Turnover of Galactans and Other Cell Wall Polysaccharides during Development of Flax Plants

We investigated the synthesis and turnover of cell wall polysaccharides of the flax (Linum usitatissimum L.) plant during development of the phloem fibers. One-month-old flax plants were exposed to a 40-min pulse with 14CO2 followed by 8-h, 24-h, and 1-month periods of chase with ambient CO2, and radioactivity in cell wall sugars was determined in various plant parts. The relative radioactivity of glucose in noncellulosic polysaccharides was the highest compared with all other cell wall sugars immediately after the pulse and decreased substantially during the subsequent chase. The relative radioactivities of the other cell wall sugars changed with differing rates, indicating turnover of specific polysaccharides. Notably, after 1 month of chase there was a marked decrease in the proportional mass and total radioactivity in cell wall galactose, indicating a long-term turnover of the galactans enriched in the fiber-containing tissues. The ratio of radiolabeled xylose to arabinose also increased during the chase, indicating a turnover of arabinose-containing polymers and interconversion to xylose. The pattern of label redistribution differed between organs, indicating that the cell wall turnover processes are tissue- and cell-specific.     

Developmental and Tissue-Specific Structural Alterations of the Cell-Wall Polysaccharides of Arabidopsis thaliana Roots

The plant cell wall is a dynamic structure that plays important roles in growth and development and in the interactions of plants with their environment and other organisms. We have used monoclonal antibodies that recognize different carbohydrate epitopes present in plant cell-wall polysaccharides to locate these epitopes in roots of developing Arabidopsis thaliana seedlings. An epitope in the pectic polysaccharide rhamnogalacturonan I is observed in the walls of epidermal and cortical cells in mature parts of the root. This epitope is inserted into the walls in a developmentally regulated manner. Initially, the epitope is observed in atrichoblasts and later appears in trichoblasts and simultaneously in cortical cells. A terminal [alpha]-fucosyl-containing epitope is present in almost all of the cell walls in the root. An arabinosylated (1->6)-[beta]-galactan epitope is also found in all of the cell walls of the root with the exception of lateral root-cap cell walls. It is striking that these three polysaccharide epitopes are not uniformly distributed (or accessible) within the walls of a given cell, nor are these epitopes distributed equally across the two walls laid down by adjacent cells. Our results further suggest that the biosynthesis and differentiation of primary cell walls in plants are precisely regulated in a temporal, spatial, and developmental manner.     

Synthesis and Turnover of Cell-Wall Polysaccharides and Starch in Photosynthetic Soybean Suspension Cultures

Soybean (Glycine max [L.] Merr.) suspension cultures grown under photoautotrophic and photomixotrophic (1% sucrose) culture conditions were used in 14CO2 pulse-chase experiments to follow cell-wall polysaccharide and starch biosynthesis and turnover. Following a 30-min pulse with 14CO2, about one-fourth of the 14C of the photoautotrophic cells was incorporated into the cell wall; this increased to about 80% during a 96-h chase in unlabeled CO2. Cells early in the cell culture cycle (3 d) incorporated more 14C per sample and also exhibited greater turnover of the pectin and hemicellulose fractions as shown by loss of 14C during the 96-h chase than did 10- and 16-d cells. When the chase occurred in the dark, less 14C was incorporated into the cell wall because of the cessation of growth and higher respiratory loss. The dark effect was much less pronounced with the photomixotrophic cells. Even though the cell starch levels were much lower than in leaves, high 14C incorporation was found during the pulse, especially in older cells. The label was largely lost during the chase, indicating that starch is involved in the short-term storage of photosynthate. Thus, these easily labeled and manipulated photosynthetic cells demonstrated extensive turnover of the cell-wall pectin and hemicellulose fractions and starch during the normal growth process.     

Enzymic Dissociation of Zea Shoot Cell-Wall Polysaccharides V. Dissociation of Xyloglucan by Urea

A procedure has been devised to extract and identify structuralcomponents of the xyloglucan of Zea mays L. (hybrid B73 ? Mo17) shoot cell-walls. A water-insoluble fraction of Zea shootcell-walls, after pretreatment with purified Bacillus subtilis(1 3),(1 4)-ß-D-glucan 4-glucanohydrolase, purifiedB. subtilis endo-(l 4)-ß-xylanase and an enzyme preparationfrom B. subtilis enriched in glucuronoxylanase (Kato and Nevins1984a, Nishitani and Nevins 1991), was subsequently treatedwith 7 M urea. The carbohydrates (0.8% of the water-insolublefraction of Zea shoot cell-walls) liberated by the urea treatment,were comprised of xyloglucan polymers with molecular weightswhich varied from 1.0 ? 10⁴ to 4.0 7times; 10⁴ Da. Other wallfragments associated with the isolated polymer suggest covalentbonding of xyloglucan to other polysaccharides. Structural analysesof the xyloglucan polymers reveal a cellulose-like backbonewith about 35% of the C-6 positions substituted with xyloseand other sugars. About 80% of xyloglucan present in the enzyme-pretreatedwater-insoluble fraction of Zea shoot cell-walls was liberatedby the urea treatment. The procedure avoids the use of alkaliin the solubilization of xyloglucan. ¹Supported in part by National Science Foundation research grantsPCM 7818588 and DMB 8505901. (Received September 10, 1990; Accepted May 15, 1991)     

Effects of ABA on Synthesis of Cell-Wall Polysaccharides in Segments of Etiolated Squash Hypocotyl I. Changes in Incorporation of Glucose and myo-Inositol into Cell-Wall Components

Externally supplied [³H]myo-inositol and [¹⁴C]glucose were incorporatedin cell-wall fractions of segments of etiolated squash hypocotyl.The extent of incorporation of [¹⁴C]glucose into cell-wall fractionswas very much greater than that of [³H]myo-inositol. Radioactivityfrom [¹⁴C]-glucose was effectively incorporated into hemicelluloseB and cellulose fractions and was incorporated uniformly intohexose, pentose and uronic acid residues, but radioactivityfrom [³H]myo-inositol was incorporated predominantly into uronicacid and pentose residues in the pectin and hemicellulose Bfractions. Exogenously applied ABA significantly suppressed the elongationof segments of squash hypocotyl and the incorporation of radioactivityfrom [^l4C]glucose and [³H]myo-inositol into the segments. Furthermore,ABA significantly inhibited the distribution of incorporatedradioactivity from [¹⁴C]glucose into the cellulose fraction,but did not affect distribution into the pectic fraction. Bycontrast, ABA only slightly inhibited the distribution of theincorporated radioactivity from [³H]myo-inositol into the pecticfraction. These results suggest that most of the cell-wall polysaccharidesin segments of squash hypocotyl are synthesized via the UDP-sugarpathway, and that ABA significantly inhibits the synthesis ofcellulose but not the synthesis of pectic polysaccharides whenABA suppresses the elongation of the segments. (Received March 25, 1988; Accepted November 15, 1988)     

兰科药用植物活性多糖研究进展

兰科(Orchidaceae)是有花植物中第二大科,目前已确认的兰科植物有736属28 000种,其中有82属343种可作药用。常见的兰科药用植物有铁皮石斛、天麻、白及和金线莲等。兰科药用植物功效成分主要为糖类、茋类、酚类、萜类、生物碱类、黄酮类和甾醇等,其中主要由甘露糖和葡萄糖等单糖构成的水溶性多糖是其重要活性成分之一,具有增强免疫力、抗肿瘤、抗氧化、降血糖和改善记忆等多种药理功能。对兰科药用植物活性多糖的结构、药理作用和生物合成等方面的研究进展进行了综述,并提出今后需要重点研究的方向,为进一步推动兰科药用植物资源保护及合理开发利用提供参考。     

Effects of Abscisic Acid on the Synthesis of Cell-Wall Polysaccharides in Segments of Etiolated Squash Hypocotyl II. Levels of UDP-Neutral Sugars

The effects of abscisic acid (ABA) on the formation of UDP-sugarsin segments of squash (Cucurbita maxima Duch.) hypocotyls wereexamined with [³H]glucose. After a 3-h incubation, 74% of totalradioactivity incorporated into neutral sugar residues of UDP-sugarswas found in glucose residues, 19% in galactose residues andless than 7% in other sugar residues. Exogenously applied ABAincreased the extent of incorporation of [³H]glucose into UDP-glucose,UDP-galactose and UDP-xylose by 30%, 30%, and 20%, respectively.However, ABA neither affected the total incorporation of radioactivityinto segments nor the incorporation into free glucose and sucrosein the segments. Since ABA inhibits the synthesis of celluloseand hemicellulosic polysaccharides in cell walls of segmentsof squash hypocotyls prior to the suppression of elongationof segments (Wakabayashi et al. 1989a, b), the present resultsindicate that ABA inhibits cell-wall synthesis by affectingsome step(s) beyond the formation of UDP-sugars and not by decreasingthe synthesis of UDP-sugars in the hypocotyl segments. ¹Present address: Biological Laboratory, Faculty of Education,Kagawa University, Saiwai-cho 1-1, Takamatsu, 760 Japan (Received May 30, 1990; Accepted February 5, 1991)     

Potato Lectin: A Cell-Wall Glycoprotein

The activity and the amount of potato lectin were measured inpotato tuber slices (Solanum tuberosum cv. Huinkul) aeratedfor 48 h. Lectin was found in a soluble form, liberated to themedium and associated with insoluble structures. Polyacrylamidegel electrophoresis in denaturating conditions and immunologicaltechniques indicated that the lectins associated to cell wall,soluble or liberated to the medium, were identical. The cell-wallfraction was found to contain 65% of total lectin in the tuber.The possible role of potato lectin in tubers was discussed. (Received June 5, 1985; Accepted September 3, 1985)     

Future Prospects for Developing Disease Resistant Plants

Transgenic Research -     

Complement-Mediated Cytolysis of Cell-Wall Mutants of Chlamydomonas reinhardtii

Treatment of the cell wall-less mutant CW 15 of Chlamydomonasreinhardtii with human serum leads to a marked increase of thecell volume, followed by an irreversible cytolysis. Heat-inactivatedserum as a control reveals no cytotoxic effects on CW 15. Experimentswith C4-, properdin-, C3-, and factor H-depleted sera indicatethe alternative pathway of complement as being responsible forthe serum-mediated lysis. After immunofluorescence marking aswell as electromicroscopically after negative staining the membraneattacking complex of complement, C5b-9, could be demonstratedon the surface of CW 15. These results together with the observationthat cells of the wild-type strain 11-32c of C. reinhardtiiare not lysed by active serum suggest that only protoplastsof Chlamydomonas carry surface structures capable to activatethe alternative pathway of complement. In order to find out whether other cell wall mutants of C. reinhardtii,besides CW 15, can also activate the human complement system,we tested three strains each of the three known mutant categories.Strains CW 4, CW 9, and CW 19, representing category A, andstrains CW 3, CW 10, and CW 92, representing category C, andCW 8 and CW 18, accounting for category B, were cytolysed bynormal human serum. Only one type used in our experiments, CW20 of category B, resisted serum treatment, suggesting the needto redefine this category. ¹This paper is dedicated to Professor Dr. Andr? Pirson on theoccasion of his 80th birthday (Received December 1, 1989; Accepted April 5, 1990)     

Incorporation of D-[U-14C]glucose and 14CO2 into the Cell-Wall Polymers of Flax Hypocotyl, in the Course of the Fibre Differentiation

Cellulose deposits in the fibres of flax hypocotyl were observedon transverse sections of the distal part, after several daysof plant growth under continuous light. The secondary celluloseof the fibres was not labelled preferentially when a pulse of¹⁴CO₂ was given. Conversely, the D-[U-¹⁴C]glucose was well incorporatedinto the fibre secondary cellulose, whatever the day of thepulse. The glucose was, first incorporated into storage polysaccharides(probably starch) and used when needed, for secondary cellulosedeposits. (Received September 16, 1992; Accepted June 2, 1993)     

Cell-wall Polysaccharides of Immature Barley Plants. II. Characterization of a Xyloglucan

A xyloglucan occurring in the hemicellulose II fraction of cell walls of immature barley plants was characterized by methylation and fragmentation analyses. The results indicated that the xyloglucan was mainly composed of the following repeating units:      

胡萝卜花药发育的组织化学研究

胡萝卜四分体时期的花药在药室内壁和绒毡层细胞中积累淀粉粒,随着花药的发育,花粉先出现大液泡,同时药室内壁和绒毡层细胞中淀粉粒消失;以后花粉中的大液泡消失,在花粉细胞质中出现淀粉粒。伴随着花粉的发育,绒毡层细胞退化,在细胞中积累较多的脂类物质,同时花粉中脂类物质含量也明显增加。胡萝卜成熟花粉粒的储存物主要为脂滴,也有少部分淀粉颗粒。胡萝卜花药在特定时间和特定部位积累营养储存物的过程也是其发育的一个特征。     

Developing a Photoautotrophic Micropropagation System for Woody Plants

in vitro including cotyledonary stage somatic embryos have the ability to grow photoautotrophically (without sugar in the culture medium), and that the low or negative net photosynthetic rate of plants in vitro is due not to poor photosynthetic ability, but to the low CO₂ concentration in the air-tight culture vessel during the photoperiod. Furthermore, we have shown that the photoautotrophic growth of several woody plants in vitro can be significantly promoted by increasing the CO₂ concentration and light intensity in the vessel, by decreasing the relative humidity in the vessel, and by using a fibrous or porous supporting material with high air porosity instead of gelling agents such as agar. In this paper, the advantages of photoautotrophic micropropagation in a conventional, small culture vessel with a microporous gas filter for enhancing natural ventilation and in a large culture vessel with a forced ventilation unit are described for woody plants such as acacia (Acacia mangium), coffee (Coffea arabusta), eucalyptus (Eucalyptus camaldlensis), mangosteen (Garcinia mangostana), neem (Azadirachta indica), paulownia (Paulownia fortunei), and pine (Pinus radiata). Received 30 August 2001/ Accepted in revised form 27 September 2001     

Amino Acid Composition of Certain Bacterial Cell-Wall Proteins

Analyses were made to determine the amino acid composition of the cell-wall proteins of Salmonella pullorum, S. senftenberg 775W, S. derby, and Escherichia coli. These proteins consist of the usual 18 amino acids found in most proteins with diaminopimelic acid in addition. Quantitative determination of these amino acids showed that their amounts were similar.     

蓝猪耳花药发育中多糖和脂滴的组织化学研究

对蓝猪耳花药发育中营养物质的分布和转化过程进行组织化学研究,结果表明:在造孢细胞时期,药壁细胞没有营养物质的积累,但在造孢细胞中有少量的脂滴;在小孢子母细胞时期,表皮细胞中出现淀粉粒,而在绒毡层细胞中出现脂滴,小孢子母细胞中也有脂滴的分布;在四分体时期,四分体小孢子中出现淀粉粒,绒毡层细胞脂滴增加;在小孢子早期,药室内壁细胞中出现淀粉粒,绒毡层继续积累脂滴,而小孢子中开始出现脂滴;到小孢子晚期,绒毡层细胞降解,细胞残留物中出现较多脂滴;在二胞花粉早期,花粉中的大液泡消失,花粉开始积累淀粉粒;在即将开花的成熟花粉中则积累了大量的脂滴和少量的淀粉粒.蓝猪耳花药发育中多糖和脂滴两种营养物质的积累和分布具有一定的时、空特点,反映出花药发育中营养物质积累的规律.     

Different Ways of Formation of Root System in Plants,Maize and Flax Seedlings Taken as Examples

Comparison of the appearance and development of lateral roots in the flax and maize seedlings has shown the way of root branching in the flax, as distinct from that in most plants. Some primordia in the flax main root did not develop immediately into lateral roots, but remained quiescent, which determines different reactions of the maize and flax root systems to experimental influences. Decapitation of the main root in the maize did not leads to a significant increase in the number of lateral roots, while in the flax, their number noticeably increased due to the development of previously quiescent primordia into lateral roots. The treatment with synthetic auxin did not induce the formation of additional primordia and lateral roots in the maize roots. In the flax, the number of primordia increased significantly and that of lateral roots increased to a somewhat lesser extent. Apparently, the development of a primordium into a lateral root proceeds in two stages and they have different regulation.