缺硼对脐橙幼苗硼分配及叶片细胞壁组分硼含量的影响

【目的】 硼在维持细胞壁正常结构方面具有重要的作用,前期结果证实缺硼严重的脐橙叶片细胞壁结构改变程度也更大,但这种变化与细胞壁组分中硼的含量变化是否有关尚不清楚。本研究通过分析缺硼对脐橙幼苗各部分硼分配及叶片细胞壁组分硼含量的影响,明确缺硼症状表现及细胞壁结构变化程度与细胞壁各组分中硼含量变化之间的关系。 【方法】 以纽荷尔脐橙幼苗为试材,利用营养液培养方法进行缺硼处理,测定根、砧木茎、接穗茎、上部叶、下部叶、叶片细胞壁以及细胞壁各组分硼含量的变化情况。 【结果】 缺硼处理9周后上部叶出现叶片卷曲及叶片失绿等症状,而下部叶没有出现任何可见的症状。缺硼处理的脐橙幼苗各部位硼含量和硼吸收量均显著降低,缺硼降低了硼向地上部的相对分配比例且上部叶受到的影响程度更大。在硼正常供应条件下,上部叶和下部叶游离态硼、原生质体硼和细胞壁硼的含量和相对分配比例没有显著差异,说明硼在不同类型脐橙叶片细胞各组分中的分配是相对稳定的。缺硼后水溶性硼 (包括游离态硼和原生质体硼) 在脐橙上部叶和下部叶中都降到极低的水平,尤其是原生质体硼百分含量下部叶甚至是低于上部叶的。缺硼后细胞壁硼占总硼的比例则由22%左右增加到80%以上。与叶片中硼含量的变化趋势一致,缺硼以后虽然上部叶和下部叶细胞壁硼含量都显著降低,但上部叶降低的程度远大于下部叶。进一步分析细胞壁组分硼含量变化,发现缺硼显著降低了上部叶细胞壁中离子结合态果胶硼含量而对下部叶的无明显影响,其他组分硼含量的变化趋势下部叶和上部叶一致。 【结论】 原生质体硼含量的高低并不是决定缺硼症状的主要因素,离子结合态果胶与硼的结合能力对缺硼条件下细胞壁的结构及缺硼症状表现起着至关重要的作用。      

Cell wall composition of smooth bromegrass plants selected for divergent fiber concentration

Neutral detergent fiber (NDF) is considered the single best laboratory predictor of voluntary intake by ruminant livestock, creating interest in using NDF as a selection criterion in forage breeding programs. Because genetic reductions in NDF lead to increases in dry matter digestibility but not to changes in digestibility of the NDF fraction, we postulated that low-NDF plants do not have altered compositions of their cell walls. We tested this hypothesis using clones of smooth bromegrass (Bromus inermis Leyss.) with divergent NDF concentrations. High-NDF and low-NDF plants did not differ in cell wall concentrations or in the concentrations of any cell wall component (fucose, arabinose, rhamnose, galactose, glucose, xylose, mannose, uronic acids, and lignin). Instead, low-NDF plants had a cell wall that was more susceptible to solubilization in neutral detergent solution, suggesting that their cell walls were less well-developed as compared to high-NDF plants. NDF should not be used as a substitute for cell wall concentration in forage plants.     

Physicochemical characteristics of onion (Allium cepa L.) tissues

The structure and mechanical properties of onions are important factors affecting their textural quality. The onion bulb consists of several layers of pigmented, papery scales surrounding fleshy storage scales that comprise an upper epidermis, an intermediate parenchyma tissue, and a lower epidermis. The purpose of this study was to examine the chemical composition of cell walls from the papery scales and outer fleshy scales of onion (Allium cepa L. cv. Sturon) in relation to their mechanical properties. Cell-wall material (CWM) was prepared from the component tissues and analyzed for its carbohydrate and phenolic composition. The CWMs were rich in uronic acid and glucose, with smaller quantities of arabinose, galactose, and xylose. In the fleshy scales, the lower epidermis contained relatively more galactose-rich pectic polysaccharides, whereas the upper epidermis and the papery scales contained virtually no galactose. Analysis of mechanical properties showed that the order of strength of the tissues was papery scales > fleshy scales, which were in the order lower epidermis > upper epidermis > intermediate parenchyma. The upper epidermis of fleshy scales was stronger in the vertical than the horizontal direction, and both orientations showed negligible notch sensitivity. Cyclohexane-trans-1,2-diaminetetraacetate-induced vortex-induced cell separation of the intermediate layer of fleshy scales indicated that calcium cross-linking may play an important role in cell-cell adhesion. A small but significant amount of ferulic acid was found in the walls, predominantly in the thick cuticle of the lower epidermis of fleshy scales. Alkali-labile wall-bound flavonoids were also detected.     

The effect of oxidation by periodate on soil carbohydrate derived from plants and microorganisms

It has previously been shown that treatment of soil with periodate and tetraborate releases much of the carbohydrate and destroys an equivalent proportion of the soil aggregates. The residual carbohydrate is proportionately richer in glucose, arabinose and xylose, sugars characteristic of plant remains, than the whole soil. The effect of sodium periodate (0.02 M, 6–168 h) and sodium tetraborate (0.1 M, 6 h) treatment of soil on carbohydrates of different origin was examined using ¹⁴C-labelled soil in which the label was present in microbial products arising from 7 and 28 day incubations of ¹⁴C-glucose in soil, or in both plant and microbial materials resulting from 12 week incubations of ¹⁴C-labelled barley leaf and 1 year incubations of ¹⁴C-labelled ryegrass in soil. Arabinose and xylose were the sugars most resistant to periodate in the glucose incubated soil; in the ryegrass incubation arabinose, xylose and glucose were more persistent than galactose, mannose and rhamnose. In the barley leaf incubation arabinose was more persistent than galactose and rhamnose. Thus periodate oxidation did not distinguish between sugars of different origin in soil and it was concluded that in the case of arabinose and xylose the persistence related to differences in chemical structures rather than to physical factors such as particle size of the plant fragments. The composition of the more stable residue can therefore not be used as an indication of polysaccharide origin in any comparison of the relative effects of plant and microbially derived material as aggregating agents.     

Esterified phenolics of the cell walls of chufa (Cyperus esculentusL. ) tubers and their role in texture

Chufas (Cyperus esculentus) are edible tubers that, like Chinese waterchestnut (CWC), are very crisp when raw and do not soften when cooked. The present study compares the mechanical properties of chufas with those of potato and CWC in relation to the carbohydrate and phenolic compositions of the cell walls. The cutting toughness of raw chufa was higher than that of raw CWC and potato; its value decreased on boiling, as also observed with CWC, but remained over twice that of raw potato. Chufa cell walls were rich in xylose, arabinose, glucose, uronic acid, and galactose, with minor quantities of mannose. The cell walls of the parenchyma exhibited a uniform pH-dependent autofluorescence indicating the presence of cinnamic acid derivatives. Analysis of these revealed that peeled tuber cell walls are rich in ferulic acid, whereas p-coumaric acid dominates the monomeric phenol fraction of the skin. Cell wall material from both skin and peeled tubers contains a significant amount of different diferulic acids ( approximately 20% of the wall ferulic acid), consisting mainly of the 8-O-4'-, 8-5'-, and 5-5'-dimers. These are potentially available to form thermally stable cross-links between polysaccharides within the wall and between cells. This may confer thermal stability of texture.     

Methyl esterification divergently affects the degradability of pectic uronosyls in nonlignified and lignified maize cell walls

Nonlignified cell walls from Zea mays (L.) cell suspensions were incubated with and without pectin methylesterase (PME) and a portion were artificially lignified to assess how methyl esters influence the release of pectic uronosyls and total sugars from cell walls by fungal enzymes. Treatment with PME reduced uronosyl concentrations from 97 to 92 mg/g, reduced uronosyl methylation from 57% to 21%, and increased Klason lignin concentrations in artificially lignified cell walls from 99 to 116 mg/g. Although PME treatment slightly enhanced uronosyl release from nonlignified cell walls, it reduced uronosyl release from artificially lignified cell walls by 55% after 4 h and by 7% after 72 h of enzymatic hydrolysis. Pectin hydrolysis in PME treated cell walls was probably impaired by enhanced benzyl ester cross-linking of uronosyls to lignin via quinone methide intermediates. Variations in uronosyl methylation had little effect on the overall release of total sugars from cell walls.     

Bestimmung cellulosisch und nichtcellulosisch gebundener Neutralzucker in Bodenhydrolysaten mit Hilfe von Hochleistungsdünnschichtchromatographie

Determination of cellulosic and noncellulosic neutral sugars occurring in soil hydrolysates by means of high-performance thin-layer chromatography Analytical methods for soil samples are described, which allow the differentiation between monosaccharides bound in cellulosic and noncellulosic polysaccharides of the plant cell wall. The four step procedure includes hydrolysis of total polysaccharides (72 % H₂SO₄, 2N H₂SO₄), hydrolysis of the noncellulosic fraction (2N trifluoroacetic acid), separation of the monomers by high-performance thin-layer chromatography (HPTLC) and scanning of the plates for quantification. The amount of cellulose can be calculated by the difference of total glucose and glucose hydrolyzed by trifluoroacetic acid. Hydrolysis of soil samples by trifluoroacetic acid is a simple method for the determination of noncellulosic cell wall polysaccharides. Losses of sugars during the whole analytical procedure (hydrolysis, separation by HPTLC and quantification) are below 10 % for all sugars studied (galactose, glucose, mannose, arabinose, xylose). Standard deviations do not overstep this value, too. By HPTLC a large number of samples are chromatographed together; therefore, the total analysis time per sample is very short. As example the depth functions of hydrolyzed sugars in a Lithic Borofolist are discussed.     

Effect of phenolic structures on the degradability of cell walls isolated from newly extended apical internode of tall fescue (Festuca arundinacea Schreb.)

Apical internodes of tall fescue (Festuca arundinacea Schreb. var. Clarine) harvested at flowering were sectioned into 5 or 10 equal parts to study in situ degradability and cell wall composition, respectively. The basal (youngest) section had the greatest primary wall content. Cell walls in the upper (older) sections had the highest xylose/arabinose ratio and lignin content and a lignin rich in syringyl units, all typical of extensive secondary wall development. Almost all of the p-coumaric (p-CA) and about half of the ferulic acid (FA) were released by 1 M NaOH and presumed to be ester-linked. The total FA content was approximately double that of p-CA in all sections other than the youngest with a distribution similar to that of total p-CA. However, the ratio of esterified to ether and ether plus ester linked (Et & Et+Es) FA differed with age. Whereas the esterified form remained essentially constant ( approximately 4.5 g/kg of cell wall), Et & Et+Es ferulate increased with increasing age of the tissue and was significantly related to lignin deposition (r = 0.79, P < 0.01). The extent of cell wall degradation after 48 h of incubation in the rumen was inversely related to maturity, falling from 835 g/kg of dry matter in the youngest section to 396 g/kg in the oldest. Both the rate and extent of cell wall degradation were significantly negatively related to the ratio of xylose to arabinose, lignin content, proportion of syringyl units present in lignin, and concentration of Et & Et+Es FA present. A positive relationship between Et & Et+Es FA was also found, with the rate (P < 0.01) being better correlated than the extent (P < 0.05) of cell wall degradation. Application of the newly extended internode model to fescue produced results consistent with the view that both the lignin content and the extent to which lignin was covalently bound to the other wall polymers crucially influenced the rate and extent of degradation.     

Functional properties and characterization of dietary fiber from Mangifera pajang Kort. fruit pulp

A dried high fiber product from bambangan (Mangifera pajang Kort.) fruit pulp was prepared and evaluated for proximate composition, functional properties, and soluble and insoluble dietary fiber composition. Mangifera pajang fibrous (MPF) consisted of 4.7% moisture, 0.8% fat, 4% protein, and 30 mg total polyphenol per g of dry sample, and 9, 79 and 88% soluble, insoluble and total dietary fiber, respectively. Water holding capacity, oil holding capacity, swelling, and solubility were found to be 9 g/g dry sample, 4 g/g dry sample, 16 mL/g dry sample, and 11%, respectively. The glucose dialysis retardation index of MPF was approximately double that of cellulose fiber. Soluble dietary fiber contained mannose, arabinose, glucose, rhamnose, erythrose, galactose, xylose, and fucose at 1.51, 0.72, 0.39, 0.16, 0.14, 0.05, 0.04, and 0.01%, respectively, with 5.8% uronic acid, while insoluble dietary fiber was composed of arabinose (18.47%), glucose (4.46%), mannose (3.15%), rhamnose (1.65%), galactose (1.20%), xylose (0.99%), and fucose (0.26%) with 15.5% uronic acid and 33.1% klason lignin. These characteristics indicate that MPF is a rich source of dietary fiber and has physicochemical properties which make it suitable as an added ingredient in various food products and/or dietetic, low-calorie high-fiber foods to enhance their nutraceutical properties.     

Structural characterization of oligosaccharides and polysaccharides from apple juices produced by enzymatic pomace liquefaction

Eight apple pomace liquefaction juices were produced to characterize soluble cell wall material released by the action of pectolytic and cellulolytic enzyme preparations. Very high colloid values from 9.7 to 19.6 g/L were recovered from the juices by ethanol precipitation. The crude polysaccharides consisted mainly of galacturonic acid (49-64 mol %), arabinose (14-23 mol %), galactose (6-15 mol %), and minor amounts of rhamnose, xylose, and glucose. Separation of the polysaccharides by anion-exchange chromatography yielded one neutral, one slightly acidic, and one acidic polymer accounting for 60% of total colloids. Preparative size exclusion chromatography of the acidic fractions resulted in four polymers of different molecular weights and different sugar compositions. Among them, high molecular weight arabinans and rhamnogalacturonans as well as oligomeric fractions consisting of only galacturonic acid could be found. Linkage studies were performed on neutral fractions from anion-exchange chromatography and size exclusion chromatography. They revealed highly branched arabinans, xyloglucans, and mainly type I arabinogalactans.     

Olive fruit cell wall: degradation of pectic polysaccharides during ripening

Olive fruits at three stages of ripening (green, cherry, and black) have been studied. After cell wall isolation, the compositions of the cell wall and that of the phosphate-soluble polysaccharides were determined. In cell walls, decreases in arabinose, xylose, glucose, and uronic acid levels were observed, together with a slight increase in mannose on ripening. At the beginning of ripening, fragments of pectic polymers were the major constituents of the phosphate-soluble fraction, with the hemicellulosic ones increasing toward the end of the process. The molecular weight of the fragments solubilized was approximately 6 kDa. After cell wall fractionation, the pectic polysaccharides soluble in imidazole and sodium carbonate were also studied. In both fractions, between the green and cherry stages of ripening, a significant loss of homogalacturonans took place. Between the cherry and black stages of ripening, rhamnogalacturonan side chains were also released in addition to homogalacturonans. In any of the pectic fractions, changes in apparent molecular weight were quantified.     

Patterns of mineral nutrient fluctuations in soybean leaves in relation to their position

Dry weight accumulation in blades for the trifoliolate leaf as well as the concentration per gram of dry weight and accumulation of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) were determined during the vegetative and reproductive phases at different leaf positions of soybean [Glycine max (L) Merrill, var. Halle] grown in the field without fertilization. The leaf blades at each position were sampled three times at seven day intervals. Mature (middle) leaves showed a higher rate of dry weight accumulation particularly during the vegetative stage in comparison to the older (lower) and younger (upper) leaves. These differences increased with the progress of plant growth. The minimization to zero of the rate of dry weight accumulation in blades after the development of pods is differentiated in leaves of different age. The N, P, and K concentration in leaf blades increase and those of Ca and Mg decrease from older (lower) to mature (middle) and younger (upper) leaves. Rates of N and P accumulation at the vegetative stage are greater than the rate of dry weight accumulation. During the reproductive stage, P mobilization and transport to reproductive sinks was observed. Older and mature leaves sustain significant levels of N and P up to the end of the plant life cycle. In the upper leaves, the decline of N and P concentration during the same period is ascribed to dilution and change of the carbon/nitrogen (C/N) ratio due to the late increase of dry weight. Potassium in blades of mature and upper leaves seems to be mobilized to reproductive sinks. This did not seem likely for the lower leaves. High Ca concentration in the blades was attributed to the high level of available Ca in the soil, combined with the prevalence of dry growth conditions during the summer. The rate of Ca accumulation is smaller than the rate of dry weight accumulation during the vegetative stage and greater during the reproductive one. The Mg fluctuations indicate a small influence of reproductive sinks on Mg concentration in the blades. The older leaves have the greatest Ca and Mg concentrations compared to the mature and upper leaves. In lower leaves, indications of faster Mg redistribution are found. Iron, Cu, and Zn concentrations in the blades are higher before flowering, then afterwards in a contrary manner than that for Mn. A decline of Fe, Cu, Zn, and Mn concentration in blades from the lower to the mature and upper leaves was determined. Iron shows the greatest change with the highest concentration being during the early vegetative stage and a rapid decline shortly afterwards. Older leaves were found to be significant Fe reserves during the vegetative stage, while after pod development, they present an impressive accumulation of Zn and Mn.     

Soluble and Insoluble Dietary Fiber Content and Composition in Oat

Six oat genotypes were grown in nursery yield trials during 1989-1992 at Lisbon, ND. Groats were analyzed for soluble and insoluble dietary fiber content and composition. Genotype-by-growing year interaction was not significant for soluble or insoluble dietary fiber. Soluble and insoluble dietary fiber differed with genotype (6.0–7.1% and 4.1– 4.9%, respectively) and with growing year (6.0–6.9% and 3.9–5.2%, respectively). The genotype-by-growing year interaction was significant for soluble β-glucan content but not for total neutral sugar or uronic acid content of the soluble dietary fiber. Genotypes did vary in total neutral sugar content but not in uronic acid content. The genotype-by-growing year interaction was not significant for total neutral sugar, β-glucan, uronic acid, or Klason lignin content of insoluble dietary fiber. Genotypes did vary in total neutral sugar, β-glucan, and Klason lignin content but not in uronic acid content of insoluble dietary fiber. The neutral sugar content of soluble dietary fiber was composed of glucose, arabinose, xylose, and galactose. The neutral sugar content of insoluble fiber was composed of glucose, arabinose, and xylose. The content and composition of soluble and insoluble dietary fiber varied with oat genotype. Therefore, oat genotypes could be bred for specific dietary fiber content and composition.     

Characterization of the Carbohydrates of Nonreduced Glutenin Fractionated by Multistacking SDS-PAGE from Two Hard Red Spring Wheat Flours

Native (nonreduced) glutenin aggregates of two hard red spring wheat flours (Len of good quality and line 205 of poor quality) containing the same high molecular weight glutenin subunits (2*, 7+9, and 5+10) were investigated for the possibility of glycosylation. Glutenins isolated by pH-precipitation were separated and purified under nonreducing conditions into five different molecular weight species by multistacking SDS-PAGE and by transfer to polyvinylidene difluoride (PVDF) membranes by electroblotting. Carbohydrate compositions of the total glutenin fraction and of the different molecular weight glutenin species separated on the stacking gels (4–12% acrylamide) were determined. More total carbohydrates were found in the total glutenin of the line 205 flour (2.33%) than in that of the Len flour (1.87%), with glucose and xylose contributing to the greater total amount in line 205. However, the total glutenin of Len had approximately twice as much of the total of arabinose, mannose, and galactose as line 205 had. After purification by electrophoresis, smaller amounts of monosaccharides (glucose, xylose, arabinose, galactose, and mannose) in the different molecular species were detected. After electroblotting to PVDF membrane to increase purification, no arabinoxylans were found. Following extraction of glutenin from membranes, the β-elimination procedure in mild base under reducing conditions was used. In that procedure, the mono- or oligosaccharide side chains are released from the protein core, and the sugars originally involved in the protein-sugar linkage are reduced to the sugar alcohol. After derivatization (with trimethylsilyl), samples were analyzed by gas chromatography and mass spectrometry. Glucose, galactose, and a small amount of mannitol were found in most of the different glutenin aggregates, except that mannitol was not found in the 8% stacking gel glutenin fraction. The content of mannitol was greater in the higher molecular weight glutenin species at the 4 and 6% origins. These results support the hypothesis that the carbohydrates and protein in the glutenin macropolymer may be covalently linked.     

Monosaccharide composition of sweetpotato fiber and cell wall polysaccharides from sweetpotato, cassava, and potato analyzed by the high-performance anion exchange chromatography with pulsed amperometric detection method

The cell wall materials (CWMs) from sweetpotato (Ipomoea batatas cv. Kokei 14), cassava (Manihot esculenta), and potato (Solanum tuberosum cv. Danshaku) and commercial sweetpotato fiber as well as their polysaccharide fractions were analyzed for sugar composition by the high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) method. The separation of arabinose and rhamnose, and xylose and mannose, by this method has been improved using a CarboPac PA 10 column. Pretreatment of the CWMs and cellulose fractions with 12 M H(2)SO(4) was required for complete hydrolysis to occur. Commercial sweetpotato fiber was found to be mainly composed of glucose (88.4%), but small amounts of other sugars were also detected. Among the root crops, sweetpotato CWM had the highest amount of pectin and galacturonic acid. Fucose was detected only in cassava CWM and its hemicellulose fraction, while galactose was present in the highest amount in potato CWM. Among the polysaccharide fractions, it was only in the hemicellulose fraction where significant differences in the sugar composition, especially in the galactose content, were observed among the root crops.     

Soybean (Glycine max) cell wall composition and availability to feed enzymes

Defatted untoasted soybean cotyledons and hulls were fractionated as water solutes (WSc and WSh) and water unextractable (WUc and WUh). Further fractionation of WUc through deproteinization yielded the isolation of a water unextractable solid (WUS) fraction that was mainly composed (molar percent) of galactose (28.1%), glucose (27.8%), arabinose (13.3%), and uronic acids (17.6%), which accounted for 76% of the water insoluble polysaccharides in soybean cotyledons (WUc). The cell wall (WUS) was sequentially fractionated with chelating agents (chelating agent soluble solids, ChSS) and a gradient of agents (dilute alkali, DASS; 1 M alkali, 1MASS; and 4M alkali, 4MASS), which gave a final cellulosic residue. The ChSS and DASS extracts were characterized as pectin-rich fractions, whereas 1MASS and 4MASS were hemicellulose- and cellulose-rich fractions. Incubation in vitro of the WUc fraction with pectinase, cellulase, and xylanase resulted in the release of low amounts (not more than 5% bound basis) of monosaccharides, mostly uronic acids, xylose, and arabinose. Protein extraction hardly increased this release after enzymatic incubation (<7%). However, progressive fractionation of the cell wall matrix markedly increased the release of monosaccharides from pectin- (ChSS and DASS) and hemicellulose-rich fractions (1MASS and 4MASS). Significant degradation of cellulose (up to 20%) was achieved only after complete protein, pectin, and hemicellulose extraction.     

Changes in Root Cell Wall Chemistry Induced by Manganese Exposure with Two Tobacco Genotypes

Abstract

Induced effects by manganese (Mn) uptake on root cell walls of two tobacco (Nicotiana tabacum L.) genotypes KY 14 (Mn sensitive) and T.I. 1112 (Mn tolerant) were evaluated. The tobacco genotypes were grown in half‐strength Hoagland solutions containing 0 (deficient), 46 (non‐toxic), and 300 µM (toxic) Mn. Root cell walls were isolated and characterized for total polysaccharides, proteins, and individual sugars and amino acids. For both genotypes, the largest and significant difference (P ≤ 0.01) in cell wall polysaccharides and proteins were between Mn levels of 0 and 46 µM. Either deficient or toxic levels of Mn exposure decreased uronic acid, a component of cell wall pectins although the decrease was smaller in T.I. 1112 than in KY 14. Beside uronic acid, significant changes in arabinose, galactose, and rhamnose contents were also observed in cell wall pectins. In addition, toxic level of Mn exposure greatly elevated serine in T.I. 1112 whereas the Mn deficient condition generally reduced serine but increased proline in both genotypes. Serine and hydroxyl‐proline are major amino acid components of extension, a major cell wall structural protein. The results suggest that Mn deficiency and toxicity may affect both metal uptake and mechanical characteristics of tobacco root cell walls. Manganese‐induced changes in root cell wall chemistry appear to differ from the effects of metal stresses of non‐essential elements such as aluminum (Al) and sodium (Na).     

Effect of flash release and pectinolytic enzyme treatments on wine polysaccharide composition

Various treatments, including flash release and addition of pectic enzymes, have been proposed to enhance degradation of grape berry cell walls and extraction of aroma and phenolic compounds into the wines. The effect of flash release and enzyme treatment used separately or in combination on wine polysaccharide composition was studied. The flash release process increased extraction of polysaccharides originating from grape berry cell walls, that is, polysaccharides rich in arabinose and galactose (PRAGs) and type II rhamnogalacturonan (RG-II), thus yielding enriched wines. Increasing the duration of high-temperature exposure before the flash release treatment further increased extraction of polysaccharides. However, the wine obtained by pressing immediately after flash release and fermenting in the liquid phase contained lower amounts of grape polysaccharides, indicating that their extraction required skin maceration. The use of enzymes without or with flash release modified the composition and the structure of pectic polysaccharides. In particular, it induced the loss of PRAG terminal arabinose residues.     

Distribution of 14C between particle size fractions and carbohydrates separated from a peat incubated with 14C-glycine

Samples of fresh Sphagnum peat from a raised bog were amended with ¹⁴C-labelled glycine. The distribution of ¹⁴C between particle size fractions obtained by wet sieving (sieve sizes 1, 0.5, 0.25, 0.15 and 0.05mm) was determined immediately on control (unincubated) samples and after 1, 6 and 12 months incubation at 10°C. The recovery of glycine in solution was almost 100%. During the incubation with ¹⁴C-glycine, ¹⁴CO₂ was released within the first 20 weeks, equivalent to 51.5% of the added ¹⁴C, but thereafter very little ¹⁴CO₂ was evolved. After 26 weeks a substantial amount of ¹⁴C was distributed amongst all the fractions, but the greatest incorporation (4.47%) occurred in the finest fraction (0.005–0.05 mm). Labelling of the other particle size fractions was <2.3% of added ¹⁴C. Carbohydrate accounted for 23% of ¹⁴C in the finest fraction and the sugars, rhamnose, arabinose, xylose, mannose, galactose and glucose all became labelled. Rhamnose showed the greatest, and arabinose, galactose and xylose the least, increase in specific activity; glucose and mannose had intermediate values. It was concluded that the finest fraction in peat contains a significant proportion of the microbially-synthesized material.     

桑轮纹病发生区桑叶表面细菌群落结构在冠层内的分异

探明桑轮纹病发生区冠层内叶表面微生物多样性、结构组成和功能的变化情况,有助于快速筛选控制桑轮纹病病原菌(Gonatophragmium mori)潜在的拮抗微生物。本研究基于高通量测序技术,分析冠层上部和下部叶片上表面和下表面细菌相对丰度的差异。结果发现:1)在多样性指数(Shannon)上,冠层上部叶片是冠层下部叶片的1.26倍,冠层内叶片上表面是下表面的1.49倍。2)在结构上,冠层下部叶片的下表面(LB)和冠层上部叶片的下表面(UB)的优势属均为泛菌属(Pantoea),其相对丰度分别为38.04%和25.31%,而冠层下部叶片的上表面(LS)为沙雷氏菌属(Serratia)、冠层上部叶片的上表面(US)为寡养单胞菌属(Stenotrophomonas),其相对丰度分别为18.0%、23.73%。3)在功能上,冠层下部叶片细菌的碳水化合物和氨基酸的运输和代谢功能比冠层上部叶片强,然而脂质的运输和代谢功能比冠层上部叶片弱;冠层上部叶片上表面细菌的细胞壁生物发生功能比下表面强,而氨基酸的运输和代谢功能弱于下表面;冠层下部叶片上表面细菌的次生代谢物的生物合成、运输和分解代谢和脂质运输和代谢功能强于下表面,而细胞运动比下表面弱。4)冠层内叶片表面芽孢杆菌属(Bacillus)、不粘柄菌属(Asticcacaulis)和苯基杆菌属(Phenylobacterium)的相对丰度与病原菌的相对丰度负相关性显著(P0.05),相关性最大的为芽孢杆菌属,系数为-0.87。上述结果表明桑轮纹病发生区冠层内桑叶上下表面细菌群落的多样性、结构组成和功能存在显著差异,对进一步研究桑轮纹病的生物防控具有一定的科学意义。