Comparative Studies of Acid Glycosidases from Three Legumes

The major isoenzymes of -mannosidase (EC 3.2.1.24 [EC] ) and ß-galactosidase(ECf 3.2.1.23 [EC] ) have been separated from cotyledons of gardenpea, Pisum sativum L. (Vicieae), chick pea, Cicer arietinumL. (Cicereae), and cowpea, Vigna unguiculata (L.) Walp. (Phaseoleae).Some of their properties have been determined, including pHoptima, K_m values for p-nitrophenyl glycosidc substrates, andthe effects of several inhibitors. Swainsonine, an indolizidinealkaloid, was the most effective inhibitor of mannosidase 1,with I₃₀ values of 5.6 x 10^–8 M (cowpea), 1x 10^–7M (chick pea) and 2.9 x 19^–7 M (pea). The most effectiveinhibitor of ß-galactosidase 2 from all sources wasD-galactonic acid-1,4-lactonwe (-lactone), with K_i values rangingbetween 3.0 and 3.9x 10^–3 M. An inhibitor of the E. coliß-galactosidose, p-aminophenyl thio-ß-D-galactopyranoside,did not inhibit any of the legume ß-galctosidases;rather it enhanced the activites of the enzymes from chick peaand cowpea cotyledons. Etiolated hull and seed tissues frompea pods developing in darkness contained similar acid glycosidaseactivities to normal green tissues, thus the chloroplast isan unlikely location for ß-galactosidase 2. The majorß-galactosidasesdetected with an indigogenic substrate (5-bromo-4-chloro-3-indoxyl-ß-D-galactopyranoside)following gel electrophoresis of extracts from pea hull, seedcoats and cotyledons appeared to be different from ß-galactosidase2. Acid glycosidase, cotyledon, isoenzyme, -lactone, legume, swainsonine     

Intraspecific Variation in Oil Components ofBoronia megastigmaNees. (Rutaceae) Flowers

Intraspecific variation in the oil composition ofBoronia megastigmaNees.(Rutaceae) was examined. Boronia absolute is extracted fromblossom primarily for use as a food additive. A major componentis ß-ionone andB. megastigmais one of the commercial,natural sources of this compound. Genotypes superior in productionof ß-ionone and low in monoterpene hydrocarbons weresought from natural populations in the south west of WesternAustralia as part of a breeding programme. Flowers were collectedfrom 25 plants in each of 29 different populations. Blossomwas extracted with ethanol and analysed using a gas liquid chromatographfitted with ionisation detectors. The contents of ß-ionone,dodecyl acetate, -pinene, ß-pinene and limonene inthe oil extract were compared. Intra-population variation wasas great as inter-population variation and no distinct chemotypeswere found. Considerable variation existed in the content ofcomponents. The highest ß-ionone content was 1787mg g^-1f. wt. Some genotypes contained all five components analysed,others lacked one or more of the monoterpenes: -pinene, ß-pineneor limonene. Principle components analysis indicated that contentsof ß-ionone and dodecyl acetate were associated andthat they were distinct from the content of the monoterpenes,which were associated with each other. Natural shading was associatedwith lower levels of monoterpenes but other oils were unaffected.Young plants contained less pinenes than older plants and oldplants contained the most dodecyl acetate. Vigorous plants producedmore pinenes. Red flowers contained the least ß-iononeand dodecyl acetate.Copyright 1999 Annals of Botany Company Boronia megastigma,boronia, Rutaceae, oil, -pinene, ß-pinene, limonene, ß-ionone, dodecyl acetate, monoterpenes, chemotypes.     

A new isoflavone glycoside from <Emphasis Type="Italic">Trifolium pratense</Emphasis> L.

The isoflavonoid composition of red clover (Trifolium pratense L.) has been studied. The following compounds have been detected: cyclopolyol (+)-pinitol, not found in clover before; known isoflavones formononetin, prunetin, genistein, and prunetin-4′-O-β-D-glucopyranoside; isoflavone monogalactosides formononetin-7-O-β-D-galactopyranoside, inermin-3-O-β-D-galactopyranoside, and genistein-7-O-β-D-galactopyranoside; and a novel compound, prunetin-4′-α-D-glucopyranoside. The structures of these compounds have been proven by UV, IR, 1H NMR, 13C NMR, mass, and circular dichroism spectra. (+)-Pinitol is known to possess biological activity.     

The Interaction of Ultraviolet-B Radiation and Water Deficit in Two Arabidopsis thaliana Genotypes

It has been demonstrated, in both herbaceous and woody species,that tissue hydration resulting from exposure to drought isless pronounced if plants are concurrently exposed to ultraviolet-Bradiation (UV-B). An explanation for the mechanisms underlyingthis phenomenon has been elusive. Arabidopsis thaliana(L.) Heynh.genotypes, defective in specific defences against UV-B exposure,may permit more insightful study of drought-UV-B interactionsthan is possible with genetically uniform plants. Arabidopsishas a rosette stature and has predominantly abaxial stomata.Thus, it is difficult to investigate its stomatal behaviourand gas exchange using conventional techniques and instrumentation.In this study, the relative abundance of¹³C and¹²C in leaf tissue(¹³C) was used as a means of determining water use efficiency(WUE) and the relative balance, at the site of carbon fixation,between CO₂supply and demand. UV-B insensitive (L er) and sensitive(fah1)Arabidopsis genotypes were raised in a growth chamberand exposed to 6 kJ m^-2 d^-1UV-B irradiation and subjected todrought. In both genotypes, leaf desiccation was less pronouncedthan that of control plants that were subjected to drought butnot exposed to UV-B. The relatively low (more negative) leaf¹³C values (indicating low WUE), but high dry matter productionof the UV-B exposed plants suggest that their higher leaf watercontent was not primarily due to stomatal closure. We proposethat the mechanisms underlying the maintenance of higher leafwater content involved UV-B and water stress induced biosynthesisof stress proteins and compatible osmolytes. Copyright 2000Annals of Botany Company Arabidopsis thaliana, ultraviolet-B, water deficit, stable carbon isotopes, ¹³C, stomatal opening, tissue dehydration, dehydrin     

Activity of Wall-bound Enzymes in Callus Cultures of Gossypium hirsutum L. During Growth

Activities of - and ß-glucosidase, - and ß-galactosidase,-mannosidase, ß-1,3-glucanase, acid and neutral invertaseswere detected in the cytoplasmic fraction as well as in cellwalls isolated from callus cultures of cotton. Activity of ß-mannosidase,however, could not be detected in the cell walls. Transfer ofcallus to a fresh medium did not immediately influence the activitiesof -glucosidase and ß-galactosidase but increasedsignificantly ß-glucosidase, -mannosidase, acid andneutral invertases. Addition of cycloheximide (1 and 100 mgl^–1) further stimulated acid and neutral invertases butnot other enzymes tested. Sodium chloride (NaCl) was effectivein extracting a-glucosidase, ß-glucosidase, ß-galactosidase,acid and neutral invertases. EDTA extracted most of the -galactosidase,-mannosidase, ß-1,3-glucanase and some -glucosidase.But, NaCl and EDTA could not extract some of the - and ß-glucosidasesand also acid and neutral invertases as evidenced from the residualand extra cellular activity. Studies with whole cells as a sourceof enzyme revealed that some of these enzymes were associatedwith the cell surface. Callus, glycosidases, glucanase, growth, Gossypium hirsutum     

Response of Self-thinning to Artificially Reduced Levels of Leaf Area in Monocultures of Trifolium pratense

Greenhouse grown monocultures of Trifolium pratense L, werepartially defoliated to test the hypothesis that the constantof proportionality (K) in the self-thinning rule is a functionof leaf area. This constant equates mean weight (w) and density(p) in self-thinning populations by the equation Pruning leaflets did not affect the pattern or occurrence ofdensity-related mortality but, as predicted, did affect K, whichwas reduced by 25 per cent as leaf area was decreased from anaverage of 7.3 to 3.9 m²m^–2. For both self-thinning andnon-self-thinning populations, leaf area was substituted forK in eqn (1) to give Multiple linear regression showed that this expression was significantfor all three defoliation treatments. Regressions with treedata grouped by genera were also significant and indicate thateqn (2) may be a more general expression of the relation betweenmean weight and density in even-aged monocultures. The self-thinningrule may be a special case of eqn (2) which expresses itselfwhen leaf area attains some upper limit. Trifolium pratense, red clover, leaf area, self-thinning, defoliation     

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)     

Flavonol glycosides in the leaves ofTrillium apetalon Makino andT. kamtschaticum pallas

Seven flavonol glycosides were isolated from the leaves ofT. apetalon. They were identified chromatographically and spectrally to be: quercetin/kaempferol 3-O-α-arabinopyranosyl-(1→6)-β-galactopyranoside (TQ and TK), quercetin/kaempferol 3-O-[2‴-O-acetyl-α-arabinopyranosyl]-(1→6)-β-galactopyranoside (TAQ and TAK), quercetin 3-O-β-glucoside (ISQ), isorhamnetin 3-O-α-arabinopyranosyl-(1→6)-β-galactopyranoside (TI) and isorhamnetin 3-O-[2‴-O-acetyl-α-arabinopyranosyl]-(1→6)-β-galactopyranoside (TAI). TQ, TAQ, TI and TAI were major constituents. This is the first report on two new isorhamnetin-type glycosides, TI and TAI. The seven flavonol glycosides identical to those ofT. apetalon were isolated and identified in the leaves ofT. kamtschaticum; TQ and TAQ were also major components, but TI and TAI were only minor components. TI and TAI were not detected in the leaves ofT. tschonoskii. These leaf-flavonoid patterns were discussed from a chemosystematic point of view. Part 3 in the series “Studies of the flavonoids of the genusTrillium”. For Part 2 see Yoshitamaet al., (1997) J. Plant Res.110: 379–381.     

{beta}-Amylase Activity as an Index for Germination Potential in Rice

Seeds of different vigour also differ in their germination ability.In rice (Oryza sativa), this difference was correlated withthe level of incorporation of ³⁵S-methionine into 25-60% ammoniumsulphate precipitable material that was rich in amylase proteins.This protein fraction, from dry seeds, contained no -amylaseactivity. In contrast, ß-amylase activity was presentin all seed stocks capable of 99% germination, although thelevel was lower in seeds that grew slowly when germinated. Inlow viability low vigour stock (i.e. extensively deterioratedseeds) ß-amylase activity was absent. Alpha-amylaseactivity in all stocks was detected only after 24 h from thestart of imbibition. These results indicate that ß-amylaseactivity is reliable indicator of the germination ability ofrice seed stocks and of their vigour during germination.Copyright1995, 1999 Academic Press Rice (Oryza sativa L.,), germination, ß-amylase, -amylase, seed vigour     

The Growth and Survival of Severely-shaded Tillers in Lolium perenne L.

The effect of shading a single tiller to below its compensationpoint for a period of 5 weeks in vegetative plants of Loliumperenne L. cv. S23, was studied in two different experimentseach employing two light regimes, one of which was common toboth experiments. In the first experiment tillers in the axils of the first leafwere shaded three weeks from appearance at both 40 and 70 Wm^–2. None of the shaded tillers died and they continuedto produce new leaves and increase in dry weight but at a reducedrate. In the second experiment, tillers with one emerged leafin any leaf axil position were shaded at 70 W m^–2 andin a treatment in which light was reduced to 13 W m^–2after initial growth at 70 W m^–2. As in the first experimentall shaded tillers survived at 70 W m^–2 but in the 70 13 W m^–2 transfer regime all shaded tillers died. In the second experiment shaded tillers in both light regimeswere supplied with ¹⁴C-assimilate by translocation from theremainder of the plant but in the 70 13 W m^–2 the initialsupport was withdrawn within 5 weeks of shading. The results are discussed in terms of the physiological relationshipsbetween the tillers of the grass plant. Lolium perenne L., growth of tillers, survival of tillers, effect of light     

Aminopeptidases Isolated from Cotyledons of Cowpea, Vigna unguiculata

Three aminopeptidases have been separated from cotyledon extractsfrom cowpea, Vigna unguiculata (L.) Walp., and numbered in orderof decreasing affinity for the anion exchange medium DEAE-Sephacel.API showed a wide acceptance of model substrates, with highestactivity under standard conditions against arginyl ß-naphthylamide(NA). AP2 did not act on basic substrates and preferred phenylalanylß-NA. AP3 displayed the narrowest substrate specificity,with strong activity against only alanyl ß-NA andglycyl ß-NA. The chelator 1,10-phenanthroline completelyor almost completely inhibited forms AP1 and AP3, whereas AP2was insensitive to phenanthroline at the same concentration(5 mM). All three aminopeptidases were totally inhibited byAg⁺ or Zn²⁺ ( 0.5 mM). Vigna unguiculata (L.) Walp., aminopeptidase, cotyledon, cowpea, isoenzyme, 1, 10-phenanthroline     

Responses of Soybean Leaf Angle, Photosynthesis and Stomatal Conductance to Leaf and Soil Water Potential

The hypothesis that soil water potential (_s) is better correlatedto heliotropic leaf orientation, photosaturated photosyntheticCO₂ assimilation and stomatal conductance during periods oflimited water availability than is bulk leaf water potential(₁) was examined in greenhouse-grown soybean (Glycine max) plants,submitted to a progressive drought. Paired plants were exposedto either 1000 or 100 µmol m^–2 s^–1 photonflux densities (PFD) for 45–60 mins. The higher irradianceinduced short-term decreases in ₁, due to increased transpiration,while _l in the plant exposed to low PFD did not decrease. Thesechanges in ₁ occurred independently of changes in soil waterstatus. Concurrent to the light treatments, a single attachedleaf from each of the two plants was isolated from the restof the plant by shading, and the pulvinus of its terminal leafletwas exposed to a perpendicular PFD of 500 µmol m–²S^–1. Leaf movement of this leaflet was recorded in responseto this light, until a stable leaflet angle was achieved. Valuesof _s and _l (before and after light treatment), and photosaturatedrates of photosynthesis and stomatal conductance, were thenmeasured on these leaves. Leaflet angle and gas exchange werebetter correlated with _s (r² = 0.50, 0.50 and 0.57 for angle,photosynthesis and conductance, respectively) than with _l especiallywhen _l was the result of short-term, high-light induced changesin leaf water status (r² = 0.36, 0.32 and 0.49, for the sameparameters). Leaflet angle was also correlated with stomatalconductance (r² = 0.61) and photosynthetic rate (r² = 0.60),suggesting a close association between leaf orientation, leafmetabolism and soil water availability. Glycine max (L.) Merr. cv. Essex, soybean, heliotropism, water potential, photosynthesis, stomatal conductance, solar tracking     

Xyloglucan and r{beta}-D-Glucan in Cell Walls of Rice Seedlings

Cell walls of 4-day old rice seedlings were extracted successivelywith ammonium oxalate-oxalic acid, 4% KOH and 24% KOH. A rß-D-glucanpreparation and a xyloglucan preparation were isolated fromthe 4% KOH extract and 24% KOH extract, respectively. Methylationanalysis and enzymic degradation studies of the polysaccharidesshowed that the former was built up predominantly of repeating-oligosaccharideunits of 3-O-rß-cellobiosyl-D-glucose and 3-O-rß-cellotriosyl-D-glucosein a molar ratio of 2.6 : 1.0, and the latter was of repeating-oligosaccharideunits of -D-xylosyl-(16)-rß-D-glucosyl-(14)-[-D-xylosyl-(16)]-rß-D-glucosyl-(14)-D-glucose,-D-xylosyl-(16)-rß-D-glucosyl-(14)-D-glucose and cellobiose. ¹ Present address: Department of Botany, Iowa State University,Ames, Iowa 50011, U.S.A. (Received August 29, 1981; Accepted January 12, 1982)     

Natural Abundance of {delta}15N Confirms Insectivorous Habit ofRoridula gorgonias, Despite it Having No Proteolytic Enzymes

Natural abundance values of plant ¹⁵N give an indication asto the source of nitrogen. In particular, carnivorous plantsare expected to be relatively enriched due to trophic enrichmentof their prey. Values of ¹⁵N for adultRoridula gorgonias(mean+3.02)are 4–9 greater than co-occurring non-carnivorous plantspecies and 5.24 greater than juvenileR. gorgoniasplants. Theyare also 3.5–4.26 greater than co-occurringDroseraspecieswhich, being sundews, are considered to be carnivorous. Thesehigh levels of ¹⁵N in adult plants are best explained as beingdue to access to trophically enriched N from insects. As isthe case for other carnivorous plants, leaves and stems ofR.gorgoniasare highly ultraviolet reflective and are thereforeprobably attractive to potential insect prey. This is furthersupport for this plant species being insectivorous.Copyright1998 Annals of Botany Company Nitrogen isotopes, carnivorous plants, insectivorous plant, ultraviolet,Roridula gorgoniasL.     

A Finite-element Model of Radial and Axial Conductivities for Individual Roots: Development and Validation for Two Desert Succulents

A morphologically explicit numerical model for analysing wateruptake by individual roots was developed based on a conductornetwork, with specific conductors representing axial or radialconductivities for discrete root segments. Hydraulic conductivity(L_p; m s^–1 MPa^–1) was measured for roots of Agavedeserti Engelm. and Opuntia ficus-indica (L.) Miller by applyinga partial vacuum to the proximal ends of excised roots in solution.L_p was also measured for 40- to 80-mm segments along a root,followed by measurements of axial conductivity and calculationof radial conductivity. Predicted values of L_p for entire rootsbased on two to ten segments per root averaged 1.04±0.07(mean±s.e. mean for n = 3) of the measured L_p for A.deserti and 1.06±0.10 for O. ficus-indica. The modelalso closely predicted the drop in water potential along theroot xylem (^xylem); when a tension of 50 kPa was applied tothe proximal ends of 0.2 m-long roots of A. deserti and O. ficus-indica,the measured ^xylem to midroot averaged 30 kPa compared witha predicted decrease of 36 kPa. Such steep gradients in ^xylemsuggest that the driving force for water movement from the soilto young distal roots may be relatively small. The model, whichagreed with an analytical solution for a simple hypotheticalsituation, can quantify situations without analytical solutions,such as when root and soil properties vary arbitrarily alonga root. Agave deserti, electrical circuit analog, hydraulic conductivity, Opuntia ficus-indica, water potential     

Water-Relations Parameters of the Phloem. Determinations of Volumetric Elastic Modulus and Membrane Conductivity using an Applied Force Method and Shrinkage and Swelling of Tissues in Solutions at Differing Osmotic Pressure

Water-relations parameters were measured on sections of secondaryphloem from red oak (Quercus borealis michx. f.) and white ash(Fraxinus americana var. biltmoreana [Beadle] J. Wright) usinga linear displacement transducer. Changes in tissue thicknessin response to changes in the osmotic pressure of the bathingsolution were used to calculate the volumetric elastic modulusplus osmotic pressure (_v + ) of the tissue, and an applied forcemethod was used to estimate the time constant for water equilibration(T). The hydraulic conductivity of the cell membranes (L_p) wascalculated utilizing _v + and r values. The time-dependent behaviour of the tissue was much more complexthan originally expected. A correction for a time-dependentprocess that we call ‘drift’ was required to obtainnumbers for _v + . Furthermore, _v + was calculated on two assumptionsin order to relate changes in tissue dimensions to sieve elementparameters. In the first case, a lower limit for _v + of thesieve elements was determined by attributing all changes intissue dimensions to these cells. For red oak the average _v+ on this assumption is 72 bars. Assuming that all cell typeswere equally responsible for the changes in tissue dimensionsresulted in an _v + value of 192 bars for oak. If _v + and rare the same for all cells in the tissue, L_p for the sieve elementsof oak is 9.6 x 10^–8 cm s^–1 bar^–1. Exudationfrom the sieve elements of white ash during excision of thephloem led to artificially high values of _v + for that species. Quercus borealis michx. f., Fraxinus americana var, biltmoreana (Beadle) J. Wright, red oak, white ash, water relations, phloem, volumetric elastic modulus, membrane hydraulic conductivity     

Flexibility in the donor substrate specificity of {beta} 1,4-galactosyltransferase: application in the synthesis of complex carbohydrates

Biosynthetically, bovine N-acetylglucosainine ß 1,4-galacto-syltransferase(GalT) catalyses the transfer of galactosyl residues from UDP-Galto the 4-position of GlcNAc units, resulting in the productionof N-acetyllactosamine sequences. UDP-Glc and UDP-GalNAc werealso found to act as donors for this enzyme, allowing the preparationof ßGlc(14)-ßGlcNAc and ßGalNAc(14)ßGlcNActerminating structures on the milligram scale. GalT could thusbe used to add ßGalNAc to ßGlcNAc(12)Manterminating structures, converting them to the ßGalNAc(14)ßGlcNAc(12)Mansequences found on glycoprotein hormones. GalT did not transferGlcNAc residues from UDP-GlcNAc, but it could utilize UDP-GlcNH₂as a donor. Synthesis of ßGlcNAc(14)ßGlcNAcsequences could therefore be accomplished by transfer of GlcNH₂from its UDP derivative, followed by N-acetylation of the productamino-disaccharide using acetic anhydride in methanol. The productsof the enzymatic reactions were characterized by ¹H-NMR-spectroscopyand fast-atom bombardment mass spectrometry. This work expandsthe scope of the combined chemical-enzymatic synthesis of complexcarbohydrates, using glycosyltrans-ferases, to the productionof oligosaccharides different from those for which these enzymeswere designed. These unnatural reactions should find applicationin glycoprotein and glycolipid remodelling. galactosyltransferase chemica1-enzymatic synthesis of oligosaccharides oligosaccharide analogues sugar-nucleotide analogues carbohydrate remodelling     

The effects of UV-B radiation on genetic and biochemical changes of Pelargonium graveolens L′Her

Ultraviolet radiation induces biochemical and genetic changes in plants. The aim of this study was to investigate the effects of UV-B radiation on genetic stability, phenolic compounds and antioxidant activity of Pelargonium graveolens L′Her. Plant cuttings were exposed to 0, 0.12. 0.26 and 0.38 W/m2 of UV-B radiation. Results indicated that by increasing the UV-B radiation intensity, total phenols, flavonoids and anthocyanin contents, Phenylalanine ammonia lyase activity and antioxidant capacity were increased. Analysis of four flavonols (quercetin, myricetin, kaempferol and rutin) contents of leaves extract by HPLC indicated that these four flavonols were enhanced in all treated plants and also the ratio of quercetin to kaempferol (Q/K) showed a significant increase (P ≤ 0.05) in UV-B treated plants in compare to control. To evaluate the genetic variation in treated plants, 10 ISSR primers were used. The highest level of percentage of polymorphism (P%), Shannon index (I), number of effective allele (Ne) and Nei’ genetic diversity (He), were observed at the highest UV-B radiation (0.38 W/m2). The AMOVA analysis also showed a significant genetic differentiation (P ≥ 0.001) among the studied groups, and confirmed the differentiation of groups obtained by the cluster analysis of molecular data. Overall, these results showed that biochemical changes in different intensities of UV-B were in line with genetic variations, so that the highest biochemical and genetic variations were observed in 0.38 W/m2 treatment.     

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)     

Characteristics of Radial Solution Flow in Roots of Cucumber (Cucumis sativus L.)

Low salt roots of Cucumis sativus L. cv. Burpeeana Hybrid weresubjected to iso-ionic treatments in which the external solutionconcentration of K⁺ was maintained at 14 mM. Solution concentrationof varied from 0 to 14 mM, other anions compensating. When Cl^– was the compensating ion, its concentrationin the exudate increased during the first 4 h and thereafterwas nearly the same as that of the external solution in alltreatments containing I mM or more. After 8 h of equilibration the concentration in the exudate increased almost exactly as its concentrationin the external solution. Rates of exudation and K⁺ transportwere almost constant between I and 14 mM KNO₂. More Cl^–was transported from solutions of similar Cl– concentrationwhen was also present. When water transport was inhibited with mannitol in treatments containing both KNO₃and KCI, exudate concentrations of K⁺ and were increased, but exudate concentration of Cl^– was notsignificantly affected except at the highest Cl