Experiments for the determination of the water potential of plant tissues

Summary

The water status of plant tissues can be expressed in terms of water potential (representing the energy level of water). The lower the water potential of a plant tissue, the greater its ability to absorb water. Conversely, the higher the water potential, the lower the ability to absorb water and the higher the ability to supply water to other, more dehydrated cells. Different plants, different parts, different ages and different periods of the tissue, water potential have certain differences, soil conditions and atmospheric conditions and other external factors on the water potential of plant tissues also have a great impact, so it should be studied in depth, in order to study the status of the plant's water potential as well as the development of the physiological indicators of irrigation to lay the foundation for the experiment lies in the use of a small stream of liquid flow method to determine the water potential of the plant tissue, and the preliminary observation of its changes.

Operation method

Experiments for the determination of the water potential of plant tissues

Principle

Water potential represents the chemical potential of water. Like an electric current that moves from a high potential to a low potential, water flows from a high water potential to a low water potential. The direction of water movement between plant body cells and between the plant body and its environment is determined by the difference in water potential. When a plant cell or tissue is placed in a solution, if the water potential of the plant cell is less than the osmotic potential (solute potential) of the solution, the tissue absorbs water and makes the solution concentration larger, and vice versa, the water in the plant cell outflows and makes the solution concentration smaller. If the water potential of the plant tissue and the osmotic potential of the solution is equal, the two water to maintain dynamic equilibrium, so the external solution concentration is unchanged, the osmotic potential of the solution is equal to the measured plant water potential. You can use the principle that the specific gravity of the solution concentration is different to determine the change of the solution concentration before and after the test. Then calculate the osmotic potential according to the formula.

Materials and Instruments

Test tubes Capillary pipettes Scissors Pipettes Tweezers Hypomethyl blue.

Move

I. Instrumental drugs

Test tube, capillary pipette, scissors, pipette, tweezers, hypomethyl blue.

Experimental Procedure

1. First prepare a series of sucrose solutions of increasing concentration (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 M). Ten milliliters of each of the above solutions were taken into eight test tubes, each tube was stoppered and numbered. The tubes were arranged in a row in numbered order and placed on a test tube rack as a control group.

2. 8 test tubes were numbered and placed on the test tube rack in the same order as the test group. Then 4 ml of solution was taken from each tube in the control group and transferred into the same numbered test tubes of the test group and then each tube was stoppered.

3. With scissors, cut cabbage leaves or potatoes into small pieces of equal size, 40 pieces, add an equal number of pieces to each test tube of the test group, plug the stopper and leave it for 30 minutes, shaking it several times during this period of time, and when the time is up, add a small amount of hypoxymethylene blue powder to each test tube and shake it, at which time the solution turns blue.

4. Use a capillary pipette to draw up a little of the colored liquid from each test tube of the test group in turn, and then reach into the middle of the liquid of the same numbered test tube of the control group and slowly put in a drop of the blue test solution and observe the direction in which the small liquid stream moves. If the small stream of liquid moves upward, it means that the solution has been washed out by drawing water from the cellular fluid and the specific gravity is smaller than it was, and if the small stream of liquid moves downward, it means that the cells have drawn water from the solution, and the solution has become thicker and the specific gravity has become greater. If the stream does not move, the density of the test solution is equal to that of the control solution, i.e., the water potential of the plant tissue is equal to the osmotic potential of the solution. Record the concentration of sucrose solution in the test tube where the small stream of liquid does not move.

5. After half an hour, repeat the measurement once.

Calculate the value of water potential: D = P (bar)

P=-RTiC

P: Indicates the osmotic potential. Expressed as a negative value of bar (1.013 bar equals 1 atm)

R: denotes the gas constant 0.083-Lbax/M-K

T: indicates the absolute temperature: i.e. 273°C + t° (experimental temperature at that time)

i: indicates the dissociation coefficient: sucrose is equal to 1

c: denotes the gram molecular concentration of the isotonic solution.

So: p = -0.083 x (273°C + t°) x C

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