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Leaf pressure-volume curve parameters

Lawren Sack, Jessica Pasquet-Kok
Contributors : LawrenSack1762 points  Adrienne Nicotra2721 points 


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Overview

This protocol explains how to make measurements of basic pressure volume parameters using simple equipment, with a spreadsheet tool to facilitate the analysis.

Background

This protocol explains two methods (“bench dry method”, “squeeze method”) to estimate the parameters of pressure-volume (PV) curves , including osmotic potential at full turgor and at the turgor loss point, relative water content at turgor loss point, modulus of elasticity at full turgor, and relative and absolute capacitances at full turgor and at zero turgor (Koide et al., 2000; Sack et al., 2003). The bench dry method is most traditional, and allows measurement of a set of 5-10 leaves at once, but requires a substantial time allocation (> 24 hours), whereas the squeeze method allows focused measurement of a single leaf in 2-3 hours.

Materials/Equipment

  • Analytical balance (to 0.001 g)
  • Razor blade
  • Fan (bench dry method)
  • Pressure chamber (Plant Moisture Stress, Model 1000, Albany, Oregon, USA)
  • Whirl-Pak bag (Whirl-Pak, Nasco, Fort Atkinson, Wisconsin, USA)

Units, terms, definitions

ψleaf, leaf water potential (MPa) πft, osmotic potential at full turgor (MPa) πtlp, osmotic potential at the turgor loss point (MPa) RWCtlp, relative water content at turgor loss point (%) ε, modulus of elasticity at full turgor (MPa) Cft, relative capacitance at full turgor (MPa-1) Ctlp, relative capacitance at zero turgor (MPa-1) Cft*, absolute capacitance per leaf area, at full turgor (g · m-2 · MPa-1) Leaf water potential equals osmotic potential plus pressure potential (due to turgor pressure). Below the turgor loss point, leaf water potential equals leaf osmotic potential. Thus the inverse of water potential declines linearly with RWC below the turgor loss point (Tyree & Hammel, 1972). Plotting the inverse of water potential against RWC allows determination of the turgor loss point as the point of transition between linear and nonlinear portions. πft is estimated by extrapolating the straight-line section to 100% RWC. The bulk modulus of elasticity (ε) estimates cell wall rigidity averaged across the leaf, and is determined from the slope of the pressure potential between full turgor and turgor loss point. The relative capacitance is calculated as the slope of RWC versus leaf water potential, and can be determined between full turgor and turgor loss point, and also separately, below turgor loss point. Absolute capacitance per leaf area can be estimated as relative capacitance multiplied by the mass of water per leaf area.

Procedure

Bench dry method: Pressure-volume curve parameters are determined by progressively drying leaves on a laboratory bench with a fan (optional), and measuring leaf water potential and leaf mass at intervals (ψleaf):

  1. Let shoots rehydrate overnight (optional)
  2. In the morning, remove leaf from shoot by cutting at base of petiole with a razor blade
  3. Measure or trace leaf for leaf area determination (optional, for determination of absolute capacitance per leaf area)
  4. Put the leaf in a Whirl-Pak bag
  5. Measure leaf water potential (ψleaf) with a pressure chamber.
  6. Weigh the bagged leaf using an analytical balance.
  7. Take the leaf from the plastic bag and let dry on the bench (optional: use fan to dry leaf faster, with leaf taped to a line or held in a frame).
  8. Let leaf equilibrate for 10 min in a Whirl-Pak bag.
  9. Repeat steps 4 to 7, attempting to capture ψleaf intervals of 0.2-0.3 MPa, until you achieve ψleaf of -3.0 MPa
  10. Weigh the Whirl-Pak bag without the leaf, dry the leaf in an oven at > 70°C for at least 48 h before dry mass determination.
  11. Use attached “Pressure volume curve analysis” spreadsheet to analyze data (below).

Squeeze method: Pressure-volume curve parameters are determined by squeezing water out of the leaf using a pressure chamber to achieve different leaf water potential and weighing.

  1. Let shoots rehydrate overnight (optional)
  2. In the morning, remove leaf from shoot by cutting at base of petiole with a razor blade
  3. Measure or trace leaf for leaf area determination (optional, for determination of absolute capacitance per leaf area)
  4. Put the leaf in a Whirl-Pak bag
  5. Measure first leaf water potential (ψleaf1st) with a pressure chamber.
  6. Weigh the bagged leaf using an analytical balance.
  7. Replace bagged leaf in pressure-bomb and increase the pressure until you reach ψleaf1st and then increase pressure by 0.2 MPa and note this pressure. Hold the pressure at this level while dabbing the petiole until there is no more water coming out.
  8. Weigh the bagged leaf using an analytical balance.
  9. Repeat steps 7-8, until you achieve ψleaf of -3.0 MPa.
  10. Weigh the Whirl-Pak bag without the leaf, dry the leaf in an oven at > 70°C for at least 48 h before dry mass determination.
  11. Use attached “Pressure volume curve analysis” spreadsheet to analyze data (below).

Other resources

Notes and troubleshooting tips

  • If the petiole is too fragile, you can put parafilm around it at the beginning of the measurement. Do not forget to weigh the parafilm at the end of the measurement.
  • If piece of leaf breaks, keep it inside the plastic bag, note when this occurred and do not forget to put all the pieces in the oven. Then, deduct the dry mass of the piece from the mass values after the breakage occurred.
  • Note that the PV_analysis spreadsheet tool fits lines by standard major axis (Model II regression) so that either variable can be predicted from the other and the parameter calculation is more robust.

Links to resources and suppliers

Measurement of leaf water potential; see tutorial videos on Plant Moisture Systems (PMS) web site Plant Moisture Stress, Model 1000, Albany, Oregon, USA Whirl-Pak bag (Whirl-Pak, Nasco, Fort Atkinson, Wisconsin, USA)

Literature references

Koide R.T., Robichaux R.H., Morse S.R. & Smith C.M. (2000) Plant water status, hydraulic resistance and capacitance. In: Plant Physiological Ecology: Field Methods and Instrumentation (eds R.W. Pearcy, J.R. Ehleringer, H.A. Mooney, & P.W. Rundel), pp. 161-183. Kluwer, Dordrecht, the Netherlands. Sack L., Cowan P.D., Jaikumar N. & Holbrook N.M. (2003) The 'hydrology' of leaves: co-ordination of structure and function in temperate woody species. Plant, Cell and Environment, 26, 1343-1356. Tyree M.T. & Hammel H.T. (1972) Measurement of turgor pressure and water relations of plants by pressure bomb technique. Journal of Experimental Botany, 23, 267-&.

Health, safety & hazardous waste disposal considerations

 


Contributors to this page: Admin36802 points  , LawrenSack1762 points  , Adrienne Nicotra2721 points  and Neil Moreton .
Page last modified on Tuesday 05 of April, 2011 20:55:34 EST by Admin36802 points . (Version 16)