Determination of plant tissue water potential

Water potential is the potential energy that drives the movement of water through an organism. Water always moves from a higher to a lower water potential in the soil-plant-atmosphere continuum. Under conditions such as drought and salinity, some plants often actively accumulate solutes within their cells to lower their osmotic potential. Reduce the water potential, increase the water absorption capacity; the height of the water potential in the plant reflects the water supply and demand, that is, the severity of water stress. Mastery of small liquid flow method to determine the basic method of plant tissue water potential.

Principle

The basic principle of the determination of plant tissue water potential is that when the plant tissue is in contact with the external fluid, if the water potential of the plant tissue is lower than the osmotic potential of the external fluid (solute potential), the tissue absorbs water, its weight increases, and the concentration of the external fluid becomes larger; on the contrary, the tissue loses water, its weight decreases, and the concentration of the external fluid becomes smaller; if the two are equal, then the exchange of water maintains a dynamic equilibrium, and the weight of the tissue and the concentration of the external fluid remain unchanged. According to the change of tissue weight or external fluid concentration, we can determine the concentration of the solution with the same water potential as the plant tissue, and then calculate the osmotic potential of the solution according to the formula, which is the water potential of the plant tissue.

Operation method

Determination of plant tissue water potential

Principle

The basic principle of the determination of plant tissue water potential is that when the plant tissue is in contact with the external fluid, if the water potential of the plant tissue is lower than the osmotic potential of the external fluid (solute potential), the tissue absorbs water, its weight increases, and the concentration of the external fluid becomes larger; on the contrary, the tissue loses water, its weight decreases, and the concentration of the external fluid becomes smaller; if the two are equal, then the exchange of water maintains a dynamic equilibrium, and the weight of the tissue and the concentration of the external fluid remain unchanged. According to the change of tissue weight or external fluid concentration, we can determine the concentration of the solution with the same water potential as the plant tissue, and then calculate the osmotic potential of the solution according to the formula, which is the water potential of the plant tissue.

Materials and Instruments

Material: plant leaves.
Reagents:
①methylene blue solution
② CaCl
2
solution, including 0. 05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40 mol・L
-1
A total of 8 concentrations (sucrose solution can also be used).
Equipment:
① 8 20 mL test tubes;
② penicillin vials 8 with cork;
③ 1 rubber-tipped capillary tube with a curved nozzle;
③ 1 rubber-tipped capillary tube with a curved tip;
⑤ A special test tube rack; ⑤ An area of 0.5~1cm
1 special test tube rack; ⑤ 0.5-1 cm2
⑤ 1 hole punch of 0.5-1 cm 2 in area;
⑤ 1 hole punch with an area of 0.5-1 cm 2; ⑥ 1 insert;
(vii) 1 dissecting needle; (viii) 2 10 mL pipettes
(viii) 1 dissection needle; (viii) 2 10 mL pipettes
(8) 2 10-mL pipettes; (9) 8 2-mL pipettes; (10) 8 0.5-mL pipettes;
⑩ 0.5 mL pipettes.

Move

The basic procedure for determining the water potential of plant tissues can be divided into the following steps:

1. Take 8 dry and clean test tubes (for group A), insert them into the corresponding positions in the test tube rack and number them. Test tubes were added 0.05 ~ 0.40 ^mol・L-1 eight concentrations of _CaCl2 solution of 10 mL each, plugged with the corresponding cork. At the same time, add 2 mL of each of the eight vials of penicillin (group B) with the corresponding concentration of _CaCl2 solution. 2.

2. Select 8~10 pieces of uniform plant leaves, stacked on top of each other, punch 8~10 pieces of leaf rounds with a hole punch, put them into 8 pieces of penicillin vials, immerse the leaves into the solution, cover the stopper tightly, and equilibrate for more than 20 min. Shake the vials several times to accelerate the water balance. 3.

3. After a predetermined time, put 1 small drop of methylene blue solution into each vial of Group B. Shake well and the solution turns blue. 4.

4. Use a capillary with a curved tip to draw a small amount of colored solution in a vial of group B, insert it into a test tube of group A containing the same concentration of solution, place the tip of the capillary with a curved tip in the middle of the solution, gently squeeze out a small drop of the colored solution, and carefully remove the capillary (do not agitate the colored droplet). Observe the rise and fall of the colored droplet.

If the droplet falls, that the solution concentration becomes larger, plant tissue water absorption, tissue water potential is lower than the osmotic potential of the solution; if the droplet rises, that the corresponding test tube in group A solution concentration becomes smaller, the plant tissue water loss, tissue water potential is higher than the osmotic potential of the solution; if the droplet does not move, it means that the plant tissue neither loss of water nor water absorption, the tissue water potential and the osmotic potential of the solution is equal to the osmotic potential of the solution, the osmotic potential of the solution that is the water potential of the plant tissue. If the droplet drops in the former concentration and rises in the latter concentration, take the average of the two concentrations.

5. Record the rise and fall of colored droplets in different concentrations (Table 2-1), find out the concentration that is equivalent to the water potential of the tissue, and calculate the water potential of the tissue according to the principle formula. Analyze the respective water status.

Caveat

1. The material taken should be in the same place on the plant, and the leaf discs should be punched to avoid the main veins and wounds.

2. the extraction of material and the striking of leaf discs should be done quickly to avoid water loss.

3. the tip of the capillary tube should be bent at a right angle to ensure that the droplets coming out of it are not affected by the downward force.

4. powdered methylene blue can also be used, but methylene blue with water of crystallization is not readily soluble in CaCl2solution, can be dried at 100 ℃ into anhydrous methylene blue powder to use.

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