Amount Of Cell Wall Polysaccharides Research Articles

The Modification of Cell Wall Properties Is Involved in the Growth Inhibition of Rice Coleoptiles Induced by Lead Stress.

Lead (Pb) is a widespread heavy metal pollutant that interferes with plant growth. In this study, we investigated the effects of Pb on the mechanical and chemical properties of cell walls and on the growth of coleoptiles of rice (Oryza sativa L.) seedlings grown in the air (on moistened filter paper) and underwater (submerged condition). Coleoptile growth of air-grown seedlings was reduced by 40% by the 3 mM Pb treatment, while that of water-grown ones was reduced by 50% by the 0.5 mM Pb. Although the effective concentration of Pb for growth inhibition of air-grown coleoptiles was much higher than that of water-grown ones, Pb treatment significantly decreased the mechanical extensibility of the cell wall in air- and water-grown coleoptiles, when it inhibited their growth. Among the chemical components of coleoptile cell walls, the amounts of cell wall polysaccharides per unit fresh weight and unit length of coleoptile, which represent the thickness of the cell wall, were significantly increased in response to the Pb treatment (3 mM and 0.5 mM Pb for air- and water-grown seedlings, respectively), while the levels of cell wall-bound diferulic acids (DFAs) and ferulic acids (FAs) slightly decreased. These results indicate that Pb treatment increased the thickness of the cell wall but not the phenolic acid-mediated cross-linking structures within the cell wall in air- and water-grown coleoptiles. The Pb-induced cell wall thickening probably causes the mechanical stiffening of the cell wall and thus decreases cell wall extensibility. Such modifications of cell wall properties may be associated with the inhibition of coleoptile growth. The results of this study provide a new finding that Pb-induced cell wall remodeling contributes to the regulation of plant growth under Pb stress conditions via the modification of the mechanical property of the cell wall.

Cell wall of feeds and their impact on protein digestibility: An in vitro method applied for pig nutrition

Plant-derived by-products of the food, drink, and fuel industry are low-cost ingredients, that are routinely used to formulate feeds for livestock, especially for pigs. Often, those ingredients are rich in dietary fibres (DF), which is known to have a negative influence on the digestive use of nutrients in pigs. The effect of DF on nutrient bioaccessibility (i.e., the release of nutrients from the plant tissue) and digestion (i.e., transformation of the plant tissue during digestion and the hydrolysis of nutrients by digestive enzymes) depends on their amount, but more importantly, on their nature and organisation within the cell wall. The aim of this work was to determine how DF from different sources affected protein bioaccessibility and proteolysis. We hypothesised that protein released from the feed matrix and hydrolysis in pig feed depend mainly on the nature and amount of cell wall polysaccharides (i.e., dietary fibre). To test this, we conducted an in vitro study where nine feed ingredients commonly used in pig feeding (i.e., soybean meal, barley, wheat, two varieties of peas, fava bean, chickpea, maize and sugar beet pulp) were digested using a simulated gastrointestinal digestion model. Cell wall integrity and proteolysis were assessed using biochemical, biophysical, and microscopic techniques. Protein bioaccessibility differed among the ingredients (P < 0.01), with sugar beet pulp and maize having the lowest fraction of protein released from the plant tissue (about 34 %) and chickpea the greatest (93 %). Protein hydrolysis values also varied greatly among the ingredients (P < 0.01) but did not always follow the same trend as that of bioaccessibility. For instance, soybean meal had the highest protein hydrolysis with 96 % and sugar beet pulp the lowest with 50 %. The particle size distribution and microscopy images provide an explanation for these differences, related to the physical barrier, swelling, and rupture of the cell wall. This study illustrated that the cell wall structure is specific for each ingredient, with consequences on bioaccessibility and digestibility that cannot be characterised by the composition in DF alone. In feed formulation, this concept ought to be accounted for to achieve optimal use and uptake of nutrients by the animal.

Impact of abiotic stress on the regulation of cell wall biosynthesis in Populus trichocarpa.

Growth of biomass for lignocellulosic biofuels and biomaterials may take place on land unsuitable for foods, meaning the biomass plants are exposed to increased abiotic stresses. Thus, the understanding how this affects biomass composition and quality is important for downstream bioprocessing. Here, we analyzed the effect of drought and salt stress on cell wall biosynthesis in young shoots and xylem tissues of Populus trichocarpa using transcriptomic and biochemical methods. Following exposure to abiotic stress, stem tissues reduced vessel sizes, and young shoots increased xylem formation. Compositional analyses revealed a reduction in the total amount of cell wall polysaccharides. In contrast, the total lignin amount was unchanged, while the ratio of S/G lignin was significantly decreased in young shoots. Consistent with these observations, transcriptome analyses show that the expression of a subset of cell wall-related genes is tightly regulated by drought and salt stresses. In particular, the expression of a part of genes encoding key enzymes for S-lignin biosynthesis, caffeic acid O-methyltransferase and ferulate 5-hydroxylase, was decreased, suggesting the lower S/G ratio could be partly attributed to the down-regulation of these genes. Together, our data identifies a transcriptional abiotic stress response strategy in poplar, which results in adaptive changes to the plant cell wall.

Cell wall polysaccharides: before and after autolysis of brewer's yeast.

Brewer's yeast is used in production of beer since millennia, and it is receiving increased attention because of its distinct fermentation ability and other biological properties. During fermentation, autolysis occurs naturally at the end of growth cycle of yeast. Yeast cell wall provides yeast with osmotic integrity and holds the cell shape upon the cell wall stresses. The cell wall of yeast consists of β-glucans, chitin, mannoproteins, and proteins that cross linked with glycans and a glycolipid anchor. The variation in composition and amount of cell wall polysaccharides during autolysis in response to cell wall stress, laying significant impacts on the autolysis ability of yeast, either benefiting or destroying the flavor of final products. On the other hand, polysaccharides from yeast cell wall show outstanding health effects and are recommended to be used in functional foods. This article reviews the influence of cell wall polysaccharides on yeast autolysis, covering cell wall structure changings during autolysis, and functions and possible applications of cell wall components derived from yeast autolysis.

Orange pulp and peel fibres: pectin-rich by-products from citrus processing for water binding and gelling in foods

Pulp and peels are the main by-products during juice extraction of citrus fruits. Typically, they contain large amounts of cell wall polysaccharides and can be a source of dietary fibres which are rich in pectin. In the past, numerous studies have focussed on hydration properties of fruit derived dietary fibres but very limited information is available on their gelling properties. The aim of the present study was to investigate both water binding and gelling properties of two orange fibre preparations from pulp and peel with a galacturonan content >27% and a degree of methoxylation >65%. The water retention capacity (WRC) of these fibres was significantly increased by mechanical pre-treatment but decreased by high temperatures (80 °C) during soaking. Moreover, intrinsic factors of the soaking solution significantly affected the water binding properties: a raising pH increased the WRC whereas the incorporation of calcium decreased it. Pulp fibre showed superior water binding properties compared to peel fibre. Gelling properties were evaluated by means of oscillation measurements as well as texture analyses and revealed that pulp and peel fibres were able to form sugar-acid gels at low pH < 2.7 and soluble solids loads of 55 and 60%, respectively. Pulp fibre exhibited similar gel points like isolated citrus pectin. Fibre gels were, however, less elastic than citrus pectin gels. Possibly this is a consequence of the swollen fibre matrix which might interfere with the pectin gel network.

Cell Wall Composition and Biomass Recalcitrance Differences Within a Genotypically Diverse Set of Brachypodium distachyon Inbred Lines.

Brachypodium distachyon (Brachypodium) has emerged as a useful model system for studying traits unique to graminaceous species including bioenergy crop grasses owing to its amenability to laboratory experimentation and the availability of extensive genetic and germplasm resources. Considerable natural variation has been uncovered for a variety of traits including flowering time, vernalization responsiveness, and above-ground growth characteristics. However, cell wall composition differences remain underexplored. Therefore, we assessed cell wall-related traits relevant to biomass conversion to biofuels in seven Brachypodium inbred lines that were chosen based on their high level of genotypic diversity as well as available genome sequences and recombinant inbred line (RIL) populations. Senesced stems plus leaf sheaths from these lines exhibited significant differences in acetyl bromide soluble lignin (ABSL), cell wall polysaccharide-derived sugars, hydroxycinnamates content, and syringyl:guaiacyl:p-hydroxyphenyl (S:G:H) lignin ratios. Free glucose, sucrose, and starch content also differed significantly in senesced stems, as did the amounts of sugars released from cell wall polysaccharides (digestibility) upon exposure to a panel of thermochemical pretreatments followed by hydrolytic enzymatic digestion. Correlations were identified between inbred line lignin compositions and plant growth characteristics such as biomass accumulation and heading date (HD), and between amounts of cell wall polysaccharides and biomass digestibility. Finally, stem cell wall p-coumarate and ferulate contents and free-sugars content changed significantly with increased duration of vernalization for some inbred lines. Taken together, these results show that Brachypodium displays substantial phenotypic variation with respect to cell wall composition and biomass digestibility, with some compositional differences correlating with growth characteristics. Moreover, besides influencing HD and biomass accumulation, vernalization was found to affect cell wall composition and free sugars accumulation in some Brachypodium inbred lines, suggesting genetic differences in how vernalization affects carbon flux to polysaccharides. The availability of related RIL populations will allow for the genetic and molecular dissection of this natural variation, the knowledge of which may inform ways to genetically improve bioenergy crop grasses.

Modifications of the cell wall of yeasts grown on hexadecane and under starvation conditions.

Electron-microscopic examinations have demonstrated local modifications in the cell wall of the yeast Candida maltosa grown on hexadecane. In our earlier studies, these modified sites, observed in other yeasts grown on oil hydrocarbons, were conventionally called 'canals'. The biochemical and cytochemical studies of C. maltosa have revealed a correlation between the formation of 'canals' and decrease in the amount of cell wall polysaccharides, glucan and mannan. The ultrathin sections and surface replicas have shown that the 'canals' are destroyed by pronase, thus indicating that a significant proportion of their content is represented by proteins. This finding was compatible with our earlier data on the localization of oxidative enzymes in 'canals' and possible participation of the 'canals' in the primary oxidation of hydrocarbons. A completely unexpected and intriguing phenomenon has been the appearance of 'canals' in the yeast C. maltosa under starvation conditions. Unlike the yeasts grown on hexadecane, mannan almost disappears in starving cells, while the quantity of glucan first decreases and then is restored to its initial level. The role of 'canals' in starving cells is as yet unclear; it is assumed that they acquire exoenzymes involved in the utilization of products of cell lysis in the starving population. In the future, 'canals' of starving cells will be studied in connection with their possible participation in apoptosis.

Suppression of Hydroxycinnamate Network Formation in Cell Walls of Rice Shoots Grown under Microgravity Conditions in Space.

Network structures created by hydroxycinnamate cross-links within the cell wall architecture of gramineous plants make the cell wall resistant to the gravitational force of the earth. In this study, the effects of microgravity on the formation of cell wall-bound hydroxycinnamates were examined using etiolated rice shoots simultaneously grown under artificial 1 g and microgravity conditions in the Cell Biology Experiment Facility on the International Space Station. Measurement of the mechanical properties of cell walls showed that shoot cell walls became stiff during the growth period and that microgravity suppressed this stiffening. Amounts of cell wall polysaccharides, cell wall-bound phenolic acids, and lignin in rice shoots increased as the shoot grew. Microgravity did not influence changes in the amounts of cell wall polysaccharides or phenolic acid monomers such as ferulic acid (FA) and p-coumaric acid, but it suppressed increases in diferulic acid (DFA) isomers and lignin. Activities of the enzymes phenylalanine ammonia-lyase (PAL) and cell wall-bound peroxidase (CW-PRX) in shoots also increased as the shoot grew. PAL activity in microgravity-grown shoots was almost comparable to that in artificial 1 g-grown shoots, while CW-PRX activity increased less in microgravity-grown shoots than in artificial 1 g-grown shoots. Furthermore, the increases in expression levels of some class III peroxidase genes were reduced under microgravity conditions. These results suggest that a microgravity environment modifies the expression levels of certain class III peroxidase genes in rice shoots, that the resultant reduction of CW-PRX activity may be involved in suppressing DFA formation and lignin polymerization, and that this suppression may cause a decrease in cross-linkages within the cell wall architecture. The reduction in intra-network structures may contribute to keeping the cell wall loose under microgravity conditions.

Possible Use of the Carbohydrates Present in Tomato Pomace and in Byproducts of the Supercritical Carbon Dioxide Lycopene Extraction Process as Biomass for Bioethanol Production

This study provides information about the carbohydrate present in tomato pomace (skins, seeds, and vascular tissues) as well as in the byproducts of the lycopene supercritical carbon dioxide extraction (SC-CO₂) such as tomato serum and exhausted matrix and reports their conversion into bioethanol. The pomace, constituting approximately 4% of the tomato fruit fresh weight, and the SC-CO₂-exhausted matrix were enzyme saccharified with 0.1% Driselase leading to sugar yields of ~383 and ~301 mg/g dw, respectively. Aliquots of the hydrolysates and of the serum (80% tomato sauce fw) were fermented by Saccharomyces cerevisiae . The bioethanol produced from each waste was usually >50% of the calculated theoretical amount, with the exception of the exhausted matrix hydolysate, where a sugar concentration >52.8 g/L inhibited the fermentation process. Furthermore, no differences in the chemical solubility of cell wall polysaccharides were evidenced between the SC-CO₂-lycopene extracted and unextracted matrices. The deduced glycosyl linkage composition and the calculated amount of cell wall polysaccharides remained similar in both matrices, indicating that the SC-CO₂ extraction technology does not affect their structure. Therefore, tomato wastes may well be considered as potential alternatives and low-cost feedstock for bioethanol production.

Gene silencing of barley P23k involved in secondary wall formation causes abnormal tiller formation and intercalary elongation

P23k is a monocot-unique protein that is highly expressed in barley. Our previous loss-of-function studies in barley leaves indicated that P23k, localized to tissues where cell wall polysaccharides accumulate, might contribute to secondary wall formation in the leaf. However, the P23k loss-of-function analysis was limited to the leaf, which is a vegetative organ. Considering the involvement of P23k in secondary wall formation, a dramatically altered phenotype is expected in the stem of P23k gene-silenced barley, where marked secondary wall deposition occurs during the reproductive growth stage. To test this hypothesis, barley striped mosaic virus-based virus-induced gene silencing of P23k was performed. Abnormal tiller formation and arrested intercalary elongation were observed in P23k-silenced barley. From these results, we speculated that cell wall architecture was altered by P23k gene silencing. Consistent with this idea, we observed a marked decrease in the amount of cell wall polysaccharides stained with calcofluor and down-regulation of the cellulose synthase-like CslF6 gene involved in (1,3;1,4)-β-D-glucan synthesis. Taken together, these results suggest that P23k is possibly involved in determining secondary wall architecture and contributes to tiller formation and intercalary elongation in barley.

Modification of chemical properties of cell walls by silicon and its role in regulation of the cell wall extensibility in oat leaves

Effects of silicon on the mechanical and chemical properties of cell walls in the second leaf of oat (Avena sativa L.) seedlings were investigated. The cell wall extensibility in the basal region of the second leaf was considerably higher than that in the middle and subapical regions. Externally applied silicon increased the cell wall extensibility in the basal region, but it did not affect the extensibility in the middle and subapical regions. The amounts of cell wall polysaccharides and phenolic compounds, such as diferulic acid (DFA) and ferulic acid (FA), per unit length were lower in the basal region than in the middle and subapical regions of the leaf, and silicon altered these amounts in the basal region. In this region, silicon decreased the amounts of matrix polymers and cellulose per unit length and of DFA and FA, both per unit length and unit matrix polymer content. Silicon treatment also lowered the activity of phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) in the basal region. In contrast, the amount of silicon in cell walls increased in response to silicon treatment in three regions. These results suggest that in the basal region, silicon reduces the net wall mass and the formation of phenolic acid-mediated cross-linkages between wall polysaccharides. Such modifications of wall architecture may be responsible for the silicon-induced increase in the cell wall extensibility in oat leaves.

Changes in levels of cell wall constituents in wheat seedlings grown under continuous hypergravity conditions

Effects of continuous hypergravity stimuli on the amounts and composition of cell wall constituents were investigated in wheat shoots. Hypergravity (300 g) treatment for three days after germination increased the net amount of cell wall polysaccharides such as hemicellulose and cellulose, but reduced the shoot elongation. As a result, the amount of cell wall polysaccharides per unit length of shoot increased under hypergravity. The hemicellulose fraction contained polysaccharides in the middle and low molecular mass range (5 kDa-1 MDa) and increased in response to hypergravity. Also, the amounts of arabinose (Ara) and xylose (Xyl), the major sugar components of the hemicellulose fraction, increased under hypergravity conditions. In addition to wall polysaccharides, hypergravity increased the amounts of cell wall-bound phenolic acids, such as ferulic acid (FA) and diferulic acid (DFA). Furthermore, the activity of phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) was enhanced under hypergravity conditions. These results suggest that continuous hypergravity stimulates the synthesis of cell wall constituents, especially hemicellulosic arabinoxylans and cell wall-bound FA and DFA in wheat shoots. The increased PAL activity may promote the formation of FA and DFA. These changes in cell wall architecture may be involved in making rigid and tough cell walls under hypergravity conditions and thereby contribute to the ability of plant to sustain their structures against gravitational stimuli.

Changes in cell-wall properties of wheat (Triticum aestivum) roots during aluminum-induced growth inhibition.

The effects of aluminum (Al) on root elongation, the mechanical extensibility of the cell wall, and the amount of cell-wall polysaccharides in the roots of Al-resistant (Atlas 66) and Al-sensitive (Scout 66) cultivars of wheat (Triticum aestivum L.) were examined. Exposure to 10 &mgr;M AlCl3 for 6 h inhibited root elongation in Scout 66 but not in Atlas 66. It also decreased the mechanical extensibility of the cell wall in the roots of both cultivars, but prominently only in the roots of Scout 66. The amount of hemicellulose in the 10-mm region of root apex of Scout 66 was increased by the exposure to Al, especially in the apical regions. Al did not influence the neutral sugar composition of either pectin or hemicellulose in Scout 66 roots. However, Al increased the weight-average molecular mass of hemicellulosic polysaccharides and the amounts of wall-bound ferulic and diferulic acids in Scout 66 roots. These findings suggest that Al modifies the metabolism of cell-wall components and thus makes the cell wall thick and rigid, thereby inhibiting the growth of wheat roots.

Hypergravity increases the molecular mass of xyloglucans by decreasing xyloglucan-degrading activity in azuki bean epicotyls.

Elongation growth of dark-grown azuki bean (Vigna angularis Ohwi et Ohashi cv. Takara) epicotyls was suppressed by hypergravity at 30 x g and above. Acceleration at 300 x g significantly decreased the mechanical extensibility of cell walls. The amounts of cell wall polysaccharides (pectin, hemicellulose-II and cellulose) per unit length of epicotyls increased under the hypergravity condition. Hypergravity also increased the amounts and the weight-average molecular mass of xyloglucans in the hemicellulose-II fraction, while decreasing the activity of xyloglucan-degrading enzymes extracted from epicotyl cell walls. These results suggest that hypergravity increases the amounts and the molecular mass of xyloglucans by decreasing xyloglucan-degrading activity. Modification of xyloglucan metabolism as well as the thickening of cell walls under hypergravity conditions seems to be involved in making the cell wall mechanically rigid, thereby inhibiting elongation growth of azuki bean epicotyls.

Leaf growth in the fast-growing Holcus lanatus and the slow-growing Deschampsia flexuosa: tissue maturation

Inherent variation in the relative growth rate of grasses is negatively correlated with that in leaf mass per unit leaf area (LMA). To scrutinize this correlation, the LMA of two grass species was analysed. Changes in LMA and cell wall synthesis in leaf blades of the fast-growing grass Holcus lanatus and the slow-growing grass Deschampsia flexuosa were investigated above the elongation zone of the leaf blade. After the leaf had obtained its final length, in H. lanatus final LMA values of 40-44 g m - 2 were obtained at full leaf length, whereas in D. flexuosa LMA values continued to rise to 110 g m -2 . During this period of tissue maturation the LMA value doubled in H. lanatus, whereas in D. flexuosa an increase of 30% was measured. During this rise in LMA a substantial increase in cell wall polysaccharides was measured. Most of the cell walls could be hydrolysed with driselase, the residue was hydrolysed with sulphuric acid. Driselase hydrolysates were identical in sugar composition, whereas the sugars released by sulphuric acid treatment changed gradually in composition as the tissue matured. The major sites of cell wall deposition during cell maturation were the outer walls of epidermal cells, fibres adjacent to the epidermis and the mestome ring around the vascular bundles. Lignin deposition was restricted to the vascular bundles and lignin levels of the leaf blade did not exceed 0.9% of the total amount of cell wall polysaccharides. Lignin accumulation occurred mainly after the increase in LMA and is unlikely to affect measurably the growth of these leaves.

Changes in amounts and molecular mass distribution of cell-wall polysaccharides of wheat ( Triticum aestivum L.) coleoptiles under water stress

Summary Polyethylene glycol (PEG)-induced water stress suppressed growth of wheat ( Triticum aestivum L.) coleoptiles. When PEG was removed, the growth rate of coleoptiles rapidly increased, and the length reached the same level as that of the unstressed coleoptiles. The amounts of cell-wall polysaccharides, such as hemi-cellulose and cellulose, per coleoptile increased under unstressed conditions as coleoptiles grew. The suppression of growth by water stress led to the reduction of the increases in the amounts of hemicellulose and cellulose. In response to the PEG removal, the increases in cell-wall polysaccharides recovered, and the amounts became close to those of unstressed coleoptiles. A close correlation was observed between the amounts of hemicellulose and cellulose and the length of coleoptiles. These results indicate that coleoptile cells keep their ability to grow even under water-stress conditions, and that cellulose and hemicellulose are produced in parallel with the cell elongation. The gel permeation chromatography of the hemicellulose fraction showed that PEG treatment reduced the increases in the amounts of middle and low molecularmass polysaccharides. However, the increases in high *nolecular-mass polysaccharides, such as β-glucans and arabinoxylans, were not affected by the suppression of growth. The synthesis of high molecular-mass portion of hemicellulosic polysaccharides seems to be related to preserving the ability of the cell walls to extend rather than to cell elongation.

Effects of hypergravity on growth and cell wall properties of cress hypocotyls.

Elongation growth of etiolated hypocotyls of cress (Lepidium sativum L.) was suppressed when they were exposed to basipetal hypergravity at 35 x g and above. Acceleration at 135 x g caused a decrease in the mechanical extensibility and an increase in the minimum stress-relaxation time of the cell wall. Such changes in the mechanical properties of the cell wall were prominent in the lower regions of hypocotyls. The amounts of cell wall polysaccharides per unit length of hypocotyls increased under the hypergravity condition and, in particular, the increase in the amount of cellulose in the lower regions was conspicuous. Hypergravity did not influence the neutral sugar composition of either the pectin or the hemicellulose fraction. The amount of lignin was also increased by hypergravity treatment, although the level was low. The data suggest that hypergravity modifies the metabolism of cell wall components and thus makes the cell wall thick and rigid, thereby inhibiting elongation growth of cress hypocotyls. These changes may contribute to the plants' ability to sustain their structures against hypergravity.

Inhibition of the synthesis of cell wall polysaccharides in oat coleoptile segments by jasmonic acid: Relevance to its growth inhibition

The inhibitory mode of action of jasmonic acid (JA) on the growth of etiolated oat (Avena sativa L. cv. Victory) coleoptile segments was studied in relation to the synthesis of cell wall polysaccharides using [14C]glucose. Exogenously applied JA significantly inhibited indoleacetic acid (IAA)-induced elongation of oat coleoptile segments and prevented the increase of the total amounts of cell wall polysaccharides in both the noncellulosic and cellulosic fractions during coleoptile growth. JA had no effect on neutral sugar compositions of hemicellulosic polysaccharides but substantially inhibited the IAA-stimulated incorporation of [14C]glucose into noncellulosic and cellulosic polysaccharides. JA-induced inhibition of growth was completely prevented by pretreating segments with 30 mm sucrose for 4 h before the addition of IAA. The endogenous levels of UDP-sugars, which are key intermediates for the synthesis of cell wall polysaccharides, were not reduced significantly by JA. Although these observations suggest that the inhibitory mode of action of JA associated with the growth of oat coleoptile segments is relevant to sugar metabolism during cell wall polysaccharide synthesis, the precise site of inhibition remains to be investigated.

UDP‐Glucose level as a limiting factor for IAA‐induced cell elongation in Avena coleoptile segments

The effects of galactose on IAA‐induced elongation and endogenous level of UDP‐glucose (UDPG) in oat (Avena sativa L. cv. Victory) coleoptile segments were examined under various growth conditions to see if there was a correlation between the level of UDPG and auxin‐induced growth. The following results were obtained: Galactose (10 mM) inhibited the auxin‐induced cell elongation of oat coleoptile segments after a lag of ca 2 h. Determinations of cell wall polysaccharides and UDP‐sugars indicated that galactose, when inhibiting the cell wall polysaccharide synthesis, decreased the level of UDPG but caused an increase in the levels of Gal‐1‐P and UDP‐Gal. When coleoptile segments treated with IAA and galactose were transferred to galactose‐free IAA‐solution, the segment elongation was restored and the amounts of cell wall polysaccharides increased. During this period, the amount of UDPG increased and the levels of Gal‐1‐P and UDP‐Gal slightly decreased or leveled off. The UDP‐pentoses changed similarly as UDPG did. Addition of sucrose (30 mM) enhanced IAA‐induced cell elongation and removed growth inhibition by 1 mM galactose. Sucrose increased the amounts of the cell wall polysaccharides and the level of UDPG in the presence or absence of IAA and also counteracted the decrease in UDPG caused by galactose. These results indicate that the level of UDPG is an important limiting factor for cell wall biosynthesis and, thus, for auxin‐induced elongation.

Distribution of Cellular Carbohydrates during Development of the Mycelium and Fruitbodies of Flammulina velutipes

Flammulina velutipes (Curt. ex Fr.) Sing. was grown on potato-glucose solution freed of most starch. Glucose uptake and dry weight changes in the colony indicated that the large fruitbodies derived their substrates partly from glucose remaining in the medium and partly from cellular constituents stored in the mycelium and small fruitbodies. Changes in the amounts of low molecular weight carbohydrates, glycogen, and four cell wall polysaccharide fractions were followed in the mycelium and fruitbodies. Trehalose, arabitol, and smaller amounts of mannitol were the main stored low molecular weight carbohydrates. A large net loss of these compounds occurred in the mycelium and small fruitbodies after their growth ceased. The carbohydrates accumulated in the large fruitbodies, but were also partly metabolized in the colony. Reducing sugars were minor components, and included about 30 to 50% glucose and a small undetermined quantity of fructose. Glycogen was the main storage carbohydrate in the mycelium, and was also stored in the small fruitbodies. It was broken down in both structures during growth of the large fruitbodies which accumulated only small amounts. During the same period, almost 45% of the maximum amount of cell wall polysaccharides were degraded in the small fruitbodies, but not in the mycelium.By feeding (14)C-glucose in replacement medium, incorporation of radioactivity into carbohydrates was followed in the colony during fruit-body development. Total incorporation was highest in trehalose, next highest in glycogen, and the rest was found in polyols and cell wall polysaccharides except for a few per cent which remained in endogenous glucose. In the large fruitbodies, specific radioactivity in glucose was much lower than in trehalose and mannitol. The labeling patterns in the mycelium and large fruitbodies suggested that trehalose, mannitol, and possibly arabitol were translocated into the stipes and pilei.