Growth,cell wall formation and differentiation in the protonema of the moss,Funaria hygrometrica: Effects of plasmolysis on the developmental program and its expression

Summary Cultivation ofFunaria protonemata under plasmolytic or slightly subplasmolytic conditions initially causes a cessation of growth which is accompanied by a transient disappearance (or strong reduction in frequency, respectively) of putative cellulose synthesizing particle rosettes in the plasma membrane. Simultaneously, the formation and exocytosis of cell wall materialsecreting Golgi vesicles is slowed down. The latter process does not become apparent for several hours, though the reduction in activity can be proved indirectly. As a consequence of the imbalance between exocytosis, cell wall material accumulates in the plasmolytic space, generally at the cell tip. This indicates that the pattern of local, polar deposition of cell wall formation and cell elongation, membrane debris as well as wall material is maintained for some time. Later, however, the whole protoplast may become covered by new wall layers. Potentially growing filament tips and the distal region of nontip cells increase in diameter after longer cultivation in subplasmolytic conditions. It is suggested that normal wall growth results from a softening of the existing wall, its stretching and simultaneous stabilization by the apposition of new wall layers. We believe that the swelling is caused by a change in the equilibrium between the obviously less affected softening process and the imperfect stabilization by new wall layers because the wall layers which are formed at reduced turgor pressure are looser than normal and may have a changed composition.Kinetin-induced buds do not develop under plasmolytic conditions. Instead, spiral filaments are formed which readily give rise to buds when the osmotic value of the (kinetin-containing) medium is normalized. The results show that plasmolysis affects the expression of the developmental program rather than its initiation or maintenance.     

Proteomic profiling and glycomic analysis of the yeast cell wall in strains with Aflatoxin B1 elimination ability

The use of microorganisms for Aflatoxin B₁ elimination has been studied as a new alternative tool and it is known that cell wall carried out a critical role. For that reason, cell wall and soluble intracellular fraction of eight yeasts with AFB₁ detoxification capability were analysed. The quantitative and qualitative comparative label-free proteomic allowed the identification of diverse common constituent proteins, which revealed that putative cell wall proteins entailed less than 10% of the total proteome. It was possible to characterize different enzymes linked to cell wall polysaccharides biosynthesis as well as other proteins related with the cell wall organization and regulation. Additionally, the concentration of the principal polysaccharides was determined which permitted us to observe that β-glucans concentration was higher than mannans in most of the samples. In order to better understand the biosorption role of the cell wall against the AFB₁, an antimycotic (Caspofungin) was used to damage the cell wall structure. This assay allowed the observation of an effect on the normal growth of those yeasts with damaged cell walls that were exposed to AFB₁. This effect was not observed in yeast with intact cell walls, which may reveal a protective role of this structure against mycotoxins.     

Kelp versus coralline: cellular basis for mechanical strength in the wave‐swept seaweed Calliarthron (Corallinaceae,Rhodophyta)1

Previous biomechanical studies of wave‐swept macroalgae have revealed a trade‐off in growth strategies to resist breakage in the intertidal zone: growing in girth versus growing strong tissues. Brown macroalgae, such as kelps, grow thick stipes but have weak tissues, while red macroalgae grow slender thalli but have much stronger tissues. For example, genicular tissue in the articulated coralline Calliarthron cheilosporioides Manza is more than an order of magnitude stronger than some kelp tissues, but genicula rarely exceed 1 mm in diameter. The great tissue strength of Calliarthron genicula results, at least in part, from a lifelong strengthening process. Here, a histological analysis is presented to explore the cellular basis for mechanical strengthening in Calliarthron genicula. Genicula are composed of thousands of fiber‐like cells, whose cell walls thicken over time. Thickening of constitutive cell walls likely explains why older genicula have stronger tissues: a mature geniculum may be >50% cell wall. However, the material strength of genicular cell wall is similar to the strength of cell wall from a freshwater green alga, suggesting that it may be the quantity—not the quality—of cell wall material that gives genicular tissue its strength. Apparent differences in tissue strength across algal taxa may be a consequence of tissue construction rather than material composition.     

Feedback from the wall

The ability of cells to perceive changes in the composition and mechanical properties of their cell wall is crucial for plants to achieve coordinated growth and development. Evidence is accumulating to show that the plant cell wall, like its yeast counterpart, is capable of triggering multiple signalling pathways. The components of the cell wall that are responsible for initiating these signal responses remain unknown; however, recent technological advances in cell wall analysis may now facilitate the identification of these components and accelerate the characterisation of changes that occur in cell wall mutants.     

The role of the root cell wall in the heavy metal tolerance ofAthyrium yokoscense

Cells of the roots ofA. yokoscense growing on metalliferous habitats were fractionated into their cell wall and cytoplasmic components. About 70–90% of the total copper, zinc and cadmium was located in the cell wall. Copper had a markedly greater affinity for the cell wall than zinc and cadmium, and was prevented from entering the cytoplasm. A large proportion of these heavy metals in the cell wall were exchanged as ions. The capacity of the cell wall for exchanging metal ions inA. yokoscense was higher than in other plants growing on metalliferous habitats. However, compared with different ferns unable to grow on metalliferous habitats, this capacity was not unique toA. yokoscense. Consequetly, the root cell wall ofA. yokoscense is considered to be an important site of metal ion storage and may play the role of an excretory organ for heavy metals. On the other hand, as proportion of the heavy metls was transported to the cytoplasm, where the metal content was much higher than the average for normal ferns. This would suggest thatA. yokoscense has another metabolic mechanism related to metal tolerance.     

Indigestibility of plant cell wall by the Australian plague locust, Chortoicetes terminifera

The plant cell wall may play an important role in defence against herbivores since it can be both a barrier to, and nutrient diluter of, the easily digested cell contents. The aim of this study was to investigate the digestibility of the cell wall of three grasses, Triticum aestivum L., Dactyloctenium radulans (R. Br.) Beauv., and Astrebla lappacea (Lindl.) Domin, by the Australian plague locust, Chortoicetes terminifera Walker (Orthoptera: Acrididae, Acridinae) as determined by the Van Soest method [ Van Soest PJ, Robertson JB & Lewis BA (1991) Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. Journal of Dairy Science 74: 3583–3597]. Determination of plant cell wall digestion by locusts required a precise methodological procedure to determine both the exact intake and the concentration of cell wall in the diet and the faeces. Plant cell wall determination is affected by the particle size distribution of the dried plant material. All three grasses differed in the percentage of cell wall per gram dry matter and the proportions of hemicellulose, cellulose, and acid‐detergent sulphuric lignin within the cell wall. The locust was unable to digest the cell wall of any of the grasses. Thus, plant cell walls are a mechanical barrier hindering locusts assimilating nutrients. That is, access, rather than nutrient concentration per se, may be limiting nutrient factor.     

Expansin-regulated cell elongation is involved in the drought tolerance in wheat

Water stress restrains plant growth. Expansin is a cell wall protein that is generally accepted to be the key regulator of cell wall extension during plant growth. In this study, we used two different wheat cultivars to study the involvement of expansin in drought tolerance. Wheat coleoptile was used as the material in experiment. Our results indicated that water stress induced an increase in acidic pH-dependant cell wall extension, which is related to expansin activity; however, water stress inhibited coleoptile elongation growth. The increased expansin activity was mainly due to increased expression of expansin protein that was upregulated by water stress, but water stress also resulted in a decrease in cell wall acidity, a negative factor for cell wall extension. Decreased plasma membrane H⁺-ATPase activity was involved in the alkalinization of the cell wall under water stress. The activity of expansin in HF9703 (a drought-tolerant wheat cultivar) was always higher than that in 921842 (a drought-sensitive wheat cultivar) under both normal and water stress conditions, which may be correlated with the higher expansin protein expression and plasma membrane H⁺-ATPase activity observed in HF9703 versus 921842. However, water stress did not change the susceptibility of the wheat cell wall to expansin, and no difference in this susceptibility was observed between the drought-tolerant and drought-sensitive wheat cultivars. These results suggest the involvement of expansin in cell elongation and the drought resistance of wheat.     

Temporal and spatial immunolocalization of glucomannans in differentiating earlywood tracheid cell walls of Cryptomeria japonica

We investigated the deposition of glucomannans (GMs) in differentiating earlywood tracheids of Cryptomeria japonica using immunocytochemical methods. GMs began to deposit at the corner of the cell wall at the early stages of S₁ formation and showed uneven distribution in the cell wall during S₁ formation. At the early stages of S₂ formation, limited GM labeling was observed in the S₂ layer, and then the labeling increased gradually. In mature tracheids, the boundary between the S₁ and S₂ layers and the innermost part of the cell wall showed stronger labeling than other parts of the cell wall. Deacetylation of GMs with mild alkali treatment led to a significant increase in GM labeling and a more uniform distribution of GMs in the cell wall than that observed before deacetylation, indicating that some GM epitopes may be masked by acetylation. However, the changes in GM labeling after deacetylation were not very pronounced until early stages of S₂ formation, indicating that GMs deposited in the cell wall at early stages of cell-wall formation may contain fewer acetyl groups than those deposited at later stages. Additionally, the density of GM labeling increased in the cell wall in both specimens before and after GM deacetylation, even after cell-wall formation was complete. This finding suggests that some acetyl groups may be removed from GMs after cell-wall formation is complete as part one of the tracheid cell aging processes.     

Changes in the water binding characteristics of the cell walls from transgenic Nicotiana tabacum leaves with enhanced levels of peroxidase activity

Pore size in the cell wall matrix may affect cell wall–water relations, particularly under osmotic stress. Cross linkage of plant cell wall matrix polymers is an important step in the formation of this structure and peroxidases have been proposed to catalyse the cross-linking of phenolic constituents. Transgenic tobacco ( Nicotiana tabacum ) plants expressing a basic tomato peroxidase gene (TPX2) showed increased apoplastic ferulic acid peroxidase activity in mature leaves. This enhanced activity was not associated with a decreased leaf growth. Differential scanning calorimetry (DSC) of control dried cell walls showed a putative glass transition, after Ca²⁺ removal, that was absent in the transgenic line. This would indicate that transgenic walls were more rigid. DSC analysis of water-hydrated cell wall preparations distinguished two pools of water, freezable and non-freezable water. The amount of non-freezable water, which corresponds to strongly bound water, was higher in the transgenic line (64 versus 55%). DSC thermograms of the transgenic cell wall were displaced to lower temperatures, and this may be interpreted as the result of a stronger interaction between this freezable water and this wall. Water sorption and desorption isotherms, obtained at relative humidity ranging from 5 to 93%, demonstrated the presence of very strongly bound water in the transgenic cell walls that was absent in controls. Water sorption–desorption hysteresis of the isotherms was evident in the control wall but not in the transgenic line. These changes in cell wall–water interaction seem to be relevant at the organ level because leaf discs of transgenic plants maintained higher relative water content than control discs, at water potentials between −1.05 and−2.31 MPa.     

Surface chemical properties of purified root cell walls from two tobacco genotypes exhibiting different tolerance to manganese toxicity

Surface chemical characteristics of root cell walls extracted from two tobacco genotypes exhibiting differential tolerance to Mn toxicity were studied using potentiometric pH titration and Fourier transform infrared spectroscopy. The Mn-sensitive genotype KY 14 showed a stronger interaction of its cell wall surface with metal ions than did the Mn-tolerant genotype Tobacco Introduction (T.I.) 1112. This observation may be attributed to the relatively higher ratio of COO⁻ to COOH in KY 14 cell walls than that found in the cell walls of T.I. 1112 in the pH range of 4 to 10. For both genotypes, the strength of binding between metal ions and cell wall surface was in the order of Cu > Ca > Mn > Mg > Na. However, a slightly higher preference of Ca over Mn was observed with the T.I. 1112 cell wall. This may explain the high accumulation of Mn in the leaves of Mn-tolerant genotype T.I. 1112 rather than the high accumulation of Mn in roots, as occurred in Mn-sensitive KY 14. It is concluded that surface chemical characteristics of cell walls may play an important role in plant metal ion uptake and tolerance.     

Immunogold localization of xyloglucan and rhamnogalacturonan I in the cell walls of suspension-cultured sycamore cells

Plant cell walls serve several functions: they impart rigidity to the plant, provide a physical and chemical barrier between the cell and its environment, and regulate the size and shape of each cell. Chemical studies have provided information on the biochemical composition of the plant cell walls as well as detailed knowledge of individual cell wall molecules. In contrast, very little is known about the distribution of specific cell wall components around individual cells and throughout tissues. To address this problem, we have produced polyclonal antibodies against two cell wall matrix components; rhamnogalacturonan I (RG-I), a pectic polysaccharide, and xyloglucan (XG), a hemicellulose. By using the antibiodies as specific markers we have been able to localize these polymers on thin sections of suspension-cultured sycamore cells (Acer pseudoplatanus). Our results reveal that each molecule has a unique distribution. XG is localized throughout the entire wall and middle lamella. RG-I is restricted to the middle lamella and is especially evident in the junctions between cells. These observations indicate that plant cell walls may have more distinct chemical (and functional?) domains than previously envisaged.     

The Importance of Cell Size in the Water Relations of Plants

Several structural changes in cotton (Gossypium hirsutum L.) leaves attendant on development under conditions of water deficit were examined. Cell size was less and cell wall thickness greater in the leaves of stressed plants than in leaves of well-watered plants. A short review of the literature suggested that the lesser cell size is a fairly general observation and that it may contribute to plant resistance to moisture stress. A simple model is developed to investigate the influence of the reduction of cell size on cellular water relations. The predictions which can be drawn from simulations with this model are that smaller cells should maintain turgor to lower values of water potential than larger cells. Rather large changes in cell water relations are predicted for small changes in cell size. These effects are related principally to the changing proportion of cell water which resides in the cell wall and is external to the plasmalemma and the osmotic adjustment system. This prediction is in agreement with several observerations on the behavior of stress-hardened plants and supports the hypothesis that plants or tissues with the smaller cell size will be more tolerant of low water potential.     

Organization of mature external glands on the trap and other organs of the bladderwortUtricularia monanthos

Summary The mature dome-shaped glands which cover the outer surfaces of the trap, leaves, anchor and runner stolons inU. monanthos are described using conventional and some high voltage transmission electron microscopy. The glands occur as scattered ordinary external glands and as a compact clump of vestibule glands at the entrance to the doorway. Each gland rests on a basal epidermal cell and consists of a single pedestal and terminal cell. Vestibule and leaf glands differ slightly from the other glands mainly in the structure of the outer wall of the terminal cell. Nuclear crystals are prominent and the cytoplasm of the pedestal and terminal cells contains tubular structures usually aggregated near the nucleus. The pedestal cell is a transfer cell with short wall protuberances on the outer wall, conspicuous mitochondria and a heavily impregnated lateral wall.The terminal cell often has an outer wall that is greatly thickened and a protoplast that may degenerate early. In the most developed cells the protoplast remains active for a long period and the outer wall is differentiated into several layers. The outermost layer is cuticularized consisting of an open meshwork of deposits. In leaf glands a local polysaccharide mass is usually developed within the cuticularized region. The inner non-impregnated region of the outer wall may show four layers. In vestibule glands fewer layers are present and the wall shows prominent lamellations. Some ordinary external glands differentiate a sponge-like substructure within the inner wall.The ultrastructure and function of the glands are discussed. We support the concept that mature external glands are responsible for secreting water, with those on traps being particularly active during the resetting of the organ. Our work provides a structural basis for recent suggestions by other workers that the mechanism of secretion probably involves establishing a standing osmotic gradient within the gland.     

CELL WALL FORMATION IN PEDIASTRUM BIRADIATUM AS REVEALED BY THE ELECTRON MICROSCOPE

Moner, J. G. (U. Massachusetts, Amherst), and G. B. Chapman. Cell wall formation in Pediastrum biradiatum as revealed by the electron microscope. Amer. Jour. Bot. 50(10): 992–998. Illus. 1963.-An electron microscopic study of cell wall development in P. birudiatum is described. Micrographs were taken of thin sections of cells from several stages involved in the transformation of the motile zoospore into the 4-pronged adult cell type during asexual reproduction. The cell wall begins as a thin membrane which does not change noticeably during the transformation of the zoospore to the adult cell type. In a subsequent period of not more than 6 hr, a definitive cell wall arises accompanied or followed shortly by the appearance of a globular network on the underside of the cell wall proper. During all of the developmental stages osmiophilic globuli are found in the cytoplasm, frequently at the cell surface. Similar, though smaller, globuli are found in the chloroplasts of Pediastrum and other plants, indicating that these bodies may have a plastid origin. It is suggested that whole osmiophilic globuli, or parts thereof, may be transferred to the cell wall proper, giving rise, ultimately, to the globular network.     

On Vessel Member Differentiation in the Bean (Phaseolus vulgaris L.)

Certain ultrastructural features of vessel member differentiationwere examined in the primary xylem of petiole of bean (Phaseolusvulgaris L.). The cells used had helical secondary wall thickeningsand simple perforation plates. The primary cell wall increasesin thickness before the helices of secondary wall develop. Ina common wall between two vessel members of different ages,theprimary thickening occurs first in the older cell so thatfor a time the middle lamella is located closer to the youngercell rather than medianly. Apparently the helix is depositedafter the primary wall of a given cell reaches maximum thickness.The perforation of the end wall is preceded by primary thickeningof the part of the wall that is later removed. The marginalregion remains relatively thin and becomes covered with a rimof secondary wall. Vesicles with fibrous content appear nearthe surface within the end wall shortly before the perforationoccurs. A highly vacuolated protoplast with a much enlargednucleus and numerous organdIes is present during cell wall differentiation.After that process is completed, the protoplast disintegratesand the primary wall bearing the helix is hydrolysed where itis exposed to the cell lumen and, under certain conditions,also under the secondary wall.     

Method for determining solutes in the cell walls of leaves

A perfusion method is described whereby large discs of amphistomatous leaves are vacuum-perfused with water so that either successive fractions of perfusate may be analyzed for solutes or the infused water may be displaced and collected after equilibration with the leaf cells. With castor bean leaves, estimates of electrolyte concentration in cell wall water by the two methods were similar. Total electrolytes in leaf cell wall water of castor beans (Ricinus communis), sunflower (Helianthus annuus), and cabbage (Brassica oleracea capitata) from nonsaline cultures were about 2, 2, and 10 milliequivalents per liter, respectively, increasing to 4, 10, and 30 milliequivalents per liter under saline conditions. Electrolytes recovered in successive fractions were similar in composition, and continuous perfusion resulted in a steady release of solutes, the concentration in the perfusate varying inversely with the perfusion rate. Diffusional release of solutes from cells was less than expected at low perfusion rates, suggesting that solute reabsorption may increase as solute concentration in the perfusate increases with decreased perfusion rates. Perfusate concentration and composition were essentially unaffected by temperature (2 and 23 C) or by perfusing with 0.5 mm CaSO₄ rather than with water. Electrolytes in perfusates on an equivalent basis were Ca²⁺, 30%; Mg²⁺, 10%; and Na⁺ + K⁺, 60%, the proportions of sodium increasing from 10 to 50% in leaves (cabbage) that accumulated sodium under saline conditions. Salinity (added NaCl) of the root culture medium caused a 3- to 5-fold increase in total cell wall electrolyte concentration, but this amounted to an increase from less than 1 or a few per cent to no more than 7% (in cabbage) of the cell sap electrolyte concentrations. Solutes in the cell wall appear to be in dynamic equilibrium with intracellular solutes.     

Differences in cell wall components and allocation of boron to cell walls confer variations in sensitivities of Brassica napus cultivars to boron deficiency

Aims

The cell wall is the main binding site of boron (B) in plants, and the differences in B requirements among different plant species are determined by pectic polysaccharide contents in the cell walls. The aim of this research was to illustrate the relationship between cell wall properties and allocation of B to cell wall and the differential sensitivity of Brassica napus cultivars to B deficiency.

Methods

Two cultivars with opposite B efficiency were used to analyse the relationship among cell wall pectin contents and glycosyl composition, B uptake and allocation, gene expression and cell wall ultrastructure.

Results

The Brassica napus B-efficient cultivar Qingyou 10 was more tolerant to B deficiency, exhibiting a higher biomass production, milder B deficiency symptoms and less cell wall thickening compared to the Brassica napus B-inefficient cultivar Westar 10. These differences were attributed to two factors; the first was that Qingyou 10 accumulated more B and distributed significantly higher proportion of it to the cell wall pectins than did Westar 10 under low B supply. Also, the cell walls of Qingyou 10 exhibited relatively less B-binding sites than those of Westar 10, which was indicated by the lower cell wall extraction rates, less pectin and glycosyl residue contents under the B-deficient and B-sufficient conditions. A comparison of the KDOPS gene expression levels in the two conditions suggests that Westar 10 had a higher potential for biosynthesizing B-binding substances than did Qingyou 10, regardless of B levels.

Conclusions

These results suggest that both higher cell wall pectin polysaccharide content, and limited accumulation and allocation of B to the cell walls contribute to the greater sensitivity of Westar 10 to B deficiency. These two physiological aspects may determine the differences in B deficiency tolerance between Brassica napus cultivars Qingyou 10 and Westar 10. Comparably, the difference in accumulation and allocation of B to cell wall plays a much more important role than cell wall components to sensitivity difference of Brassica napus cultivars to B deficiency.     

Comparison of freezing tolerance in cultured plant cells and their respective protoplasts

The possibility that the plant cell wall influences the severity of freezing injury was examined by comparing the freeze stress response of intact cells and protoplasts from four different suspension cultures. In no case did the intact cells suffer more injury than the respective wall-less protoplasts, showing that mechanical strain imposed by the cell wall during freeze-thaw stress is not a major determinant of injury. For three of the four species studied, cells from which the wall was removed showed significantly greater freezing injury, indicating that the plant cell wall may have a protective role. Other researchers have suggested that cell wall rigidity may minimize freezing injury by slowing freeze-induced loss of cell water. We found that decreased enzyme digestibility (perhaps indicating greater rigidity) of cell walls accompanied cold acclimation in various tissues. These results provide impetus to research which will characterize low-temperature-induced cell wall modification in cold acclimating tissues.     

Microtubular configurations during the cellularization of coenocytic endosperm in Ranunculus sceleratus L.

Summary Endosperm cellularization in Ranunculus sceleratus was studied in terms of the initiation of cell-wall formation in the coenocytic endosperm. The first endosperm cell walls were in an anticlinal position relative to the cell wall of the embryo sac and originated from the cell plates and not from wall ingrowths from the embryo-sac wall itself. Alveolar endosperm was formed 3 days after pollination. Microtubules were associated with the freely growing wall ends of the anticlinal walls and were observed in various orientations that generally ranged from angles of 45 ° to 90 ° to the plane of the wall. They were absent in the regions where vesicles had already fused. These microtubules may function in maintaining the growth and the direction of growth of the anticlinal wall until cellularization is completed. At the site where three neighbouring alveoli share their freely growing wall ends, remarkable configurations of microtubules were observed: in each alveolus, microtubules ran predominantly parallel to the bisector of the angle formed by the common walls. These microtubules may form a physically stable framework and maintain the direction of growth of the wall edges. It is concluded that the growing edge of the anticlinal endosperm wall and its associated microtubules are a special continuum of the original phragmoplast that gave rise to the anticlinal wall.