Cellulase, Fruit Softening and Abscission in Red RaspberryRubus idaeusL. cv Glen Clova

The ripening of raspberry fruit (Rubus ideausL. cv Glen Clova)is associated with a climacteric rise in ethylene production.As the fruit pigments change from green to red there is a progressivesoftening, loss of skin strength and a breakdown of cell wallsin the mesocarp. An increase in cellulase (endo-1,4-ß-D-glucanase)in both drupelets and receptacles accompanies these changes.The localization of cellulase in the regions of the fruit associatedwith abscission zones suggest the enzyme may be involved infruit separation as well as softening. Rubus idaeusL; raspberry; fruit ripening; ethylene; abscission; cell wall breakdown; cellulase; endo-1,4-ß-D-glucanase     

A laboratory study on digestive processes in the Antarctic krill,Euphausia superba,with special regard to chitinolytic enzymes

Feeding experiments of 9, 14 and 20 days duration were carried out on the Antarctic krill, Euphausia superba. Two groups were fed with the chitinous diatom Cyclotella cryptica and the non-chitinous green algae Dunaliella bioculata, respectively. A control group remained unfed. The time courses of the activities of endo- and exochitinase in the stomach and the midgut gland were compared with those of the digestive enzymes protease, cellulase (1,4-β-d-glucanase) and laminarinase (1,3-β-d-glucanase). Specific activities of all enzymes were higher in the stomach than in the midgut gland. Characteristic time courses of activity were evident after 4 days. In starved animals, enzyme activities decreased to a minimum after 4 days and recovered within 14 days to initial values. In the stomach, the activities of endo- and exochitinase increased when krill were fed on Cyclotella. For animals fed with Dunaliella, activities stayed constant or decreased slightly. The results confirm chitinases as digestive enzymes and, therefore, the capability of krill to utilize various food sources. Accepted: 4 October 1998     

Purification and Characterization of Wall-bound Exo-l,3-{beta}-D-Glucanase from Barley (Hordeum vulgare L.) Seedlings

A ß-D-glucanase activity hydrolyzing 1,3:1,4-ß-D-glucanwas released from the cell walls of barley by 3M LiCl treatment.It was purified by sequential cation-exchange, gel-filtrationand hydrophobic chromatography. The molecular mass of the glucanasewas 66 kDa as determined by SDS-polyacrylamide gel electrophoresis.Sequence determination of the first thirty amino acids of theN-terminus revealed a high homology of this enzyme to the Pseudomonasl,4-ß-D-glucosidase (56.5%). The purified ß-D-glucanasehas a pH optimum at 5.0, and hydrolyzes oligosaccharides containingß-D-1,3 or ß-D-1,4 linkage. The glucanaseshowed maximum hydrolytic activity toward laminaritetraose,the rate being about two times that of cellotetraose and aboutfour times that of gentiobiose. Polysaccharides such as lichenan,l,3:l,4-ß-D-glucan (from barley), laminarin and pustulanare also hydrolyzed, but not carboxylmethyl-curdlan, carboxymethyl-cellulose,xyloglucan and maltose. The purified ß-D-glucanaseyielded monomeric glucose from laminarihexaose, and exhibitedcharacteristics of an exo-l,3-ß-D-glucanase (EC 3.2.1.58 [EC] ).The activity and biochemical characteristics of this enzymesuggest that it is an exo-l,3-ß-D-glucanase involvedin the rapid turnover of l,3:l,4-ß-D-glucan in barleycell walls during seedling growth. (Received September 24, 1996; Accepted December 9, 1996)     

Characterization of the Hydrolytic Activity of Avocado Cellulase

The cellulase produced by ripening avocado fruits (Persea americanaMill cv. Fuerte) was isolated and purified using chromatofocusing(pH 7–4) and gel filtration on a Bio- Gel P-100 column.Characteristics of the cellulase were assessed by using, assubstrates, a range of polysaccharides containing various sugarresidues and varying types of linkages between the residues.Only those substrates containing (14)-ß-glucosyl linkageswere hydrolyzed by the purified enzyme. Two polysaccharidesthat were extensively hydrolyzed by the cellulase were carboxymethylcelluloseand (13),(14)-ß-D-glucans such as from Avena endospermcell walls. Characterization of the activity in the degradationof the mixed linked glucan of Avena and cellodextrins indicatedthat the enzyme has a limit recognition-hydrolytic site of four(l4)-ß linked glucose residues. It was also foundthat the enzyme could cleave only (14)-ß-linkagesthat were adjacent to other (l4)-ß-D-glucosyl linkages.Activity of the cellulase against isolated avocado fruit cellwalls indicated that the purified enzyme was incapable of appreciablysolubilizing the cellulosic components of these walls. ¹Supported in part by National Science Foundation Research GrantPCM 7818588. ²USDA-ARS, Dairy Forage Research Center, University of Wisconsin,Madison, WI 53706. ³Department of Vegetable Crops, University of California, Davis,CA 95616. (Received September 14, 1985; Accepted February 12, 1986)     

A novel {beta}-galactosidase gene isolated from the bacterium Xanthomonas manihotis exhibits strong homology to several eukaryotic {beta}-galactosidases

The gene encoding a ß-galactosidase from Xanthomonasmanihotis was cloned into Escherichia coli. The gene resideson a 2.4 kb DNA fragment which was isolated from a partial Sau3Alibrary in the cloning vector pUC19 using 5-bromo-4-chloro-3-indolyl-ß-D-galactopyranoside(X-gal) as the selection. The enzyme produced by the clone hasa specificity for ß1-3->ß1-4-linked galactose.The nucleotide sequence of the gene was determined. The deducedprotein sequence contained 597 amino acids yielding a monomericmolecular mass of 66 kDa. The cloned ß-galactosidaseshowed no similarity to any known prokaryotic ß-galactosidase.However, extensive similarity was observed with eukaryotic ß-galactosidasesfrom animals, plants and fungi. The strongest similarity waswith the ß-galactosidases found hi the human and mouselysosomes (42 and 41% identity, respectively). Alignment ofthe X.manihotis and eukaryotic ß-galactosidase sequencesrevealed seven highly conserved domains common to each protein.Additionally, Domain 1 in X.manihotis showed similarity to regionswithin catalytic domains from seven xylanases and cellulasesbelonging to family 10 of glucosyl hydrolases. A region spanningDomain 2 showed similarity to the catalytic domain of endo ß1-3glucanases from tobacco and barley. cellulase ß-galactosidase G_M$$$gangliosidosis Morquio B syndrome Xanthomonas     

Biosynthesis of Xyloglucan in Suspension-cultured Soybean Cells. Evidence that the Enzyme System of Xyloglucan Synthesis does not Contain {beta}-1,4-Glucan 4-{beta}-D-Glucosyltransferase Activity (EC 2.4.1.12)

Xyloglucan 4-ß-D-glucosyltransferase, an enzyme responsiblefor the formation of the xyloglucan backbone, in a particulatepreparation of soybean cells has been compared with ß-1,4-glucan4-ß-D-glucosyltransferase of the same origin. Thefollowing observations indicate that the enzyme system of xyloglucansynthesis does not contain ß-1,4-glucan 4-ß-D-glucosyltransferaseactivity, although both enzymes transfer the glucosyl residuefrom UDP-glucose to form the ß-1,4-glucosidic linkage:1. The incorporation of [¹⁴C]glucose into xyloglucan dependedon the presence of UDP-xylose in the incubation mixture. 2.No measurable amount of radioactivity was incorporated fromUDP-[¹⁴C]xylose into the cello-oligosaccharides, although theincorporation of [¹⁴C]xylose into xyloglucan depended on thepresence of UDP-glucose in the incubation mixture (Hayashi andMatsuda 1981b). 3. The activity of xyloglucan 4-ß-D-glucosyltransferasewas stimulated more strongly by Mn²⁺ than by Mg²⁺, whereas Mg²⁺was the most active stimulator for the activity of ß-1,4-glucan4-ß-D-glucosyltransferase. 4. An addition of GDP-glucose(100 µM) to the incubation mixture inhibited the activityof xyloglucan 4-ß-D-glucosyltransferase by 17%, whereasthe activity of ß-1,4-glucan 4-ß-D-glucosyltransferasewas inhibited 56% under the same conditions. 5. Irpex exo-cellulasedid not hydrolyze the xyloglucan synthesized in vitro. 6. Theß-1,4-glucan synthesized in vitro was not a branchedxyloglucan because it gave no 2,3-di-O-methyl glucose derivativeon methylation analysis. 7. Pulse-chase experiments indicatedthat the ß-1,4-glucan was not transformed into thexyloglucan. The subcellular distribution of the xyloglucan synthase, however,was similar to that of the ß-1,4-glucan synthase (Golgi-located1,4-ß-D-glucan 4-ß-D-glucosyltransferase).Thus, it appears that the latter enzyme is located at a siteclose to xyloglucan synthase and is set aside for the assemblyof these polysaccharides into the plant cell surface. (Received May 21, 1981; Accepted October 13, 1981)     

Characterization of a Non-abscission Mutant in Lupinus angustifolius L.: Physiological Aspects

A single-gene recessive mutant (Abs^-) of Lupinus angustifoliusL. ‘Danja’ that does not abscise any organs wascompared with its parent during continuous exposure of explantsfrom 14 d old seedlings to 10 µl l^-1ethylene. Both endo-(1,4)-ß- D -glucanase (cellulase) and polygalacturonase(PGA) activities increased significantly and progressively inpetiole-stem abscission zones of the parent before the onsetof abscission, and were reflected in a rapid decline in breakstrengthfrom 300 to 70 g within 32 h. In the mutant there was negligibleincrease in hydrolytic enzyme activity, breakstrength declinedslowly (to 180–200 g by 72 h) and there was no abscission.Isoelectric focusing showed two cellulase isoforms (pI 5.0 andpI 8.5) expressed in abscission zones of the parent; these wereexpressed at much lower levels in the mutant. These data areinterpreted to indicate that expression of at least two formsof cellulase activity is enhanced by ethylene in normal petioleabscission zones of lupin. PGA activity also increased in theabscission zone tissue of the parent but to a lesser extentin that of the mutant. We attribute the Abs^-phenotype to mutationof a gene regulating ethylene-responsive expression of abscission-specifichydrolytic enzymes. Copyright 2001 Annals of Botany Company Lupinus angustifolius, abscission, breakstrength, cellulase, ethylene, legume, lupin, mutant, polygalacturonase     

Catalytic properties and amino acid sequence of endo-1→3-β-D-glucanase from the marine mollusk <Emphasis Type="Italic">Tapes literata</Emphasis>

A specific 1→3-β-D-glucanase with molecular mass 37 kDa was isolated in homogeneous state from crystalline style of the commercial marine mollusk Tapes literata. It exhibits maximal activity within the pH range from 4.5 to 7.5 at 45dgC. The 1→3-β-D-glucanase catalyzes hydrolysis of β-1→3 bonds in glucans as an endoenzyme with retention of bond configuration, and it has transglycosylating activity. The K _m for hydrolysis of laminaran is 0.25 mg/ml. The enzyme is classified as a glucan endo-(1→3)-β-D-glucosidase (EC 3.2.1.39). The cDNA encoding this 1→3-β-D-glucanase from T. literata was sequenced, and the amino acid sequence of the enzyme was determined. The endo-1→3-β-D-glucanase from T. literata was assigned to the 16th structural family (GHF 16) of O-glycoside hydrolases.     

Cell Wall Degrading Enzymes in Cuscuta reflexa and Its Hosts

Pectin degrading enzymes, hemicellulose degrading enzyme andcellulose degrading enzymes were studied in Cuscuta reflexaRoxb., its susceptible hosts, Brassica campestris L., Cocciniaindica W. & A. Datura innoxia Mill, Helianthus annuus L.,Holoptelea indica Planch, Lantana camara L., Medicago sativaL., Manihot utilissima Pohl, Petunia hybrida X Hort exvilm,Pisum sativum L., Phaseolus vulgaris L. and Solanum nigrum L.and non-susceptible plants Ipomoea batata Lam. and Solanum tuberosumL. Pectin esterase and polygalacturonase were present in higheramounts in Cuscuta parasitic on P. vulgaris and S. nigrum, whichneeded more time for haustorial establishment. Exo-l, 4-ß-D-glucosidaseactivity was found in Cuscuta but could not be detected in itshosts. Xylanase and cellulase activity of host plants increasedwhile cellobiase activity decreased as a result of infectionby the parasite. Higher pectin esterase, polygalacturonase,xylanase and exo-l, 4-ß-D-glucosidase activities inthe haustorial region of the parasite is likely to bring aboutthe lysis of the cell wall of the host plant and thus facilitatethe penetration of the parasite haustoria into the host sieveelement, which is necessary for the transport of nutrients betweenthe host and the parasite. Key words: Cell wall degrading enzymes, Cuscuta reflexa     

Effect of brown algae metabolites on the synthesis of O-glycosyl hydrolases by bacteria degrading the thallus of <Emphasis Type="Italic">Fucus evanescens</Emphasis>

The effect of fucoidan, extractive substances from Fucus evanescens and the Laminaria cichorioides protein (an inhibitor of endo-1→3-β-D-glucanase) on the degradation of F. evanescens thallus and on the growth of bacteria involved in this process was studied. The complex of O-glycosyl hydrolases and the level of their enzymatic activity in bacteria cultivated under various conditions depended significantly on the composition of the growth medium. The highest taxonomic diversity was observed for bacteria isolated from the thallus degraded in the control medium (sea water). These bacteria were characterized by very low levels of activity of the enzymes degrading polysaccharides (fucoidan, laminaran, and pustulan). In the presence of 1→3-β-D-glucanase inhibitors, the taxonomic diversity of the microorganisms degrading F. evanescens thallus was decreased, and the activity of O-glycosyl hydrolases (particularly, of fucoidan hydrolases) was increased.     

Endogenous production of endo-β-1,4-glucanase by decapod crustaceans

The potential ability to produce cellulase enzymes endogenously was examined in decapods crustaceans including the herbivorous gecarcinid land crabs Gecarcoidea natalis and Discoplax hirtipes, the amphibious freshwater crab Austrothelphusa transversa, the terrestrial hermit crab, Coenobita variabilis the parastacid crayfish Euastacus, and the crayfish Cherax destructor. The midgut gland of both G. natalis and D. hirtipes contained substantial total cellulase activities and activities of the cellulase enzymes endo-β-1,4-glucanase and β-glucosidase. With the exception of total cellulase and β-glucosidase from D. hirtipes, the enzyme activities within the midgut gland were higher than those within the digestive juice. Hence, the enzyme activities appear to reside predominantly within midgut gland, providing indirect evidence for endogenous synthesis of cellulase enzymes by this tissue. A 900 bp cDNA fragment encoding a portion of the endo-β-1,4-glucanase amino acid sequence was amplified by RT-PCR using RNA isolated from the midgut gland of C. destructor, Euastacus, A. transversa and C. variabilis. This provided direct evidence for the endogenous production of endo-β-1,4-glucanase. The 900 bp fragment was also amplified from genomic DNA isolated from the skeletal muscle of G. natalis and D. hirtipes, clearly indicating that the gene encoding endo-β-1,4-glucanase is also present in these two species. As this group of evolutionary diverse crustacean species possesses and expresses the endo-β-1,4-glucanase gene it is likely that decapod crustaceans generally produce cellulases endogenously and are able to digest cellulose.     

Types, Formation, and Metabolism of Cytokinins in Leaves of Alnus Glutinosa (L.) Gaertn.

The nature of the cytokinins present in mature, expanded leavesof alder (Alnus glutinosa (L.) Gaertn.) was investigated usinga chromatographic system capable of partially resolving zeatinfrom (?)-dihydrozeatin. A zeatin-like cytokinin, present asboth a ‘free’ form and as a polar conjugate, postulatedto the the O-ß-D-glucoside of zeatin, accounted forthe bulk of the cytokinin activity (detected by the soybeancallus assay). Studies on the fate of [8-¹⁴C]zeatin supplied to detached alderleaves indicated this cytokinin to undergo extensive metabolism.An appreciable proportion of the radioactivity was incorporatedinto 80% methanol-insoluble and soluble acidic/neutral fractions,while adenosine- and adenine-like peaks were prominent metabolitesin the basic n-butanol-soluble fraction. Small amounts of glucosides,with the properties of both zeatin-O-ß-D-glucosideand dihydrozeatin-O-ß-D-glucoside were formed, thelatter becoming the most prominent with time. The ability of alder leaves to form glucoside directly from(?)-dihydrozeatin was assessed using the soybean callus assay.(?)-Dihydrozeatin was subject to a relatively rapid, continuousand substantial conversion to its putative O-ß-D-glucosideand cytokinin activity was consequently conserved while, incontrast, leaves supplied with zeatin exhibited a progressiveloss of cytokinin activity and, in agreement with the radioactivityexperiments, produced only a small amount of activity attributableto the putative O-glucosides. The significance of the observed cytokinin metabolism is discussedin relation to the endogenous cytokinin status of the leaf.     

The Occurrence of 1,3-{beta}-Glucanase in Healthy and Verticillium-infected, Resistant and Susceptible Tomato Plants

Leaf, stem, and root extracts of near-isogenic tomato plantscv. Craigella, resistant and susceptible to Verticillium albo-atrum,showed constitutive 1,3-ß-glucanase activity whichincreased following inoculation with the pathogen. Partiallypurified enzyme extracts were obtained by dialysing a 30–80%ammonium sulphate fraction of the tissue brei. The enzyme hadpH and temperature optima of 5?5 and 44 ?C respectively, withhigh activity between 50 and 60 ?C. The response to laminarinconcentration was linear between 1?2 and 7?5 mg ml^–1.Root inoculation of susceptible plants with 10⁶ propagules ml^–1V. albo-atrum led to a umform 300 per cent increase in all steminternodes except the terminal one, which was 500 per cent ofthe controls. No spatial relationship of enzyme activity tothe localization of fungus within the stem was apparent. Petioles,leaves, and roots of susceptible infected plants similarly showedan increase in activity but less than that in stems. Changedlevels of stern enzyme activity at different times after inoculationwere associated with reductions in the number of vessels containinghyphae. Extracts of plants of the resistant isoline showed increasedglucanase activity over controls, but this was substantiallylower than that in susceptible plants and was associated withthe greatly reduced mycelial colonization in resistant plants. It is concluded that single gene resistance in tomato to Verticilliumis not associated with innately higher levels of 1,3-ß-glucanasein healthy plants. The increased activity in infected plantsis proportional to the overall quantity of pathogen in the plantor of pathogenic metabolites.     

Development of an abscisic acid biosynthesizing cell-free system from flavedo of Citrus sinensis fruit

Cell-free extracts prepared from an acetone powder derived fromthe flavedo of mature, coloured fruits of Citrus sinensis L.cv. Midknight transformed mevalonic acid, isopentenyl pyrophosphate,all-trans-ß-carotene and 1' ,4' -trans-ABAdiol intoABA. This is the first report of a cell-free system capableof producing ABA from both a terpenyl pyrophosphate and carotenoidorigin. ABA biosynthesizing activity was stimulated by reducednicotinamide nucleotides, molybdate, AM01618 and a cold-pooltrap of ()-ABA, but was inhibited by FAD. Addition of FAD causedaccumulation of label from isopentenyl pyrophosphate in a compoundwith similar chromatographic and spectrophotometric propertiesto those of ß-carotene. 1',4'-Trans-ABAdiol, ABA andPA were unequivocally characterized as products of ß-carotenemetabolism in this cell-free system, a process that was markedlyimproved by extraction of enzyme in the presence of detergents.Dithiothreitol enhanced ABA biosynthesis from all-trans-ß-carotene.Stigmasterol, and to a lesser extent cholesterol reduced conversionof ß-carotene to ABA, but did not influence transformationof 1',4'-trans-ABAdiol to ABA. AM01618 stimulated formationof ABA and appeared to exert its effect at the level of conversionof 1',4'-trans-ABAdiol to ABA. Ancymidol and zeatin reducedincorporation of label from all-trans-ß-carotene intoABA suggesting involvement of a mixed function oxidase in thisreaction sequence. Sodium dodecylsulphate polyacrylamide gelelectrophoresis of the enzyme extract derived from Citrus flavedorevealed the presence of a 53 kDa protein with peroxidase activitycharacteristic of a cytochrome P-450. Key words: Abscisic acid, biosynthesis, cell-free system Citrus sinensis, flavedo, Rutaceae     

Relationship between Flower Induction by Benzoic Acid and its Metabolism in Lemna paucicostata 151

The flower-inducing activities in Lemna paucicostata 151 offour major metabolites of benzoic acid (N-benzoyl aspartate,benzyl 6-O-ß-D-apiofuranosyl-O-ß-D-glucopyranoside,O-benzoyl isocitrate and O-benzoyl malate) were measured, andthe effects on the uptake and metabolism of benzoic acid dueto change in the level of the benzoic acid concentration orto the addition of plant hormones were investigated. N-Benzoylaspartate had weak activity, and O-benzoyl isocitrate and malatehad fairly strong activities, while benzyl 6-O-ß-D-apiofuranosyl-ß-D-glucopyranosideshowed no activity. As the concentration of benzoic acid rose,the ratio of N-benzoyl aspartate increased and that of benzyl6-O-ß-D-apiofuranosyl-O-ß-D-glucopyranosidedecreased. GA₃ and IAA, inhibitors of flower induction by benzoicacid, seemed to promote conversion to N-benzoyl aspartate insteadof to benzyl 6-O-ß-D-apiofuranosyl-ß-D-glucopyranoside.The conversion to N-benzoyl aspartate was considered to be adetoxification process and that to benzyl 6-O-ß-D-apiofuranosyl-ß-D-glucopyranosidemay be directly related to flower induction in Lemna. (Received November 2, 1987; Accepted January 23, 1988)     

室内饲养与野外台湾乳白蚁木质纤维素水解酶活性的比较研究

以台湾乳白蚁Coptotermes formosanus Shiraki的室内群体与野外群体为研究对象,测定工蚁体内4种糖基水解酶和滤纸酶活(FPA)的活力大小及分布。结果表明:内切-β-1,4-葡聚糖酶(EG)、β-葡萄糖苷酶(BG)、外切-β-1,4-葡聚糖酶(CBH)、内切-β-1,4-木聚糖酶(EX)及FPA的活性在不同组织中有较大差异。两类群体的BG、EX及CBH有相似分布,BG和EX分别高度集中于中肠和后肠,CBH主要在中肠及后肠分布。FPA和EG在两类群体中有不同分布,室内群体的主要在中肠,野外群体的则集中于后肠。两类群体各种酶活力大小顺序同为:EX>EG≥BG>CBH。此外,室内饲养群体的大小及年限对台湾乳白蚁木质纤维素酶活力无显著影响。     

Involvement of Endomannanase in the Control of Tomato Seed Germination under Low Temperature Conditions

The cause of differences in germination rates in a cold-toleranttomato line (PI341988), a control line (UC82B), and six progenylines stemming from crosses and backcrosses between the twoparent lines was investigated. Pursuant to earlier work showingthat differences in germination ability at 12°C are dueto the barrier imposed by the endosperm layer, we analysed theactivity of cell-wall-hydrolysing enzymes extracted from theselines. A significant increase in endomannanase activity wasfound in plant line PI341988 prior to germination at 12°C.Extracts of PI341988 seeds that had imbibed at either 12 or25°C exhibited higher endomannanase activity than theircounterparts from plant line UC82B. Moreover, a positive relationshipwas found between germination ability at low temperature andendomannanase activity in the six progeny lines. Analysis ofendomannanase activity in sub-regions of the seed indicatedthat the increase in activity prior to germination was higherin the micropylar endosperm cap than in the rest of the seed.Exogenous application of mannanase originating from soil-bornebacteria increased germination rates under both moderate andlow temperature conditions. Cellulase (endo-1,4-ß-glucanase)activity was also found to be higher in plant line PI341988.However, the activity of this enzyme probably increases aftergermination and it is therefore not considered as a key enzymecontrolling germination at low temperatures.Copyright 1995,1999 Academic Press Lycopersicon esculentum, tomato, seed germination, cell wall     

The physiological role of the peritrophic membrane and trehalase: Digestive enzymes in the midgut and excreta of starved larvae of Rhynchosciara

Amylase, cellulase, trehalase, aminopeptidase and trypsin were determined using the midgut and trehalose using the haemolymph of starved and of subsequently fed larvae of Rhynchosciara americana. Midgut trehalase activity decreases steadily during starvation and increases again on feeding, whereas haemolymph trehalose titres remain constant, suggesting that trehalase is a true digestive enzyme. The decrease in amylase, cellulase and trypsin activity in the midgut during starvation is of the same order as that recovered from the excreta. Since this finding is exactly what one would expect if enzyme production stops in response to starvation, this supports the hypothesis that synthesis that synthesis of these enzymes is controlled. The excretion rate of amylase, cellulase and trypsin is very low in comparison to their activity inside the peritrophic membrane and the travel time of the food bolus through the gut. It is proposed that the peritrophic membrane separates two extracellular sites for digestion as an adaptation to conserve secreted enzymes. This could be accomplished by the existence of an endo-ectoperitrophic circulation of the enzymes involved in the initial attack on the food and by restricting to the ectoperitrophic fluid the enzymes which participate only in intermediary digestion of food.     

Anatomical and Biochemical Changes Associated with the Induction of Oilseed Rape (Brassica napus) Pod Dehiscence by Dasineura brassicae (Winn.)

Dehiscence of pods at an early stage of development is a characteristicof oilseed rape pods damaged by Dasineura brassicae (pod midge).Anatomical examination of pods exhibiting symptoms of infestationrevealed a loss of cohesion between intact cells of the dehiscencezone, a narrow tissue of thin-walled cells present between thevalve margins. Determination of hydrolytic enzyme activity inpericarp tissues of damaged siliquae showed localized enhancementof both polygalacturonase (EC 3.2.1.15 [EC] ) and cellulase (ß1,4 glucanase, EC 3.1.2.4 [EC] ) activity, positionally consistent withthese factors being responsible for the observed cell wall degradation.Mechanistic similarities of midge-induced and maturation-associatedpod dehiscence are discussed. Oilseed rape, Brassica napus L. cv., Bienvenu, pod shatter, pod midge, Dasineura brassicae (Winn.), cellulase, polygalacturonase     

Partial Purification and Characterization of Polyphenol Oxidase from Cocoyam, Xanthosoma sagittifolium

Polyphenol oxidase has been partially purified from Xanthosomasagittifolium. The enzyme showed activity towards pyrogallol,DL-ß-3,4-dihydroxyphenylalanine (DOPA) and catechol.Of these three, pyrogallol was the best substrate. The effectsof various compounds as inhibitors of the reaction catalysedby the enzyme were tested. p-Nitrophenol competitively inhibitedthe binding of both catechol and pyrogallol to the enzyme. Inhibitionby the substrate analogue, p-cresol was of the mixed type whilethiourea and diethyldithiocarbamate inhibited the enzyme uncompetitively.The approximate molecular weight of the enzyme determined bygel filtration was 47 000.