Suberin Lamellae Research Articles

Composition and fine structural features of longitudinal veins in leaves of Thalassodendron ciliatum

Longitudinal veins in leaf blades of the sea-grass Thalassodendron ciliatum (Forssk.) Den Hartog consist of a sheath of cells with thickened walls which encloses xylem, phloem and vascular parenchyma cells. While the xylem is reduced, phloem is well developed and consists of sieve tubes and companion cells. Two types of sieve tubes are distinguishable: those with thick walls and those with thin walls. Companion cells generally have dense cytoplasmic contents and are connected to sieve tubes by branched plasmodesmata. Vascular parenchyma cells possess an organelle-rich cytoplasm with chloroplasts as plastids. Numerous plasmodesmata interconnect contiguous vascular parenchyma cells. Plasmodesmata connecting vascular parenchyma cells to sieve tubes and companion cells are observed less frequently. Each bundle sheath cell is encased within a multilayered suberin lamella. Bundle sheath cell walls have prominent pit fields which are traversed by plasmodesmata. The plasmodesmata perforate the suberin lamella and interconnect sheath cells with contiguous vascular parenchyma and mesophyll cells. Bundle sheath cells generally possess sparse cytoplasmic contents but have relatively well developed chloroplasts. The suberin lamella appears to form an apoplastic barrier between mesophyll and vascular tissues. Structural features of the veins are compared with those found in similar veins in leaves of terrestrial monocotyledonous plants.

Ultrastructural Study of the Development of Oil Cells in the Mesocarp of Avocado Fruit

The development of idioblastic oil cells in the mesocarp of avocado fruit was studied with the electron microscope. Observations concentrated on the formation of the complex cell wall and on the process of oil accumulation. The cell wall of the mature oil cells has three distinct layers: an external primary wall, a suberin lamella, and an interior tertiary wall No significant oil accumulation was observed until after the suberin layer was deposited and tertiary wall formation had begun. Formation of an extensive network of smooth tubular endoplasmic reticulum was observed concomitant with the initial accumulation of oil in the cytoplasm. In the latter stages of tertiary wall formation, the primary site of oil accumulation shifted from the cytoplasm to the vacuoles By the time the deposition of the tertiary wall was complete, most of the cell volume was occupied by a massive oil droplet; and the cytoplasm, which was devoid of membranes, was displaced to the cell periphery

Cellular differentiation in small clumps of Lotus corniculatus callus

Lotus callus cultures were studied in an attempt to determine, at the cellular and subcellular levels, what morphological changes precede and accompany differentiation. Small clumps of homogenized callus were plated onto a medium containing benzyladenine, which was known to induce differentiation in this system. Initially callus was yellowish and consisted of large, vacuolated cells with deposits of starch. Marked changes occurred in these cells; peripheral and endogenous meristematic areas were initiated giving rise to shoots and either groups of tracheary elements or roots, respectively. Roots developed within 5 day s, while shoot apical meristems with leaf primordia formed by day 9. Many of the cells surrounding meristematic areas developed suberin lamellae in their walls, while others, both within and on the periphery of meristematic areas, accumulated phenolic substances. Cells within meristematic areas had large nuclei with prominent nucleoli, plastids with thylakoids but little or no starch, many mitochondria, and dictyosomes. Morphological observations tend to support the view that physiological isolation of tissue may precede differentiation.

Water Uptake by Different Regions of the Barley Root. Pathways of Radial Flow in Relation to Development of the Endodermis

The water uptake by different lengths of lateral roots and 1-0 cm or 5-0 cm lengths of the seminal axes from different regions of the root were measured in potometers with the shoot in air at two humidity regimes. A model of the contribution by these different regions of the root to the total water absorption by the plant agreed well with measurements of water uptake by the whole root system. According to this model, about one half of the water taken up by the main axis came from the older suberized regions further than 10 cm from the tip, and together with its associated lateral roots this region provided 75% of the total water transpired. The development of State III endodermal cells was correlated with decreases in both the water uptake by the older regions of the root and the translocation of calcium. Thus in the younger regions of the root where water uptake is maximal, the flow of water is principally apoplastic although there is also likely to be flow via the symplast. Despite a 43% difference in transpirational demand between the two humidity treatments, the leaf water potentials remained constant, implying a change in root resistance. This change in resistance might be explained if there were an apoplastic pathway within the suberin lamellae of State III endodermal cells. The response to the increased transpirational demand is met by the older regions of the root, in particular by the zone of lateral emergence where an apoplastic pathway is known to exist as the Casparian band in the endodermis breaks down with the emergence of the lateral roots.

Anatomy and development of the superficial layers in stolons of white clover (Trifolium repensL.)

Abstract Scanning and transrrussion electron microscopy, together with bright field and fluorescence microscopy, were used to examine the cuticle, epidermis, hypodermis, and cork cambium (phellogen) of white clover (Trifolium repens L.) stolons during growth and maturation. Development of the hypodermis included the deposition of a suberin lamella in the cell walls. No suberin was deposited in the cell walls of the epidermis. The cork cambium was formed in the third to fifth internodes basipetal to the stolon apex, and produced layers of suberised cork cells (phellem) when internodes were 11 to 14 basipetal to the apex. Breakdown of the cuticle began at a very early stage. Bacteria were seen to colonise the cuticle and apparently lyse the cuticle and epidermal cell walls and penetrate eventually into the hypodermis. The suberin lamella appeared to be more resistant to bacterial attack than the cellulose portion of the cell wall. It was concluded that variation in the degree of breakdown of the cuticle was probably responsible for the large variation in phosphate absorption of stolon internodes previously observed.

The suberin lamella, a possible barrier to water movement from the veins to the mesophyll ofThemeda triandra forsk

Precipitation of ferrous ions by ferricyanide in transpiring leaves ofThemeda triandra Forsk. produced crystalline deposits, which were visible with the light and electron microscope. Prussian blue crystals were formed within the lumina of the tracheary elements and the apoplast, or cell wall continuum of the vascular tissues and bundle-sheath cells. Little if any deposition was noted within the lignified secondary thickenings of the tracheary elements. The localization pattern suggests that the ferrous ions moved from the lumina of the tracheary elements via the exposed primary walls. Prussian blue crystals were abundant in the outer tangential and radial walls of the bundle-sheath cells. By contrast, crystals were lacking in the walls of neighbouring mesophyll cells, suggesting that the suberin lamella in the bundle-sheath walls effectively inhibited the apoplastic movement of ferrous ions and possibly may impede, or restrict the movement of water across the bundle-sheath/mesophyll interface.

Ultrastructural characteristics of an achlorophyllous callus line ofLotus corniculatus

An achlorophyllus isoline originated spontaneously from a green callus line derived from a genotype ofLotus corniculatus L. cv. Leo. This isoline is characterized by significantly faster callus growth than the green line and by differentiating significantly fewer plants per gram of callus when subcultured on a shoot differentiating medium. The isoline does, however, develop loci of meristematic cells when transferred from a medium containing 2,4-D to one containing benzyl adenine. After this transfer, plastids, mitochondria, dictyosomes, and endoplasmic reticulum appear to be more prevalent in many cells. Nuclei and nucleoli become more prominent in these cells. Ingrowths, lined with plasmalemma, develop along the outer tangential cell wall of many cells in contact with the culture medium and along various walls of cells found in the interior of the callus. These cells have characteristics of transfer cells. A few cells at the periphery of meristematic groups of cells elaborate lamellar structures similar to suberin lamellae in their cell walls.

ULTRASTRUCTURE OF THE SEAGRASS RHIZOSPHERE

SummaryBacterial colonies, fungi and other micro‐organisms occur in the rhizosphere and peripheral root tissues of seagrasses of the genus, Posidonia. Fungi penetrate the epidermal cells and lyse the thick polysaccharide materials in the walls of the hypodermal cells. A suberin lamella in the wall of the hypodermal cell is more resistant but fungi and bacteria occur both within the lumen of hypodermal cells and in cortical cells adjacent to the hypodermis. It is suggested that these micro‐organisms in the rhizosphere and peripheral root tissues may be involved in nutrient uptake and nitrogen fixation into seagrasses.

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.

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.

The root endodermis in Ranunculus acris. I. Structure and ontogeny

The root endodermis in Ranunculus acris was investigated using light and transmission electron microscopy to obtain a more complete picture of endodermal development in a dicotyledonous species. Following the formation of a lateral bulge in anticlinal walls of proendodermal cells, portions of the plasma membrane became tenaciously associated with the primary wall material. The plasma membrane in the zone of the Casparian band appeared extremely electron dense and displayed a distinct tripartite organization. Cytoplasm of primary stage endodermal cells contained Golgi bodies with associated vesicles, lipid-like droplets, and multivesicular bodies containing membrane-enclosed vesicles. Cellulose microfibrils in the radial walls of endodermal cells became impregnated with an osmiophilic substance possibly through the incorporation of paramural bodies at a ledge-like invagination of the plasma membrane on either side of the Casparian strip. It is proposed that the intense organelle activity in the vicinity of the Casparian strip could signify an early stage of suberin lamellae synthesis. Between 8 and 10 suberin lamellae were laid down on radial and tangential walls of those endodermal cells which underwent secondary development, with the heaviest deposition occurring in the region of the Casparian strip. The parallel orientation of the suberin lamellae was frequently disrupted by electron-dense 'platelets' and small granules. A fibrillar suberin-like material was found in dilated cisternae of endoplasmic reticulum located adjacent to areas of deposition. Nuclei, membranous configurations, mitochondria, plastids, and other cytoplasmic organelles were found to persist in tertiary stage endodermal cells. Histochemistry and SEM showed that the mature endodermal wall complex of field-grown plants was comprised of alternating bands of cellulose, lignin, and possibly, suberin.

The root endodermis in Ranunculus acris. II. Histochemistry of the endodermis and the synthesis of phenolic compounds in roots

Results of histochemical tests performed on fresh root tissue of Ranunculus acris provide the following information on the chemical nature of the root endodermis: (i) the Casparian strip is impregnated with lipid and possibly lignin, (ii) the suberin lamellae stain positively for lipid and phenols with free hydroxyl groups, and (iii) the tertiary wall contains alternating bands of lignin and cellulose.At the ultrastructural level, phenolic 'globules' present in vacuoles of adjacent cortical cells increase in size by accretion of flocculent material and the addition of dispersed granular material through the apparent fusion of smaller vacuoles with the large central vacuole. Globules adhering to fragments of the tonoplast membrane are clearly seen with the SEM.The ferric chloride test for catechol-type phenols at the TEM level proved useful in categorizing phenolic compounds present in intercellular spaces, in walls and vacuoles of cortical cells, surrounding starch grains in amyloplasts, and in the cytoplasm of endodermal cells. Prominent plastids containing large deposits of lipid, osmiophilic material, thylakoid membranes, and starch are seen to be a major constituent of cytoplasm in endodermal and cortical cells.

The development of the endoder mis andPhi layer of apple roots

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.

Studies on the physiological sheaths in roots I. Ultrastructure of the exodermis inHoya carnosa L.

InHoya roots most exodermal cells are elongated and a band of suberin lamellae is formed in all their walls early in development; later on carbohydrate tertiary wall layers are deposited inside the suberin lamellae. Some exodermal cells which are restricted to root hair-bearing areas are short and unsuberized but their outer tangential wall is conspicuously thickened. Combined evidence from light microscopy and transmission and scanning electron microscopy reveals the bulk of this cap-formed thickening as a mosaic structure with two different components forming an extensive labyrinth. Irregular masses of a lignified, amorphous substance are separated by radially oriented, tortuous channels containing a very dense, granular-fibrillar material. The innermost wall layer is fibrillar and shows a texture and density similar to the material in the separating channels. The cap contains prominent pits with plasmodesmatal connections between short cells and the epidermis. In mature and non-functional short cells a band of suberin lamellae and eventually tertiary wall layers are deposited.

A correlated histochemical and ultrastructural study of the epidermis and hypodermis of onion roots

Cell walls of mature epidermal and hypodermal cells are autofluorescent when viewed under ultraviolet or blue light. This autofluorescence develops in a centripetal direction, beginning in the outer tangential wall of the epidermis and ending in the inner tangential wall of the hypodermis. The intercellular regions between the epidermis and hypodermis and between the hypodermis and the cortex are dense and also become autofluorescent. Although the walls of the hypodermis provide a barrier to the movement of a high molecular weight fluorescent dye, the walls of the epidermis are permeable. Histochemical studies indicate that lipids and polyphenolics are components of the epidermal and hypodermal cell walls. Both layers are resistant to the wall-degrading enzyme Driselase and to concentrated sulphuric acid, whereas the cortex is digested with both treatments. Observations with the transmission electron microscope show that a complex suberin lamella encases each hypodermal cell but is absent from the epidermis. However, the outer tangential wall and radial walls of the epidermal cells are complex in that layers of different densities are present. Some of these layers, as well as the intercellular regions and the radial walls of the hypodermal cells, bind ferric ions when tissue is fixed in ferric chloride-glutaraldehyde indicating the presence of poly-phenolics in these regions. An extracellular layer covering the outer tangential wall of the epidermis stained positively with a number of histochemical tests for polyphenolics.

Morphology, anatomy and histochemistry of the Australian seagrasses of the genus Posidonia könig (posidoniaceae). II. Rhizome and root of Posidonia australis Hook. f

Rhizome branching of Posidonia australis Hook. f. occurs at irregular intervals in leaf axils, with one or no branch per axil. The cell walls of the rhizome epidermis and hypodermis are slightly thickened and lignified. Cortical cells have many starch grains. Fibre strands and vascular bundles are scattered among the cortical tissues. The cell walls of rhizome fibre cells consist mainly of cellulose and hemicellulose with a little lignin but the middle lamellae are heavily lignified. The fibres of both leaf sheath and rhizome resist decay and build up banks beneath the living seagrass. The rhizome stele has a central xylem surrounded by the phloem bundles which are finally surrounded by the endodermis. At the node region, one or a pair of roots may be produced. The thickened hypodermal walls of the root have a suberin lamella. The radial walls of the root endodermis are slightly thickened and have a Casparian strip. Both hypodermis and endodermis may restrict exchange of the water and solutes. A vascular system with weakly lignified tracheids is present in all roots.

Distribution and structure of the plasmodesmata in mesophyll and bundle-sheath cells of Zea mays L.

In leaf blades of Zea mays L. plasmodesmata between mesophyll cells are aggregated in numerous thickened portions of the walls. The plasmodesmata are unbranched and all are characterized by the presence of electron-dense structures, called sphincters by us, near both ends of the plasmodesmatal canal. The sphincters surround the desmotubule and occlude the cytoplasmic annulus where they occur. Plasmodesmata between mesophyll and bundle-sheath cells are aggregated in primary pit-fields and are constricted by a wide suberin lamella on the sheath-cell side of the wall. Each plasmodesma contains a sphincter on the mesophyll-cell side of the wall. The outer tangential and radial walls of the sheath cells exhibit a continuous suberin lamella. However, on the inner tangential wall only the sites of plasmodesmatal aggregates are consistently suberized. Apparently the movement of photosynthetic intermediates between mesophyll and sheath cells is restricted largely or entirely to the plasmodesmata (symplastic pathway) and transpirational water movement to the cell walls (apoplastic pathway).

Intercellular communication in the maize root endodermis

The endodermal cells of the maize roots are linked to each other via plasmodesmata mainly localized at the proximity of the Casparian band on the anticlinal walls. In this part of the walls was noticed the absence of the suberin lamella in the thickening endodermal cells.

Die Bedeutung der molekularen Lamellenbauweise von Korkzellwänden )

Summary According to earlier work, the lipidic suberin layers of cork cell walls are finely laminated: surface-parallel lamellae of suberin alternate with tilms of wax. This lamellar fine structure, which is easily seen in sections after staining with OsO 4 , can be made visible also with permanganate as a contrasting agent. Lipophilic OsO 4 penetrates readily into suberin layers. On the other hand, MnO 4 - ions infiltrate only slowly in an anisotropic fashion, in that MnO 4 - penetration in directions parallel to the wall surface is about 20 times faster than in perpendicular direction. As the diffusion coefficient of permanganate ions in the extremely hydrophobic wax films is only about 1 % of that in the semihydrophilic suberin lamellae, the anisotropic penetration of suberin layers is a consequence of their laminated fine structure. The excellent isolating properties of suberized cell walls (and cuticles, too) can easily be understood on the basis of these results. Some consequences are briefly discussed.

The entry of ions and molecules into roots: an investigation using electron-opaque tracers

Various solutions containing ions or molecules which may be visualized in the electron microscope have been presented to barley (Hordeum vulgare L.) roots. Large molecules such as gold sol particles (<6.0 nm) or ferritin (approx. 12.0 nm) were not found to be taken into the cytoplasm of any cells. Very dilute solutions of uranyl acetate or lanthanum nitrate resulted in the presence of typical electron-opaque crystals in the cortical apoplasm, as well as in cytoplasmic vesicles of cortical and some endodermal cells, but not in the cytoplasm or cell walls of stellar cells. Colloidal lanthanum hydroxide, however, while also impeded by the Casparian band, accumulated in vesicles in endodermal cells, and also penetrated into the stele.These results support the concept that different pathways exist for the movement of water and different ions across barley roots. They also indicate the relevance of the Casparian bands, the suberin lamellae, the formation of endocytotic vesicles, and the plasmodesmata, in studies on water and ion uptake.