Enzyme Activities Associated with Carbon Dioxide Exchange in Illuminated Leaves of Hordeum vulgare L.: III. Effects of Concentration and Form of Nitrogen Supplied on Carbon Dioxide Compensation Point

Increasing the nitrate concentration in the nutrient media wasfound not to influence the carbon dioxide compensation point(). However, a higher value of was obtained in the presenceof ammonia nitrogen in the nutrient media. Increasing the nitrateconcentration in the media gave a higher activity of RuDP carboxylase,nitrate reductase, glycollate oxidase, and catalase. Similarlythe plants grown in ammonia nitrogen showed higher activitiesof RuDP carboxylase and catalase, and a considerably higherglycollate oxidase activity.     

Enzyme Activities Associated with Carbon Dioxide Exchange in Illuminated Leaves of Hordeum vulgare L.: I. Effects of Light Period, Leaf Age, and Position, on Carbon Dioxide Compensation Point ({Gamma})

The carbon dioxide compensation point () was found to vary underconstant environmental conditions, as the duration of lighttreatment increased, and also with leaf age. The activitiesof RuDP carboxylase, catalase, glycollate oxidase, and nitratereductase were found to vary with duration of the light treatmentduring the course of a single day. RuDP carboxylase activity was found to exhibit a rhythmic fluctuationof activity with age, which had a frequency common to all theleaves examined. The activities of RuDP carboxylase, glycollateoxidase, and nitrate reductase in the leaves was found to increasewith ascending leaf position; the activities generally decreasedwith leaf age. The ratio of nitrate reductase activity to RuDPcarboxylase activity was found to give an excellent correlationwith measured T, and the value of nitrate reductase as an indirectmeasure of photorespiration and the relationship between nitrogenmetabolism and photorespiration is discussed.     

{gamma}-Aminobutyric Acid Metabolism in Plants: Part 2. Metabolism in Higher Plants

The metabolism of -aminobutyric acid (AB) has been studied inhigher plants, particularly in peas and peanuts. Transaminationappeared to form the first step in AB degradation although transaminaseactivities were very low. The relatively active AB transaminaseassociated with whole pea plants possessing nodulated rootsappears to reside almost entirely within the nodules. AB transaminationwas demonstrated conclusively in extracts of mitochondria fromcotyledons of peanut seedlings; pyruvic acid acted as a betteramino-group acceptor than -ketoglutaric acid (KG). AB transaminaseactivity present in the microsomal and soluble cytoplasmic fractionsof the cells was very low AB was not metabolized perceptibly by intact mitochondria frompeanut, but when various organic acids were supplied simultaneously,an extra uptake of oxygen occurred and was associated with ABdisappearance. Aspartate, alanine, and ammonia were formed usingthe nitrogen atom of AB. The metabolic pathway followed by the carbon skeleton of ABwas traced by supplying C¹⁴-labelled material to leaf discsof peas and to mitochondria from peanut cotyledons. Radioactivitywas incorporated into organic acids, amino-acids, and respiratorycarbon dioxide in a manner suggesting that AB was convertedinto succinate which was then metabolized by the enzymes ofthe Krebs cycle present in the plant mitochondria. Glutamic decarboxylase was shown to be present largely in thenon-particulate (soluble) cytoplasm of cells. The enzymes responsiblefor AB synthesis and degradation, glutamic decarboxylase, andAB transaminase, respectively, therefore largely reside in differentsub-cellular fractions.     

The Nitrogen Metabolism of Groundnut Plants: the Role of {gamma}-methyleneglutamine and {gamma}-methyleneglutamic Acid

The changes occurring in the nitrogenous compounds during thegrowth of groundnut seedlings in the dark and light were compared,particular attention being centred on the levels of -methyleneglutamine,the principal amide of these plants, and -methyleneglutamicacid. The distribution of amino acids and amides in the mainorgans of normal young and mature plants was also examined.Suggestions are made concerning the possible pathways of synthesisand the functions of -methyleneglutamic acid and -methyleneglutaminein groundnut plants.     

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     

The Incorporation of C14-labelled Substrates into the Amino-acids of Groundnut Plants (Arachis hypogaea)

The amino-acid metabolism of groundnut plants has been studiedwith special reference to -methyleneglutamic acid (-MGA) andy-methyleneglutamine (-MG), constituents not found in the greatmajority of plant species. The sequence in which C¹⁴ from radioactive C¹⁴-carbon dioxideenters the amino-acids of leaves was determined. The patternof labelling was very similar to that found for leaves of otherspecies. The metabolic relationships existing between photosynthesisand amino-acid synthesis therefore do not seem to be affectedby the large quantities of -MGA and -MG present in the leaves.-MGA and -MG only gained traces of radioactivity. Experiments designed to study the incorporation of C¹⁴ fromuniformly labelled C¹⁴-alanine into the amino-acids of roots,immature leaves and cotyledons of seedlings and young plantsindicated that the main site of synthesis of -MGA was the cotyledons. Various C^I4-labelled substrates were fed to germinating seedsand, after a period of growth, the specific activities of theamino-acids of seedlings receiving different treatments weredetermined. Comparison of the specific activities enabled certaindeductions to be made concerning the probable biosynthetic pathwaysleading to -MGA and -MG. The results were consistent with theintact incorporation of pyruvate molecules, or another related3-carbon-atom containing compound, into -MGA.     

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]     

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’.     

{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.     

Dry Matter Distribution between the Shoot and Storage Root of Carrot (Daucus carota L.): I. Comparison of Varieties

The distribution of dry matter between shoot and storage rootof a wild variety and cultivars of carrot was investigated ina glasshouse experiment and a field experiment. In both experimentsthe deliberate introduction of variation in plant size revealeda linear relationship between the log weights of these partsat any time throughout growth. In the glasshouse experiment,in which growth was examined from approximately 10–600mg mean dry wt per plant, the slope of the relationship betweenIn shoot and In storage root dry wts decreased markedly duringdevelopment to 100 mg. Subsequently the slope became reasonablyconstant and the intercept progressively more negative. Datafrom the field experiment covered a similar timescale (48–115days) to the glasshouse experiment but the plants grew morequickly and were much heavier (180 mg–6 g dry wt). Therelationship between shoot and storage root for these data wassimilar to that for the plants of comparable size in the glasshouseexperiment. Over the range of development for which the slopeof the relationship was constant, data from both experimentswere described fairly well by the following equations: In shoot = – time+ In storage root where , and are constants. Between cultivars the slope ()and time constant () were similar, but the intercept () increasedwith maturity time of the cultivars. For wild carrot the slopewas larger and the time constant smaller than estimates forthe cultivars. These results on dry matter distribution arediscussed in relation to a model for partitioning assimilatein an individual plant. Daucus carota L., carrot, assimilate distribution, dry matter distribution, storage root, partitioning model     

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     

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     

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     

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.     

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 {alpha}-Hydroxysulphonate on Respiration of Mung Bean Root Tips

Hydroxysulphonate (-HPMS) was found to have an inhibitory effecton dark respiration of mung bean root tips. Inhibition was greatestin regions nearest the apex. The inhibition of root respirationby -HPMS was not due to an inhibition of glycolic acid oxidase.It is suggested that the action of -HPMS was probably on acetylCOA synthetase.     

Competition for Light in a Plant Monoculture Modelled as a Spatial Stochastic Process

In a glasshouse experiment closely spaced plants were regularlysub-irrigated with nutrient solution and it was assumed thatcompetition between individuals was for light. Interaction betweenneighbours is modelled as a spatial process in relation to differencesin plant height. The influence one plant has on another is calculatedas the ratio of the angle ß between their apices,and an angle which represents the intensity of competitionin the population as a whole. When ß < suppressionis considered to occur, i.e. tall plants suppress short plantsbut not vice versa, competition is one-sided. The status ofeach plant within the population is calculated by multiplicationof its individual plant neighbour interaction terms where ß< . This need not be restricted to nearest neighbours. Plantswith status = 1 are free from competition, those with status= 0 are totally suppressed. It is acknowledged that other processes than that modelled ascompetition may result in variation in relative growth rates.To account for this plant status is used to modify a relativegrowth rate drawn from a population of mean µ and standarddeviation . Plants for which status µ is less than anestimated are considered to die. Parameter values were estimatedfor a sequence of fortnightly harvests of glasshouse grown Tagetespatula. There was a decrease in µ and , increased andplants came to compete with their second nearest neighboursas well as their nearest as the community developed. The greatest was at an intermediate stage, suggesting that more frequentassessments of the competition process are required at somestages than at others. Model parameters fitted to one data setwere used in a Monte Carlo testing procedure with a second,independent data set. The importance of this technique is stressedbecause plants in a single community are not independent realizationof the competition process. Simulations with the model reproducedboth bimodality in the frequency distributions of plant sizeand an even spatial distribution of large or surviving plants,features which have been observed in a range of plant monocultures.To achieve these features it was essential that plant interactionbe modelled as a one-sided process. Tagetes patula L., competition, light, monoculture, growth model     

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     

Seasonal Distribution of Carbohydrates in Nodules and Stem Exudate from Field-grown Soya Bean Plants

The concentration of carbohydrates in tap root nodules fromfield-grown soya bean [Glycine max (L.) Merr.] plants was verysimilar to the concentration of compounds previously reportedin greenhouse-grown nodules during vegetative growth of seedlings.The concentration of D-pinitol, sucrose and starch in nodulesdeclined during rapid fruit growth, but the concentration ofother compounds did not decline. The availability of carbohydratein nodules during fruit growth did not seem likely to be thecause of the decline in nitrogen-fixing activity of noduleswhich has been reported by others. All compounds except glucoseand , -trehalose declined to concentrations near zero duringa 10-day period of nodule decay. However, the decline in carbohydratedid not appear to cause nodule senescence because it did notprecede the period of decay and because decayed nodules containedsubstantial quantities of glucose and , -trehalose. Seasonalmean concentrations (72 samples from 24 dates) of compounds,in mg carbohydrate per g f. wt of nodule, were: sucrose, 2.84;D-pinitol, 1.14; D-chiro-inositol, 1.27; glucose, 1.40; , -trehalose,1.34; myo-inositol, 0.65; maltose, 0.31; and fructose, 0.21. Quantities of sugars and cyclitols in stem exudate collectedin the field on 13 dates were small (< 10 percent) relativeto the quantity of nitrogenous compounds transported from rootsto shoots. The seasonal pattern of pinitol transport in thexylem was very similar to the seasonal pinitol concentrationin nodules. A large increase in sugar concentration in stemexudate subsequent to 80 days after planting supports the viewthat lack of carbohydrate was not a cause of nodule senescence. Glycine max (L.) Merr, soya bean, cyclitols, , -trehalose, starch, D-pinitol, carbohydrates, root nodules, senescence