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’.     

Integrated likelihood functions for non-Bayesian inference

Consider a model with parameter = (, ), where is the parameterof interest, and let L(, ) denote the likelihood function. Oneapproach to likelihood inference for is to use an integratedlikelihood function, in which is eliminated from L(, ) by integratingwith respect to a density function (|). The goal of this paperis to consider the problem of selecting (|) so that the resultingintegrated likelihood function is useful for non-Bayesian likelihoodinference. The desirable properties of an integrated likelihoodfunction are analyzed and these suggest that (|) should be chosenby finding a nuisance parameter that is unrelated to and thentaking the prior density for to be independent of . Such anunrelated parameter is constructed and the resulting integratedlikelihood is shown to be closely related to the modified profilelikelihood.     

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]     

{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.     

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.     

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     

{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 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.     

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 Priming and Endosperm Integrity on Seed Germination Rates of Tomato Genotypes: II. GERMINATION AT REDUCED WATER POTENTIAL

Seed germination rates (GR =inverse of time to germination)are sensitive to genetic, environmental, and physiological factors.We have compared the GR of tomato (Lycopersicon esculentum Mill.)seeds of cultivar T5 to those of rapidly germinating L. esculentumgenotypes PI 341988 and PI 120256 over a range of water potential(). The influence of seed priming treatments and removal ofthe endosperm/testa cap enclosing the radicle tip on germinationat reduced were also assessed. Germination time-courses atdifferent 's were analysed according to a model that identifieda base, or minimum, allowing germination of a specific percentage(g) of the seed population (_b(g)), and a ‘hydrotime constant’(_H) indicating the rate of progress toward germination per MPa.h.The distribution of _b(g) determined by probit analysis was characterizedby a mean base (_b) and the standard deviation in _b among seeds(_b). The three derived parameters, _b, _b) and _H, were sufficientto predict the time-courses of germination of intact seeds atany . A normalized time-scale for comparing germination responsesto reduced is introduced. The time to germination at any (t_g())can be normalized to be equivalent to that observed in water(t_g(0)) according to the equation t_g(0)=[l–(/_b(g))]t_g().PI 341988 seeds were more tolerant of reduced and had a morerapid GR than T5 seeds due to both a lower _b and a smaller _H.The rapid germination of PI 120256, on the other hand, couldbe attributed entirely to a smaller _H. Seed priming (6 d in–1.2 MPa polyethylene glycol 8000 solution at 20 ?C followedby drying) increased GR at all >_b(g), but did not lower theminimum allowing germination; i.e. priming reduced _H withoutlowering _b. Removing the endosperm/testa cap (cut seeds) markedlyincreased GR and lowered the mean required to inhibit germinationby 0.7 to 0.9 MPa. However, this resulted primarily from downwardadjustment in _b during the incubation of cut seeds at low inthe test solutions. The difference in _b between intact and cutseeds incubated at high was much less (0.l MPa), indicatingthat at the time of radicle protrusion, the endosperm had weakenedto the point where it constituted only a small mechanical barrier.In the intact seed, endosperm weakening and the downward adjustmentin embryo _b ceased at < –0.6 MPa, while the reductionin _H associated with priming proceeded down to at least –1.2MPa. Based on these data and on the pressure required to pushthe embryos from the seeds at various times after imbibition,it appears that the primary effect of priming was to shortenthe time required for final endosperm weakening to occur. However,as priming increased GR even in cut seeds, priming effects onthe embryo may control the rate of endosperm weakening. Key words: tomato, Lycopersicon esculentum Mill., water potential, germination rate, seed priming, genetic variation     

Monte Carlo Estimation for Nonlinear Non-Gaussian State Space Models

We develop a proposal or importance density for state spacemodels with a nonlinear non-Gaussian observation vector y p(y¦)and an unobserved linear Gaussian signal vector p(). The proposaldensity is obtained from the Laplace approximation of the smoothingdensity p(¦y). We present efficient algorithms to calculatethe mode of p(¦y) and to sample from the proposal density.The samples can be used for importance sampling and Markov chainMonte Carlo methods. The new results allow the application ofthese methods to state space models where the observation densityp(y¦) is not log-concave. Additional results are presentedthat lead to computationally efficient implementations. We illustratethe methods for the stochastic volatility model with leverage.     

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     

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     

An Error in the Calibration of Xylem-water Potential against Leaf-water Potential

An error occurs in the calibration of xylem pressure potential() against leaf-water potential () when the calibration is madeusing plant material in which the water stress has been inducedartificially after excision. The impostion of water stress afterexcision affects the determination more than it affects , consequentlythe relationship between these two indices of water stress isaltered. Care should be exercised to ensure that identical proceduresare adopted during . calibrations and during susbsequent fieldmeasurements of with the pressure-chamber apparatus.     

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     

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