The mature plant cells have large vacuoles in the center, which are filled with a solution with a certain osmotic potential, so the infiltration
Water potential in plant cells
The potential is certainly one of the components of the cell's water potential. It is the decrease in the water potential of the cell due to the presence of solute in the vacuole. It is also called the solute potential and is represented by ψs. Since the water potential of pure water is the largest and is specified as 0, the water potential of any solution is smaller than that of pure water, and the osmotic potential is higher than that of pure water, all of which are negative. When the cells are in a high osmotic potential solution, the cells absorb water and expand in volume. Due to the different flexibility of the cell protoplasts and cell walls, the former is larger than the latter, so the water absorption of the cells will definitely cause the cells to produce a kind of protoplasts on the cell wall. The external thrust, that is, swell pressure. In turn, the cell wall also exerts a pressure on the cell protoplasts and on the cell fluid. This pressure is the force that causes the water inside the cells to flow outward, which is equivalent to increasing the water potential of the cells. This increase in the water potential of the cell due to the presence of pressure is called the pressure potential and is expressed by ψp. Its direction is opposite to the osmotic potential and is generally positive. The gravitational potential is the force when water is moved downward by gravity and is equal to the opposite force. It is the value that increases the free energy of the cell and increases the water potential, expressed as a positive value. The gravitational potential depends on the height of the water (h), the density of the water (Ïw) and the acceleration of gravity (g) in the reference state, ie, calculated by the formula ψg=Ïwgh. When the water is 1 m high, the gravitational potential is 0.01 MPa. In addition, the cytoplasm is a hydrophilic colloid that binds a certain amount of water, which is equivalent to reducing the water potential of the cells. The value of the water potential decrease due to the hydrophilicity of the colloidal substance (liner) of the cell is called the lining potential of the cell, and is expressed by ψm. Therefore, the water absorption of plant cells is determined not only by the osmotic potential of the cells, but also by the pressure potential of the cells, and also by the lining potential of the cells. The water potential of a typical plant cell should consist of three parts, namely ψw=ψs+ψp+ψm.
Water potential gradient
Water always leads from a higher water potential to a lower water potential. During the daytime, the water in the soil is harvested by the plant, reaches the blade through the conduit in the vascular bundle, and is lost to the air through the pores (ie, transpiration), because the water potential in the atmosphere is very low, and it is in the atmosphere and soil. A water potential gradient is formed between the plants. When the constant state is reached, the gradient of each stage is proportional to the transport resistance of that stage. Generally, the greatest resistance is the resistance of the pores, and the transport resistance of the xylem in the stem is small. Thus the largest water potential drop occurs inside and outside the pores. When the soil is dry, the water potential decreases, and the water transport resistance in the soil increases. The water potential difference between the root and the soil body increases, and the water potential in the plant decreases. At about -1.5 MPa, wilting occurs.
Water potential measurement The water potential in plants reflects the relationship between water supply and demand, that is, the severity of water stress. The most commonly used method for determining the water potential ( ψ W) is: 1 pressure chamber method, the leaves or branches to be tested are placed in a pressure chamber, and the petiole or stem is clamped with a rubber or plastic plug. When the pressure chamber is pressurized to a slight excess of its water potential, the water flows out of the conduit to form water droplets; common measuring instruments are the PSI plant water pressure chamber and the ARIMAD 3000 plant water potential pressure chamber in Israel. 2 fine liquid flow method (or dye method); 3 thermocouple dry wet bulb hygrometer method or dew point hygrometer method, determine the partial pressure of water vapor in the air balanced with the measured material, the water potential is 0 when saturated with water vapor The water potential is calculated; the common instrument is the PSYPRO dew point water meter. In addition, Australia's ICT has now developed a new instrument for in situ measurement of plant stem water potential, model PSY1 in situ stem water potential meter, PSY1 in situ stem water potential meter is a self-contained independent instrument, Used to measure stem water potential. It can continuously record (with a time interval of 10 minutes) changes in plant water status, directly reflecting the energy required by the plant to obtain water or the pressure on the plant. The PSY1 in-situ stem water potential meter is a very powerful tool that integrates all surrounding environmental parameters affecting plants, such as solar radiation, temperature, humidity, wind speed and water supply, into a continuously variable variable. When the SFM1 stem flow meter and the DBL60 plant stem growth meter are combined at the same time, a complete plant water relationship and plant growth potential can be obtained, thereby continuously monitoring the ecological physiological transformation time. It provides a more convenient and non-invasive measurement method for measuring plant water potential, which provides greater convenience for researchers.
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