Interference of cell wall regeneration ofBoergesenia forbesii protoplasts by Tinopal LPW,a fluorescent brightening agent

Summary Wounding cells ofBoergesenia forbesii (Harvey) Feldmann induces the synchronous formation of numerous protoplasts which synthesize large cellulose microfibrils within 2–3 hours after wounding. The microfibrils appear to be assembled by linear terminal synthesizing complexes (TCs). TC subunits appear on both E- and P-faces of the plasma membrane, thus suggesting the occurrence of a transmembrane complex. The direction of microfibril synthesis is random during primary wall assembly and becomes ordered during secondary wall assembly. The average density of TCs during secondary wall deposition is 1.7/m², and the average length of the TC is 510 nm. TC organization is similar to that ofValonia macrophysa; however, the larger TCs ofBoergesenia (510 nm vs. 350 nm) produce correspondingly larger microfibrils (30 nm vs. 20 nm).The effects of a fluorescent brightening agent (FBA), Tinopal LPW, on cell wall regeneration ofBoergesenia protoplasts was investigated. The threshold level of Tinopal LPW for interfering with microfibril assembly is 1.5 M. At 95 M Tinopal (for short periods up to 15 minutes), microfibril impressions have atypical spherical impressions at their termini. At longer incubations (24 hours), TCs and microfibril impressions are absent. When washed free of Tinopal, the protoplasts eventually resume normal wall assembly; however, TCs do not reappear until at least 30 minutes after the removal of Tinopal. In consideration of the presence of ordered TCs before FBA treatment, their random distribution upon recovery implies an intermediate stage of assembly or possiblyde novo synthesis.     

TIP CELL GROWTH AND THE FREQUENCY AND DISTRIBUTION OF CELLULOSE MICROFIBRIL-SYNTHESIZING COMPLEXES IN THE PLASMA MEMBRANE OF APICAL SHOOT CELLS OF THE RED ALGA PORPHYRA YEZOENSIS1

The supramolecular organization of the plasma membrane of apical cells in shoot filaments of the marine red alga Porphyra yezoensis Ueda (conchocelis stage) was studied in replicas of rapidly frozen and fractured cells. The protoplasmic fracture (PF) face of the plasma membrane exhibited both randomly distributed single particles (with a mean diameter of 9.2 ± 0.2 nm) and distinct linear cellulose microfibril-synthesizing terminal complexes (TCs) consisting of two or three rows of linearly arranged particles (average diameter of TC particles 9.4 plusmn; 0.3 nm). The density of the single particles of the PF face of the plasma membrane was 3000 μm^?2, whereas that of the exoplasmic fracture face was 325 μm^?2. TCs were observed only on the PF face. The highest density of TCs was at the apex of the cell (mean density 23.0 plusmn; 7.4 TCs μm^?2 within 5 μm from the tip) and decreased rapidly from the apex to the more basal regions of the cell, dropping to near zero at 20 μm. The number of particle subunits of TCs per μm² of the plasma membrane also decreased from the tip to the basal regions following the same gradient as that of the TC density. The length of TCs increased gradually from the tip (mean length 46.0 plusmn; 1.4 nm in the area at 0–5 μm from the tip) to the cell base (mean length 60.0 plusmn; 7.0 μm in the area at 15–20 μm). In the very tip region (0–4 μm from the apex), randomly distributed TCs but no microfibril imprints were observed, while in the region 4–9 μm from the tip microfibril imprints and TCs, both randomly distributed, occurred. Many TCs involved in the synthesis of cellulose microfibrils were associated with the ends of microfibril imprints. Our results indicate that TCs are involved in the biosynthesis, assembly, and orientation of cellulose microfibrils and that the frequency and distribution of TCs reflect tip growth (polar growth) in the apical shoot cell of Porphyra yezoensis. Polar distribution of linear TCs as “cellulose synthase” complexes within the plasma membrane of a tip cell was recorded for the first time in plants.     

Cellulose-synthesizing terminal complexes and microfibril structure in the brown alga Sphacelaria rigidula (Sphacelariales,Phaeophyceae)*

The brown alga Sphacelaria rigidula Kützing synthesizes cellulose microfibrils as determined by CBH I-gold labeling. The cellulose microfibrils are thin, ribbon-like structures with a uniform thickness of about 2.6 nm and a variable width in the range of 2.6-30 nm. Some striations appear along the longitudinal axis of the microfibrils. The developed cell wall in Sphacelaria is composed of three to four layers, and cellulose micro-fibrils are deposited in the third layer from the outside of the wall. A freeze fracture investigation of this alga revealed cellulose-synthesizing terminal complexes (TCs), which are associated with the tip of microfibril impressions in the plasmatic fracture face of the plasma membrane. The TCs consist of subunits arranged in a single linear row. The average diameter of the sub-units is about 6 nm, and the intervals between the neighboring subunits, about 9 nm, are relatively constant. The number of subunits constituting the TC varies between 10 and 100, so that the length of the whole TC varies widely. A model that has been proposed for the assembly of thin, ribbon-like microfibrils was applied to microfibril assembly in Sphacelaria.     

Arrays of plasma-membrane “rosettes” involved in cellulose microfibril formation of Spirogyra

The cell-wall structure and plasma-membrane particle arrangement during cell wall formation of the filamentous chlorophycean alga Spirogyra sp. was investigated with the freeze-fracture technique. The cell wall consists of a thick outer slime layer and a multilayered inner wall with ribbon-like microfibrils. This inner wall shows three differing orientations of microfibrils: random orientation on its outside, followed by axial bundles of parallel microfibrils, and several internal layers of bands of mostly five to six parallel associated microfibrils with transverse to oblique orientation. The extraplasmatic fracture face of the plasma membrane shows microfibril imprints, relatively few particles, and “terminal complexes” arranged in a hexagonal package at the end of the imprint of a microfibril band. The plasmatic fracture face of the plasma membrane is rich in particles. In places, it reveals hexagonal arrays of “rosettes”. These rosettes are best demonstrable with the double-replica technique. These findings on rosette arrays of the zygnematacean alga Spirogyra are compared in detail with the published data on the desmidiacean algae Micrasterias and Closterium.     

Occurrence of the putative microfibril-synthesizing complexes (linear terminal complexes) in the plasma membrane of the epiphytic marine red algaErythrocladia subintegra Rosenv.

Summary Cells of thalli at different developmental stages of the epiphytic marine red algaErythrocladia subintegra have been studied by freeze-etching. It was found that the plasma membrane exhibits linear microfibril-termnal synthesizing complexes (TCs), randomly distributed consisting of four rows of linearly-arranged particles (average diameter of particles 8.6 nm); each row of TCs consists of 5–33 particles (average 15). The TCs were observed on both fracture faces (PF and EF) but more clearly on the PF face. These structures appear to span both the outer and inner leaflets of the plasma membrane (transmembrane complexes)-The TCs have stable width (35 nm) and vary in length (41–311 nm, average 181 nm). The TCs subunits are highly ordered arrays forming a semicylinder. The average density of TCs on the PF face is 5.5TC/m². The microfibrils are randomly distributed and have a mean width of 39.4 nm (ranging from 16 to 70 nm). Many TCs are associated with the ends of microfibrils and microfibril imprints. The structural characteristics of linear TCs in the red algaErythrocladia are compared with those of the so far investigated Chlorophyta spp. All results favour the suggestion that TCs in the plasma membrane ofErythrocladia cells are involved in the biosynthesis, assembly and orientation of microfibrils.     

Cellulose synthesizing terminal complexes and morphogenesis in tip-growing cells of Syringoderma phinneyi (Phaeophyceae)

The intramembrane particles and cellulose synthesis of the brown alga Syringoderma phinneyi Henry et Müller were examined using replicas of freeze‐fractured apical cells. Like in other brown algae, linear terminal complexes (TCs) were found in the plasmatic fracture face (PF) of the plasmalemma, which are the putative cellulose synthases. Terminal complexes consist of a single row of particles, each particle composed of two sub‐units, and are found in close relationship with cellulose microfibril imprints. Examination of the distribution of TCs revealed a clear apico‐basal gradient, with a higher density of TCs in the apical part. This seems to reflect the tip growth of the apical cells. The rate of cellulose synthesis per TC subunit was calculated based on the dimensions of the TCs and cellulose microfibrils.     

Cellulose microfibril assembly inErythrocladia subintegra Rosenv.: An ideal system for understanding the relationship between synthesizing complexes (TCs) and microfibril crystallization

Summary The marine red algaErythrocladia subintegra synthesizes cellulose microfibrils as determined by CBH I-gold labelling, X-ray and electron diffraction analyses. The cellulose microfibrils are quite thin, ribbon-like structures, 1–1.5 nm in thickness (constant), and 10–33 nm in width (variable). Several laterally associated minicrystal components contribute to the variation in microfibrillar width. Electron diffraction analysis suggested a uniplanar orientation of the microfibrils with their (101) lattice planes parallel to the plasma membrane surface of the cell. The linear particle arrays bound in the plasma membrane and associated with microfibril impressions recently demonstrated inErythrocladia have been shown in this study to be the cellulose-synthesizing terminal complexes (TCs). The TCs appear to be organized by a repetition of transverse rows consisting of four TC subunits, rather than by four rows of longitudinallyarranged TC subunits. The number of transverse rows varied between 8–26, corresponding with variation in the length of the TCs and the width of the microfibrils. The spacings between the neighboring transverse rows are almost constant being 10.5–11.5 nm. Based on the knowledge thatAcetobacter, Vaucheria, andErythrocladia synthesize similar thin, ribbon-like cellulose microfibrils, the structural characteristics common to the organization of distinctive TCs occurring in these three organisms has been discussed, so that the mode of cellulose microfibril assembly patterns may be deciphered.     

Plasma-membrane rosettes in root hairs of Equisetum hyemale

Particle arrangement in the plasma membrane during cell wall formation was investigated by means of the double-replica technique in root hairs of Equisetum hyemale. Particle density in the protoplasmic fracture face of the plasma membrane was higher than in the extraplasmic fracture face. Apart from randomly distributed particles, particle rosettes were visible in the PF face of the plasma membrane. The rosettes consisted of six particles arranged in a circle and had an outer diameter of approx. 26 nm. No gradient in the number of rosettes was found, which agrees with micrifibril deposition taking place over the whole hair. The particle rosettes were found individually, which might indicate that they spin out thin microfibrils as found in higher-plant cell walls. Indeed microfibril width in these walls, measured in shadowed preparations, is 8.5±1.5 nm. It is suggested that the rosettes are involved in microfibril synthesis. Non-turgid cells lacked microfibril imprints in the plasma membrane and no particle rosettes were present on their PF face. Fixation with glutaraldehyde caused, probably as a result of plasmolysis, the microfibril imprints to disappear together with the particle rosettes. The PF face of the plasma membrane of non-turgid hairs sometimes showed domains in which the intramembrane particles were aggregated in a hexagonal pattern. Microfibril orientation during deposition will be discussed.Abbreviations EF extraplasmic fracture face - PF protoplasmic fracture face     

THE SITES OF CELLULOSE SYNTHESIS IN ALGAE: DIVERSITY AND EVOLUTION OF CELLULOSE-SYNTHESIZING ENZYME COMPLEXES

Information on the sites of cellulose synthesis and the diversity and evolution of cellulose-synthesizing enzyme complexes (terminal complexes) in algae is reviewed. There is now ample evidence that cellulose synthesis occurs at the plasma membrane-bound cellulose synthase, with the exception of some algae that produce cellulosic scales in the Golgi apparatus. Freeze-fracture studies of the supramolecular organization of the plasma membrane support the view that the rosettes (a six-subunit complex) in higher plants and both the rosettes and the linear terminal complexes (TCs) in algae are the structures that synthesize cellulose and secrete cellulose microfibrils. In the Zygnemataceae, each single rosette forms a 5-nm or 3-nm single “elementary” microfibril (primary wall), whereas rosettes arranged in rows of hexagonal arrays synthesize criss-crossed bands of parallel cellulose microfibrils (secondary wall). In Spirogyra, it is proposed that each of the six subunits of a rosette might synthesize six β-1,4-glucan chains that cocrystallize into a 36-glucan chain “elementary” microfibril, as is the case in higher plants. One typical feature of the linear terminal complexes in red algae is the periodic arrangement of the particle rows transverse to the longitudinal axis of the TCs. In bangiophyte red algae and in Vaucheria hamata, cellulose microfibrils are thin, ribbon-shaped structures, 1–1.5 nm thick and 5–70 nm wide; details of their synthesis are reviewed. Terminal complexes appear to be made in the endoplasmic reticulum and are transferred to Golgi cisternae, where the cellulose synthases are activated and may be transported to the plasma membrane. In algae with linear TCs, deposition follows a precise pattern directed by the movement and the orientation of the TCs (membrane flow). A principal underlying theme is that the architecture of cellulose microfibrils (size, shape, crystallinity, and intramicrofibrillar associations) is directly related to the geometry of TCs. The effects of inhibitors on the structure of cellulose-synthetizing complexes and the relationship between the deposition of the cellulose microfibrils with cortical microtubules and with the membrane-embedded TCs is reviewed In Porphyra yezoensis, the frequency and distribution of TCs reflect polar tip growth in the apical shoot cell.The evolution of TCs in algae is reviewed. The evidence gathered to date illustrates the utility of terminal complex organization in addressing plant phylogenetic relationships.     

Cell wall development in Oocystis solitaria in the presence of polysaccharide binding dyes

Cell wall and thus cellulose microfibril formation in the presence of Congo red or Calcofluor white by Oocystis solitaria autospores was investigated ultrastructurally and chemically. The prevention of microfibril formation by both substances is accompanied by drastic changes of microfibril synthesis and orientation as well as the morphology of plasma-membrane-associated E-face terminal complexes. Removal of Congo red and Calcofluor white from the culture medium results in the recovery of microfibril formation, of a normal patterned microfibril arrangement, and of terminal complexes with extending microfibril imprints.     

Development of cell wall appendages inAcanthosphaera zachariasi (Chlorococcales): Kinetics,site of cellulose synthesis and of microfibril assembly,and barb formation

Summary The investigation of the formation of cell wall appendages inAcanthosphaera by means of light and electron microscopy and by the use of dyes which interfere with microfibril assembly resulted in several observations which are helpful to an understanding of the formation of normal cell walls. The barbs are built up in the ER, pass through the Golgi apparatus, and are extruded exocytotically after cytokinesis, a remarkable example of the secretion of a structured product. Each cellulose microfibril in a spike develops in a distinct pit of the plasmalemma. The pits are aggregated in a pit field, generating one spike, and are closely adjacent to a basal vesicle which might have morphogenetic and/or regulatory functions. The pits are the site of cellulose synthesis; here the plasmalemma is conspicuously thickened. As shown directly and by the application of Calcofluor white and Congo red, the microfibrils assemble at a certain distance from the plasma membrane,i.e. cellulose synthesis and microfibril assembly are separated by a gap. It is discussed whether single glucan chains or small bundles of them are released from the plasmalemma. The elongation rate of the spikes indicates that about 1000 glycosidic linkages per glucan chain per minute are formed.     

Development of cellulose synthesizing complexes inBoergesenia andValonia

Summary The development of linear cellulose synthesizing complexes (=TCs) of two selected siphonocladalean algae,Boergesenia forbesii andValonia ventricosa was investigated by following the time course of the regeneration of cell walls with the freeze fracture technique after aplanospore induction. The following structural changes of TC development were examined: (1) TCs initiatede novo; (2) the first nucleation of TC subunits occurs within 2 hr inBoergesenia and 5 hr inValonia after aplanospore induction, immediately followed by the assembly of cellulose microfibrils; (3) TCs increase their length during the assembly of randomly oriented microfibrils; and, (4) TCs stop increasing in length after the assembly of ordered microfibrils begins, with some time lag. The data demonstrate that linear TCs are not artificial products but dynamic entities which are involved in the assembly of cellulose microfibrils.     

Lattice images from ultrathin sections of cellulose microfibrils in the cell wall of Valonia macrophysa Kütz.

The crystalline ultrastructure and orientation of cellulose microfibrils in the cell wall of Valonia macrophysa were investigated by means of high-resolution electron microscopy of ultrathin (approx. 28 nm) sections. With careful selection of imaging conditions, ultrastructural aspects of the cell wall that had remained unresolved in previous studies were worked out by direct imaging of crystal lattice of cellulose microfibrils. It was confirmed that each microfibril is a single crystal having a lateral dimension of 20·20 nm², because lattice images of 0.39 nm resolution were clearly recorded with no major disruption in the whole area of the cross section of the microfibril. There was no evidence for the existence of 3.5-nm elementary fibrils which have been considered to be basic crystallographic and morphological units of cellulose in general. It was also confirmed that the axial directions (crystallographic fiber direction) of adjacent microfibrils in each single lamella of the cell wall are opposite to each other.     

Assembly of Cellulose Synthesizing Complexes on the Plasma Membrane of Boodlea coacta

The assembly of cellulose synthesizing complexes (terminal complexes,TCs) on the plasma membrane of Boodlea coacta was investigatedduring the formation of both the matrix-rich layer (MRL) andfibril-rich layers (FRLs) of cell walls. The TCs appeared tobe located mostly within the outer leaflet of the plasma membrane,and were observed as elliptical protrusions consisting of manyparticles of about 9 nm in diameter. Their length varied from100 to 500 nm (average, 220 nm) during MRL formation and from100 to 860 nm (average, 360 nm) during FRL formation. A correlationwas found between the length of TCs and the microfibril widthin both MRL and FRL. On the E-face of the plasma membrane, numerous round protrusions(30–130 nm in diameter), consisting of many particles,8–10 nm in diameter, were also present. Their densitywas greater during FRL formation than during MRL formation.Some of these structures larger than 100 nm were associatedwith microfibril impressions and some appeared to be bound tothe TCs. These protrusions increased in number with Calcofluortreatment but decreased in number when the dye was removed fromthe culture medium. Thus, the TCs may be assembled from massesof particles aggregated on the outer surface of the plasma membrane,and may grow longer by incorporation of these masses. The appearanceof the longer TCs during FRL formation is probably due to thegreater density of these masses. (Received May 1, 1985; Accepted August 16, 1985)     

Cell-wall formation in Pelvetia embryos. A freeze-fracture study

The cell-wall formation in the egg of Pelvetia fastigiata (J.G. Agardh) DeToni (Fucaceae) was studied with freeze-fracture. 1. The wall is lamellated with microfibrils approximately parallel in each lamella. The average orientation of microfibrils turns about 35° in each subsequent lamella. This slow turn gives rise to bow-shaped arcs when the wall is obliquely cross fractured. 2. The organization of the fibrils in the innermost lamellae is visualized by their imprints on the plasma membrane. These imprints are the result of both turgor pressure and adhesion of fibrils to the membrane. 3. Strings of membrane particles appear on the plasma membrane shortly after fertilization. They seem to be formed by a fertilization-induced aggregation of isolated membrane particles. Later each string comes to lie under a fibril and along its imprint. Peculiar lateral rips indicate that some strings are tightly bound to a fibril and may be involved in its orientation. 4. Wall formation in Pelvetia is marked by pronounced secretory activities. Following fertilization, the fusion of cortical vesicles and other vesicles make numerous loci in the plasma membrane. In older embryos, fibril-free patches in the plasma membrane mark the position of microfibril elongation centers in the wall matrix. Prior to germination, these elongation centers and their corresponding membrane patches reach a high density at the presumptive rhizoid end.We wish dedicate this paper to R.D. Preston     

The assembly of cellulose microfibrils in Valonia macrophysa Kütz

The assembly of cellulose microfibrils was investigated in artificially induced protoplasts of the alga, Valonia macrophysa (Siphonocladales). Primary-wall microfibrills, formed within 72 h of protoplast induction, are randomly oriented. Secondary-wall lamellae, which are produced within 96 h after protoplast induction, have more than three orientations of highly ordered microfibrils. The innermost, recently deposited micofibrils are not parallel with the cortical microtubules, thus indicating a more indirect role of microtubules in the orientation of microfibrils. Fine filamentous structures with a periodicity of 5.0–5.5 nm and the dimensions of actin were observed adjacent to the plasma membrane. Linear cellulose-terminal synthesizing complexes (TCs) consisting of three rows, each with 30–40 particles, were observed not only on the E fracture (EF) but also on P fracture (PF) faces of the plasma membrane. The TC appears to span both faces of the bimolecular leaflet. The average length of the TC is 350 nm, and the number of TCs per unit area during primary-wall synthesis is 1 per m². Neither paired TCs nor granule bands characteristic of Oocystis were observed. Changes in TC structure and distribution during the conversion from primary- to secondary-wall formation have been described. Cellulose microfibril assembly in Valonia is discussed in relation to the process among other eukaryotic systems.Abbreviations TC terminal complex - EF E (outer leaflet) fracture face of the plasma membrane - PF P (inner leaflet) fracture face of the plasma membrane - MT microtubule - PS protoplasmic surface of the membrane     

The control of cellulose microfibril deposition in the cell wall of higher plants

In maize (Zea mays L.) and pine (Pinus taeda L.) seedlings, cellulose microfibril impressions are present on freeze-fractured plasma membranes. It has been proposed that impressions of newly synthesized microfibrils are a record of the movement of terminal synthesizing complexes through the plasma membrane (Mueller and Brown, 1980, J. Cell Biol. 84, 315–326). The association of terminal complexes with the ends of microfibril impressions or with the ends of microfibrils torn through the membrane indicates the orientation of microfibril tips. Unidirectionally-oriented microfibril tips (all pointing in the same direction) are associated with the organized deposition of parallel arrays of microfibrils. Multidirectionally-oriented microfibril tips were observed in a cell in which microfibril deposition was unusually disorganized. Microfibril patterns around pit fields are asymmetric and resemble flow patterns. Unidirectionally-oriented tears are associated with these microfibrils. Although microfibril orientations are deflected around pit fields, the main axis of microfibril orientation is maintained across the surface of the cell. The hypothesis is proposed that the interaction of a flowing plasma membrane with microfibril synthesizing complexes in the plane of the membrane may result in unidirectional deposition and asymmetric microfibril impressions around pit fields.Some of this work has been published in preliminary form (Brown 1979)     

Cell expansion and microfibril deposition inClosterium ehrenbergii

Cells ofClosterium ehrenbergii expanded for about 4.5 hr after vegetative cell division and about 3 hr after sexual cell division. Short cells were produced by the sexual expansion. At the early stage of the vegetative and the sexual expansion, most microfibrils were deposited transversely to the cell axis on the inner surface of the new wall. Then, bundles of microfibrils, running in various directions, overlaid the transverse microfibrils already deposited, at the late stage of the both types of expansion. The pattern of microfibril deposition changed from the transverse to the bundled pattern about 4 hr after the vegetative and about 2 hr after the sexual cell division, respectively. The change of pattern of microfibril deposition seemed to be highly correlated with cessation of cell expansion.     

Colchicine and microfibril orientation

Summary Investigations on the mechanism of orientation of the cellulose microfibrils of the green algaOocystis solitaria have been carried out. This organism demonstrates easily observable and highly ordered microfibrils in its wall, which are arranged parallel to one another and regularly alternate at 90 from layer to layer of which there are approximately 30. During the entire wall development, and always parallel to one of the microfibril directions, are microtubules lying in the cortical cytoplasm. In the presence of 10^–2 M colchicine, microtubules are no longer detected and the typical cell wall pattern is not developed. The possible role of microtubules in the orientation of cellulose microfibrils is briefly discussed.     

On the alignment of cellulose microfibrils by cortical microtubules: A review and a model

Summary The hypothesis that microtubules align microfibrils, termed the alignment hypothesis, states that there is a causal link between the orientation of cortical microtubules and the orientation of nascent microfibrils. I have assessed the generality of this hypothesis by reviewing what is known about the relation between microtubules and microfibrils in a wide group of examples: in algae of the family Characeae,Closterium acerosum, Oocystis solitaria, and certain genera of green coenocytes and in land plant tip-growing cells, xylem, diffusely growing cells, and protoplasts. The salient features about microfibril alignment to emerge are as follows. Cellulose microfibrils can be aligned by cortical microtubules, thus supporting the alignment hypothesis. Alignment of microfibrils can occur independently of microtubules, showing that an alternative to the alignment hypothesis must exist. Microfibril organization is often random, suggesting that self-assembly is insufficient. Microfibril organization differs on different faces of the same cell, suggesting that microfibrils are aligned locally, not with respect to the entire cell. Nascent microfibrils appear to associate tightly with the plasma membrane. To account for these observations, I present a model that posits alignment to be mediated through binding the nascent microfibril. The model, termed templated incorporation, postulates that the nascent microfibril is incorporated into the cell wall by binding to a scaffold that is oriented; further, the scaffold is built and oriented around either already incorporated microfibrils or plasma membrane proteins, or both. The role of cortical microtubules is to bind and orient components of the scaffold at the plasma membrane. In this way, spatial information to align the microfibrils may come from either the cell wall or the cell interior, and microfibril alignment with and without microtubules are subsets of a single mechanism.Dedicated to Professor Brian E. S. Gunning on the occasion of his 65th birthday