Transverse Cell Walls Research Articles

Cytomorphology of the wound healing process in the green filamentous algae, Ulothrix zonata (F. Weber & Mohr) K tzing 1833

Abstract. For the first time, we present a cytomorphological description of the self-healing (repair) process of damaged thalli sites, wound healing , in the green filamentous algae, Ulothrix zonata (F. Weber & Mohr) K tzing 1833. In the filaments of this species from Lake Baikal and the Angara (Baikal outflow), Zhilishche (Baikal inflow) and Ida (Angara inflow) rivers, light microscopy methods revealed dome-like and conical protrusions and elongations of transverse cell walls directed into adjacent dead (without protoplast) and defective (with deformed chloroplasts) cells. At the same time, there were mostly patterns where two cells formed protrusions directed into the same damaged filament site between them, i.e. towards each other. The growth of previously unconnected cells towards each other led to their convergence and adjacency. This had two important physiological consequences that ensured the restoration of the filament integrity. The first consequence was the formation of intercellular junctions. The second one was the fusion of the protoplasts and nuclei of the adjacent cells (cell fusion) with the formation of vegetative polyploid cells with increased size. During subsequent divisions of these cells, extended areas emerged with a two- to three-fold increase in the diameter of the algal filaments. It was also found that the process of wound healing promoted the development of giant hypnospores. We showed that the H-shaped septa between cells of filamentous algae were not thickenings of the outer walls but the sheaths of the dead cells preserved after this reparation process. Analysis of the wound healing patterns revealed that the Ulothrix cell nuclei did not migrate to the polarized regions of the cells but retained their central position, which testifies to their fixation in the protoplast. We observed sporadic cases of the development of lateral filaments in U. zonata were due to the self-repair of defective cells and their subsequent division during wound healing . A comparison of various cell deformations allowed us to determine the characteristic stages of the wound healing process in U. zonata, which have some similarities and differences with those in marine red filamentous algae. Our study indicates that wound healing is an evolutionarily developed and genetically programmed adaptation that may be widespread in the population of filamentous algae.

Concomitant use of polarization and negative phase contrast microscopy for the study of microorganisms.

A simultaneous application of negative phase contrast and polarization microscopy was used to study the internal structure of microbial cells. Negative phase contrast allowed us to display the fine cell structures with a refractive index of light approaching that of the environment, e.g., the cytoplasm, and converted an invisible phase image to a visible amplitude one. In the polarizing microscope, cross-polarizing filters, together with first-order quartz compensator and a turntable, showed maximum birefringence of individual structures. Material containing algae was collected in ponds in the villages Sýkořice and Zbečno (Protected Landscape Area Křivoklátsko). Objects were studied in a laboratory microscope (Carl Zeiss Jena, type NfpK), equipped with a basic body In Ph 160 with an exchangeable module Ph, LOMO St. Petersburg turntable mounted on a centering holder of our own construction and a Nikon D 70 digital SLR camera. Anisotropic granules were found only in the members of two orders of algae (Euglenales, Euglenophyceae and Chlorococcales, Chlorophyceae). They always showed strong birefringence and differed in both number and size. An important finding concerned thin pellicles in genus Euglena (Euglenales, Euglenophyceae) which exhibited weak birefringence. In genus Pediastrum (Chlorococcales, Chlorophyceae), these granules were found only in living coenobium cells. In contrast, dead coenobium cells contained many granules without birefringence-an important finding. Another important finding included birefringent lamellar structure of the transverse cell wall and weak birefringence of pyrenoids in filamentous algae of genus Spirogyra (Zygnematales, Conjugatophyceae). It was clearly displayed by the negative phase contrast and has not been documented by other methods. This method can also record the very weak birefringence of the frustule of a diatom of genus Pinnularia (Naviculales, Bacillariophyceae), which was further reinforced by the use of quartz compensator-an important finding. Simultaneous use of negative phase contrast and polarization microscopy allowed us to study not only birefringent granules of storage substances in microorganisms, but also the individual lamellae of the cell walls of filamentous algae and very thin frustule walls in diatoms. These can be visualized only by this contrast method, which provides a higher resolution (subjective opinion only) than other methods such as positive phase contrast or relief contrast.

A novel small molecule immunoassay to detect the mycobacterial siderophore carboxymycobactin

Background: To diagnose tuberculosis (TB), it is necessary to demonstrate the presence of Mycobacterium tuberculosis in a clinical specimen such as sputum. A simple, low-cost rapid test for blood or urine is urgently needed but remains elusive. Tests for host response-derived biomarkers or secreted bacterial compounds have so far failed to provide sufficient sensitivity or specificity and alternative approaches are needed. Carboxymycobactins are amphiphilic siderophores unique to the mycobacteria that have the ability to transverse mammalian cell walls. They have insufficient mass to induce an antibody response and there are currently no simple sensitive tests for their detection. Methods: We report the development of an enzyme-linked immunosorbent assay (ELISA) for carboxymycobactin. Polyclonal antibodies were raised in rabbits following conjugation to a carrier protein, bovine serum albumin allowing development of a sensitive indirect double antibody ELISA. A second keyhole limpet hemocyanin conjugate was manufactured to adhere the hapten to the wells of the microplate. We established a limit of detection for the assay of 1 pg/ml. Carboxymycobactin was detected in culture supernatant from mycobacteria including clinical isolates of M. tuberculosis , but not from cultures of Rhodococcus, Nocardia, Streptomyces, Bacillus cereus, Klebsiella oxytoca, Staphylococcus aureus, Escherichia coli , and Pseudomonas aeruginosa . Sample concentration was achieved following extraction with chloroform. Results: We have demonstrated for the first time the direct detection of carboxymycobactin in culture supernatant by immunoassay. Conclusions: We recommend testing samples from humans and animals to establish the potential utility of carboxymycobactin as a diagnostic marker of active mycobacterial disease.

Rape embryogenesis. II. Development of embryo proper

It was found in the continued studies on rape embryogenesis, started by the description of the proembryo (Tykarska, 1976) that the development of embryo is extremely regular and based on differentiating divisions. It appeared that the transverse segmentation boundary and cell walls separating the mother cells of the histogens in the proembryo can be distinguished in all the later stages of the embryo. The border between the cytoledons and epicotyl part of the embryonal axis, and the hypocotyl corresponds to the segmentation boundary between layer l and layer l' at the octant stage. As border between the hypocotyl and radicle was assumed the upper boundary of the root cap reaching usually to the level of the boundary between segments II and III of dermatogen and periblem. The apical meristem of the shoot forms from dermatogen and the periaxial cells of the globular embryo subepidermis. The promeristem of the radicle constists of 3 layers of initial cells surrounding on all sides the inactive layer of central binding cells.

Wood morphology and properties from molecular perspectives

Abstract•BackgroundIt is with increasing interest that wood materials are now being considered as a green resource. For improving the product performance of wood derived materials new ways of separating them from wood are required. Thus, there is a great demand for a better understanding of the ultrastructure of wood and how the components are interaction on a molecular level in building up its properties.•Material and methodBy the use of microscopic and spectroscopic techniques combined with mechanical forces, new knowledge regarding especially the role of the matrix polymers, the hemicelluloses and lignin, has been gained. This relates specifically to molecular interaction and orientation.•ResultsIt is here demonstrated that all of the wood polymers within the secondary cell wall exhibit a preferred orientation along the fibrils. The degree of orientation decreases in the order cellulose, hemicelluloses to the lignin which only shows a small degree of orientation, probably induced by structural constrains.•ConclusionThis orientation distribution is probably what has to be considered to better predict transverse cell wall properties. Moisture accessible regions are also aligned in a parallel arrangement in the cellulose fibrils explaining its high moisture resistance. The lignin is surprisingly inactive in the stress transfer in the secondary wall. This could perhaps be related to the function of lignin providing compressive, hydrostatic resistance in the lenticular spaces between fibrils, when longitudinally straining the fibre. This knowledge of the ultrastructural properties of the wood polymers, here presented, provides for a better understanding of the cell wall properties.

Ultrastructural appearance of embedded and polished wood cell walls as revealed by Atomic Force Microscopy

Atomic Force Microscopy (AFM) was used to investigate the ultrastructural appearance of transverse wood cell wall surfaces in embedded and polished Norway spruce wood blocks. The prepared surfaces showed only little height differences, suitable for high resolution AFM phase contrast imaging. Our results revealed randomly arranged wood cell wall components in the thick secondary 2 (S2) layers of the tracheid cell walls. It is concluded that the observed distribution pattern of the cellulose fibril/matrix structure is close to the original cell wall structure. In this context, the plasticity of wood cell wall components to re-arrange and adjust to different conditions resulting in diverse structural pattern is discussed.

Cellular and Subcellular Localization of Phototropin 1

Phototropin 1 (phot1) is a Ser/Thr photoreceptor kinase that binds two molecules of flavin mononucleotide as its chromophores and undergoes autophosphorylation in response to blue light. Phot1 is plasma membrane associated and, as with phot2, has been shown to function as a photoreceptor for phototropism, blue light-induced chloroplast movement, and blue light-induced stomatal opening. Phot1 likely also plays a redundant role with phot2 in regulating the rate of leaf expansion. Understanding the mechanism(s) by which phot1 initiates these four different responses requires, at minimum, knowledge of where the photoreceptor is located. Therefore, we transformed a phot1 null mutant of Arabidopsis with a construct encoding translationally fused phot1-green fluorescent protein (GFP) under the control of the endogenous PHOT1 promoter and investigated its cellular and subcellular distribution. This PHOT1-GFP construct complements the mutant phenotype, restoring second positive curvature. Phot1 is expressed strongly in dividing and elongating cortical cells in the apical hook and in the root elongation zone in etiolated seedlings. It is localized evenly to the plasma membrane region in epidermal cells but is confined largely to the plasma membrane region of the transverse cell walls in the cortical cells of both root and hypocotyl. It is found at both apical and basal ends of these cortical cells. In light-grown plants, phot1-GFP is localized largely in the plasma membrane regions adjacent to apical and basal cell end walls in the elongating inflorescence stem, where the photoreceptor is expressed strongly in the vascular parenchyma and leaf vein parenchyma. Phot1 also is localized to the plasma membrane region of leaf epidermal cells, mesophyll cells, and guard cells, where its distribution is uniform. Although phot1 is localized consistently to the plasma membrane region in etiolated seedlings, a fraction becomes released to the cytoplasm in response to blue light. Possible relationships between observed phot1 distribution and the various physiological responses activated by blue light are discussed.

Taxonomy and ecological distribution of the genus Microspora (Microsporaceae, Chlorophyta) in lotic ecosystems of São Paulo State, southeastern Brazil

Occurence of populations of the genus Microspora was investigated in 172 stream segments, which were sampled from May to October in 1992-1993 and 1996-1997 in six natural regions (parts of biomes or geological areas) of Sao Paulo State, southeastern Brazil. Three species were recognized, distinguished on the basis of shape and size of vegetative cells, H-shaped cell wall pieces and presence of rings in transverse cell walls. M.floccosa had cells with larger diameter (> 9.5 μm) and H-shaped structures clearly discernible throughout the filament lenght. M. quadrata and M. stagnorum had cells with smaller diameter (≤ 9.5 μm), the former with straight inner corners and the latter with rounded inner corners. H-pieces were discernible throughout the filament length in M. quadrata, whereas in M. stagnorum they were more clearly distinguishable at the terminal cells of the filament. In addition, the transverse cell walls of M. stagnorum had reddish to brownish rings. In comparison to macroalgal communities as a whole, the genus Microspora occurred under similar mean values of temperature (19.7 x 19.6 °C, respectively), specific conductance (72 x 69 μS cm -1 ), turbidity (8 x 9 NTU) and pH (6.9 x 6.8) but higher current velocity (48 x 63 cm s -1 ) and lower oxygen saturation (66 x 58 %). Trends for occurrence of individual species were considerably variable around these values. In terms of species occurrence in the regions of Silo Paulo State, the species of Microspora showed a relatively restricted distribution: M. floccosa occurred in only 9 sampling sites of three regions, whereas M. quadrata and M. stagnorum were present in only 3 sites of two regions. The three species were previously reported in boreal, temperate and tropical regions of the world.

A light and electron microscopy study on the formation, structure and germination of akinetes of Stigeoclonium tenue (Chaetophorales, Chlorophyceae)

Akinete formation in Stigeoclonium tenue (AG) KUTZ began under unfavourable conditions (exhaustion of nutrients and/or evaporation of the culture medium). Cells from both prostrate and erect portions produced akinetes. A gradual change in the shape of vegetative cells was observed. They lost their typical straight edges and acquired an oval contour with constrictions at the level of the transverse cell walls. At the ultrastructural level, the changes were: 1) accumulation of starch and lipids as reserve substances; 2) disorganization of the chloroplast; 3) reduction of the vacuole until it disappeared in mature akinetes; 4) thickening of the wall resulting from the synthesis of both an additional new own wall next to the parental wall and a mucilage external layer; 5) disorganization of the plasmodesmata in the transverse walls of vegetative cells. All of these drastic cytological changes are essential to the development of akinetes which provide S. tenue with an effective survival mechanism under unfavourable conditions.

Ultrastructure and Taxonomy of Sporocladopsis novae-zelandiae (Ulvophyceae, Chlorophyta)

The ultrastructure of vegetative and reproductive cells in Sporocladopsis novae-zelandiae has been studied for the first time to determine the precise taxonomic position of this genus. Vegetative cells contained one parietal chloroplast with 5–8 ulvophycean-type pyrenoids and transverse cell walls with plasmodesmata. The growth of the transverse walls was centripetal by furrow ingrowth. Ovoid zoosporangia initially had one nucleus and a large basal vacuole. Zoospore release occurred by the apical disintegration of the zoosporangial wall and expansion of an apical mucilage plug. Emptied zoosporangia could be occupied by a series of successive new zoosporangia developed from the same mother cell. Zoospores were bi- or quadriflagellate. The flagellar apparatus showed a 180 ° rotational symmetry and overlapped basal bodies with bilobed terminal caps covering their proximal ends. Our study permits us to conclude that Sporocladopsis is an ulvophycean genus. This conclusion is based on the occurrence of overlapping basal bodies, cytokinesis by infurrowing, and ulvophycean type of pyrenoids. Bilobed terminal caps and zoospore release by apical disintegration of the cell wall (which is accompanied by expansion of a mucilage plug) in Sporocladopsis suggest affinities with the order Ulvales. However, the absence of plasmodesmata and the absence of percurrent proliferation of zoosporangia in all members of the order Ulvales challenge this taxonomical position. The plasmodesmata in Sporocladopsis are similar to those in the Trentepohliales and could suggest a relationship with the latter, but the typical features of the Trentepohliales are absent in Sporocladopsis and this absence does not support an affinity between Sporocladopsis and the Trentepohliales. In conclusion, the fine structural characters of Sporocladospsis are paradoxical and it is therefore difficult to relate this genus to an order within the class Ulvophyceae. Molecular data of the genus, which are not available at present, would be necessary before making a final taxonomic decision concerning its ordinal position inside the class Ulvophyceae.

Secondary cell wall deposition causes radial growth of fibre cells in the maturation zone of elongating tall fescue leaf blades.

A gradient of development consisting of successive zones of cell division, cell elongation and cell maturation occurs along the longitudinal axis of elongating leaf blades of tall fescue (Festuca arundinacea Schreb.), a C3 grass. An increase in specific leaf weight (SLW; dry weight per unit leaf area) in the maturation region has been hypothesized to result from deposition of secondary cell walls in structural tissues. Our objective was to measure the transverse cell wall area (CWA) associated with the increase in SLW, which occurs following the cessation of leaf blade elongation at about 25 mm distal to the ligule. Digital image analysis of transverse sections at 5, 15, 45, 75 and 105 mm distal to the ligule was used to determine cell number, cell area and protoplast area of structural tissues, namely fibre bundles, mestome sheaths and xylem vessel elements, along the developmental gradient. Cell diameter, protoplast diameter and area, and cell wall thickness and area of fibre bundle cells were calculated from these data. CWA of structural tissues increased in sections up to 75 mm distal to the ligule, confirming the role of cell wall deposition in the increase in SLW (r2 = 0.924; P < or = 0.01). However, protoplast diameter of fibre cells did not decrease significantly as CWA increased, although mean thickness of fibre cell walls increased by 95 % between 15 and 105 mm distal to the ligule. Therefore, secondary cell wall deposition in fibre bundles of tall fescue leaf blades resulted in continued radial expansion of fibre cells rather than in a decrease in protoplast diameter.

Use of light and scanning electron microscopy to examine colonisation of barley rhizosphere by the nematophagous fungus Verticillium chlamydosporium

Barley roots were readily colonised by the nematophagous fungus Verticillium chlamydosporium. Light microscopy (LM) but also low temperature scanning electron microscopy (LTSEM) revealed details of the colonisation process. Hyphae were found on the rhizoplane often with dictyochlamydospores. Hyphae of V. chlamydosporium penetrated epidermal cells, often by means of appressoria. A hyphal network was formed in epidermal and cortical cells. Likewise, hyphal coils were found within root cells next to transverse cell walls. Cortical cells were the limits of fungal colonisation, since no hyphae were seen in the vascular cylinder. Modifications of root cell contents (phenolic droplets and callose appositions) were common three weeks after inoculation with V. chlamydosporium. These features may indicate induction of plant defence reactions in late stages of root colonisation by the fungus. Both LTSEM and LM have proved extremely useful to describe root colonisation by the fungus. The results found may have implications in the mode action of nematophagous fungi against plant parasitic nematodes.

Callose deposition and breakdown, followed by phytomelan synthesis in the seed coat ofGasteria verrucosa (Mill.) H. Duval

In the seed coat ofGasteria verrucosa the deposition of phytomelan takes place during seed development in three stages. Phytomelan is a black cell wall material which is chemically very inert. First the radial walls and part of the transverse cell wall of the outer epidermis of the outer integument become thickened by exocytosis of dictyosome vesicles. Callose is deposited at the tangential plasma membrane against those walls. After the callose deposition about two thirds of the original cell volume is filled with callose. During the second stage the callose is broken down, probably into glucose monomers or small polymers. At the same time cellulose is deposited at the outer tangential plasma membrane, forming a wall between the dissolving callose and the plasma membrane. In the third phase small granules appear in the solution of dissolved callose. which grow out and finally fuse to form a block of phytomelan, consisting of spherical 15-nm units. Remarkable is the function of the callose: it determines the size of the phytomelan block, and it probably functions as carbohydrate source for the phytomelan synthesis and/or for the cellulose inner layer. In this study transmission electron microscopy and cryo scanning electron microscopy are used to study the three developmental stages of the formation of the phytomelan layer.

Ultrastructure and taxonomy of the genus Endophyton (Ulvales, Ulvophyceae)

Fine structure of vegetative cells, development and morphology of sporangia and general morphology of zoospores were studied for the first time in the genus Endophyton Gardner. Vegetative cells contained one parietal perforate chloroplast with 2–4 ulvophycean pyrenoids and transverse cell walls without plasmodesmata. Sporangial walls were formed by two distinct electron-dense and fuzzy layers which contained a contiguous electron-translucent, fibrillar material. Zoospores were naked, with an anterior dense aggregation of vesicles and a cup-shaped chloroplast with one eyespot. The flagellar apparatus showed 180° rotational symmetry and counterclockwise absolute orientation of its components. Microtubular roots had a cruciate pattern, in which d = 2 and s = 4 with 3/1 arrangement. Electron-dense bilobed terminal caps covered the proximal end of each basal body. These observations support the suggested close relationship of Endophyton to the allied genus Entocladia and other ulvalean algae, and reinforce the criteria for including the genus in the class Ulvophyceae, order Ulvales, family Ulvellaceae.

Ultrastructure and taxonomy of the genus Endophyton (Ulvales, Ulvophyceae)

Fine structure of vegetative cells, development and morphology of sporangia and general morphology of zoospores were studied for the first time in the genus Endophyton Gardner. Vegetative cells contained one parietal perforate chloroplast with 2–4 ulvophycean pyrenoids and transverse cell walls without plasmodesmata. Sporangial walls were formed by two distinct electron-dense and fuzzy layers which contained a contiguous electron-translucent, fibrillar material. Zoospores were naked, with an anterior dense aggregation of vesicles and a cup-shaped chloroplast with one eyespot. The flagellar apparatus showed 180° rotational symmetry and counterclockwise absolute orientation of its components. Microtubular roots had a cruciate pattern, in which d=2 and s=4 with 3/1 arrangement. Electron-dense bilobed terminal caps covered the proximal end of each basal body. These observations support the suggested close relationship of Endophyton to the allied genus Entocladia and other ulvalean algae, and reinforce the criteria for including the genus in the class Ulvophyceae, order Ulvales, family Ulvellaceae.

Plant virus movement proteins

C. Michael Deem,” Moshe Lapidot,t and Roger N. Beachyt *Department of Plant Pathology University of Georgia Athens, Georgia 30602 tDivision of Plant Biology The Scripps Research Institute La Jolla, California 92037 The ease with which plant viruses move throughout their hosts appears quite remarkable, considering that viral progeny must cross the plant cell wall to move from cell to cell. The cell wall acts as a barrier to the extracellular release and subsequent uptake of virus progeny by either surface fusion or receptor-mediated endocytosis, the two general pathways for entry used by animal viruses. Conse- quently, plant viruses have evolved a distinct mechanism for cell-to-cell movement. With few exceptions, virus particles are initially intro- duced into host cells during mechanical damage or biologi- cal damage (via vectors) to the integrity of the cell wall and the plasma membrane. If, following entry and replication, progeny viruses are not capable of moving into adjacent healthy cells, a subliminal infection occurs, and the host appears to be resistant to thevirus. If, however, virus prog- eny are capable of spreading into adjacent cells, a progres- sive virus infection results. While the specific virus-host interaction will ultimately define the nature of the infection, virus movement represents an important component in determining pathogenicity and virulence. The movement of virus progeny throughout a host is an active process that can be divided into two broadly defined phases. The first phase is characterized by cell-to-cell (short-distance) spread of the virus. The second phase is long-distance movement from an infected tissue, such as a leaf, to other tissues via the vascular tissue. The exit of the virus from the vascular tissue subsequently results in short-distance movement of virus progeny from cell to cell. In some virus-host interactions, virus spread may be lim- ited to short-distance movement, for example, in the inocu- lated leaf or in vascular or vascular-associated tissue. It is generally accepted that plant viruses circumvent the cell wail by exploiting plasmodesmata. Plasmodesmata, the plant functional analog of gap junctions in animals, are channels that transverse cell walls and provide cyto- plasmic continuity between adjacent cells. These intercel- lular connections play an important role in cell-cell com- munication and the dissemination of water and nutrients throughout the plant. Plasmodesmata have not been iso- lated or biochemically characterized, and structural mod- els of plasmodesmata are based on interpretations of elec- tron micrographs. (A prevailing model is seen in Figure 1.) Extending through the plasma membrane-lined chan- nel is the desmotubule, a modified extension of the endo- plasmic reticulum. The area between the desmotubule and the plasma membrane, the cytoplasmic sleeve, likely

Analysis of mitotic synchrony induced by cold treatment in root meristems of Vicia faba L.

In cold-pretreated seedlings (24 hr at 4°C), 3 hr after transfer to 20°C 50% of the cells were in S phase. After 13 hr of postincubation at 20°C the mitotic index rapidly increased from 1 to 19% and through 3H-thymidine incorporation, 60% of mitotic cells became radioactive. A comparison of cytoplasmic protein content in 3H-labelled and unlabelled prophase cells indicated that the cells containing more cytoplasmic protein entered mitosis earlier. Synchronization of mitotic divisions occurred within cell packets. The number of plasmodesmata in transverse cell walls between cells in mitosis was greater than that between interphase cells.

Changes in Cell Dimensions in Developing Roots of In vitro Cultured Immature Maize Embryos (Zea mays L.)

The pattern of tissue organization in roots of cultured immature maize embryos was studied using morphometric methods. After five periods of in vitro culture, ranging from 0 h up to 48 h, cell dimensions were measured in various regions of the root using an image analyzer. Cell elongation was scored directly; because mitotic figures were rarely observed, cell division activity was derived indirectly from planes of new cell walls and the decrease in cell lengths. The tissues, distinguished as protoderm, outer ground meristem, pro-endodermis, pericycle, procambium, and pith, displayed different patterns of development. Proceeding from the root tip to the base, various regions were defined. After 24 h of culture new transverse cell walls were observed in most tissues. In the stele they occurred just behind the root tip. In the ground meristem-protoderm complex they were found at some distance from the tip. After 42 h of in vitro culture new cells were observed from the region bordering the quiescent center u...

Root contraction in hyacinth IV. Orientation of cellulose microfibrils in radial longitudinal and transverse cell walls

Cellulose microfibrils (MFs) were visualized on the inner surface of root cortex cell walls ofHyacinthus orientalis L. using a replica technique. Microfibril orientation was determined in radial longitudinal and transverse cell walls of the root tip, uncontracted, contracting, and fully contracted regions of the root. In longitudinal walls, the innermost MFs were ordered and parallel to one another and were oriented transversely, axially or obliquely, depending upon the developmental stage of the region. In transverse walls MFs in a single layer formed crisscross or ordered parallel arrays, depending upon the region. Parallel arrays were oriented either parallel, perpendicular, or oblique to the radius of the root. Inner walls of certain cells in the contracting region had MFs which appeared interrupted over their lengths. In general, these findings parallel earlier immunofluorescence and electron microscopic observations of changing cortical microtubule (MT) orientation accompanying root contraction. The major exception to MT-MF congruence occurred in cells of the actively contracting region. In middle and outer cell layers, MFs appeared short and partially obscured, while MTs in these cells occurred in conspicuous laterally aggregated strands parallel to one another over the length of the cells or were absent. This alteration in MF-MT parallelism may be related to the reorientation in cell growth occurring in the contractile zone or to the collapse of specific cells during the process of root contraction.

Root contraction in hyacinth III. Orientation of cortical microtubules visualized by immunofluorescence microscopy

Cortical microtubules (MTs) were visualized in root cortex cells ofHyacinthus orientalis L. using immunofluorescence techniques. Cellular MT orientation was determined adjacent to radial longitudinal and transverse walls of root tip, uncontracted, contracting, and fully contracted regions. As seen in longitudinal views, MTs formed parallel, apparently helical arrays which were oriented transversely, axially or obliquely depending upon the region. Transverse sectional views showed that MTs adjacent to transverse cell walls formed a variety of patterns which varied with developmental stage and cell location. Microtubules were oriented in crisscross or parallel arrays. The parallel arrays were oriented either parallel, perpendicular or oblique to the radius of the root. There was an apparent temporal progression in MT reorientation from outer cortical to inner cortical cell layers. A resultant progression of reoriented cell growth could account for root contraction. These findings corroborate earlier electron microscopic observations of changing MT orientation accompanying root contraction, and provide cytological evidence to test mathematical and biophysical models of the mechanics of cell expansion.