Water Movement Into and Through Tradescantia virginiana (L.) Leaves: III. UPTAKE DURING CONDITIONS OF DYNAMIC CHANGE

Water uptake into the ventral epidermis and the other tissuesof T. virginiana leaves was recorded when the uptake rate wassuddenly increased. Results indicated that there was considerableevaporation, or stomatal transpiration, from the epidermal tissues,and that the water relationships of the epidermis are more affected,at least in the short term, by changes in factors which affectthe transpiration rate than are the water relationships of theother leaf tissues.     

Water Pathways in Leaves of Hedera helix L. and Tradescantia virginiana L.

Hydraulic conductances of leaf tissues of Hedera helix and Tradescantiavirginiana leaves were measured. It was found that water couldflow most easily through the veins, but that the cell wallsof at least the ventral epidermis were more efficient at resupplyingwater lost from the epidermal tissue than was the mesophyllat rehydrating itself. Vein and bundle-sheath extensions, whichare characteristic of mesomorphic leaves (e.g. T. virginiana),seem to be important in maintaining a close hydraulic connectionbetween the epidermis and the vascular tissue. In leaves notcontaining vein and bundle-sheath extensions, typically xeromorphicleaves (e.g. H. helix), there is not such a close connectionbetween the epidermis and vascular tissue. This was shown inexperiments involving the sudden application of a reduced pressurepotential to either the epidermis or the other tissues of leaves,and the measurement of transient stomatal opening.     

Root Water Uptake, Leaf Water Storage and Gas Exchange of a Desert Succulent: Implications for Root System Redundancy

A technique used for hydroponics was adapted to measure instantaneousroot water uptake from the soil for a leaf succulent CAM species,Agave deserti. Comparisons were made to previously modelledwater fluxes for A. deserti and to Encelia farinosa, a non-succulentC₃species. Net CO₂uptake and transpiration forA. deserti underwell-watered conditions occurred primarily at night whereasroot water uptake was relatively constant over 24 h. Leaf thicknessdecreased when transpiration commenced and then increased whenrecharge from the stem and soil occurred, consistent with previousmodels. A drought of 90 d eliminated net CO₂uptake and transpirationand reduced the water content of leaves by 62%. Rewetting theentire root system for 7 d led to a full recovery of leaf waterstorage but only 56% of maximal net CO₂uptake. Root water uptakewas maximal immediately after rewetting, which replenished rootwater content, and decreased to a steady rate by 14 d. Whenonly the distal 50% of the root system was rewetted, the timefor net CO₂uptake and leaf water storage to recover increased,but by 30 d gas exchange and leaf water storage were similarto 100% rewetting. Rewetting 10 or 20% of the root system resultedin much less water uptake; these plants did not recover leafwater storage or gas exchange by 30 d after rewetting. A redundancyin the root system of A. deserti apparently exists for dailywater uptake requirements under wet conditions but the entireroot system is required for rapid recovery from drought.Copyright1999 Annals of Botany Company Agave deserti Engelm., desert, drought, gas exchange, rewetting, roots, succulent, water uptake.     

Transpiration and water uptake of Senecio medley-woodii and Aloe jucunda under changing environmental conditions: measurements with a potometric water-budget-meter

Transpiration, water uptake by the roots and CO₂ exchange oftwo leaf succulents, Senecio medleywoodii (Asteraceae) and Aloejucunda (Asphodeliaceae), were monitored simultaneously andcontinuously with a gas exchange cuvette combined with an apparatusto quantify water uptake (= waterbudget- meter). Measurements,which are primarily valid for plants with a sufficient watersupply, were made with the same plant for up to 29 consecutivedays. Ambient air temperature varied between 17 and 35 C witha constant dewpoint temperature of 13C of the ambient air anda 12 h photoperiod at 400–500mol m^–2s^–1 photonirradiance. The net water flux (J_w(net)=water uptake–transpiration)and the water balance (J_w(net) integrated for a timespan) werecalculated. Various tests were made to determine the accuracyof the measurements made with this rather complex equipment.In most cases the errors for transpiration and uptake rateswere much lower than 8% determined under the conditions of drastically(about 10 K per 30 min) increased or decreased ambient air temperatures.The experimental set-up proved to be a most valuable tool todetermine and analyse interactions between transpiration andwater uptake, changes in plant water status and the bufferingof negative J_wnet). Increasing the temperature of ambient air resulted, for bothspecies investigated, in a quick and considerably enhanced transpiration,but there was only a minor impact on water uptake. Water lossexceeding uptake was buffered by internal water reserves whichwere refilled within about 1 d after the plant was relievedof heat and drought stress caused by a period of high ambientair temperatures and high water vapour saturation deficits ofthe air. Repeated simulation of such stress periods showed thatthe absolute values of transpiration and the water uptake for24 h can vary, but the diurnal course of the values showed thesame pattern if the environmental conditions were identical.Such standardized diurnal transpiration and water uptake curvescould be very useful for the validation of mathematical modelsused to describe plant water relations. Key words: Plant water relations, water budget, drought stress, transpiration, water uptake     

Regulation of Amino Acid Uptake into Oat Mesophyll Cells: A Comparison between Protoplasts and Leaf Segments

The uptake of -aminoisobutyric acid (AIB) into protoplasts andinto 1 cm sections of leaves from 7 d old light-grown oats (Avenasativa L. cv. ‘Garry’) was studied. Both protoplastsand leaf sections with cuticle and epidermis removed accumulatedAIB against a concentration gradient although the rate of uptakeinto protoplasts was one-third to one-sixth that into leaf sections.AIB uptake into both protoplasts and leaf cells in situ wasstimulated by ‘aging,’ and low pH, and inhibitedby osmotic shock, respiratory poisons, and KCl concentrationsabove 1 mM. It was concluded that the rate of uptake of AIBand its accumulation ratio could be accounted for by the energyinherent in the proton-motive force, the proton-motive forcebeing the sum of the pH gradient and potential difference acrossthe plasma membrane. The similarities between oat mesophyllprotoplasts and leaf cells in situ suggest that these protoplastsare suitable material for the study of certain membrane-regulatedevents.     

The Use of 14C-Ethane Diol as a Quantitative Tracer for the Transpirational Volume Flow of Water and an Investigation of the Effects of Salinity upon Transpiration, Net Sodium Accumulation and Endogenous ABA in Individual Leaves of Oryza sativa L.

Yeo, A. R., Yeo, M. E., Caporn, S. J. M., Lachno, D. R. andFlowers, T. J. 1985. The use of ¹⁴C-ethane diol as a quantitativetracer for the transpirational volume flow of water and an investigationof the effects of salinity upon transpiration, net sodium accumulationand endogenous ABA in individual leaves of Oryza sativa L.—J.exp. Bot. 36: 1099–1109. Oryza sativa L. (rice) seedlings growing in saline conditionsexhibit pronounced gradients in leaf sodium concentration whichis always higher in the older leaves than the younger ones.Individual leaf transpiration rates have been investigated todiscover whether movement of sodium in the transpiration streamis able to explain these profiles from leaf to leaf. The useof ¹⁴C labelled ethane diol to estimate transpiration was evaluatedby direct comparison with values obtained by gas exchange measurements.Ethane diol uptake was linearly related to the transpirationalvolume flow and accurately predicted leaf to leaf gradientsin transpiration rate in saline and non-saline conditions. ¹⁴C-ethanediol and ²²NaCl were used to compare the fluxes of water andsodium into different leaves. The youngest leaf showed the highesttranspiration rate but the lowest Na accumulation in salineconditions; conversely, the older leaves showed the lower transpirationrates but the greater accumulation of Na. The apparent concentrationof Na in the xylem stream was 44 times lower into the youngerleaf 4 than into the older leaf 1. Exposure to NaCl (50 molm^–3) for 24 h elicited an increase in endogenous ABA inthe oldest leaf only, but no significant changes occurred inthe younger leaves. Key words: —Salinity, rice, Oryza sativa L., transpiration, volume flow, abscisic acid     

Diurnal Changes in Stem Diameter Depend Upon Variations in Water Content: Direct Evidence in Peach Trees

Three to five-year-old peach trees (Prunus persica (L.) Batschcv. ‘Maycrest’) grafted on P. ‘Damas 1869’grown in a sand trench were removed in the spring and grownhydroponically for several months. The system comprised twobalances continuously recording the mass of the nutrient solutionand that of the tree, so as to estimate transpiration and wateruptake rates separately. Diurnal variation in plant water content(transpiration minus water uptake) was observed, with rapidlydecreasing values when the solar radiation increased, whilethe reverse occurred when radiation decreased. Changes in stemdiameter were continuously recorded using linear variable differentialtransducers. Data collected over several days of contrastingclimatic conditions revealed that rapid changes in the stemdiameter occurred throughout the day and were closely relatedto plant water content. A lag-time not exceeding 10 min wasfound between changes in stem diameter and plant water content.These results are discussed in relation to the use of micromorphometricmethods to control irrigation in fruit trees. Moreover, we givevalues for the water stored in the shoots which may contributeto the transpiration stream. Key words: Prunus persica, stem shrinkage, plant water storage, water uptake, transpiration     

Stomatal responses to light and CO2 in greening wheat leaves

The development of two types of stomatal transpiration, oneinduced by light (light-induced stomatal transpiration) andthe other induced by CO₂-free air in the dark (CO₂-sensitivestomatal transpiration), in greening leaves of wheat (Triticumaestivum L.) was studied in respect to the development of CO₂uptake and chlorophyll formation. Light-induced stomatal transpirationwas not observed at all in etiolated leaves and was generatedafter 3 hr of illumination for greening, when the activity ofCO₂ uptake was generated. CO₂-sensitive stomatal transpirationwas low in etiolated leaves and started to increase at the sametime during greening as the start of CO₂ uptake. The activitiesof both light-induced and CO₂-sensitive stomatal transpirationincreased as the activity of CO₂ uptake and the chlorophyllcontent increased. Pre-illumination of etiolated leaves for1 min followed by 4 hr of dark incubation eliminated the lagfor the development of the two types of stomatal transpirationand CO₂ uptake. (Received September 4, 1978; )     

The Rate of Water-loss from Stripped Leaves

Stripping off the epidermis of Sedum leaves is found to increasethe rate of water-loss by amounts of the order of 700 per cent.A high resistance of the pores of the stomatal epidermis tothe diffusion of water-vapour from the mesophyll is thus indicated. Stripping one surface of a leaf considerably increases the rateof transpiration from the other (untouched) surface. The explanationof this is under investigation. In conclusion, the writer wishes to thank Dr. F. M. Haines forsuggestions, interest and criticism. Thanks are also due tothe staff of the Chelsea Physic Garden and to Mr. I. R. McGregorfor his valuable technical assistance.     

A Possible Role for the Thick-walled Epidermal Cells in the Mycorrhizal Hair Roots of Lysinema ciliatum R. Br. and other Epacridaceae

Hair roots ofLysinema ciliatum R. Br. and some other Epacridaceaehave thick-walled cells in the epidermis. These are preferentiallycolonized with mycorrhizal fungi. Individual epidermal cellscontaining hyphal coils separate at the middle lamella and arereleased into the soil. Other colonized cells remain attachedto the roots, usually in groups, surrounded by bare exodermis,where epidermal cells have either collapsed or been sloughedoff. It is suggested that these colonized thick walled cellscan serve to prolong the mycorrhizal association and to infectnew hair roots as these emerge. The thick wall has a very specializedstructure and composition and could have a number of roles,either acting as a substrate or protective coat or in controllingwater status and uptake. Young hair-roots are surrounded bya mucilage sheath that is similar in appearance to that in Ericaceaeand apparently produced by root cap cells, not the epidermis. Lysinema ciliatum R. Br.; ericoid mycorrhiza; hair root; root cap; cortex; epidermis; exodermis     

Genotypic Variation in the Thickness of Silica Deposition on Flowering Rice Spikelets

Silicon may play an important role in regulating the transpirationrate of rice (Oryza sativa L.), particularly cuticular transpiration.The control of cuticular transpiration is important in ricespikelets because water stress at anthesis may severely disruptfertility and grain yield. Data on the quantitative variationamong rice cultivars in the thickness of the silica layer ofthe flowering spikelet were obtained in order to assess thepotential for genetic selection for silica layer thickness asa potential means for increasing spikelet resistance to waterloss. Flowering spikelets were collected from 17 genotypes and thicknessmeasurements were made of the major anatomical layers in crosssection. The silica layer of the lemma varied from 42 to 177µm among cultivars. Similar variation was observed inthe palea. Differences among cultivars were also found in thethickness of the epidermis and sclerenchyma-parenchyma layer. The total cross-sectional thickness of the lemma and palea averagedslightly over 100 µm. Total thickness was not significantlycorrelated with the length, width or product of length width.Thickness of silica deposition was significantly correlatedwith spikelet length width suggesting that these easily measuredparameters may be useful in screening for silica thickness. Oryza sativa L., rice, panicle, silicon, lemma, palea, husk     

Photosynthesis and Diffusion Conductance of the Valencia Orange Fruit under Field Conditions

CO₂ uptake and diffusion conductance of Valencia orange fruits(Citrus sinensis L. Osbeck) were measured in the field duringthe growing season of 1977/78 to ascertain if, as in the leaf,stomata control photosynthesis and transpiration under changingenvironmental conditions. Measurements were made on 15 yearold trees grown in a sandy loam soil and receiving either adry or a wet treatment. Fruit diffusive conductance was measuredwith a modified water vapour diffusion conductance meter andgross photosynthesis was measured with a ¹⁴CO₂ uptake meter.Photosynthetically active radiation (PAR) was measured witha quantum sensor. Fruits exposed to light assimilated CO₂ ata rate which was 25–50% of that assimilated by leaves.The uptake was dependent on fruit size, PAR, chlorophyll content,and on diffusive conductance of the fruit epidermis. Epidermalconductance showed a diurnal trend which was similar in shapeto that of the leaf except in the late afternoon. Cuticularconductance of the fruit was calculated and ranged between 0.22and 0.30 mm s^–1. It was speculated that the CO₂ uptakeby the fruit could support the growth of flavedo cell layerswhen exposed to light. Dry soil caused an increase in the ¹⁴CO₂uptake by fruit possibly caused by the increased potential areaof the stomatal opening per unit of fruit surface area.     

Effect of Ferricyanide on Potassium Uptake by Intact Epidermal Tissue and Guard Cell Protoplasts

The effect of ferricyanide on K^$ fluxes in epidermis and inguard cells of Commelina communis L. were studied. Ferricyanideenhanced guard cell protoplasts swelling, which results fromenhanced K^$ uptake. In intact epidermis ferricyanide inhibitedK^$ uptake and consequently, stomatal opening. This was foundin floated and submerged epidermal tissues, indicating thatthe degree of contact with the solution does not affect theresponse to ferricyanide. Investigation of the rate of plasmolysisand de-plasmolysis of guard cells in epidermal tissue revealedthat ferricyanide enhances deplasmolysis, caused by K^$ uptake,only in completely plasmolysed cells, which resemble protoplastsin situ. (Received January 21, 1988; Accepted March 24, 1988)     

Accumulation of calcium in the centre of leaves of coriander (Coriandrum sativum L.) is due to an uncoupling of water and ion transport

The aim of this study is to understand the parameters regulatingcalcium ion distribution in leaves. Accumulation of ions inleaf tissue is in part dependent on import from the xylem. Thisimport via the transpiration stream is more important for ionssuch as calcium that are xylem but not phloem mobile and cannottherefore be retranslocated. Accumulation of calcium was measuredon bulk coriander leaf tissue (Coriandrum sativum L. cv. Lemon)using ion chromatography and calcium uptake was visualized usingphosphor-images of ⁴⁵Ca²⁺. Leaves of plants grown in hydroponicshad elevated calcium in the centre of the leaf compared withthe leaf margin, while K⁺ was distributed homogeneously overthe leaf. This calcium was shown to be localised to the mesophyllvacuoles using EDAX. Stomatal density and evapotranspiration(water loss per unit area of leaf) were equal at inner and outersections of the leaf. Unequal ion distribution but uniformityof water loss suggested that there was a difference in the extentof uncoupling of calcium and water transport between the innerand outer leaf. Since isolated tissue from the inner and outerleaf were able to accumulate similar amounts of calcium, itis proposed that the spatial variation of leaf calcium concentrationis due to differential ion delivery to the two regions ratherthan tissue/cell-specific differences in ion uptake capacity.There was a positive correlation between whole leaf calciumconcentration and the difference in calcium concentration betweeninner and outer leaf tissue. Exposing the plants to increasedhumidity reduced transpiration and calcium delivery to the leafand abolished this spatial variation of calcium concentration.Mechanisms of calcium delivery to leaves are discussed. An understandingof calcium delivery and distribution within coriander will informstrategies to reduce the incidence of calcium-related syndromessuch as tip-burn and provides a robust model for the transportof ions and other substances in the leaf xylem. Key words: Calcium, Coriandrum sativum, distribution, ion chromatography, leaves, radioisotope, spatial variation, transpiration, uptake Received 29 August 2008; Accepted 16 October 2008     

The Regulation of the Water Potential Gradient in the Host and Parasite Relationship betweenSorghum bicolorandStriga hermonthica

A glasshouse experiment was carried out to investigate the factorscontrolling the abstraction of xylem fluid from its host bythe parasiteStriga hermonthica(Scrophulariaceae).Strigahad amean daily transpiration rate far exceeding that of its hostsorghum (Sorghum bicolor), with infestation byStrigaalso shownto lower the transpiration rate of the host. Stopping the host'stranspiration was shown to decrease the transpiration rate ofthe parasite. Stopping the parasite's transpiration only gavean initial increase in the host's transpiration rate which wasnot sustained. The parasite had a lower water potential thanits host, values being -0.42 MPa and -0.23 MPa, respectively,and an accompanying higher osmotic pressure of 0.68 MPa against0.51 MPa for sorghum. Modifying the water potential gradientby bagging both partners together showed that the differentialin osmotic pressure and water potential was largely maintainedby the parasite's higher rate of transpiration. A favourablewater potential gradient towards the parasite still existedfollowing the cessation of transpiration, this being generatedby the haustorial resistance to hydraulic conductivity whichwas found to be some 1.5–4.5 times greater than that offeredby the parasite shoot. Both the high rate of transpiration andthe increased resistance across the haustoria would appear tobe necessary means to facilitate the diversion of host resourcesto the parasite.Copyright 1997 Annals of Botany Company Striga hermonthica; sorghum; water relations; haustorium; root parasite     

Morphology and Ultrastructure of Immature Cereal Grains in Relation to Transport

The surfaces of the pericarps of wheat and barley grains, 15–30days after anthesis, were examined. Stomata were found in thepericarp epidermis on the ventral side at the apical end inone variety of wheat and four varieties of barley. Layers whichstained red with Sudan IV were observed on the pericarp epidermisand on either side of the testa in immature barley grains. Theultrastructure of these layers was investigated. It was concludedthat the cuticular layer inside the testa is derived from thenucellus. The significance of these cuticular layers in relationto the supply of carbon dioxide to the photosynthesizing cellsof the pericarp is discussed. The movement of photosynthateand oxygen produced in the pericarp is also considered. Hordeum vulgare L, Triticum aestivum L, barley, wheat, cereal grain, cuticle, stomata, pericarp     

The Relationships between Transpiration and Potassium Uptake in Ricinus communis

The water uptake by individual water-culture-grown castor-oilplants (Ricinus communis) was varied and corresponding ratesof potassium uptake measured. The water flux was varied by changingthe rate of transpiration or by detopping the transpiring plants.Transpiration was altered by changing the atmospheric humidityat constant temperature and light intensity in a climatologicalwind tunnel. It was found that the uptake of potassium was divisibleinto two components: (a) an accumulation by the cells of theroot and (b) a passage through the root to the shoot via thevessels. These components were found to be entirely independentof one another. Also while (a) was unaffected by the water flux(b) was linearly related to it. The concentration of potassiumin the vessels was between 15 and 26 times that of the mediumand this ratio which was found to be similar in both intactand detopped exuding plants remained constant in the face ofwide changes in water flux. This essential similarity betweenexuding and transpiring plants and the finding that there wasa lag between the change in water flux and the response in potassiumuptake indicated that there is no continuous mass-flow pathwaybetween medium and xylem in these plants. Instead, increasedtranspiration seems in some way to increase the rate of theexudation process. These conclusions are discussed in relationto the results of other workers.     

Are Roots a Source of Abscisic Acid for the Shoots of Flooded Pea Plants?

Flooding the soil for 2–5 d decreased stomatal conductancesof pea plants (Pisum sativum L., cv. Sprite) with six or sevenleaves. This coincided with slower transpiration, increasedleaf water potentials and increased concentrations of abscisicacid (ABA) in the leaves. No increase in ABA was found in theterminal 20 mm of roots of flooded plants over the same timeperiod. Small stomatal conductances associated with increases in foliarABA were also found in plants grown in nutrient solution whenaeration was halted, causing the equilibrium partial pressuresof dissolved oxygen to fall below 05 It Pa. No increase in ABAconcentration in young secondary roots of the non-aerated plantswas detected after 24, 48 or 72 h, even when the shoot, thepresumed site of deposition for any ABA from the roots, wasremoved 5–6 h before analysis. Similarly, ABA concentrations in roots were not increased whenthe nutrient solution was de-oxygenated by continuous purgingwith nitrogen gas. The abscisic acid concentration in leaf epidermis,the tissue most likely to be the recipient of any ABA movingin the transpiration stream from oxygen-deficient roots, waslower than in the remaining parts of the leaf when examinedin the mutant Argenteum which possesses easily removable epidermallayers. It is concluded that the leaves of plants subjectedto flooding of the soil or oxygen shortage in the root environmentare not enriched substantially with ABA from the roots. A moreprobable source of this growth regulator is the leaf itself. Key words: Pisum sativum, flooding, roots, hormones, aeration stress, abscisic acid, Argenteum mutant     

Measured and Calculated Transpiration in Trifolium repens under Different Water Potentials

The relationship between transpiration measured gravimetrically,a generalized transpiration equation, and the ratio VPD/r_leafwas investigated in Trifolium repens plants subjected to varyingwater potentials. Dawn leaf water potential was measured witha pressure chamber, leaf diffusion resistance with a diffusionporometer, leaf temperatures with a thermistor, and relativehumidity with an aspirated psychrometer. During drought transpirationrates determined by both methods were quite similar particularlyat the lowest water potentials. After rewatering calculatedrates were somewhat higher than measured ones. It is concludedthat transpiration calculated by the indirect method is a usefuland reasonable estimate of transpiration for single plants undervarying water potentials.     

Responses of a CAM Plant to Drought and Rainfall: Capacitance and Osmotic Pressure Influences on Water Movement

Daily and seasonal patterns in water flow and water potentialwere investigated for the Crassulacean acid metabolism succulentAgave deserti during an extended summer drought and for a periodfollowing rainfall. Field measurements of transpiration andof osmotic pressure changes over selected 24 h periods wereused as input variables for a computer model of water flow thatwas based on an electrical circuit analog of the whole plant.Parameters such as root resistance and tissue capacitance werealso varied to reflect the effects of changing plant or soilwater status. The model predicted internal water flow and waterpotential during the drought cycle and was used to assess therole of tissue osmotic properties in water uptake from the soiland in internal water redistribution. For plants under wet soil conditions, 55% of the night-timetranspiration was derived from water storage, this storage beingrecharged during the day. As drought progressed, transpirationand the nocturnal increase in osmotic pressure declined, althoughthe osmotic pressure itself increased. The difference in osmoticpressure between the water storage tissue and the chlorenchymacaused a net flow of water into the chlorenchyma after 3 weeksof drought, thereby increasing chlorenchyma turgor pressure.Simulations also indicated that a large increase in root resistancemust occur to prevent substantial water loss from the plantto the dry soil. After rainfall, recharge of plant water storagewas complete within one week, although full recovery in theamplitude of daily osmotic pressure variations took longer. Key words: Agave deserti, transpiration, water potential, water storage