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     

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.     

{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.     

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     

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     

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]     

Sex-ratio differences in Mnium hornum Hedw. and M. undulatum Sw. in relation to spore germination and vegetative regeneration

As Mnium undulatum was shown to be homosporous, it was concludedthat neither male nor female derived an advantage from sporesize that might be related to the observed excess of femaleplants. The rate of germination was greater at 20 °C thanat 10 °C in M. hornum and M. undulatum, and was also reducedin short days (7.25 hours) at both temperatures. Spores of M.undulatum germinated more slowly than those of M. hornum undereach of the environmental regimes used. Isolated spores of M.undulatum showed a ratio of 1: 4.1 compared with 1: 0.89 inM. hornum. The excess of female plants of M. undulatum thathad been established by the end of germination, was maintainedamongst the first protonemal buds produced (1: 3.5), whereasan excess of male M. hornum was observed in the first protonemalbuds (1: 0.45). Frost reduced the rate of germination in M.undulatum, but unlike desiccation did not affect the final percentage.Male and female were amongst the spores which survived desiccationat 10 °C. Regeneration of detached leaves occurred more rapidly in M.undulatum than in M. hornum, and no difference between maleand female was detected. It was found that frost prior to orduring regeneration did not produce long-term harmful effectsin M. undulatum. None of the young male gametophytes producedby regeneration from leaves survived desiccation, compared with77 per cent of similarly produced female gametophytes.     

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 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     

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     

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     

{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.     

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     

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.     

The Interaction of Photoperiod and Temperature on the Flowering Response of Rice

Eight varieties of the species Oryza sativa L. and two varietiesof O. glaberrima Steud. were grown under controlled conditionsin combinations of three photo-periods (8 10 and 11 hours lightper day), each giving the same total daily radiant energy, andfour temperature régimes (‘night’ and ‘day’temperatures of 25-35° 30-35° 30-40° and 35-35°respectively). The flowering responses were measured as thenumber of days from sowing to the first appearance of the panicle.Under the range of conditions investigated, one variety (Kogbati3) was completely insensitive to both photoperiod and temperature.The remainder were affected by both factors and the optimumphotoperiod (i.e. the photoperiod resulting in earliest flowering)varied between 8 and 10 hours. In general, the higher the temperaturerégime, the longer the duration of the vegetative phase.In some varieties, but not all, there was some indication thatthe value of the optimum photoperiod increased with increasingtemperature. No specific effects of night temperatures as opposedto day temperatures on the flowering response could be detected,but there was some evidence that high night temperatures weremore deleterious to vegetative growth than high day temperatures.The 8-hour photoperiod also resulted in particularly poor vegetativegrowth by comparison with other photoperiodic treatments.     

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.     

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