation, cell distribution, antioxidant enzymes stimulation and enhanced endodermal apoplasmic barrier development

The objective of this study was to assess the effect of different Cd and Si concentrations on the maize plants. The following Cd and/or Si treatments were used: 5 Cd; 10 Cd; 100 Cd; 5 Cd + 0.08 Si; 10 Cd + 0.08 Si; 100 Cd + 5 Si treatments (Cd concentration in μM, Si concentration in mM). The plant growth, photosynthetic pigments content, antioxidant enzymes activities (POX, SOD, CAT), Cd and Si accumulation, translocation and cell wall deposition of the maize plants was observed. Changes in the endodermal cell walls development and late metaxylem elements lignification due to Cd and/or Si treatment were also evaluated. The negative effect of Cd (5 and 10 μM) on the growth parameters was alleviated by Si at 0.08 mM. The positive effect of Si was not observed at higher Cd and Si concentrations. This indicates that the alleviating effect of Si on Cd toxicity depends on the Cd and Si concentrations. Plants responded to Cd toxicity by an increase of antioxidant enzyme activity. Silicon addition in Cd + Si treatment stimulated an increase in the activity of antioxidant enzymes in comparison with the Cd treatment. Chlorophyll and carotenoid content in the Cd treated plants was not significantly affected by Si. The young maize plants retained much more Cd in their roots as they translocated into the shoots. 5 Cd + 0.08 Si and 10 Cd + 0.08 Si treatments correlated with an increase in Cd concentration in the roots and shoots, and in the cell walls. Silicon caused a slight decrease of the Cd translocation into the shoots in 5 Cd + 0.08 Si and 10 Cd + 0.08 Si treatments. Negative correlation between the root Cd cell wall deposition and Cd translocation was observed. Cadmium and/or Si altered root anatomy. Cadmium enhanced suberin lamellae development and late metaxylem lignification; silicon in Cd + Si treatments accelerated suberin lamellae deposition and enhanced the tertiary endodermal cell walls formation in comparison with Cd treatments. Negative correlation between the endodermal cell walls development and Cd translocation was observed.     

Silicon-induced changes in viscoelastic properties of sorghum root cell walls

Silicon is deposited in the endodermal tissue in sorghum (Sorghum bicolor L. Moench) roots. Its deposition is thought to protect vascular tissues in the stele against invasion by parasites and drying soil via hardening of endodermal cells. We studied the silicon-induced changes in mechanical properties of cell walls to clarify the role of silicon in sorghum root. Sorghum seedlings were grown in nutrient solution with or without silicon. The mechanical properties of cell walls were measured in three separated root zones: basal, apical and subapical. Silicon treatment decreased cell-wall extensibility in the basal zone of isolated stele tissues covered by endodermal inner tangential walls. The silicon-induced hardening of cell walls was also measured with increases in elastic moduli (E) and viscosity coefficients (eta). These results provided new evidence that silicon deposition might protect the stele as a mechanical barrier by hardening the cell walls of stele and endodermal tissues. In contrast to the basal zone, silicon treatment increased cell-wall extensibility in the apical and subapical zones with concomitant decrease in E and eta. Simultaneously, silicon promoted root elongation. When root elongation is promoted by silicon, one of the causal factors maybe the silicon-enhanced extensibility of cell walls in the growing zone.     

应用电子探针对植物根际和根内营养元素微区分布的探讨

用电子探针可检测出玉米、大豆根际和根内含有Na,Mg,Al,Si,P,S,Cl,K,Ca,Ti,Fe,Cu和Zn 13种元素。这些元素在根际土壤、粘液层和根组织内的含量分布有一定的规律性。除Si,Al,Ca,Fe在根际土壤中峰值较高外,Ti仅在土壤中达到可检测量;S,Fe和Zn富集在粘液层,Mg,P,Cl只在根组织内才有较明显的峰。这些规律可作为区分根—土界面的参考指标。K含量在根内明显高于根际土壤,并由表皮层到中柱径向增加;Ca则与K不同,且受植物种类的影响。     

The effect of aluminium on the distribution of calcium,magnesium and phosphorus in mycorrhizal and non-mycorrhizal seedlings of Eucalyptus rudis: a cryo-microanalytical study

The distribution of Al, Ca, Mg and P in the lateral roots and leaves of mycorrhizal and non-mycorrhizal seedlings of Eucalyptus rudis grown with and without Al was analysed using energy-dispersive X-ray microanalysis on a cryo-scanning electron microscope. Al accumulated in all tissues of nonmycorrhizal plants: the endodermis was not a barrier to the translocation of Al. In mycorrhizal roots, Al was concentrated within the sheath. The presence of Al reduced the levels of Ca and Mg in both mycorrhizal and non-mycorrhizal roots and shoots in comparison with control plants. The presence of mycorrhizas increased the levels of Ca and Mg in plants grown with Al in comparison with non-inoculated plants, although there was no evidence that mycorrhizas increased the levels of P in plants grown in Al-amended soils. P levels were higher in the mycorrhizal sheath of plants grown with Al than the controls.     

Response of understorey vegetation and Scots pine root systems to fertilization at multiple deficiency stress

The stump and root systems of Scots pine (Pinus sylvestris L.) and field-layer vegetation were sampled before and three growing seasons after drainage and fertilization of a low-shrub pine bog in SE Norway. Although the understorey vegetation roots responded significantly to nutrient application with higher concentrations of Ca and P, root biomass weights did not change. The fine and small pine roots responded with higher N, Ca, P and S concentrations, while those of Mn and Zn were significantly reduced. The NPK-application resulted in significantly higher pine root biomass. Relative to the total stores in the root zone the amounts of most elements in roots shifted to higher ratios at NPK-application. High figures for K, B and Mn indicate tight biochemical cycles of these elements. Compared to totals in above and below ground biomass, major parts of Fe and Pb were held by the roots. In contrast the field layer roots kept a very small per cent of total K, while the pine roots were low in Mn. The understorey vegetation was primarily restricted by P-deficiency, while the pine trees were also restricted by low supply of N. The field and the tree layer species seem to differ with respect to required nutrient concentrations in the root zone. These characteristics are important for direction and extent of successional changes after fertilization in low-shrub pine bog ecosystems.     

Vascular tissue-specific gene expression of xylem sap glycine-rich proteins in root and their localization in the walls of metaxylem vessels in cucumber

Root-specific cDNAs of glycine-rich protein (cucumber root glycine rich protein-1 and -2; CRGRP-1 and CRGRP-2) were cloned previously by use of an antiserum raised against whole xylem sap of Cucumis sativus. The accumulation of the corresponding mRNA at high levels was detected in the root-hair zone of cucumber tap root [Sakuta et al. (1998) Plant Cell Physiol. 39: 1330]. The RNA gel blot analysis with the CRGRP-1- and -2-specific probes revealed that the CRGRP genes expressed only in root but not at all in aboveground organs. When the localization of these mRNAs were examined by in situ hybridization, CRGRP mRNAs were found only in the parenchyma cells in the central cylinder of young lateral roots and it was most abundant in the cells that surrounded xylem vessels in the root-hair zone of the tap root. In immunoblotting of xylem sap collected from cucumber stem with an antiserum raised against CRGRP-1 that had been produced in an E. coli expression system, the antibodies, which did not cross-react with GRP1.8 of kidney bean, reacted with two proteins, whose mobilities corresponded to those of proteins deduced from the CRGRP-1 and -2 cDNAs. Immunohistochemical staining revealed that the CRGRPs accumulated specifically in the lignified walls of metaxylem vessels in the root, stem and leaf and in the lignified cell walls of perivascular fibers in cucumber stems. Immunostaining was also detected in the walls of metaxylem vessels and in the cell walls of adjacent sclerenchyma in the hypocotyl of kidney bean. These data clearly indicate that the novel glycine-rich proteins were produced in the vascular tissue of the root, transported systemically over a long distance via the xylem sap and immobilized in the walls of metaxylem vessels and sclerechyma cells in aboveground organs.     

Cell Wall Thickening of the Xylem Tracheary Elements in Different Zones of the Adventitious Root of Allium cepa L.

Cell wall thickness of the xylem tracheary elements was measuredin the proto- and metaxylem of the Allium cepa L. adventitiousroot. Measurements were taken in root fragments of known age(1, 3, 5, 7 and 9 d) located in either the basal or medio-apicalzone. Tracheary elements in the protoxylem matured within ashorter period of time than those in the metaxylem. Final cellwall thickness was greater in metaxylem than in protoxylem components.The cell wall thickening in the tracheary elements in both proto-and metaxylem was more rapid in the basal zone of the root thanin the medio-apical zone. Additionally, cell walls of the maturetracheary elements were thicker in the basal zone than in areasfurther from the bulb. Allium cepa, onion, root, cell wall, xylem maturation     

星星草营养器官适应盐胁迫的结构特征

采用0．6％Na2CO3胁迫处理星星草[Puccinellia tenuiflora（Turcz．）Scribn．et Merr．]幼苗,光镜和电镜观察其根和叶的显微和超微结构。结果表明,星星草根的表皮向外突出形成密集的根毛;外皮层由1～2层细胞组成,排列较紧密;中皮层薄壁细胞排列疏松,形成发达的通气组织;内皮层呈典型的五面加厚;中柱鞘排列紧密,其壁加厚;初生木质部与初生韧皮部相间排列,初生木质部为5～7原型,中央为后生木质部导管,无髓存在。叶的表皮有表皮毛和丰富的蜡质层;叶上表皮泡状细胞数目较少,且深陷;气孔下陷,其下有较大的气室;叶脉有大、中、小3种维管束,大、中型维管束为C3型,小型维管束为C4型。星星草可能是介于C3和C4植物之间的类型,具有耐盐碱及耐干旱特征。     

Vessels in Nelumbo (Nelumbonaceae)

Vessels have been previously reported in the roots (but not rhizomes) of Nelumbo on the basis of light microscopy. We have reinvestigated vessel occurrence in Nelumbo by means of scanning electron microscopy (SEM). On the basis of these studies, vessels are characteristic of root metaxylem. Pores in primary walls of pits of end walls of these vessels are various in size, but feature incomplete lysis of pit membranes, often with residual webs or threads of primary wall material, much as in vessels of primitive woody dicotyledons. In addition, we newly report occurrence of vessels in metaxylem of rhizomes; pores in these vessels are smaller and more confined than in those of roots. The present study offers not only data of possible use in determining the phylogenetic position of Nelumbonaceae, but also contributes evidence that vessel origin in Nelumbonaceae relates to habit and ecology. We conclude that organographic distribution of vessels in Nelumbo follows the patterns seen in monocotyledons, which, like Nymphaeaceae and other aquatics, have sympodial architecture.     

SILICON IN THE ROOTS OF HIGHER PLANTS

Silicon (Si) distribution in the roots of Sorghastrum nutans (L.) Nash and Sorghum bicolor (L.) Moench. was investigated by means of the electron-probe microanalyzer and scanning electron microscope. In both species, Si was confined to the inner tangential wall of the tertiary-phase endodermal cells in the form of nodular silica aggregates of similar morphology and X-ray intensity. The results are compared to those for six closely related genera, as well as to studies of Si in the roots of species of other tribes of the family Poaceae. The various types of root deposits occurring in the family are described, and their relationships discussed. It is concluded that the type of Si distribution exhibited is determined largely by the phylogenetic status of the genus, rather than by the basic pattern of root anatomy.     

X-ray microanalytical studies of mineral localization in the needles of white pine (Pinus strobus L.)

Eastern white pine (Pinus strobus L.) shoots from mature trees were collected from two sites of contrasting soil pH: the Glendon campus of York University in Toronto, Ontario (pH 6.7 at 40 cm); and Muskoka near Huntsville, Ontario (pH 4.2 at 40 cm). Needles of ages 1-3 years were removed from the shoots, and the percentage of ash and silica was determined for all ages. Other needles were frozen in liquid nitrogen and kept in a cryo-biological storage system before x-ray microanalysis. Percentages of ash and silica were higher in the needles from Muskoka. Ash and silica increased with needle age for trees from the Muskoka site, but less so at the Toronto site. Of the 13 elements (Na, Mg, Al, Si, P, S, Cl, K, Ca, Mn, Fe, Cu and Zn) detected by microanalysis, Mn, Fe, Cu and Zn were detected in small amounts in the epidermis, endodermis and transfusion tissue (the layer of tracheids and parenchyma immediately surrounding the vascular bundles), and K, P, S and Cl were almost ubiquitous in distribution. Sodium was occasionally detected in the transfusion tissue, and magnesium was concentrated in the endodermal cells. The epidermal walls, transfusion tissue and endodermis were major sites of calcium localization. Silicon was concentrated in the extreme tips of the needles in all tissues, but particularly in the transfusion tissue, and more so in the Muskoka samples. Microanalysis revealed a higher Al content in the Muskoka needles, that Al was concentrated in the needle tips and that the transfusion tissues were major sites of accumulation.     

OBSERVATIONS ON THE ROOT ANATOMY OF RICE (ORYZA SATIVA L.)

Rice plants were grown hydroponically and roots were prepared for light and electron microscopy using standard techniques. The roots are bounded by an epidermis, exodermis, and fibrous layer. The exodermis has a suberin lamella along its inner tangential wall. The fibrous layer is composed of thick-walled lignified cells with little pitting. The cortical parenchyma is compact when young, but expands and separates to form a zone of cell walls and air spaces in a spoked arrangement. Supporting columns of living parenchyma cells are occasionally present, particularly near lateral roots. The endodermis is typical for grasses with Casparian strips, suberin lamellae, and tertiary state walls with numerous pits. The pericycle and pith become sclerified. Protoxylem elements alternate with protophloem in the young root; later, early metaxylem, late metaxylem, and metaphloem proliferate. The exodermis, fibrous layer, lacunate cortex, and endodermis appear to present a formidable barrier to radial ion movement in the mature portions of the root.     

Scanning Electron Microscopical Observation and X-ray Microanalysis of Erysiphe pisi DC on Infected Leaves of Pea (Pisum sativum L)

Observations on scanning electron microscope (SEM) and low vacuum scanning electron microscope (LVSEM) of Erysiphe pisi in infected leaves of pea (Pisum sativum). are reported together with data from X-ray micro-analysis. Morphology of ungerminated and germinated conidia was observed and LVSEM revealed halo formation around the penetration peg of the pathogen. X-ray microanalysis of the composition of halo showed the accumulation of Si and P. Presence of S. Mg, Cl, K and Ca was also discerned. Deposition of Si in the halo and profuse growth of the pathogen indicate that Si deposition is not an essential signal for inducing resistance in the host. LVSEM appears to be a suitable and rapid method to study the morphology as well as halo formation in E. pisi. X-ray microanalysis and LVSEM studies of E. pisi are reported for the first time.     

Silicon Deposition in the Roots, Culm and Leaf of Phalaris canariensis L

Silicon deposition in the roots, culm and leaf of canary grass(Phalaris canariensis L.) was investigated using light microscopy,scanning electron microscopy and electron probe microanalysis. In adventitious roots grown in solution silicon was concentratedin four endodermal walls. Silicon was not detected in the endodermisof aerial adventitious roots, but was present in the epidermisand outer cortical cell layers. Silicon deposition in the culm mainly took place in the epidermis,and particularly in epidermal papillae. The silica deposition pattern in the leaf was typical of thesub-group Festucoideae. The leaf blade showed deposits in costalprickle hairs and wavy rods, but few intercostal deposits. Inthe ligule deposition was confined to isolated groups of pricklehairs on the abaxial surface. The major sites of silica depositionin the leaf sheath were the stomatal subsidiary cells, papillaeand intercostal idioblasts. Prickle hairs were much less commonin the sheath than the blade, and costal wavy rods appearedto be absent in the sheath. Phalaris canariensis L., canary grass, silicification, root, culm, leaf, electron probe microanalysis     

Water in aerenchyma spaces in roots. A fast diffusion path for solutes

During a study of the diffusivity of sulphorhodamine G in the cortical apoplast of maize roots widely discrepant rates were found between different samples. In roots which had developed large aerenchyma spaces, the diffusion in some regions was very fast, indistinguishable from the rate in water. In other regions the rate was as much as 100 times slower. Examination of frozen intact roots with the cryo-scanning electron microscope showed the presence of liquid filling some of the aerenchyma spaces, while other spaces of the same root contained air. X-ray microanalysis of the liquid (for oxygen) showed that the liquid was water with few detectable ions. Similar liquid was present in small intercellular spaces within the spoke-like radial files of cells between the large spaces, or between remnants of collapsed cell walls at the edges of the large spaces. It is proposed that regions of roots with high diffusivity are those in which some of the aerenchyma spaces are filled with water. In seeking the origin of this liquid, the progress of aerenchyma formation could be followed in the frozen tissues. The first change observed in a group of contiguous cells was a loss of vacuolar solutes and of cell turgor. Next the walls broke apart and collapsed back onto the surrounding turgid cells leaving a volume of ion-poor liquid. The liquid was probably not that found in some aerenchyma spaces of the mature roots, because the final stage of space formation was a loss of the liquid, leaving an air filled cavity surrounded by a composite lining formed from the collapsed walls of the broken cells. It is likely that the liquid in the spaces of mature aerenchyma is exuded from the remaining living cortical cells at times when the root turgor is high. This would be consistent with several recent studies which have shown periodic exudation of water from the surface of turgid roots. The spasmodic occurrence of root cortex tissue with enhanced diffusivity would have important implications for the transport of nutrient ions across the root.Abbreviations CSEM cryo-scanning electron microscope - EDX energy dispersive X-ray microanalysis - SR-G sulphorhodamine G     

The development of the endoder mis andPhi layer of apple roots

Summary Suberin lamellae and a tertiary cellulose wall in endodermal cells are deposited much closer to the tip of apple roots than of annual roots. Casparian strips and lignified thickenings differentiate in the anticlinal walls of all endodermal andphi layer cells respectively, 4–5 mm from the root tip. 16 mm from the root tip and only in the endodermis opposite the phloem poles, suberin lamellae are laid down on the inner surface of the cell walls, followed 35 mm from the root tip by an additional cellulosic layer. Coincidentally with this last development, the suberin and cellulose layers detach from the outer tangential walls and the cytoplasm fragments. 85 mm from the root tip the xylem pole endodermis (50% of the endodermis) develops similarly, but does not collapse. 100–150 mm from the root tip, the surface colour of the root changes from white to brown, a phellogen develops from the pericycle and sloughing of the cortex begins. A few secondary xylem elements are visible at this stage.Plasmodesmata traverse the suberin and cellulose layers of the endodermis, but their greater frequency in the outer tangential and radial walls of thephi layer when compared with the endodermis suggests that this layer may regulate the inflow of water and nutrients to the stele.