Selected Methods Of Measuring Drought Stress In Plants
(Selected!) Methods of measuringdrought stress in plantsSilvia B. KikutaDepartment of Integrative BiologyInstitute of BotanyUniversity of Natural Resources andApplied Life Sciences, Vienna
ContentsDefinition of stress / strainDefinition of drought stressResistance mechanisms of plantsMorpho-anatomical traitsDefinition of water potential (Ψ)Total water potential (Ψt) and componentsTechniques of measuring plant water statusPressure chamberThermocouple psychrometryPlant water contentPressure-volume (pV) curvesOsmotic adjustmentElastic adjustmentWater use efficiency
Definition of stress / strain(Larcher 2003)Stress is considered to be a significant deviation fromoptimal conditions of lifeStress causes changes and responses at all functionallevels of the organismTerm stress (stress factor, stressor) indicates the eventTerm strain indicates the state (stress response, stateof adaptation) evoked within an organism
Drought stressToo little water is available in a suitable thermodynamic stateDemand exceeds the supply of water Reasons:Soil drynessInadequate water uptake by plants in shallowsoilsOsmotic binding in saline soilsHigh evaporationDrought stress develops slowlyIntensity increases with timeStress level, time scale crucial!
Drought resistanceCapacity of plants to withstand periods of drynessSerious terminological problems with the term droughtresistance!Difference of drought resistance inNatural vegetationSpecies conservation, plant survivalCultivated plantsSustainable and economically viable plantproduction
How plants cope with drought stressDifferent survival mechanisms of plants atdry sites:1) Drought escape2) Dehydration avoidance3) Dehydration tolerance
Drought escapeDrought periods must occur at a predictable timeImportant strategy for mediterranean and monsoon climates,not efficient for Central Europei) Temporal:Whole life cycle or physiologically active phase shifted toperiods without stresse.g. winter wheat, winter barley – well suited for theirplace of origin (Iraq, Iran; summer drought)Selection of early-ripening genotypesii) Spatial:Development of water-storing belowground organse.g. geophytes
Drought (dehydration) avoidanceTissues are sensitive to dehydration must maintainhigh water potentials as long as possible2 groups of drought avoiders:i) Water saversConserve waterii) Water spendersAbsorb water so fast as to meet transpirationallossesAnatomical and morphological traits help the plant toincrease water uptakereduce water spending
Morpho-anatomical traits(A)Water uptake is improved(1)(2)extensive root system with large active surface areashoot/root ratio shifted in favour of the roots(B)Water loss is ation reduced (timely stomatal closure)smaller but more densely distributed stomatathick cuticleepicuticular waxesleaf colour (yellow, glaucous)white hairs on leavesleaf angleleaf rollingplant senescenceleaf senescenceleaf shedding
Drought (dehydration) toleranceSpecies-specific capacity of protoplasma to toleratesevere water lossPhysiological processesdehydration levelsproceedevenathighTolerance mechanisms take over when tissues are nolonger protected by avoidance mechanismsDrought tolerance usually found(drought avoidance in mesophytes)inxerophytesTolerance aims at plant survival rather than plantgrowth
Definition of water potential (Ψ)Quantifies the water status in plant systemsChemical potential of water (µw) indicates the capacity ofwater to do workIt is not feasible to measure the chemical potentialabsolutely potentials are referenced to a standardstate (µ w) set equal to 0, and calculated by difference(J mol-1)By convention, water in this standard state ispureat atmospheric pressureat same temperature and vertical height as thewater in the system of interest
Definition of water potential (Ψ)Conversion of chemical potential of water (µw) towater potential (Ψ) by dividing µw by the partialmolal volume of water (Vw; m3 mol-1):Ψ oWµW µVWSince J mol-1 N m mol-1, water potential can beexpressed in terms of pressurePascal (Pa) appropriate SI unit for pressure1 MPa 106 pascals 10 bar
Total water potential (Ψt)Central parameter of plant water relationsDescribes the energy state of water at a givenpoint in the soil-plant-atmosphere continuum(SPAC)Plants may be considered as conduits for waterbetween humid soil and dry airWater flows from points where it has more energycontent (higher water potential) to those with lessenergy content (lower water potential)
Components of total water potential (Ψt)2 equations describe the influencecomponents on total water potentialDEMANDS come fromcontinuum (equation 1):theofvarioussoil-plant-atmosphere(-) Ψt (-) ΨS (-) ΨG (-) ΨFwhereΨS substrate (soil) potentialΨG gravitational potentialΨF frictional potential
Components of total water potential (Ψt)RESPONSE mechanisms in the plant adjust total waterpotential to the value preset by potential losses in thesoil-plant-atmosphere continuum (equation 2):(-) Ψt (-) Ψo ( ) ΨpwhereΨo osmotic potentialΨp pressure potential
Measurement of total water potential (Ψt)A) Pressure Chamber TechniqueB) Thermocouple Psychrometer Method
A) Pressure Chamber TechniqueAdvantages Method issimplefastaccuratesuitable for use in the fieldDisadvantages Method isdestructivematerial-consuming
A) Pressure Chamber TechniqueMeasurement procedurePlant organ (leaf, leaf strip, twig, root) cleanly cut fromthe plantImmediately placed in the chamber head with the cut endprotruding through a flexible rubber gasket sealing thechamberCompressed air is led slowly into the chamber thusincreasing the pressure inside gradually
A) Pressure Chamber TechniqueMeasurement procedure (cont.)Pressure applied until water begins to return to the cutsurfaceThis 'balance pressure' required to force water back tothe cut end is equal in magnitude but opposite in sign toxylem tension that existed in the intact plant organ priorto excision
Pressure Chamber (Plant Water Status Console)3000 Series, SOILMOISTURE, Santa Barbara,California, USA (http://www.soilmoisture.com)
(A)(B)(D)(E)(F)(G)(L)(M)(P)(S)release valvestereo microscopelidinlet valvefoilsealing (rubberstopper)light sourcemanometersamplepressure chambermade from steel
A) Pressure Chamber TechniquePrecautions:1) Prevent water loss between sampling andmeasurement(cover the plant organ prior to excision with aplastic bag or aluminium foil to minimize waterloss)2) Prevent condensation of water on the samplebefore measurement3) Avoid recutting of petioles, twigs
A) Pressure Chamber TechniquePrecautions (cont.):4) Prevent evaporative water loss into the pressurechamber by keeping the sample enclosed in a plasticbag during measurement5) Increase pressure slowly (0.003 to 0.005 MPa s-1) toprevent large temperature changes in the chamber6) Identify endpoint accurately7) Use soft, elastic rubbers to avoid the crushing ofpetioles or twigs
B) Thermocouple Psychrometer MethodMeasurement principle:Total water potential may be determined bymeasuring relative vapour pressure (equal torelative humidity) of water in the atmospheresurrounding and in equilibrium with the sample
B) Thermocouple Psychrometer MethodMeasurement principle (cont.):Total water potential is related to relative vapourpressure by following equation:ψ RT elnVW eowhereΨRTVwe/eo water potential (Pa)universal gas constant (8.314 J mol-10 K -1)absolute temperature (K)molar volume of water (1.8 x 10-5m3 mol-1)relative humidity expressed as a fraction
B) Thermocouple Psychrometer MethodMeasurement principle (cont.):Tissue sample is sealed in a small chamber containing a(Peltier) thermocoupleAfter an equilibration period a cooling current is applied tothe thermocouple in order to condense water on the junctionAmount of condensed water is proportional to tissue waterpotentialWater is allowed to evaporate causing a change inthermocouple outputOutput is calibrated for water potential, using NaCl solutions
B) Thermocouple Psychrometer MethodAdvantages Method is non-destructive Continuous measurements of plant waterstatus of intact plants or organs are possible Long-time observations during plant growthor tissue dehydration can be done
B) Thermocouple Psychrometer MethodDisadvantagesMain limitations when applied in field or greenhouse: Sensors are extremely sensitive to wind and radiation Very (!) careful isolation is a prerequisite to obtainreliable results Method is quite time-consuming (slow equilibrationbetween sample and air in the thermocouplechamber)
2) Measurement of osmotic potential (ΨO)A) Direct approach:Freeze-thawed or heat-killed plant tissue(e.g. leaf discs or leaf strips) press sap(Attention: Dilution by apoplastic water)measured with Vapor Pressure OsmometerB) Indirect approach:Pressure-volume (pV) curve technique
3) Measurement of pressure potential (Ψp)Indirect approach: Difference between total water potential andosmotic potential:( ) Ψp (-) Ψt - (-) Ψo Pressure-volume (pV) curve technique
Plant water contentDescribed by:Relative water content (R)( FW DW )R ( SW DW )FW:SW:DW:Fresh WeightSaturation WeightDry Weight
Relative water contentVery relevant physiological measure of plant water deficitEstimates current water content of the sampled leaftissue relative to the maximal water content it can hold atfull turgidityNormal values of R range between 98% in turgid andtranspiring leaves to about 40% in severely desiccatedand dying leavesIn most crop species typical R at about wilting is around60 % to 70 %
Relative water contentMeasurement protocolAll components of leaf water relations change duringthe day as irradiance and temperatures change!For 2 hours at and after solar noon, the change isvery smallTime “window” for leaf sampling, unless a daily curveof R is of interest
Relative water contentMeasurement protocol (cont.)4 to 6 top-most fully expanded leaves taken fromdifferent plants (of one treatment, genotype)Samples placed in pre-weighed airtight (possiblyalso oven proof) vialsVials immediately placed in a picnic cooler (ca. 10 to15oC)
Relative water contentMeasurement protocol (cont.)In the lab vials weighed to obtain sample freshweightThen samplesimmediately hydrated to full turgidity (saturation)weighed to obtain saturation weightoven dried at 80oC for 24hweighed (after being cooled down in a desiccator) todetermine dry weight
Plant water contentDescribed by:Water saturation deficit (WSD)( SW FW )WSD ( SW DW )WSD 1 R
Relative drought indexIndex compares actual water saturation deficit (WSDact)with critical threshold value for water saturation deficit(WSDcrit):RDI WSDact / WSDcritRDI Rcrit / RactRDI Ψact / ΨcritCritical threshold may refer to first visible signs of droughtinjuriesBy comparing individuals of the same species in differentlocations information on severity of drought can be gained
Pressure-volume (pV) curvesDescribe the relationship between total water potential(Ψt) and relative water content (R) of living organsEquationΨo * V constantsays that the product of osmotic potential and volumeof solution should be a constant for any given amountof osmotically active solutes in an ideal osmotic systemDecrease in cellular pressure with progressive waterloss is related to decrease in volume
Pressure-volume (pV) curvesLinear relationships may be obtained by converting eitherpotential or water content to its reciprocalΨo 1 / V * constantV 1 / Ψo * constant
Typ I Transformation (ψt vs. R-1)ψtψoψo(sat)ψo(tlp)Total Water PotentialOsmotic PotentialOsmotic Potential at full saturationOsmotic Potential at turgor loss point
Typ II Transformation (1/ψt vs. R)1234561 / Osmotic potential at full saturation1 / Osmotic potential at turgor loss pointRelative water content at turgor loss pointRelative symplast volumeTotal water volume at saturationRelative apoplast volume
Day courses ofTotal water potentialTurgor potentialRelative water content
Day courses ofTotal water potentialTurgor potentialRelative water content
Pressure-volume (pV) curves (Typ I transformation) of two water regimes ofTriticum durum (Probstdorfer Grandur). Controls: Plants were grown at80% of soil water saturation. Stress variant: Plants were grown at 33% ofsoil water saturation. 63 days of drought stress duration.
Elastic adjustmentEpsilon is the elastic modulus for plant cellsIs a proportionality factor for change in Ψp that occurswhen cell volume changesCan be estimated from pressure-volume relationship:ε [ Ψp / R] * R ΨpRchange in average turgor pressure of the tissuerelative water contentEpsilon is high in tissues with rigid cell walls: greater dropin Ψp per unit change in R occurs than in more elastictissues
Turgor adjustment as displayed by pressure-volumecurves from control ( ) and drought stressed ( ) durumleaves. A: area difference caused by osmotic adjustment.B C: area difference caused by elastic adjustment.
Water use efficiency of productivity (WUEP)Informative for ecological, agricultural, forestry purposesDefined as:WUEP [g DM .kg–1Organic dry matter productionH2O] Water consumptionWater requirement per unit of dry mass produced variesamong species and varietiesStrongly dependent on individual state of plantdevelopment, plant density, environmental conditions,water supply, evaporation
Water use efficiency of productivity (WUEP)Selection of species and varieties appropriate for growingconditions in dry areas possible amount of irrigationwater regulatedWater use efficiencydecreases with increased water useincreases with increased dry matter productionA plant adopting to drought by stomatal closure (watersaver) increases its WUE by decreasing transpiration, butit simultaneously decreases efficiency by lowering itsphotosynthetic rate
Drought resistance and crop yieldPassioura proposed a general description of yield andwater use which is widely accepted by agronomists:Yield T x WUE x HIwhereT WUE HI total seasonal crop transpirationcrop water use efficiencycrop harvest index (ratio of economic yieldto total aboveground biomass)
Methods of measuring drought stress in plants Silvia B. Kikuta Department of Integrative Biology . Techniques of measuring plant water status Pressure chamber Thermocouple psychrometry Plant water content Pressure-volume ( pV) curves . Tolerance aims at plant survival rather than plant growth.
and Mitigation Unit (DMMU). However, the country has no drought plan, drought policy, legislation and institutional framework to strategically facilitate drought management. The National Drought Plan is intended to contribute to the protection of Zambia’s land from over-use and drought for
Monterey Peninsula Water Management District Agenda U.S. Bureau of Reclamation Overview of Drought Contingency Plan (DCP) development steps and elements Participating Local Agencies Drought Monitoring Vulnerability Assessment Regional Drought Response Actions Regional Drought Mitigation Measures
Jun 07, 2018 · %3*3 -./01"( 2/&'(/. 456#7('8#,!Assessment of current drought conditions and currentdrought impacts The U.S. Drought Monitor is NOTa model The map is made manually each week based off the previous map!The U.S. Drought Monitor is NOTinterpreting just precipitation The U.S. Drought Moni
and the response to biotic or abiotic stresses, such as salinity, drought, low temperature, and nutrient deficits [37]. 5.1. Roles of bHLH in Drought Tolerance Drought is a major abiotic stress that limits plant growth and survival, crop quality, and production. bHLH genes respond to drought stress and enhance plant tolerance to water
The purpose of the Zuni Drought Contingency Plan is to provide the Zuni Tribe with a policy and system for monitoring, assessing, and mitigating Zuni drought conditions, while supporting the sovereignty of the Zuni tribal government with respect to other governmental agencies when addressing drought situations on Zuni lands.
Stress genes were selected whose expression level change was twofold under drought conditions. The 143 non-stress genes were selected on the basis of their expression level change being between 0.33. Eight other O. sativa genes were selected because they were shown to be induced by abiotic stress (cold, drought, osmotic stress) in our other .
per IEC 60751 Class A Measuring deviation of the transmitter per IEC 60770 0.25 K Total measuring deviation according to IEC 60770 Measuring deviation of the measuring element the transmitter Measuring span Minimum 20 K, maximum 300 K Basic configuration Measuring range 0 . 150
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