Genotypic Differences in Leaf Water Relations between Brassica juncea and B. napus

Various kinds of measurement of tissue water status were madeseveral times during water stress and recovery in Brassica juncea(cv Canadian Black) and B napus (cv Drakkar) Unstressed plantsof the two species had similar leaf water potentials (_w), solute(_s) and turgor potentials (_p) Values of relative water content(RWC) and the slope of the linear relationship between _p andRWC (_p/RWC) were greater in B napus than in B juncea Statistical correlations of pooled data for the watered andstressed treatments differentiated the relationships among RWC,_w and its components in the two species The major statisticaldifference was that _p/RWC was related to RWC in B napus andto _w and _s in B juncea A decline in _p/RWC with decreasing _sin B juncea may be a mechanism for maintaining _p at low soilwater potentials through maintenance of more elastic cell walls. Brassica juncea, Brassica napus, osmotic adjustment, tissue elasticity, water relations     

Wilting of Leaves in Vicia faba L.

Wilting of leaves of Vicia faba L., which occurs when the pressurepotential (_p) is zero, and the leaf-water potential () at wiltingboth depend entirely upon the solute potential at incipientplasmolysis (_so) and not on soil-water status. Wilting in V.faba is acropetal; this is consistent with the hypothesis thatthere is a gradient of decreasing _so up the plant and that wateris transferred from the lower to the upper leaves, hasteningthe overall water loss from the lower leaves to the point when_p is zero. The gradient in _so up the plant is of the order of3–8 bar. It is proposed that wilting when _p>0 (i.e. > _so) shouldbe ‘apparent wilting’ and that when _p0 (i.e. _so),‘true wilting’.     

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     

Osmotic Properties of Drought Stressed Periwinkle (Catharanthus roseus) Genotypes

The pressure-volume technique was employed to compare waterrelations and moisture stress-induced osmotic adjustment ofPeriwinkle (Catharanthus roseus) cv. Pink (PC), Oscillatus (REC)and White (WC). Leaf water potential (_w), osmotic potential(_s), turgor potential (_p), bulk modulus of elasticity (), boundwater (RWC_w) and leaf hydration (H), were estimated by exposingthe plants to a drying cycle during which well watered plantswere dehydrated to zero turgor, and then irrigated. Osmoticadjustment (_w ¹⁰⁰) was calculated by comparing _a at full hydration(_a ¹⁰⁰) in stressed plants after recovery, with _a ¹⁰⁰ in controlplants. Values of ₂¹⁰⁰ were 0.76, 0.33 and 0.11 MPa in cv. PC,REC and WC, respectively. Maintenance of _p at lower ₃ and relativeleaf water content (RWC) in prestressed PC was attributableto a higher alkaloid content and greater leaf cell wall elasticity.RWCW was plotted against _p to determine its contribution tohydration maintenance at lower _p. Genotype PC showed greaterRWC_w at lower _p compared with REC and WC. The present studyhas demonstrated that there are cultivar differences in alkaloidaccumulation and water relations in acclimated plants and thatthe relative ranking for drought resistance within periwinkleappeared to correspond with the changes in osmotic properties. Medicinal plant, drought resistance, alkaloids, periwinkle [Catharanthus roseus (L.) G. Don]     

Abscisic Acid and Water Relations of Rice (Oryza sativa L.): Sequential Responses to Water Stress in the Leaf

Water stress was imposed by withholding water at an early vegetativestage from plants of two rice cultivars (IR20 and 63–83)grown in pots. As stress intensified the following sequenceof responses of the leaves was observed: (i) rise in abscisicacid (ABA) content, (ii) closure of stomata, (iii) initiationof leaf rolling. In both cultivars, turgor (_p) declined linearly with total waterpotential () of the leaf. Bulk leaf ABA content increased linearlyas _p declined, and attained twice the control (unstressed) levelfollowing a reduction in _p of about 0.12 MPa. Stomatal conductance exhibited a sigmoidal relationship to _p,declining abruptly when a particular ‘critical’_p was reached (threshold response). The critical potentialsvaried considerably between experiments, but were closely correlatedwith control potentials and with the potentials at which ABAconcentration doubled relative to controls. Leaf rolling was initiated at s near to zero _p. Increases inthe ratio of adaxial to abaxial conductance were associatedwith rolling. Variations in the above responses could be accounted for byvariations in the rate of stress development, which in termsof reduction ranged from 0.38 to 0.86 MPa day^–1. Fastdrying rates resulted in: (a) reduced osmotic adjustment, (b)increased amounts of ABA in the leaf at a given level of or_p, (c) an increase in the ABA concentration present at 50 percent stomatal closure, and (d) initiation of leaf rolling ata higher . Oryza sativa L., rice, water stress, stomata, leaf rolling, abscisic acid     

The Theory of Diffusion of Solutes in Pollen; Theory, Design and Experimental Procedure

The theory of diffusion of solutes in pollen is developed andused to derive formulae from which the mean diffusion coefficient() can be determined. A mathematical relation ß_PGC t = ln (C₀/C_f) is developedby employing Fick's law. In this relation is the average diffusion coefficient, ß_PGC is a constantcharacteristic of the pollen, the ‘Pollen Grain Constant’,C₀ and C_f are the initial and final concentration differencesbetween the solution of the solute and the pollen grain andt is the time of diffusion in seconds. A diffusion apparatushas been designed and made. The design is simple to operateand an experimental procedure is described to determine theß_PGC using dilute potassium chloride solutions. Knowingthe pollen grain constant, the method to determine diffusioncoefficient () with any other solute is explained. Diffusion, design, pollen, solutes, theory     

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     

Water Relations of Sitka Spruce Seedlings After Root Damage

Sitka spruce[Picea sitchensis(Bong.) Carr] seedlings were subjectedto varying degrees of root damage in a growth room, rangingfrom careful transplanting to exposure of the root system toair for up to 3 h. After replanting, transpiration (E), leafwater potential (₁) and growth of the shoot and root were measuredand observations made on plant survival. Some plants in the root exposure treatments died 20–85days after planting. In plants which eventually died, E wasdepressed directly after treatment, but ₁ showed a variableresponse. In some plants ₁ decreased from —8·0x 10⁵ to —30 x 10⁵ Pa after only 10 days but in othersthere was little change in ₁ for 50 days. In spite of the maintenanceof a high water potential in some of the latter plants for longperiods, no root or shoot growth occurred. In plants which lived, the root damage reduced root and shootgrowth relative to untreated controls, and most treatments stronglydepressed E but had little or no effect on ₁. The changes of E and ₁ in treated plants suggest that the suppressionof E was often independent of ₁ although water stress eventuallydeveloped in some of the severely treated plants. Sitka spruce, Picea sitchensis (Bong.)Carr, water relations, root damage, transpiration, leaf water potential     

An Analysis of Seed Development in Pisum sativum III. The Relationship Between the r Locus, the Water Content and the Osmotic Potential of Seed Tissues in vivo and in vitro

The water content and osmotic potential (₂) of the differentparts of the pea fruit have been measured during developmentof the seed in two lines near-isogenic except for the r locus.During the early development of both genotypes, the testa possesseda more negative ₂ than either embryo, endosperm or pod while,at stages when liquid endosperm was present, the embryo alwaysmaintained ₂, more negative than the endosperm. A clear effectof the r locus on water content and ₂ was only observed in embryotissue — wrinkled (rr) embryos possessing more water andmaintaining a more negative ₂ than round (RR) for most of thedevelopmental period studied. The more negative ₂ of wrinkledembryos correlated with their greater uptake of water in vivo. When cultured in vitro, the embryos of both genotypes showedmaximum growth (fresh or dry weight) if 10 per cent sucrosewas added to the medium (equivalent to about — 1.2 MPa).Round embryos, however, increased in weight more than wrinkledat all sucrose concentrations examined. Cultured embryos maintaineda similar or more negative ₂ than their surrounding medium;wrinkled more negative than round. Embryo culture, osmotic potential, Pisum sativum, pea, r locus, seed development, tissue culture, water content     

Water Relations of Potato Leaves. II. Pressure--Volume Analysis and Inferences About the Constancy of the Apoplastic Fraction

Water relations characteristics of potato (Solanum tuberosumL. cv. Bintje) leaves were determined from pressure—volumeanalysis using a pressure chamber. Turgor was 077 MPa and thebulk volumetric modulus of elasticity 81 MPa at full turgidity;turgor loss occurred when water potential () had declined to–087 MPa at a relative water content (RWC) of 0912;the apoplastic water fraction (A) was 0235. As is usually found,there was a linear relation between 1/ and RWC beyond turgorloss. This finding supports the assumptions of the constancyof A during leaf dehydration. Beyond turgor loss the difference between and [measured afterfreezing and thawing (_d)] was about 01 MPa. This differencedid not increase as the leaf water content decreased. This resultcontradicts the constancy of A. It was concluded from calculations with a simple model of leafdehydration that analysis of the relation between and _d providesmore insight in the changes in the apoplastic fraction thanthe relation between 1/ and RWC. Research on the size of theapoplastic fraction and its changes with water potential wouldcomplement current understanding of leaf water relations. Solanum tuberosum, L., water potential, pressure chamber, osmotic potential, pressure potential, relative water content, apoplast, symplast     

Effects of Low Temperature on Potential Net Photosynthesis in Two Field-grown Winter Cereals

Winter wheat and winter barley were tested for their photochemicaland osmotic potentials during the course of one growth cyclein the field. Prolonged winter conditions induced an absolutehigh in potential net photosynthesis (P_N) of winter wheat. Barleyexhibited relatively low P_N rates, which may explain the inferiorfrost hardiness of this species. Osmotic potentials () in bothspecies were quite similar, followed rather uniform trends andwere never extreme. There are doubts, however, whether the assessments truly reflected the osmotic stress on cell membranesin frost-hardened leaves. Increased deposition of cryoprotective assimilates in wheatas the cause of continued frost hardiness is discussed. Triticum aestivum, Hordeum sativum, wheat, barley, potential photosynthesis, winter hardiness     

{gamma}-Amiobutyric Acid Metabolism in Plants: Part 1. Metabolism in Yeasts

The metabolism of -aminobutyric acid (AB) by two yeasts, Saccharomycescerevisiae and Torulopsis utilis, was investigated. Both yeastsgrew well upon AB as a sole source of nitrogen (N), and thelag phase for Torulopsis was shorter than when provided the N-source. The metabolism of AB by Torulopsis, whichwas associated with an increased O₂ uptake, was adaptive incharacter. The enzyme whose formation was induced by the supplyof AB was a transaminase, which was apparently specific forAB as the amino donor. Small amounts of transaminase were presentin unadapted, -grown cells. The optimum pH, equilibrium constant, Michaelis' constant, and coenzyme requirementwere investigated for the transamination reaction involving-ketoglutaric acid (KG) as amino group acceptor. Succinic semi-aldehyde(SSA) was a product of this transamination reaction.The possibility;that some AB was converted into SSA by a direct oxidative deaminationremained unconfirmed. The further conversion of SSA into succinic acid was establishedusing intact. cells for both yeasts. This oxidation processwas shown to be linked to the reduction of pyridine nucleotidesvising extracts of Saccharomyces as a source of SSA dehydrogenase.Dehydrogenase activity could be ascribed to two separate enzymes,one linked to DPN, and the other utilizing TPN and requiringMg⁺⁺ as an activator. The properties of the former enzyme, whichwas more important quantitatively, were investigated and comparedwith those described in the literature for an aldehyde dehydrogenaseof baker's yeast and for SSA dehydro-genases of Pseudomonas.Torulopsis extracts could catalyse the reduction of SSA to -hydroxybutyricacid (OHB); the OHB dehydrogenase involved required TPNH asa coenzyme. Certain other properties of this enzyme are recorded. The possibility is discussed that AB and SSA act as intermediatesin a metabolic pathway that may form a by-pass of the KG-succinatestage of the tricarboxylic acid cycle.     

Abscisic Acid and Water Relations of Rice (Oryza sativa L.): Effects of Drought Conditioning on Abscisic Acid Accumulation in the Leaf and Stomatal Response

The effects of a period of water stress (drought conditioning)on responses to a second (challenge) stress were examined inyoung vegetative rice (Oryza sativa L.) plants. Drought conditioningdid not affect the rate of subsequent stress development, nor,in a first experiment, did it influence relations between turgor(_p) and total () leaf water potential. However, conditioningdid extend the range of _p over which stomata remained open andsignificantly reduced the amount of ABA which accumulated inthe leaf at a given _p. The change in stomatal behaviour (stomataladjustment) was quantitatively accounted for by the change inleaf ABA accumulation. The reduction in ABA accumulation due to conditioning did notinvolve a change in the potential capacity to produce ABA, asABA accumulation in partially dehydrated detached leaves wasnot reduced by conditioning. It is suggested that effects ofconditioning on leaf ABA content in the intact plant involvechanges in the rate of ABA export from the leaf. Oryza sativa L, rice, drought conditioning, stomata, water stress, abscisic acid     

Photosynthetic Oxygen Evolution at Low Water Potential in Leaf Discs Lacking an Epidermis

Land plants encountering low water potentials (low _w) closetheir stomata, restricting CO₂ entry and potentially photosynthesis.To determine the impact of stomatal closure, photosyntheticO₂ evolution was investigated in leaf discs from sunflower (Helianthusannuus L.) plants after removing the lower epidermis at low_w. Wounding was minimal as evidenced by O₂ evolution nearlyas rapid as that in intact discs. O₂ evolution was maximal in1 % CO₂ in the peeled discs and was markedly inhibited when_w was below –1·1 MPa. CO₂ entered readily at all_w, as demonstrated by varying the CO₂ concentration. Resultswere the same whether the epidermis was removed before or afterlow _w was imposed. Due to the lack of an epidermis and readymovement of CO₂ through the mesophyll, the loss in O₂ evolvingactivity was attributed entirely to photosynthetic metabolism.Intact leaf discs showed a similar loss in activity when measuredat a CO₂ concentration of 5 %, which supported maximum O₂ evolutionat low _w. In 1 % CO₂, however, O₂ evolution at low _w was belowthe maximum, presumably because stomatal closure restrictedCO₂ uptake. The inhibition was larger than in peeled discs at_w between –1 and –1·5 MPa but became thesame as in peeled discs at lower _w. Therefore, as photosynthesisbegan to be inhibited by metabolism at low _w, stomatal closureadded to the inhibition. As _w became more negative, the inhibitionbecame entirely metabolic.     

Analysis and Significance of Gravity-induced Asymmetric Growth in the Grass Leaf-sheath Pulvinus

The negative gravitropic response in the grass leaf-sheath pulvinusis a consequence of cell elongation involving all cells exceptthose of the uppermost region of the upper flank of an horizontallyoriented pulvinus. The lowermost layer of cells elongate maximally,and the regions in between elongate to intermediate extents.The resulting curvatures of a responding pulvinus can be expressedmathematically by relating the angle of curvature () to theoriginal length (L₀) and the maximal length of the lower surface(L₁) and the diameter of the organ (D), using the equation, = (L₁–L₀)/D, where is in radians. The elongation response(S) of any individual cell within the pulvinus can be expressedby the equation, S = 0.5-r cos, where r is the radius of thepulvinus and is in degrees. Microscopic measurement of celllengths in different regions of the pulvinus supports the mathematicalpredictions. Indirect support is also obtained from the useof colchicine, coumarin, dichloro-benzonitrile (DCBN) and isopropylN-chlorophenyl carbamate which exaggerate the inherent asymmetryduring gravitropic response. Coumarin and DCBN also induce thickeningsin the radial walls which appear first in the statenchyma, andlater, in cells located towards the outer periphery of the pulvinus.The distribution patterns of these thickenings suggest thatthe asymmetric growth response of the pulvinus may be due toa differential and radial, centrifugal transport of growth promotorsfrom the central statenchyma region. Gravity perception, grass pulvinus     

The Effect of Calmodulin Antagonists on Gibberellic Acid-induced Enzyme Secretion in Barley Aleurone Layers

Calmodulin activity was detected and assayed in barley aleuronecells. The effect of calmodulin antagonists on GA₃-induced enzymesynthesis and secretion in barley aleurone layers was also investigated.These calmodulin antagonists (chlorpromazine, haloperidol) inhibitedonly GA₂-induced -amylase secretion. This inhibitory effectwas intensified after 6 h of GA₃-incubation. This leads us tosuggest that some calmodulin-controlled mechanism is involvedin GA₂-induced -amylase secretion. Hordeum vulgare L., barley aleurone cells, gibberellic acid, -amylase secretion, calmodulin, calmodulin antagonist     

Osmotic Adjustment in Lolium perenne; Its Heritability and the Nature of Solute Accumulation

Plants derived from Lolium perenne L. cv. ‘Melle’were selected on the basis of extreme high or low lamina solutepotential (_s) and pair-crossed to produce divergent G₂ lines.The high and low lines had mean lamina _s values significantlydifferent from each other and from ‘Melle’, andshowed an enhanced range of phenotypic expression of _s duringdrought. Both mature lamina _s and meristem _s values of droughtedplants were highly heritable. Extreme G₂ genotypes were selectedand clonally replicated for further study. During drought mean ₂ values fell from –1·21 to–1·80 MPa. Fructans of large molecular weight,and total free amino acids, especially proline, all accumulatedwhen estimated on a dry-matter (DM) or plant-water (PW) basis.Oligosaccharide content was largely unchanged. Minerals declinedwhen estimated on a DM basis but accumulated on a PW basis becausehydration (g water in turgid tissue per g DM) declined morerapidly. In comparison with genotypes having high constitutive _s, low-_sgenotypes (a) were larger, had faster leaf extension rate, hadfewer tillers, and were proportionally more affected by drought,(b) showed greater osmotic adjustment, (c) contained and accumulatedmuch more fructan (but not oligosaccharides), and amino acids,especially proline, and (d) accumulated more mineral ions ona PW basis, but less on a DM basis. The relatively high repeatabilitiesfor organic solutes in particular show that further divergentselection for individual solutes would not be difficult. Solutes accumulated, probably because they were not consumedin growth. There was no evidence of ‘competition’between growth and osmotic adjustment for metabolites, or thatplants which accumulated more solutes were better able to recoverwhen water deficits were relieved. Perennial ryegrass, drought, genetic variation, carbohydrate, amino acids, proline, mineral uptake, Lolium perenne L. cv. ‘Melle’     

Sugar-responsive gene expression, invertase activity, and senescence in aborting maize ovaries at low water potentials

• Background and Aims Ovary abortion can occur in maize(Zea mays) if water deficits lower the water potential (_w) sufficientlyto inhibit photosynthesis around the time of pollination. Theabortion decreases kernel number. The present work exploredthe activity of ovary acid invertases and their genes, togetherwith other genes for sucrose-processing enzymes, when this kindof abortion occurred. Cytological evidence suggested that senescencemay have been initiated after 2 or 3 d of low _w, and the expressionof some likely senescence genes was also determined. • Methods Ovary abortion was assessed at kernel maturity.Acid invertase activities were localized in vivo and in situ.Time courses for mRNA abundance were measured with real timePCR. Sucrose was fed to the stems to vary the sugar flux. • Key Results Many kernels developed in controls but mostaborted when _w became low. Ovary invertase was active in controlsbut severely inhibited at low _w for cell wall-bound forms invivo and soluble forms in situ. All ovary genes for sucroseprocessing enzymes were rapidly down-regulated at low _w exceptfor a gene for invertase inhibitor peptide that appeared tobe constitutively expressed. Some ovary genes for senescencewere subsequently up-regulated (RIP2 and PLD1). In some genes,these regulatory changes were reversed by feeding sucrose tothe stems. Abortion was partially prevented by feeding sucrose. • Conclusions A general response to low _w in maize ovarieswas an early down-regulation of genes for sucrose processingenzymes followed by up-regulation of some genes involved insenescence. Because some of these genes were sucrose responsive,the partial prevention of abortion with sucrose feeding mayhave been caused in part by the differential sugar-responsivenessof these genes. The late up-regulation of senescence genes mayhave caused the irreversibility of abortion.     

Nitrogenous Compounds and Nitrogen Metabolism in the Liliaceae: II. The Nitrogenous Compounds of Leaves of the Genus Tulipa: Environmental Effects on the Composition of Tulipa gesneriana

Because of the predominance of -methyleneglutamine in Tulipagesneriana a quantitative, chromatographic investigation hasbeen made to show the factors which determine the compositionof the alcohol-soluble nitrogen fraction in Tulipa A comparative study of the amino-acids that occur free in theleaves of fourteen different species of Tulipa has been made,-methyleneglutamine varied from as much as 60–70 per cent,of the amino-acid nitrogen down to levels below those whichpermit its chromatographic detection. The effects of temperature during growth and of diurnal variationon the nitrogenous compounds of the leaves of T. getnerianaare described. Excised shoots of T. gesneriana were exposed to light and darknessto affect the balance of protein synthesis and breakdown sothat the concomitant effects on the -methyleneglutamine acidcompounds and other main components of the soluble nitrogenfraction could be determined. Lastly, the relative ease of entry of C¹⁴ from C¹⁴O₂ into thesugars and certain other compounds of T. gesneriana is contrastedwith the relative difficulty with which it enters the -methyleneglutamineof the mature leaves on excised shoots. The occurrence and metabolism of -methyleneglutamine in T. gesnerianaleaves may, therefore, be regarded as additional to and superimposedupon an otherwise typical pattern of nitrogen metabolism: inthese leaves -methylene-glutamine does not assume the role usuallydischarged by glutamine.