Methods to determine Plant water potential.pptx

This ppt briefs about different methods to determine plant water potential and their advantages and disadvantages

1. Methods to determine Plant water potential Presented By Rajat Kumar (F-24-55-M) To Dr. Nitin sharma (Assistant professor)

2. PRESSURE CHAMBER A pressure chamber is a device that measures a plant water potential by applying air pressure to a leaf or stem sample and measuring the pressure required to force water out of the cut surface . The amount of pressure required is equal to the plant water potential which is a measure of the tension in the plant’s water The pressure is measured in negative pressure units such as bars or Mpa . A higher pressure unit indicates a higher level of tension or water stress. A sealed chamber is used to enclose a plant sample and pressure is gradually increased until water starts to come out of the xylem . The pressure is then used to estimate the water potential .

3. PRINCIPLE Water in the plant is pulled with a suction force as water evaporates from the leaves. Water within the plant mainly moves through very small inter-connected cells, collectively called xylem, which are essentially a network of pipes carrying water from the roots to the leaves. The water in the xylem is under tension. As the soil dries or humidity, wind or heat load increases, it becomes increasingly difficult for the roots to keep pace with evaporation from the leaves. This causes the tension to increase. Under these conditions you could say that the plant begins to feel high pressure. Since tension is measured, negative values are typically reported. An easy way to remember this is to think of water stress as a “deficit”. The more the stress the more the plant is experiencing a deficit of water. The scientific name given to this deficit is the water potential .

4. ADVANTAGES Optimizing Irrigation – Farmers can use the pressure chamber to determine when plants are water stressed and how much water they need . Direct measurements – The pressure chamber allow direct and precise measurements of plant water status . Portable – The pressure chamber is lightweight and portable making it easy to use in the field. Reference technique – The pressure chamber method is used as reference to validate and calibrate other techniques .

5. CELL PRESSURE PROBE A cell pressure probe is a micro manometer that measure and manipulates the hydrostatic pressure of the plant cells . It is used to study the hydraulic architecture of plant tissues . And how they response to water stress. It measures cell turgor pressure (P), hydraulic conductivity ( L p ), and volumetric elastic modulus (ε) in higher plant cells. This technique permits volume changes, ΔV, and turgor pressure changes, ΔP, to be determined with an accuracy of 10 −5  to 10 −6   μl and 3 to 5·10 −2  bar, respectively .

6. PRINCIPLE The main principle of the new method is the same as the pressure probe developed by Zimmermann and Steudle in which pressure is transmitted to a pressure transducer by means of an oil-filled capillary introduced into the cell. In order to use the pressure probe for small tissue cells, the effective compressible volume of the apparatus has to be sufficiently small in comparison to the volume of the cell itself. This is achieved by accurately fixing the oil/cell sap boundary in the very tip of the microcapillary by means of an electronic feedback mechanism, so that the effective volume of the apparatus is reduced to about 2 to 10% of the cell volume and by this errors can be excluded.

7. ADVANTAGES Versatile – Can be used to measure manipulate and record plant cell hydrostatic pressure . Can study cell wall elasticity . Can control guard cell turgor pressure. Can microinject fluorescent probes. Can map turgor pressure .

8. OTHER METHODS PSYCHROMETRIC METHODS – Involves equilibrating tissue with air in a closed chamber and estimating the vapour pressure using wet and dry thermocouples . DEW POINT POTENTIAMETER – Calculates water potential from the measured dew point and sample temperature XYLEM PRESSURE PROBE – Estimate mild xylem tensions .

9. THANK YOU