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1.
Water Potential, Translocation and Assimilate Partitioning 总被引:5,自引:1,他引:4
Lang, A. and Thorpe, M. R. 1986. Water potential, translocationand assimilate partitioning.J. exp. Bot. 37: 495503. The effect of water status upon translocation and assimilatepartitioning is examined both from theory and in an experimentwith young Phaseolus plants. Theory predicts that translocationis unlikely to be directly affected by water status. However,water potential differences within plants should influence translocationflow, with regions at lower potentials attracting disproportionatelylarge shares of assimilate. This prediction is supported in the experiment with Phaseolusin which the pattern of partitioning in the root changed rapidlyin response to bathing portions of it in solutions of differentosmolarity. The relevance of these findings to the growth of plants undernatural conditions is considered and evidence is presented thatwater potential gradients may be an Important factor in thecontrol of partitioning Key words: Phloem translocation, xylem transport, partitioning, water potential, control, osmotic potential 相似文献
2.
Diurnal changes in leaf water potential and leaf thickness ofwell-watered citrus trees were found to be highly correlated.Midday decreases in leaf thickness of about 3035 µm reflected midday decreases in leaf water potential of about1.11.3 MPa from predawn values. Leaf water potentialwas also correlated with changes in leaf-to-air temperaturedifference and ambient vapour pressure deficit. Leaf thicknessas well as leaf to air temperature difference could possiblybe used to monitor leaf water status continuously as an indicatorof citrus tree water stress. 相似文献
3.
Leaf and xylem water potentials were measured in rice plantswith and without transpiration using a thermocouple psychrometerand a pressure chamber. The leaf water potential practicallycoincided with the xylem water potential in leaves without transpiration,while the latter was 35 bars lower when intense transpirationwas occurring. The pressure chamber should not be used to measureleaf water potential during intense transpiration in the field.The water status in transpiring leaves is discussed. (Received March 6, 1978; ) 相似文献
4.
Water and Seed Survival 总被引:18,自引:1,他引:17
Between about 350 and 14 MPa the rate of lossof viability in orthodox seeds is a positive function of waterpotential. The relative effect of water potential has been analysedin an oily seed (lettuce) and a non-oily seed (barley) and foundto be more or less identical. The lower limit for the relationin various species coincides with a seed moisture content (wetbasis) between about 2 and 6%. Below this level there is littleor no improvement in longevity with reduction in moisture content.The upper limit coincides with moisture contents of between15 and 28%, depending on whether the seeds are oily or non-oily.A water potential of about 14 MPa is the threshold forrespiration which increases more-or-less linearly with increasein water potential above this level. Above this threshold, andproviding oxygen is available to sustain respiration, seed longevityincreases with increase in water potential except that, unlessthe seeds are dormant, germination may be initiated at a waterpotential of about 1·5 to 0·5 MPa.In the absence of oxygen there may be a slight further declinein longevity with increase in water potential above 14MPa before longevity reaches a minimum value Since they cannot be dried very much without immediate lossof viability, recalcitrant seeds survive longest in the presenceof oxygen at maximum water potential commensurate with preventinggermination. The threshold water potential for immediate lossof viability has not been determined for most species but itis probable that it is close to the water potential typicalof the permanent wilting point in these plants, say 2MPa Lactuca saliva L., lettuce, Hordeum oulgare L., barley, seed storage, moisture content, relative humidity, water potential, temperature, oxygen 相似文献
5.
Douglas E. Kenyon 《Bulletin of mathematical biology》1979,41(1):79-90
Water flux in porcine aortic segments produced by the sudden application of a hydrostatic pressure gradient has been described
in a recent paper by Harrison and Massaro (1976). A mathematical model is developed here to explain the results obtained when
pressure is applied to either covered or uncovered samples. The model predicts that the rate of exudation in both instances
should be substantially identical for a period of time ∼ 0.2τ, where τ is the consolidation time. The consolidation time is
proportional to the hydraulic resistance to liquid flow, and inversely proportional to the compressive stiffness of the artery.
The existence of a time-dependent water flux in an arteryin vivo during periodic pressurization is predicted by the mathematical model if the resistance to water flow at the endothelium
is not excessive. The pore pressure within the bulk of the media is predicted to pulsate in a highly unexpected fashion. These
predictions follow naturally from the fact that the consolidation phenomenon in large arteries, as determined by the compression
tests of Harrison and Massaro, is of long duration, much longer than the period of a heartbeat. Pressure gradientsin vivo in interstitial fluid are then confined to a very small fraction of the total arterial wall thickness. A potential for plasma
“sloshing” across the endothelial junctions exists. The convective flux of water across an endothelial layer may therefore
be of a pulsatile character in normal arteriesin vivo. 相似文献
6.
WOOKEY P. A.; ATKINSON C J.; MANSFIELD T. A.; WILKINSON J. R. 《Journal of experimental botany》1991,42(5):589-595
A system, designed by Snow and Tingey (1985) for subjectingplants to reproducible water stress levels for extended periodsof time, is considered. Modifications are also outlinedwhich enable water table heights to be maintained without theneed for complex float chambers. Sunflower plants (Helianthus annuus L. cv. Frankasol) were grownusing the system and these were either well-wateredor subjected to water deficits. The temporal development ofwater deficits was closely monitored by regular psychrometricmeasurements of leaf water potential. Diurnal stomatal behaviour,mid-day abaxial stomatal conductance, and photosynthetic assimilationrates were also determined throughout the experiment, with growthanalysis at the end. A reduction in stomatal conductance occurred within 24d after the onset of a restriction in water supply. Data fromboth viscous flow and diffusion porometry suggested that stomatalclosure apparently began without a fall in bulk leaf water potential.Leaf water potentials of plants with a restricted supply ofwater did, however, subsequently decline during the early partof the experiment reaching values as low as 0.99±0.07 MPa after 14 d. No further reduction in bulk water potentialwas observed after a further 5 d, suggesting that a steady-statehad been reached. Corresponding values of leaf water potentialfor well-watered plants were about 0.60 ± 0.04MPa. Biomass determinations indicated the potential for quantifyingthe effects of water deficits, of controlled magnitudes, onrates of leaf production and expansion. However, the possibilityof physical limitations of root developmentimposed bothby the plant container and also by the imposition of restrictedwater suppliesmust be carefully considered when planningexperiments with this system. 相似文献
7.
This paper is a theoretical discussion of the concept of suctionpotential or suction pressure as applied to plant cells, especiallywith reference to the possible occurrence of activewater-secreting mechanisms. Following an attempt to define whatis meant by suction potential there is a discussion of the distinctionbetween active and passive agenciesin relation to water movement and a tabulation of such agencies. Some of the less commonly considered mechanisms are discussedin some detail, and an attempt is made to evaluate how effectivethey might be in producing increments of turgor pressure. Theconclusion is reached that if active mechanisms are operativein cell-water relations, then suction potential cannot adequatelybe denned in the ordinary wayin fact the water-absorbingeffort of a cell cannot be completely specified in termsof pressure alone. There are appendixes on the possible role of frictional or contactelectrification in cell physiology; on the increase of permeabilityof the plasma membrane to ions and water caused by electricalforces; and on the energy requirement of active water-secretingmechanisms. 相似文献
8.
Shoot Resistance to Water Flow in Cotton 总被引:2,自引:0,他引:2
MERON M.; GRIMES D. W.; PHENE C. J.; HUTMACHER R. B. 《Journal of experimental botany》1989,40(8):919-923
Studies using excised cotton (Gossypium hirsutum L.) plants,attached to a free water source and undergoing transpirationcycles, were conducted at intervals over a 2 year period inorder to quantify shoot resistance components of cotton canopies.Leaf water potential was found to be a linear function of transpirationrate at rates above 0.1 mm h1, so shoot resistance wasevaluated as the slope of this function. The value of 4.8 104h (0.48 MPa h mm1) total shoot resistance was consistentfor 1.10 m tall, well irrigated, fruit-bearing cotton plants.Further tests, with pre-wrapped and exposed leaves, revealedthat total shoot resistance was comprised of an axial component(40%) and a leaf component (60%). The total shoot resistanceof 0.48 MPa h mm1 is likely to be relevant for modellingcotton water relations when LWP is evaluated on exposed, topof the canopy leaves, such as in the big leaftype models. Key words: Leaf water potential, axial resistance, leaf resistance 相似文献
9.
Stomatal Control of Water Loss in Siratro (Macroptilium atropurpureum (DC) Urb.), a Tropical Pasture Legume 总被引:1,自引:0,他引:1
Stomatal conductance of siratro declined linearly as leaf waterpotential fell until zero conductance was reached at 10bar. In a grass/legume pasture stomata of siratro respondedto humidity (saturation deficit), and to a lesser extent toleaf water potential, such that leaf water potential did notfall below 9 bar, whereas that of the grass continuedto decline for most of the day. The dual response of siratroto both humidity and leaf water potential suggests that thisspecies has an efficient two-stage stomatal control of waterloss which provides an explanation of its higher leaf waterpotential and greater drought avoidance compared with sown grassesin semi-arid areas of north-eastern Australia. Macroptilium atropurpureum (DC) Urb., siratro, Desmodium uncinatum, stomatal control, stomatal conductance, water loss, leaf water potential, drought avoidance, saturation deficit 相似文献
10.
I. Poirier P.-A. Maréchal C. Evrard P. Gervais 《Applied microbiology and biotechnology》1998,50(6):704-709
Escherichia coli and Lactobacillus plantarum were subjected to final water potentials of −5.6 MPa and −11.5 MPa with three solutes: glycerol, sorbitol and NaCl. The water
potential decrease was realized either rapidly (osmotic shock) or slowly (20 min) and a difference in cell viability between
these conditions was only observed when the solute was NaCl. The cell mortality during osmotic shocks induced by NaCl cannot
be explained by a critical volume decrease or by the intensity of the water flow across the cell membrane. When the osmotic
stress is realized with NaCl as the solute, in a medium in which osmoregulation cannot take place, the application of a slow
decrease in water potential resulted in the significant maintenance of cell viability (about 70–90%) with regard to the corresponding
viability observed after a sudden step change to same final water potential (14–40%). This viability difference can be explained
by the existence of a critical internal free Na+ concentration.
Received: 20 May 1998 / Received revision: 31 July 1998 / Accepted: 31 July 1998 相似文献
11.
Effects of Temperature and Water Potential on Germination, Radicle Elongation and Emergence of Mungbean 总被引:2,自引:1,他引:1
Controlled environment experiments were performed to determinethe effects of temperature and water potential on germination,radicle elongation and emergence of mungbean (Vigna radiata(L.) Wilczek cv. IPB-M79-17-79). The effects of a range of constant temperatures (1545°C) and water potentials (0 to 2.2 MPa) on germinationand radicle elongation rates were studied using an osmoticumtechnique, in which seeds were held against a semi-permeablemembrane sac containing a polyethylene glycol solution. Linearrelationships were established between median germination time(Gt50) and water potential at different temperatures, and betweenreciprocal Gt50 (germination rate) and temperature at differentwater potentials. Germination occurred at potentials as lowas 2.2 MPa at favourable temperatures (3040 °C),but was fastest at 40 °C when water was not limiting, withan estimated base temperature (Tb) of about 10 °C. Subsequentradicle elongation, however, was restricted to a slightly narrowertemperature range and was fastest at 35 °C. The conceptof thermal time was used to develop an equation to model thecombined effects of water potential and temperature on germination.Predictions made using this model were compared with the actualgermination obtained in a related series of experiments in columnsof soil. Some differences observed suggested the additionalimportance of the seed/soil/water contact zone in influencingseed germination in soil. Seedling emergence appeared to reflectfurther the radicle elongation results by occurring within anarrower range of temperatures and water potentials than germination.Emergence had an estimated Tb of 12.6 °C and was fastestat 35 °C. A soil matric potential of not less than about0.5 MPa at sowing was required to obtain 50% or moreseedling emergence. Key words: Germination, temperature, water potential 相似文献
12.
Summary The effects of four soil water potential regimes under greenhouse conditions on growth, development, and yield of ‘Homestead
selection’ pawpaw were investigated. The objectives were to determine the critical soil water potential regime and the moisture
sensitive stages of growth of pawpaw. Repeated cycles of stress to −6.0 bar soil water potential imposed as from vegetative
phase prevented fruit formation by constantly causing flower abscission. The stressed plants were stunted in size. The −2.0
bar soil water potential value was considered the critical level for normal growth and reproductive development of pawpaw.
The mid-vegetative, flowering and fruit enlargement phases were moisture sensitive. 相似文献
13.
Contribution of physiological and morphological adjustments to drought resistance in two Mediterranean tree species 总被引:1,自引:0,他引:1
Plant water potential (ψ), its components, and gas exchange data of two Mediterranean co-occurring woody species (Quercus ilex L. and Phillyrea latifolia L.) were measured in response to seasonal changes in water availability over two consecutive years. The relative contribution
of physiological and morphological adjustments to drought resistance was assessed through Principal Component Analyses. There
were large adjustments in stomatal conductance (∼36 % of accounted variance). Net photosynthetic rate and water use efficiency
were closely tuned to water availability and accounted for ∼17 % of variance. The slope of the water potential vs. relative water content (dψ/dRWC0) below zero pressure potential increased as a result of seasonal and ontogenic increases in apoplastic water fraction and
accounted for ∼20 % variance. This tolerance mechanism was accompanied by an increased range of positive pressure potential,
suggesting a functional role of sclerophylly in these Mediterranean evergreens. Similarly, changes in the slope of dψ/dRWC
in the range of positive pressure potential (∼13 % of accounted variance) were associated to variations in cell wall elasticity
and resulted in lower RWC at zero pressure potential. When considering the species studied separately, the results indicated
the primary role of stomatal regulation in the drought resistance of Qilex, while increased apoplastic water fraction had a major contribution in the drought resistance of P. latifolia.
This research was supported by Spanish CICYT grants CLI99-0479 and REN-2002-00633. L.S. acknowledges the financial support
from Ministerio de Ciencia y Tecnologia (“Ramon y Cajal” program, Spain).
An erratum to this article is available at . 相似文献
14.
Water-storage capacity was measured inThuja occidentalis L.,Tsuga canadensis (L.) Carr., andAcer saccharum Marsh. during the dehydration of stem segments 1.5–2.5 cm in diameter. Stem water potential was measured with a temperature-corrected
stem hygrometer and cavitations were detected acoustically. Water loss was measured by weight change. Dehydration isotherms
consistently displayed three phases. The first phase, from water potential (Ψ) 0 to about −0.2 MPa, had a high capacitance
(C>0.4kg water lost· (1 of tissue)−1· MPa−1) and we have attributed this high C to capillary water as defined by Zimmermann (1983, Xylem structure and the ascent of
sap, Springer-Verlag). The second phase from Ψ=−0.5 to about −2.0 had the lowest C values (<0.02 kg·l−1·MPa−1) and was accompanied by a few cavitation events. This phase may have been a transition zone between capillary storage and
water released by cavitation events as well as water drawn from living cells of the bark. The third phase also had a high
C (about 0.07–0.22kg·l−1·MPa−1) and was associated with many cavitation events while Ψ declined below about −2.5 MPa; we presume the high capacitance was
the consequence of water released by cavitation events. We discuss the ecological adaptive advantage of these three phases
of water-storage in trees. In moist environments, water withdrawn from capillary storage may be an important fraction of transpiration,
but may be of little adaptive advantage. For most of the growth season trees draw mainly on elastic storage, but stem elastic
storage is less than leaf elastic storage and therefore unlikely to be important. In very dry environments, water relased
by cavitation events might be important to the short-term survival of trees. 相似文献
15.
R. Russell M. Paterson 《Mycological Progress》2007,6(2):115-113
Production of the mycotoxin zearalenone (ZEN) was examined in drinking water inoculated with Fusarium graminearum. The strain employed was isolated from a US water distribution system. ZEN was purified with an immunoaffinity column and
quantified by high-performance liquid chromatography (HPLC) with fluorescence detection. The extracellular yield of ZEN was
15.0 ng l−1. Visual growth was observed. Ergosterol was also indicative of growth and an average of 6.2 μg l−1 was obtained. Other compounds were also detected although remain unidentified. There is no equivalent information available.
More work is required on metabolite expression in water as mycotoxins have consequences for human and animal health. The levels
detected in this study were low. Water needs to be accepted as a potential source as it attracts high quality demands in terms
of purity.
An erratum to this article can be found at 相似文献
16.
Victoria Gonzalez-Dugo 《Mycorrhiza》2010,20(6):365-373
The hypothesis that mycorrhizal colonization improves the soil–root conductance in plants was experimentally tested in a growth
chamber using pot cultures of Agrostis stolonifera L. colonized by Glomus intraradices. Plants were grown in 50-l pots filled with autoclaved sand/silt soil (1:1), with and without the mycorrhizal fungus. Within
the mycorrhizal treatment, half of the pots remained well watered, while the other half was subjected to a progressive water
deficit. Soil water potential (estimated as plant water potential measured at the end of the dark period), xylem water potential
measured at the tiller base, transpiration rate, and soil water content were monitored throughout the experiment. Soil–root
hydraulic conductance was estimated as the ratio between the instantaneous transpiration rate and the soil and xylem water
potential difference. To obtain cultures with similar nutritional status, the P in the modified Hoagland’s nutrient solution
was withheld from the inoculated pots and applied only once a month. Even though there were no differences on growth or nutrient
status for the mycorrhizal treatments, water transport was enhanced by the inoculum presence. Transpiration rate was maintained
at lower xylem water potential values in the presence of mycorrhizae. The analysis of the relationship between soil–root hydraulic
resistance and soil water content showed that mycorrhizal colonization increased soil–root hydraulic conductance as the soil
dried. For these growing conditions, this effect was ascribed to the range of 6–10%. 相似文献
17.
Airaksinen S Karjalainen M Kivikero N Westermarck S Shevchenko A Rantanen J Yliruusi J 《AAPS PharmSciTech》2005,6(2):E311-E322
Phase transformations in formulations can lead to instability in physicochemical, biopharmaceutical, and processing properties
of products. The influences of formulation design on the optimal dosage forms should be specified. The aim here was to investigate
whether excipients with different water sorption behavior affect hydrate formation of nitrofurantoin in wet masses. Nitrofurantoin
anhydrate was used as a hydrate-forming model drug, and 4 excipients with different water-absorbing potential (amorphous low-substituted
hydroxypropylcellulose, modified maize starch, partially amorphous silicified microcrystalline cellulose, and crystalline
α-lactose monohydrate) were granulated with varying amounts of purified water. Off-line evaluation of wet masses containing
nitrofurantoin anhydrate and excipient (1∶1) was performed using an X-ray powder diffractometer (XRPD) and near-infrared spectroscopy,
and drying phase was evaluated by variable temperature XRPD. Only amorphous excipient in the formulation retarded hydrate
formation of an active pharmaceutical ingredient (API) at high water contents. Hygroscopic partially crystalline excipient
hindered hydrate formation of API at low water contents. Crystalline excipient was unable to control hydrate formation of
API. The character of excipient affects the stability of formulation. Thus, correct selection of excipients for the formulation
can control processing-induced phase transitions and improve the storage stability of the final dosage form.
Published: October 6, 2005 相似文献
18.
Use of the root contact concept,an empirical leaf conductance model and pressure-volume curves in simulating crop water relations 总被引:5,自引:0,他引:5
A simulation model “DanStress” was developed for studying the integrated effects of soil, crop and climatic conditions on
water relations and water use of field grown cereal crops. The root zone was separated into 0.1 m deep layers of topsoil and
subsoil. For each layer the water potential at the root surface was calculated by a single root model, and the uptake of water
across the root was calculated by a root contact model. Crop transpiration was calculated by Monteith's combination equation
for vapour flow. Crop conductance to water vapour transfer for use in Monteith's combination equation was scaled up from an
empirical stomatal conductance model used on sunlit and shaded crop surfaces of different crop layers. In the model, transpirational
water loss originates from root water uptake and changes in crop water storage. Crop water capacitance, used for describing
the water storage, was derived from the slope of pressure-volume (PV) curves of the leaves. PV curves were also used for deriving
crop water potential, osmotic potential, and turgor pressure. The model could simulate detailed diurnal soil-crop water relations
during a 23-day-drying cycle with time steps of one hour.
During the grain filling period in spring barley (Hordeum distichum L.), grown in a sandy soil in the field, measured and predicted values of leaf water and osmotic potential, RWC, and leaf
stomatal conductance were compared. Good agreement was obtained between measured and predicted values at different soil water
deficits and climatic conditions. In the field, measured and predicted volumetric soil water contents (θ) of topsoil and subsoil
layers were also compared during a drying cycle. Predicted and measured θ-values as a function of soil water deficits were
similar suggesting that the root contact model approach was valid.
From the investigation we concluded: (I) a model, which takes the degree of contact between root surface and soil water into
account, can be used in sandy soil for calculation of root water uptake, so that the root conductance during soil water depletion
only varies by the degree of contact; (II) crop conductance, used for calculation of crop transpiration, can be scaled up
from an empirical single leaf stomatal conductance model controlled by the level of leaf water potential and micrometeorological
conditions; (III) PV curves are usable for describing crop water status including crop water storage. 相似文献
19.
Görres Josef H. Savin Mary C. Neher Deborah A. Weicht Thomas R. Amador José A. 《Plant and Soil》1999,212(1):75-83
The porous soil environment constrains grazing of microorganisms by microbivorous nematodes. In particular, at matric potentials
at which water-filled pore spaces have capillary diameters less than nematode body diameters the effect of grazing, e.g. enhanced
mineralization, should be reduced ('exclusion hypothesis') because nematodes cannot access their microbial forage. We examined
C and N mineralization, microbial biomass C (by fumigation-extraction), the metabolic quotient (C mineralization per unit
biomass C), nematode abundance, and soil water content in intact soil cores from an old field as a function of soil matric
potential (−3 to −50 kPa). We expected, in accordance with the exclusion hypothesis, that nematode abundance, N and C mineralization
would be reduced as matric potential decreased, i.e. as soils became drier. N mineralization was significantly greater than
zero for −3 kPa but not for −10, −20 and −50 kPa. Microbial biomass C was less at −50 kPa than at −10 kPa, but not significantly
different from biomass C at −3 and −20 kPa. The metabolic quotient was greatest at −50 kPa than any of the other matric potentials.
From the exclusion hypothesis we expected significantly fewer nematodes to be present at −50 and −20 kPa representing water-filled
capillary pore sizes less than 6 and 15 μm, respectively, than at −3 and −10 kPa. Microbivorous (fungivorous+bacterivorous)
nematode abundance per unit mass of soil was not significantly different among matric potentials. Body diameters of nematodes
ranged from 9 μm to 40 μm. We discuss several alternatives to the exclusion hypothesis, such as the 'enclosure hypothesis'
which states that nematodes may become trapped in large water-filled pore spaces even when capillary pore diameters (as computed
from matric potential) are smaller than body diameters. One of the expected outcomes of grazing in enclosures is the acceleration
of nutrient cycling.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
20.
I. M. Piskarev V. A. Ushkanov N. A. Aristova P. P. Likhachev T. S. Myslivets 《Biophysics》2010,55(1):13-17
It has been shown that the redox potential of water saturated with hydrogen is −(500–700) mV. The time of the establishment
of the potential is 24 h. The potential somewhat increases with increasing volume of hydrogen introduced to a reservoir with
water and practically does not depend on the presence of additions in water, provided these additions are not reduced by hydrogen.
The pH value of water does not change after the addition of hydrogen. In a glass vessel with a metallic cover resting on the
side, no decrease in potential during the 2.5-month storage was observed. In plastic bottles, the content of hydrogen decreased;
on storage for more than two weeks, it disappeared almost completely, and as a result, the potential increased after storage
for three to four weeks to a level near zero. In an open vessel, the potential remained negative for two days. 相似文献