Effect of maturation and storage on asparagus (Asparagus officinalis) cell wall composition

Changes in the cell wall composition of stems of asparagus ( Asparagus officinalis L. cv. Connovor Collossus) during maturation and during storage in modified atmospheres were investigated. Alcohol-insoluble residues from portions of stems were analysed for changes in alkali-soluble phenolics and in the constituent sugars and their glycosidic linkages. Maturation-related changes down the stem involved increased levels of (l–4)-linked xylosyl residues from xylans, cellulose and phenolics, which arise from the lignified vascular and sclerenchyma tissues, and a decrease in the levels of (l–5)-linked arabinosyl residues from pectic arabinans from the parenchy-matous tissues. Storage under aerobic conditions permitted stem elongation in the apical sections and secondary thickening in the basal sections. This was due to continued tissue maturation. Storage under anaerobic conditions inhibited such changes. In accordance with these effects of storage on stem physiology, maturation-related changes in cell wall components were enhanced by storage only under aerobic conditions. However, levels of (1–4)-linked galactosyl residues which remained relatively constant during maturation, decreased substantially (ca 50%) in all stem sections during both aerobic and anaerobic storage.     

Rumen bacterial and fungal degradation of Digitaria pentzii grown with or without sulfur.

Sheep fed the forage Digitaria pentzii fertilized with sulfur were compared with those fed unfertilized forage for the rumen microbial population involved with fiber degradation. No differences were detected in the bacterial population as determined by anaerobic cultures on a habitat-simulating medium, xylan, or pectin, by 35S labeling techniques for microbial protein, or by transmission electron microscopic studies of bacterium-fiber interactions. Rumen volume and water flow from the rumen were not different for sheep fed each of the forages. Rumen fungi were prevalent in sheep fed sulfur-fertilized D. pentzii as shown by sporangia adhering to forage fiber and by colonies developing from zoospores in roll tubes with cellobiose plus streptomycin and penicillin. Fungi were absent or in extremely small numbers in sheep fed unfertilized forage. Nylon bag digestibility studies showed that the fungi preferentially colonized the lignified cells of blade sclerenchyma by 6 h and caused extensive degradation by 24 h. In the absence of bacteria in in vitro studies, extensive hyphal development occurred; other lignified tissues in blades (i.e., mestome sheath and xylem) were attacked, resulting in a residue with partially degraded and weakened cell walls. Nonlignified tissues were also degraded. Breaking force tests of leaf blades incubated in vitro with penicillin and streptomycin and rumen fluid from sheep fed sulfur-fertilized forage or within nylon bags in such sheep showed a residue at least twice as fragile as that from sheep fed unfertilized forage. In vitro tests for dry matter loss showed that rumen fungi, in the absence of actively growing bacteria, could remove about 62% of the forage material. The response of rumen fungi in sheep fed sulfur-fertilized D. pentzii afforded a useful in vivo test to study the role of these microbes in fiber degradation. Our data establish that rumen fungi can be significant degraders of fiber and further establish a unique role for them in attacking and weakening lignocellulosic tissues. The more fragile residues resulting from attack by fungi could explain the greater intake consistently observed by sheep eating sulfur-fertilized compared with unfertilized D. pentzii forage.     

Microbial degradation in the rumen of wheat straw and anhydrous ammonia treated wheat straw observed by electron microscopy

With the exception of the phloem and the crown of the parenchyma, which borders the medullary lacuna, the walls of the tissues of both treated and untreated straw were lignified. The walls of the treated straw were not fluorescent in the ultraviolet probably because the treatment had modified the phenolic acids. They also had a stronger reaction to Schiff reagent particularly in the sclerenchyma indicating that their polysaccharides were more accessible. The tissues of the treated straw degraded faster in the rumen. The walls of the sclerenchyma of the treated straw were attacked by micro-organisms. Both treated and normal straw were abundantly colonized by rumen fungi, especially in the sclerenchyma. The increase in the digestibility of the treated straw was due to the greater access the micro-organisms had to the polysaccharides of the lignified walls.     

Degradation of Phthalic Acids by Denitrifying, Mixed Cultures of Bacteria

Mixed cultures of bacteria, enriched from aquatic sediments, grew anaerobically on all three isomers of phthalic acid. Each culture grew anaerobically on only one isomer and also grew aerobically on the same isomer. Pure cultures were isolated from the phthalic acid (o-phthalic acid) and isophthalic acid (m-phthalic acid) enrichments that grew aerobically on phthalic and isophthalic acids. Cell suspension experiments indicated that protocatechuate is an intermediate of aerobic catabolism. Pure cultures which grew aerobically on terephthalic acid (p-phthalic acid) could not be isolated from the enrichments, and neither could pure cultures that grew anaerobically on any of the isomers. Cell suspension experiments suggested that separate pathways exist for the aerobic and anaerobic oxidation of phthalic acids. Each enrichment culture used only one phthalic acid isomer under anaerobic conditions, but all isomers were simultaneously adapted for the anaerobic catabolism of benzoate. Cells grown anaerobically on a phthalic acid immediately attacked the isomer under anaerobic conditions, whereas there was a lag before aerobic breakdown occurred, and, for phthalic and terephthalic acids, chloramphenicol stopped aerobic adaptation but had no effect on anaerobic catabolism. This work suggests that phthalic acids are biodegradable in anaerobic environments.     

Anatomical and histological factors affecting the ruminal degradation of stem tissues in Bothriochloa species

Anatomical and histological features affecting the degradation of stem tissues by ruminal microorganisms were examined in ‘Caucasian’, ‘Ganada,’ and ‘WW-Spar’ Old World bluestem grasses (Bothriochloa spp.). Tissue degradation and/or staining results revealed variation among cultivars in the degree of lignification of parenchyma, sclerenchyma, and epidermal cells. In both immature and mature stems, parenchyma and sclerenchyma cell degradation by microorganisms was rapid and extensive for Ganada as compared with Caucasian and WW-Spar. In general, Caucasian tissues were more resistant to degradation than WW-Spar. There also were differences in tissue composition and degradation as a result of stem maturity. Increased lignification in parenchyma cells was primarily responsible for a decreased rate and extent of degradation in older stem portions. The major difference in tissue composition among cultivars was found in older stems; WW-Spar had more vascular and less parenchyma tissues than Caucasian and Ganada. However, Caucasian had a greater percentage of xylem-metaxylem complex tissues than the other two cultivars. The amount of lignified tissues did not seem to be related strongly with rate and extent of tissue degradation. Instead, the data suggest that our previously reported differences in digestibility among the three Old World bluestem grasses could be attributed to differences in the degradation of their individual tissue types. Fungal attachment was greatest on mature tissues, hence, the rate and extent of degradation of lignified tissues may be associated with the colonization of fungi in mature stems. Also, there was minimal colonization of fungi on immature tissues suggesting that their degradation was primarily affected by enzymatic or direct involvement of bacteria.     

Microscopic investigation of changes in histology and digestibility in the rumen of a forage grass and a forage legume during the first growth stage.

An Italian "Dalita" ryegrass (Lolium italicum) and a European lucerne (Medicago sativa) were harvested at 5 different growth stages to determine the anatomical factors limiting their digestibility and in particular the effects of lignification of the tissues. In vitro digestibility, cell wall contents of the whole plant and stem of lucerne and of the whole plant, stem and leaf blade of ryegrass were determined. The rate and the extent of degradation in the rumen of the different tissues were observed by scanning electron microscopy. This degradation occurred very rapidly with the lucerne stems; the xylem of lucerne was the only undegradable tissue whatever the stage. The collenchyma was degraded in the rumen although with acid phloroglucinol it stained positive for the presence of phenolic compounds. Ryegrass stems were digested more slowly than lucerne stems, and the sclerenchyma and xylem of ryegrass were indigestible whatever the stage. The parenchyma located close to the sclerenchyma became indigestible as the cell walls lignified progressively from the third stage. These results contribute to the understanding of the decrease in digestibility over the first growth stage and the variation in rate of digestion of lucerne and ryegrass in the rumen.     

Evaluation by electron microscopy and anaerobic culture of types of rumen bacteria associated with digestion of forage cell walls.

Different morphological types of rumen bacteria which degraded cell walls of forage grasses with various in vitro digestibilities were evaluated with electron microscopy. The majority of these bacteria (i.e., about 70% or more) consisted of two distinct types: (i) encapsulated cocci and (ii) irregularly shaped bacteria, resembling major fiber digesters found in the rumen. Each type was capable of degrading structurally intact cell walls. Differences (P less than or equal to 0.02) in the percent ratio of encapsulated cocci to irregularly shaped bacteria were observed between Bermuda grass and fescue; the ratio of encapsulated cocci to irregularly shaped bacteria between Bermuda grass and orchard grass was similar and variations were high. The proportion of irregularly shaped bacteria usually increased with increased time of digestion. Differences (P greater than 0.1) were not found in the percentage ratio of encapsulated cocci to irregularly shaped bacteria attached to specific tissue types in either Bermuda grass or fescue. However, encapsulated cocci tended to be more prevalent on sclerenchyma than other tissues in Bermuda grass, but less prevalent on sclerenchyma than other tissues in fescue. Transmission electron microscopy of tissue digestion of rapidly degraded orchard grass blades revealed that mesophyll, parenchyma bundle sheath, and parts of the epidermal cell wall apparently were degraded without direct attachment of bacteria although bacteria were near the cell walls undergoing digestion. Anaerobic growth studies showed that the total culturable bacteria developing on medium 10 and media containing carbohydrates similar to those in forage cell walls (i.e., pectin, xylan, and cellobiose) were 80% higher from rumen bacterial populations adapted in vitro to cell walls of orchard grass compared to those from Bermuda grass; the number of colonies from the orchard grass-adapted population was significantly (P less than or equal to 0.05) greater on the medium containing xylan. Filter paper tests showed that the cellulolytic activity of populations adapted to fescue was greater than that of orchard grass or Bermuda grass.     

菰适应湿地环境的解剖和屏障结构特征研究

菰(Zizania latifolia)是一种多年生挺水植物,为了探讨该植物根、茎和叶的解剖结构、组织化学及其质外体屏障的通透性生理。该文利用光学显微镜和荧光显微镜,对菰的根、茎、叶进行了解剖学和组织化学研究。结果表明:(1)菰不定根解剖结构由外而内分别为表皮、外皮层、单层细胞的厚壁机械组织层、皮层、内皮层和维管柱;茎结构由外而内分别为角质层、表皮、周缘厚壁机械组织层、皮层、具维管束的厚壁组织层和髓腔。叶鞘具有表皮和具维管束皮层,叶片具有表皮,叶肉和维管束。(2)不定根具有位于内侧的内皮层及其邻近栓质化细胞和外侧的外皮层组成的屏障结构;茎具内侧厚壁机械组织层,外侧的角质层和周缘厚壁机械组织层组成的屏障结构,屏障结构的细胞壁具凯氏带、木栓质和木质素沉积的组织化学特点,叶表面具有角质层。(3)菰通气组织包括根中通气组织,茎、叶皮层的通气组织和髓腔。(4)菰的屏障结构和解剖结构是其适应湿地环境的重要特征,但其茎周缘厚壁层和厚壁组织层较薄。由此推测,菰适应湿地环境,但在旱生环境中分布有一定的局限性。     

Immunogold labelling of xylans and arabinoxylans in the plant cell walls of maize stem

Summary— Polyclonal antibodies against 4-O-methyl-glucuronoxylan and α L-1-3 arabinofuranosyl poly-β-d-1-4-xylopyranosyl were raised from rabbits. An immunocytochemical technique was used to localize xylans and arabinoxylans in the plant cell walls of the apical internode of two maize lines of different digestibility. The sclerenchyma, fibres and xylem (lignified tissues) and the parenchyma (non-lignified tissue) were studied. The arabinoxylans were more heavily labelled than the xylans in the lignified tissues of the less digestible maize whereas in the more digestible line the labelling of the two polysaccharides was similar. The xylans and arabinoxylans were localized in the secondary cell wall. In both maize lines, labelling increased from the base upwards of the apical internode, reflecting the changes in growth stage.     

Both the anaerobic pathway and aerobic desaturation are involved in the synthesis of unsaturated fatty acids in Vibrio sp. strain ABE-1.

Vibrio sp. strain ABE-1 is a unique marine bacterium in terms of its ability to synthesize delta 9-trans-hexadecenoic acid and delta 7-cis-tetradecenoic acid (14:1(7c); Okuyama, H., Sasaki, S., Higashi, S. and Murata, N. (1990) J. Bacteriol. 172, 3515-3518). The present study, involving labeling with [1-14C]acetate, demonstrated that 14:1 is synthesized by the anaerobic pathway. When cells of this bacterium were grown in the presence of [1-14C]myristic acid (14:0), this compound was converted to palmitic (16:0) and hexadecenoic (16:1) acids but not to 14:1, under aerobic conditions. These results suggest that the incorporated 14:0 was elongated to 16:0 and then converted to 16:1 by the aerobic desaturation of 16:0. It appears that the anaerobic pathway and aerobic desaturation are both involved in the synthesis of unsaturated fatty acids during aerobic growth of Vibrio sp. strain ABE-1.     

Anaerobic degradation of acetone and higher ketones via carboxylation by newly isolated denitrifying bacteria

Five strains of Gram-negative denitrifying bacteria that used various ketones as sole carbon and energy sources were isolated from activated sludge from a municipal sewage plant. Three strains are related to the genus Pseudomonas; two non-motile species have not yet been affiliated. All strains grew well with ketones and fatty acids (C2 to C7), but sugars were seldom utilized. The physiology of anaerobic acetone degradation was studied with strain BunN, which was originally enriched with butanone. Bicarbonate was essential for growth with acetone under anaerobic and aerobic conditions, but not if acetate or 3-hydroxybutyrate were used as substrates. An apparent Ks value of 5.6 mM-bicarbonate was determined for growth with acetone in batch culture. The molar growth yield was 24.8-29.8 g dry cell matter (mol acetone consumed)-1, with nitrate as the electron acceptor in batch culture; it varied slightly with the extent of poly-beta-hydroxybutyric acid (PHB) formation. During growth with acetone, 14CO2 was incorporated mainly into the C-1 atom of the monomers of the storage polymer PHB. With 3-hydroxybutyrate as substrate, 14CO2 incorporation into PHB was negligible. The results provide evidence that acetone is channelled into the intermediary metabolism of this strain via carboxylation to acetoacetate.     

Anaerobic Growth of Candida albicans Does Not Support Biofilm Formation Under Similar Conditions Used for Aerobic Biofilm

C. albicans is an opportunistic fungus causing life-threatening systemic infections particularly in immunocompromised individuals. The organism is a commensal in humans and grows either aerobically, e.g., the oral cavity, or anaerobically, e.g., the gut. We studied anaerobic growth of C. albicans in a defined yeast nitrogen base dextrose medium after adaptation and subculturing in an anaerobic chamber. At 37°C in suspension culture, much slower growth was observed anaerobically with a generation time of 248 min compared to 98 min for aerobic growth. Although the organism grew well on solid medium, shaking increased the growth rate in suspension culture at 37°C. Growth was enhanced at acidic pH compared to neutral or alkaline pH. Cells grown anaerobically produced hyphae, but did not produce biofilm on plastic surface or denture acrylic under either static conditions or with mild shaking, conditions that support aerobic biofilm formation.     

Polysaccharide inducible outer membrane proteins of Bacteroides xylanolyticus X5-1

Little is known about how bacteria degrade structural polysaccharides or the regulatory systems that control this degradation. Bacteroides xylanolyticus X5-1 is a Gram-negative, anaerobic bacterium that can grow on structural polysaccharides such as xylan and pectin. In order to determine the response of this organism to specific substrates,B. xylanolyticus was grown on a variety of mono-, di-, and polysaccharides. Electrophoretic analysis revealed no distinct differences in the polypeptide profile of the inner membrane enrichments of cells grown on different carbohydrates. However, distinct differences in protein composition of outer membrane enrichments were clearly observed. The profiles from cells grown on starch, xylan, and pectin were distinct from each other and their respective monosaccharide. In addition, cells initially grown on xylan did not alter their total membrane protein composition after three generations of growth in medium containing xylan and glucose. Thus,B. xylanolyticus X5-1 altered its outer membrane protein composition in response to specific polysaccharide substrates, but analysis of this specific response revealed no evidence that glucose was preferred over xylan as a substrate.     

Ultrastructure of rigid and lignified forage tissue degradation by a filamentous rumen microorganism.

A small (less than 1 mum)-filamentous, branching microorganism was observed in Gram-stained smears of the rumen microflora and was found to degrade tissues in forage samples incubated in vitro and in vivo with rumen fluid and observed by scanning and transmission electron microscopy. The microbe had prokaryotic cytoplasmic features and a gram-positive type of cell wall structure. Round to oval bodies apparently attached to hyphae resembled the sporulation pattern reported for Micromonospora. Filaments and rod and coccal forms of the microbe degraded rigid forage cell walls and lignified, thick-walled sclerenchymal cells. Location of the microbe at a slight distance from the degraded zones suggested the action of extracellular enzymes. The presence of a microbe with the capability of degrading lignified tissue represents an important and unique function in the rumen ecosystem.     

毛竹茎细胞壁半纤维素多糖的免疫细胞化学定位研究

本文以毛竹(Phyllostachys pubescens)为材料,采用免疫细胞化学标记方法对两种细胞壁半纤维素多糖成分,即木聚糖(Xylan)和(1-3)(1-4)-β-葡聚糖［(1-3)(1-4)-β-glucan］在毛竹茎中的分布进行了观察。结果表明,应用免疫细胞化学方法可以准确、有效地观察这两种半纤维素多糖成分在细胞壁中的分布;木聚糖分布在已木质化的组织细胞的细胞壁中,与细胞壁木质化有密切关系;(1-3)(1-4)-β-葡聚糖在幼竹茎基本组织中分布于短薄壁细胞细胞壁中及长薄壁细胞胞间层,而在老龄竹茎基本组织中,仅分布于短薄壁细胞细胞壁中,而长薄壁细胞细胞壁却无此成分,反映出长、短薄壁细胞细胞壁组成上的差异。     

Anoxia tolerance in the aquatic monocot Potamogeton pectinatus absence of oxygen stimulates elongation in association with an unusually large pasteur effect

Elongation by stems of overwintered tubers of Potamogeton pectinatus (L.) is strongly promoted over several days by oxygen-free conditions. Characteristics of the respiration underpinning this unusual response were examined. Anaerobic plants produced ethanol and CO(2) in approximately equimolar amounts, indicating that glycolysis coupled to alcoholic fermentation was the principal CO(2)-producing respiratory pathway. Rates of CO(2) evolution by aerobic and anaerobic whole plants (shoot and tuber) were similar, suggesting a rate of glycolysis three times that of aerobic plants, i.e. a strong Pasteur effect. In the shoot alone, anaerobic CO(2) production was twice the aerobic rate indicating a 6-fold increase in the rate of glycolysis in this tissue. Anoxic stems contained more sucrose at a stronger concentration than slower-growing aerobic stems or anaerobic leaves, demonstrating that sugar supply to the site of most rapid growth exceeded demand in the absence of oxygen. Concentrations of potentially toxic acetaldehyde in the external medium were small (approximately 0.2 mol m(-3)) during anoxia and on return to aerated conditions. Lactic acid was undetectable under anaerobic conditions and in vivo (31)P-NMR analysis of shoots revealed a cytoplasmic acidification of only 相似文献   

蜈蚣草的解剖结构与组织化学特征

蜈蚣草（Pteris vittata）是多年生的超积累砷植物,并用于修复受重金属污染的土壤。利用光学显微镜和荧光显微镜来研究蜈蚣草的解剖结构及组织化学特征,以此明确该物种适应干旱岩生环境,以及具有离子超富集作用的特点。结果表明（：1）蜈蚣草孢子体的根状茎、不定根和叶的结构均为初生结构,不定根的结构由内而外包括维管柱、内皮层、皮层、木质化厚壁组织层和表皮。（2）根状茎结构由内而外包括网状中柱、内皮层、皮层、表皮外覆盖的角质层。（3）羽状复叶的总叶柄的结构由内而外包括维管束、内皮层、皮层、厚壁组织层、表皮外覆盖的角质层。叶片为异面叶,表皮内方具厚壁层,叶表皮具角质层,仅下表皮有气孔。（4）蜈蚣草根表皮、皮层与根毛的表面富含果胶,皮层木质化;黄连素离子通透性试验结果显示,根毛、根表皮和皮层滞留大量黄连素离子。综上,植物体的内皮层、木质化厚壁组织层、异面叶和厚的角质层结构说明蜈蚣草适应岩生环境,根具木质化皮层和富含果胶的组织化学特点,以及离子通透性试验表明其与离子超积累功能有关。     

Changes in fatty acid composition during development of tissues of coconut (Cocos nucifera L.) embryos in the intact nut and in vitro.

Intact coconuts were germinated in situ and compared with excised zygotic embryos germinated in vitro. The growth of the embryonic tissue and their fatty acid compositions were measured. Haustoria, plumules and radicles of coconuts germinated in situ grew continuously and proportionately throughout the 120 d experiment with haustauria increasing to 45 g x nut(-1) and weighing 4-5-fold more than the other two tissues. The plumules and radicles of the seedlings cultured in vitro also grew continuously but the haustoria grew sporadically between 15 d and 75 d in culture and, at 250 mg x nut(-1) after 75 d, were smaller than the other two tissues. All the tissues of the nuts grown in situ contained significant amounts of lauric acid, the acid characteristic of coconut oil, as well as longer chain saturated and unsaturated fatty acids. The content of medium and long chain fatty acids increased in all growing tissues as the experiment proceeded, especially the haustorium which contained 24-35% of its fatty acid as lauric acid; the fat content of solid endosperm reduced during this period. Seedlings grown in vitro, on the other hand, failed to accumulate lauric acid in any of their tissues (haustorium contained 6-11% of its fatty acid as lauric acid). The results may have implications for the design of growth media for growing zygotic and somatic cultures of coconut and may provide a marker for successful germination.     

New Uses for Calcium Chloride Solution as a Mounting Medium

Fresh cross sections of stems [Psilotum nudum, Coleus blumei, and Pelargonium peltatum] and roots (Setcreasea purpurea) 120 μm thick were fixed in FPA₅₀ (formalin: propionic acid: 50% ethanol, 5:5:90, v/v) for 24 hr and stored in 70% ethanol. The sections were transferred to water and then to 1% phloroglucin in 20% calcium chloride solution plus either hydrochloric, nitric, or lactic acid in the following ratios of phloroglucin-CaCl₂ solution:acid: 25:4, 20:2, or 15:5. The sections were mounted on slides either in one of the three mixtures or in fresh 20% calcium chloride solution. A rapid reaction of the acid-phloroglucin with lignin produced a deep red color in tracheary elements and an orange-red color in sclerenchyma. Fixed and stored leaf pieces from Nymphaea odorata were autoclaved in lactic acid, washed in two changes of 95% ethanol, transferred to water, and treated with the three acid-phloroglucin-calcium chloride mixtures. The abundant astrosclereids stained an orange-red color similar to that of sclerenchyma in the sections. In addition, a new method is reported for specifically staining lignified tissues. When sections or leaf pieces are stained in aqueous 0.05% toluidine blue O, then placed in 20% calcium chloride solution, all tissues destain except those with lignified or partially lignified cell walls. Thus, toluidine blue O applied as described becomes a reliable specific test for lignin comparable to the acid-phloroglucin test.     

Highly substituted glucuronoarabinoxylans (hsGAXs) and low-branched xylans show a distinct localization pattern in the tissues of Zea mays L

Polyclonal antibodies which recognized highly substituted glucuronoarabinoxylans (hsGAXs) and low-branched xylans and did not cross-react with each other, were raised in order to examine localization of these epitopes in internodes of maize. Immunofluorescent labeling revealed different pattern between two succeeding developmental stages. The hsGAX epitope was localized evenly in primary walls in all tissue types, and strongly in unlignified secondary walls in phloem. However, lignified secondary walls in protoxylem, parenchyma and a part of fibers were faintly labeled with this epitope. Moreover, the epitope showed limited binding in lignified parenchyma and fiber walls at ultrastructural level. Low-branched xylan epitope was localized evenly throughout lignified walls in all tissue types. This epitope was also localized only in lignified walls of other organs such as leaf, root apex and dark-grown mesocotyl. Low-branched xylans are significantly related to lignification. Localization of hsGAX epitope in their organs was similar to that in internodes. The hsGAX epitope was distributed both in unlignified walls of all tissues and in lignified walls of parenchyma and annular thickening of protoxylem. We propose that hsGAX has separate functions in lignified and unlignified tissues. In conclusion, at tissue level, hsGAX is localized mainly in unlignified walls, and low-branched xylans in lignified walls.