Determination of osmotic potential of plant cells
The osmotic potential of plant cells mainly depends on the concentration of solutes in the vesicles, and some plants actively accumulate solutes in their cells to reduce their osmotic potential and increase their water absorption capacity. This experiment is mainly to understand the relationship between different tissues and cells in the plant body, the transfer of water between the plant and the environment and the osmotic potential of plant tissues, and to learn the basic method of determining the osmotic potential of plant tissues by the mass-wall separation method.
Principle
The basic principle of the determination of the osmotic potential of plant cells is to put plant tissues into a series of different concentrations of sucrose or mannitol solution, after a certain period of time to achieve osmotic equilibrium, the cells in which the initial plasma wall separation occurs in the solution osmotic potential is equal to the osmotic potential of the cytosol, the solution is known as an isotonic solution, and the concentration of its concentration is known as the isotonic concentration. Practical determination, the initial plasmic wall separation state is difficult to observe directly under the microscope, generally based on the initial plasmic wall separation caused by the concentration of the solution and the neighboring does not cause plasmic wall separation of the average value of the concentration of the solution, isotonic concentration, and calculate the osmotic potential of this solution, that is, the osmotic potential of the cell. Operation method Determination of osmotic potential of plant cells Principle Plant tissues are placed into a series of sucrose solutions of varying concentrations, and over a period of time an osmotic equilibrium will be reached between the plant cells and the sucrose solution. If the cell dehydration reaches equilibrium in a certain solution just at the critical mass-wall separation state, the pressure potential ψρ of the cell is just about to drop to zero. At this time, the osmotic potential of the cytosol ψπ is equal to the osmotic potential of the external fluid ψπ0 , this solution is the isotonic solution of the tissue, and its concentration is the isotonic concentration of the tissue. Knowing the isotonic concentration, the osmotic potential of the cytosol (ψπ) can be calculated according to the formula. In practice, because the critical mass-wall separation state is difficult to observe directly under the microscope, the initial mass-wall separation is generally used as a criterion for determining the isotonic concentration. The volume of cells in the initial state of plasmic wall separation is slightly smaller than that of water absorption and saturation, so the cytosol is concentrated and the osmotic potential is slightly lower than that of water absorption and saturation, and the osmotic potential in this state is called the basal state osmotic potential. Materials and Instruments Onion Purple plantain Onion bulbs Move I. Materials, instrumentation and reagents For more product details, please visit Aladdin Scientific website.
Sucrose Solution Preparation
Microscope Slides and coverslips Thermometer Pointed tweezers Blades Petri dishes Reagent bottles Beakers Volumetric flasks Measuring cylinders Pipettes Straws
1. Materials: onion, purple duckweed, onion bulb.
2. Instrumentation: microscope; slides and coverslips; thermometer; pointed tweezers; razor blades; Petri dishes (diameter 5cm); reagent bottles; beakers; volumetric flasks; measuring cylinders; blotting paper; pipettes etc.
3. reagents and preparation:
1mol-L-1 sucrose solution was prepared: 34.23g of sucrose was weighed, dissolved in distilled water and condensed to 100 ml.
0.03% neutral red solution.
Experimental steps
1. Series of sucrose solution preparation
Nine sets of Petri dishes of 5 cm diameter were taken, numbered and prepared into 0.30-0.70 mol-L-1 sucrose solution as per the table below. 
After adding the reagents in the table, shake well and cover the petri dish with a lid for spare.
2. Peel off the lower epidermis of the test material with tweezers, the size of which should be 0.5cm2. Immediately immersed in different concentrations of sucrose solution, each concentration put 4 to 5 pieces. Record the room temperature at the same time.
In order to facilitate observation, the slices can be stained in 0.03% neutral red for about 5 min, absorb the water, and then immersed in sucrose solution, but if the separation of the plasma wall can be distinguished without staining, it is still preferable not to stain.
3. Epidermal cells were immersed in sucrose solution for 20-30 min, removed and placed on a slide, a drop of the same concentration of sugar solution, covered with a coverslip, observed under the microscope, to determine the concentration that caused more than 50% of the cells to undergo the initial plasma wall separation (i.e., protoplasmic bodies were just separated from the corner of the cell wall), and the number of cells observed in each 1 slide should not be less than 100. If, in two sections of adjacent concentrations, one does not undergo plasmodesmosis and the other undergoes plasmodesmosis in more than 50% of the cells, the average of these two concentrations is its isotonic concentration. The examination may begin with the intermediate concentration.
Calculation of results
According to the measured isotonic concentration and room temperature, the following formula can be used to calculate the osmotic potential of the test solution (ψπ0), which is the osmotic potential of the cells (ψπ).
ψπ = ψπ0 = -i C R T (Mpa)
In the formula: ψπ0 - osmotic potential of the supply solution, unit: Mpa (MPa)
C - isotonic sugar solution concentration ( mol-L-1 )
R - gas constant (0.0083 L-Mpa-mol-1-K-1 )
T - thermodynamic temperature (273 + t °C)
i - dissociation coefficient (sucrose = 1, CaCl2 = 2.60)