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PubMed2006

Caterpillar-elicited methanol emission: a new signal in plant-herbivore interactions?

Plants release into the atmosphere large quantities of volatile organic compounds (VOCs), of which methanol (MeOH), a putative waste product, is the second most abundant. Using online proton-transfer-reaction mass spectrometry (PTR-MS), we demonstrate that when Manduca sexta larvae attack Nicotiana attenuata plants, the wound-induced release of MeOH dramatically increases. The sustained MeOH emission 24 h after herbivore feeding is already substantially greater than the release of the well-characterized green-leaf VOC E-2-hexenal. Herbivore attack and treatment of puncture wounds with larval oral secretions (OS) increased the transcript accumulation and activity of leaf pectin methylesterases (PMEs), and decreased the degree of pectin methylation, as determined by (1)H-NMR; therefore, we propose that the released MeOH originates from the activation of PMEs by herbivore attack. The herbivore- and OS-elicited MeOH results not from the activity of previously characterized elicitors in OS but from a pH shift at the wound site when larval OS (pH 8.5-9.5) are introduced into the wounds during feeding. Applying MeOH to plants in quantities that mimic the herbivory-elicited release decreases the activity of the potent plant defense proteins trypsin proteinase inhibitors (TPI), and increases the performance of the attacking larvae. The pH of lepidopteran larvae regurgitants is commonly very high, and the MeOH released during feeding that is elicited by the pH change at the wound site functions as a quantitative signal that influences the outcome of the plant-herbivore interaction.

Animals↗

PubMed1995

Cry j 2, a major allergen of Japanese cedar pollen, shows polymethylgalacturonase activity.

We examined Cry j 2, a major allergen of Japanese cedar (Cryptomeria japonica) pollen, for polygalacturonase enzyme activity, since a nucleotide sequence of cDNA of Cry j 2 showed a significant homology with that of tomato polygalacturonase. Polygalacturonase is well known to depolymerize preferentially polygalacturonic acid (PGA) by hydrolysis. However, Cry j 2 did not act on PGA, but was found to depolymerize pectin and methylesterified PGA in a dose-dependent manner. The substrate specificity of Cry j 2 was different from that of polygalacturonase derived from Aspergillus niger. The depolymerizing activity of Cry j 2 reached a maximum at 50%-60% of methylesterification of PGA. In contrast, polygalacturonase showed its maximum activity of PGA, and the activity decreased as the degree of methylesterification increased. Interestingly, the pectin-depolymerizing activity of Cry j 2 was due to a hydrolysis, but not a lyase, activity which splits the glycosidic bonds by beta-elimination, since no unsaturated uronides were found by measurement of absorbance at 235 nm in the reaction mixture. The enzyme activity was markedly inhibited by anti-Cry j 2 antibodies. These results indicate that Cry j 2 probably has polymethylgalacturonase enzyme activity, as postulated by von Neukom in 1963, although existence of this activity has not yet been proven.

Allergens↗

PubMed1979

Isolation and characterization of large treponemes from the bovine rumen.

Ten strains of strictly anaerobic spiral organisms were isolated in pure culture from a 10(-7) dilution of bovine rumen contents. Three strains were studied in detail. These strains morphologically resembled previously isolated and described rumen treponemes except the new isolates were larger, 0.7 micrometer wide and 12 to 25 micrometer long. They rapidly fermented pectin and, less readily, L-arabinose, inulin, and sucrose. Acetic and formic acid were the main fermentation products from pectin; small amounts of succinic acid were also formed.

Anaerobiosis↗

PubMed1987

Difference in sporogenous bacterial populations in thermophilic (55 degrees C) and mesophilic (35 degrees C) anaerobic sewage digestion.

Spores, sporeforming vegetative cells, and asporogenous populations were enumerated in two semicontinuous anaerobic fermentors digesting municipal primary sludge at 35 and 55 degrees C for more than 87 days. In the 35 degrees C fermentor, the anaerobic total population was 312.5 X 10(6)/ml, with 25.0 X 10(6)/ml being sporogenous. The populations that digest casein, starch, pectin, and cellulose were 23.1 X 10(6), 59.2 X 10(6), 26.2 X 10(6), and 7.3 X 10(6)/ml, respectively, with 2.8 X 10(6), 6.7 X 10(6), 3.4 X 10(6), and 1.5 X 10(6)/ml being sporogenous, respectively. The sporeformers accounted for 8.0 to 20.0% of each of the respective populations. In the 55 degrees C fermentor, the anaerobic total population was 512.5 X 10(6)/ml, with 336.6 X 10(6)/ml being sporogenous. The populations that digest casein, starch, pectin, and cellulose were 97.7 X 10(6), 190.7 X 10(6), 75.8 X 10(6), and 11.2 X 10(6)/ml, respectively, with 47.8 X 10(6), 110.6 X 10(6), 43.3 X 10(6), and 5.1 X 10(6)/ml, respectively, being sporogenous. The sporeformers represented 45.5 to 65.7% of each of the respective populations. The numbers of thermophilic sporeforming vegetative cells in the 55 degrees C fermentor were 9.0 to 19.8 times higher than their counterparts in the 35 degrees C fermentor. Most sporeformers were in the vegetative state in the 35 and 55 degrees C fermentors. After 18 days of fermentation at 55 degrees C, sporeformers carried out most of the digestion; however, the digestion was shared by both sporeformers and asporogenous bacteria after 87 days of fermentation. In the 35 degrees C fermentor, asporogenous bacteria digested most of the sludge. During the 18- and 87-day experimental periods, sporeformers were never predominant.

Bacteria, Anaerobic↗

PubMed1995

Purification and characterization of an extracellular pectate lyase from an Amycolata sp.

The extracellular pectate lyase (EC 4.2.2.2) of a nonsporulating Amycolata sp. was purified to homogeneity by anion- and cation-exchange chromatographies followed by hydrophobic interaction chromatography. The enzyme cleaved polygalacturonate but not highly esterified pectin in a random endolytic transeliminative mechanism that led to the formation of a wide range of 4,5-unsaturated oligogalacturonates. As shown by high-performance anion-exchange chromatography and pulsed amperometric detection, these unsaturated oligogalacturonates were further depolymerized by the enzyme to the unsaturated dimer and trimer as final products. The pectate lyase had a molecular weight of 31,000 determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and a molecular mass of 30,000 Da determined by matrix-assisted laser desorption ionization mass spectrometry. The isoelectric point of the protein was 10. Maximum activity occurred at pH 10.25. Calcium was essential for activity, and EDTA inactivated the enzyme under standard assay conditions. Interestingly, EDTA did not inhibit the ability of the enzyme to cleave the native pectin (protopectin) of ramie (Boehmeria nivea) fibers. The Km value with sodium polygalacturonate as the substrate was 0.019 g liter-1. The purified enzyme lost its activity after a 1-h incubation at 50 degrees C but was stabilized by calcium or polygalacturonate. The N-terminal sequence showed high similarity within a stretch of 13 amino acids to the N-terminal sequences of pectate lyases PLa and PLe from Erwinia chrysanthemi. The Amycolata sp. did not produce additional isozymes of pectate lyase but produced further activities of pectinesterase, xylanase, and carboxymethyl cellulase when grown in a medium with decorticated bast fibers from ramie as the sole carbon source.

Actinomycetales↗

PubMed1999

Comparison of bacterial community structures in the rhizoplane of tomato plants grown in soils suppressive and conducive towards bacterial wilt.

It has been reported that the growth of Ralstonia solanacearum is suppressed at the rhizoplane of tomato plants and that tomato bacterial wilt is suppressed in plants grown in a soil (Mutsumi) in Japan. To evaluate the biological factors contributing to the suppressiveness of the soil in three treated Mutsumi soils (chloroform fumigated soil; autoclaved soil mixed with intact Mutsumi soil; and autoclaved soil mixed with intact, wilt-conducive Yamadai soil) infested with R. solanacearum, we bioassayed soil samples for tomato bacterial wilt. Chloroform fumigation increased the extent of wilt disease. More of the tomato plant samples wilted when mixed with Yamadai soil than when mixed with Mutsumi soil. Consequently, the results indicate that the naturally existing population of microorganisms in Mutsumi soil was significantly able to reduce the severity of bacterial wilt of tomato plants. To characterize the types of bacteria present at the rhizoplane, we isolated rhizoplane bacteria and classified them into 22 groups by comparing their 16S restriction fragment length polymorphism patterns. In Yamadai soil a single group of bacteria was extremely predominant (73.1%), whereas in Mutsumi soil the distribution of the bacterial groups was much more even. The 16S rDNA sequence analysis of strains of dominant groups suggested that gram-negative bacteria close to the beta-proteobacteria were most common at the rhizoplane of the tomato plants. During in vitro assays, rhizoplane bacteria in Mutsumi soil grew more vigorously on pectin, one of the main root exudates of tomato, compared with those in Yamadai soil. Our results imply that it is difficult for the pathogen to dominate in a diversified rhizobacterial community that thrives on pectin.

Bacteria↗

PubMed1970

Similarities in the action patterns of exopolygalacturonate lyase and pectinesterase from Clostridium multifermentans.

Exopolygalacturonate lyase and pectinesterase from Clostridium multifermentans were assayed simultaneously in the same reaction mixture which contained a highly esterified pectin, polymethyl polygalacturonic acid methyl glycoside. Lyase is specific for unesterified galacturonide residues and cannot degrade this substrate in the absence of the esterase. The rate for esterase was twice the rate for lyase throughout the entire course of the combined reaction. Thus, the molar ratio of the two enzyme activities was the same since the product of the lyase is an unsaturated digalacturonic acid containing two free carboxyl groups. Since clostridial exopolygalacturonate lyase is known to degrade polygalacturonate in a linear manner beginning from the reducing ends of polygalacturonate chains, it was apparent that clostridial pectinesterase must hydrolyze methyl groups in highly esterified pectins with an action pattern similar to that of the lyase. Otherwise it would be impossible for the two enzyme rates to have corresponded on the basis of a 2:1 ratio.

Calcium Chloride↗

PubMed1979

Glycogen, hyaluronate, and some other polysaccharides greatly enhance the formation of exolipase by Serratia marcescens.

Among 21 different polysaccharides tested, 5 greatly enhanced the spontaneous and cyclic AMP-induced formation of exolipase: glycogen, hyaluronate, laminarin, pectin B, and gum arabic. These polysaccharides have in common the tendency to form highly ordered networks because of the branching or helical arrangement, or both, of their molecules. None of the polysaccharides could be utilized by the cells as the sole carbon source. Strong lipid extraction of four different polysaccharides did not reduce their exolipase-enhancing efficacy. At a constant cell density the stimulation of exolipase formation by various concentrations of glycogen followed saturation kinetics, suggesting a limited number of "sites" for the glycogen to act. The active principle present in a solution of pectin was destroyed by degradation (beta-elimination) of the polymer. Hyaluronate lost its exolipase-enhancing activity by exhaustive hydrolysis with hyaluronidase but was resistant to proteinase K. Exopolysaccharide, isolated from growth medium of Serratia marcescens SM-6, enhanced the exolipase formation as efficiently as hyaluronate. The results of this work are discussed mainly in terms of the "detachment hypothesis."

Calcium↗

PubMed1990

Molecular cloning of the structural gene for exopolygalacturonate lyase from Erwinia chrysanthemi EC16 and characterization of the enzyme product.

The ability of Erwinia chrysanthemi to cause soft-rot diseases involving tissue maceration in many plants has been linked to the production of endo-pectate lyase E. chrysanthemi EC16 mutant UM1005, however, contains deletions in the pel genes that encode the known endopectate lyases, yet still macerates plant tissues. In an attempt to identify the remaining macerating factor(s), a gene library of UM1005 was constructed in Escherichia coli and screened for pectolytic activity. A clone (pPNL5) was identified in this library that contained the structural gene for an exopolygalacturonate lyase (ExoPL). The gene for ExoPL was localized on a 3.3-kb EcoRV fragment which contained an open reading frame for a 79,500-Da polypeptide. ExoPL was purified to apparent homogeneity from Escherichia coli DH5 alpha (pPNL5) and found to have an apparent molecular weight of 76,000 with an isoelectric point of 8.6. Purified ExoPL had optimal activity between pH 7.5 and 8.0 and could utilize pectate, citrus pectin, and highly methyl-esterified Link pectin as substrates. A PL- ExoPL- mutant of EC16 was constructed that exhibited reduced growth on pectate, but retained pathogenicity on chrysanthemum equivalent to that of UM1005. The results indicate that ExoPL does not contribute to the residual macerating activity of UM1005.

Amino Acid Sequence↗

PubMed1992

Environmental conditions affect transcription of the pectinase genes of Erwinia chrysanthemi 3937.

To depolymerize plant pectin, the phytopathogenic enterobacterium Erwinia chrysanthemi produces a series of enzymes which include a pectin-methyl-esterase encoded by the pem gene and five isoenzymes of pectate lyases encoded by the five genes pelA, pelB, pelC, pelD, and pelE. We have constructed transcriptional fusions between the pectinase gene promoters and the uidA gene, encoding beta-glucuronidase, to study the regulation of these E. chrysanthemi pectinase genes individually. The transcription of the pectinase genes is dependent on many environmental conditions. All the fusions were induced by pectic catabolic products and responded, to different degrees, to growth phase, catabolite repression, temperature, and nitrogen starvation. Transcription of pelA, pelD, and pelE was also increased in anaerobic growth conditions. High osmolarity of the culture medium increased expression of pelE but decreased that of pelD; the other pectinase genes were not affected. The level of expression of each gene was different. Transcription of pelA was very low under all growth conditions. The expression of the pelB, pelC, and pem genes was intermediate. The pelE gene had a high basal level of expression. Expression of pelD was generally the most affected by changes in culture conditions and showed a low basal level but very high induced levels. These differences in the expression of the pectinase genes of E. chrysanthemi 3937 presumably reflect their role during infection of plants, because the degradation of pectic polymers of the plant cell walls is the main determinant of tissue maceration caused by soft rot erwiniae.

Anaerobiosis↗

PubMed1999

Azospirillum irakense produces a novel type of pectate lyase.

The pelA gene from the N2-fixing plant-associated bacterium Azospirillum irakense, encoding a pectate lyase, was isolated by heterologous expression in Escherichia coli. Nucleotide sequence analysis of the region containing pelA indicated an open reading frame of 1,296 bp, coding for a preprotein of 432 amino acids with a typical amino-terminal signal peptide of 24 amino acids. N-terminal amino acid sequencing confirmed the processing of the protein in E. coli at the signal peptidase cleavage site predicted by nucleotide sequence analysis. Analysis of the amino acid sequence of PelA revealed no homology to other known pectinases, indicating that PelA belongs to a new pectate lyase family. PelA macerates potato tuber tissue, has an alkaline pH optimum, and requires Ca2+ for its activity. Of several divalent cations tested, none could substitute for Ca2+. Methyl-esterified pectin (with a degree of esterification up to 93%) and polygalacturonate can be used as substrates. Characterization of the degradation products formed upon incubation with polygalacturonate indicated that PelA is an endo-pectate lyase generating unsaturated digalacturonide as the major end product. Regulation of pelA expression was studied by means of a translational pelA-gusA fusion. Transcription of this fusion is low under all growth conditions tested and is dependent on the growth phase. In addition, pelA expression was found to be induced by pectin. An A. irakense pelA::Tn5 mutant still displayed pectate lyase activity, suggesting the presence of multiple pectate lyase genes in A. irakense.

Azospirillum↗

PubMed1997

Assembly and enlargement of the primary cell wall in plants.

Growing plant cells are shaped by an extensible wall that is a complex amalgam of cellulose microfibrils bonded noncovalently to a matrix of hemicelluloses, pectins, and structural proteins. Cellulose is synthesized by complexes in the plasma membrane and is extruded as a self-assembling microfibril, whereas the matrix polymers are secreted by the Golgi apparatus and become integrated into the wall network by poorly understood mechanisms. The growing wall is under high tensile stress from cell turgor and is able to enlarge by a combination of stress relaxation and polymer creep. A pH-dependent mechanism of wall loosening, known as acid growth, is characteristic of growing walls and is mediated by a group of unusual wall proteins called expansins. Expansins appear to disrupt the noncovalent bonding of matrix hemicelluloses to the microfibril, thereby allowing the wall to yield to the mechanical forces generated by cell turgor. Other wall enzymes, such as (1-->4) beta-glucanases and pectinases, may make the wall more responsive to expansin-mediated wall creep whereas pectin methylesterases and peroxidases may alter the wall so as to make it resistant to expansin-mediated creep.

Cell Wall↗

PubMed1988

Radiographic analysis of the effect of dietary fibers on rat colonic transit time.

The effect of different fiber sources on colonic transit time was charted using serial radiographs. Sixty male Sprague-Dawley rats, 10 rats per group, were provided with either a fiber-free control diet or the control diet uniformly diluted to provide 8% dietary fiber from guar, pectin, cellulose, wheat bran, or oat bran. At surgery, radiopaque markers were inserted at defined distances in the mesentary closest to the large bowel. Three weeks postsurgery, the animals were intubated with 0.5 ml of a radiopaque marker, and radiographs were taken at 15-min intervals. Of the two poorly fermented fibers, cellulose was as slow as and wheat bran was faster than the fiber-free controls at five out of the six bowel segments measured. The fermentable fibers (pectin, guar, and oat bran) were fast through some bowel segments and slow through others. This study provides in vivo data on colonic transit time and shows that neither 24-h fecal weight nor total transit time is a good predictor of the rate of transit through particular gut segments.

Animals↗

PubMed1985

Do calories, osmolality, or calcium determine gastric emptying?

To determine whether calories, osmolality, or calcium mediate gastric emptying we employed a standardized radioactive meal in 10 normal human volunteers. A variety of simple and complex sugars, medium-chain fatty acid (MCFA), pectin, and gluten were dissolved in water and ingested with the test meal. The studies were also performed with calcium chloride, EDTA, and an equimolar combination of these chemicals. Results of gastric emptying showed that incremental glucose produced an increase in emptying time with a tendency for emptying time to show a proportionally greater delay with increasing glucose concentrations. Fructose and polyhexose had similar effects to glucose. Pentoses (xylose and arabanose) markedly prolonged gastric emptying when compared with the same amount of glucose. The effect of sucrose and gluten on gastric emptying did not significantly differ from controls. Twenty-five grams MCFA had an effect similar to 50 g glucose. Pectin, a complex carbohydrate, produced a varied effect in different individuals. There was no obvious relationship between osmolality and gastric emptying. Calcium chloride and EDTA prolonged gastric emptying, but the equimolar combination gave values similar to controls. Our findings suggest 1) calories nor osmolality alone determine gastric emptying, 2) both calcium and calcium chelation with EDTA prolong gastric emptying, and 3) a specific food does not necessarily produce the same effect on gastric emptying in different individuals.

Adult↗

PubMed1982

Disaccharidase levels of the rat jejunum are altered by dietary fibre.

Rat jejunal disaccharidases were measured after feeding high fat fibre-free, high fat pectin, high fat cellulose, high fat galactomannan and high fat tannin diets for 27 weeks. Compared with the high fat fibre-free diet, pectin lowered both lactase and sucrase levels (p less than 0.025). Galactomannan and tannin lowered only the lactase level (p less than 0.05), while cellulose had no significant effect on disaccharidase levels. These data suggest that dietary fibre components have individual and specific effects on jejunal disaccharidase levels, in the presence of a high fat diet.

Animals↗

PubMed1985

Carbohydrate fermentation in the human colon and its relation to acetate concentrations in venous blood.

There is now substantial evidence that some dietary polysaccharides, notably dietary fiber, escape absorption in the small bowel and are then broken down in the large intestine of man. The main end products of this colonic digestive process, which is anerobic, are short chain fatty acids (SCFA), and acetic, propionic, and butyric acids. Although these acids are known to be absorbed from the colon, their subsequent fate and significance is unknown. We have measured venous blood SCFA levels in healthy subjects after a 16-h fast, and then following oral doses of either 50 mmol SCFA, 5, 10, or 20 g doses of the fermentable carbohydrate lactulose, or 20 g of pectin. Fasting venous blood acetate was 53.8 +/- 4.4 mumol/liter (SEM) (n = 14). Fasting arterial blood acetate, taken simultaneously with venous blood in six subjects, was higher; 125.6 +/- 13.5 mumol/liter (arterial) vs. 61.1 +/- 6.9 mumol/liter (venous). Significant levels of propionate or butyrate were not detected in any blood samples. Following an oral dose of 50 mmol mixed SCFA, venous blood acetate reached a peak of 194.1 +/- 57.9 mumol/liter at 45 min and returned to fasting levels at 2 h. Blood acetate also rose in response to lactulose, peak levels occurring 2-4 h after the dose: 5 g, 98.6 +/- 23.1 mumol/liter; 10 g, 127.3 +/- 18.2 mumol/liter; and 20 g, 181.3 +/- 23.9 mumol/liter. Pectin fermentation was much slower, with blood acetate levels starting to rise after 6 h and remaining elevated at about twice fasting levels for the subsequent 18 h. However, areas under the blood acetate curves were closely related (r = 0.97; n = 5), whatever the source of acetate. These studies show that the large intestine makes an important contribution to blood acetate levels in man and that fermentation may influence metabolic processes well beyond the wall of this organ.

Acetates↗

PubMed2001

In vitro biosynthesis of homogalacturonan by a membrane-bound galacturonosyltransferase from epicotyls of azuki bean.

A membrane preparation of 7-d-old seedlings from azuki bean (Vigna angularis) contained galacturonosyltransferase (GalAT) capable of transferring galacturonic acid (GalA) from UDP-GalA into polygalacturonic acid (PGA) as an exogenous acceptor. The enzyme was maximally active at pH 6.8-7.8 and 25-35 degrees C in the presence of 5 mM Mn2+ and 0.5% (w/v) Triton X-100. Acid-soluble low-Mr (average Mr 10,000) PGA was a more efficient acceptor substrate than acid-insoluble polymer (Mr 70,000). The apparent Michaelis constants for UDP-GalA and low-Mr PGA were 0.14 mM and 0.02 mg/ml, respectively. Various pectins with different degrees of methyl-esterification (DE) were poor acceptors, and the enzyme activity tended to decrease with decreasing DE of the pectins. The transfer products from incubation of the enzyme with UDP-14C-GalA and the low-Mr PGA yielded 14C-GalA2 as the major product upon digestion with an endopolygalacturonase (EPGase), confirming the incorporation of GalA into PGA through contiguous alpha-1,4-linkages.

Carbohydrate Conformation↗

PubMed2003

Effect of dietary fiber on the lipid metabolism and immune function of aged Sprague-Dawley rats.

Eight-month-old Sprague-Dawley rats were fed on diets containing dietary fiber at the 5% level for 3 weeks to examine the effect on the lipid metabolism and immune function. Among cellulose, guar gum, partially hydrolyzed guar gum (PHGG), glucomannan and highly methoxylated pectin, guar gum induced a significant decrease in the food intake and weight gain, as well as a significant increase in the liver weight. In addition, the epidydimal adipose tissue weight of the rats fed on PHGG was significantly higher than that of the rats fed on cellulose. There was no significant effect on the serum lipid levels, but the serum IgG level of the rats fed on guar gum was significantly lower than that of the rats fed on cellulose. The IgA and IgG productivity in mesenteric lymph node (MLN) lymphocytes was significantly higher in the rats fed on guar gum, glucomannan and pectin than in those fed on cellulose, while the effect on Ig productivity in spleen lymphocytes was not as marked. In addition, only guar gum induced a significant increase of IgM productivity in MLN lymphocytes when compared to the cellulose group. These results suggest that enhancement of the immune function by dietary fiber is mainly expressed in the gut immune system.

Aging↗