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Plant Physiology Chapter 1 Water Physiology
Summary of Chapter 1 of Plant Physiology: The dissimilation of water physiology: the process by which plants decompose complex organic matter in the body into simple inorganic matter to obtain energy.
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Plant Physiology Chapter 1 Water Physiology
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- Outline
Chapter 1 Water Physiology
Glossary
Metabolism: a general term for the chemical changes that sustain life activity processes
Assimilation: A process in which plants absorb simple organic matter from the environment, undergo various chemical changes to form various complex inorganic matter, integrate it into a part of themselves, and convert solar energy into chemical energy and store it in the organic matter.
Alienation: The process by which plants decompose complex organic matter in their bodies into simple inorganic matter to obtain energy.
1. Moisture status and physiological and ecological effects
1.1 Water content of plants
Plant water content: the ratio of the water contained in the plant to the fresh weight of the plant
Relative water content: The actual water content of the plant as a percentage of the water content when the water is saturated (generally, the relative water content is used to determine irrigation needs)
Moisture content difference
Different plants are different, aquatic (>90%) is greater than mesophytic, greater than terrestrial, greater than xerophytic (as low as 6%)
Plants of the same species live in different environments and have different water contents.
Different organs and tissues of the same plant have different water contents
The same organ has different water contents in different growth stages
Parts with strong life activities and high water content
1.2 Moisture presence status
Free water: water that is not attracted by colloidal particles or hydrophilic groups of osmotic substances or has very little attraction and can move freely
Bound water: Water that is attracted to the hydrophilic groups of colloidal particles or osmotic substances and is firmly bound to the surroundings and cannot move freely.
Free water/bound water is one of the physiological indicators to measure the metabolism and resistance of plants.
Characteristics of bound water: does not participate in metabolism, is not suitable for freezing, does not act as a solvent, and has small content changes
hydration
Definition: Water molecules are polar due to uneven charge distribution. When H2O encounters charged ions or molecules, due to the action of charges, the water molecules will be oriented and arranged around the ions or molecules to form a water film.
Function: Stabilize the intracellular environment
Influencing factors: The smaller the ionic radius, the higher the number of charges, and the stronger the hydration ability
free water/bound water
When it is higher: the plant protoplasts are in a sol state, the plant metabolism is active, the growth is fast, and the stress resistance is poor.
When it is low: the plant protoplasm is in a gel state, with low metabolic activity, slow growth and strong stress resistance.
2. Water migration process
2.1 Migration method: the movement of water from soil through plants and then into the atmosphere
2.1.1 Convergence
The main mode of long-distance transport, concentration has a higher transport rate than diffusion and requires energy
2.1.2 Diffusion: Osmosis is a special way of diffusion
How water moves within the cell membrane system
aquaporin
A type of channel protein that is specific to water and can reduce the resistance of water transport across membranes and speed up the movement of water in and out of biological membranes.
Mediates the rapid passive transport of water between cells or organelles and the medium. It is the main way for water to enter cells.
All living cells have aquapoeins
Structure: MIP is a group of channel proteins. The monomer is a narrow tetramer, showing a drip model.
Typical characteristics of the MIP family: Contains 6 human transmembrane α-helical segments, composed of 5 transmembrane half-loops (LA, HB, LC, LD, HE), of which HB and HE contain conserved NPA sequences (asparagine- proline-alanine)
Chloromercury benzenesulfonate strongly inhibits water channels and has no effect on urea channels.
Function
The opening and closing of water channels can effectively regulate the transmembrane movement of water
Possible physiological functions: reproductive growth, cell elongation and differentiation, guard cells and occipital movement, etc.
Factors affecting aquaporin activity
The external environment and plant hormones can affect the abundance and distribution of aquaporin genes by regulating their expression, thereby affecting water metabolism.
Regulated by phosphorylation, dephosphorylation and synthesis
Hg, high concentrations of external solutes can cause the channel to close
Water potential and turgor pressure affect the opening and closing of pores
Water potential gradient determines water transfer
2.1.3 Osmosis
Definition: The phenomenon of diffusion of solute molecules through a semipermeable membrane, moving according to the water potential gradient
2.2 Water potential
definition
Thermodynamic definition: When the temperature, pressure and the amount of other substances are constant, the free energy of 1 mol of water in the system
In a system at the same temperature and pressure, the difference between the chemical formula of partial molar volume of water in the system and the chemical potential of pure water at the same temperature and pressure
Unit: atmospheric pressure (atm) or bar (bar) 1bar=0.1Mpa
The water potential of pure water is 0
The components of water potential in aqueous systems: osmotic potential, pressure potential, gravity potential, lining potential, and temperature potential
Osmotic potential: related to solute concentration
Pressure potential: It is related to the state of cell wall separation. It is a positive value under normal circumstances. When the protoplast loses water rapidly during violent transpiration, it is a negative value when the cell wall and membrane are not separated. It is 0 when the cell wall is separated.
Lining potential: 0 for cells with a large central vacuole. Air-dried seeds and meristematic cells without a large central vacuole have a very low lining potential.
2.2.3.1 Osmotic water absorption of plant cells
Plant cells and solution environment together form an osmotic system
The cell's vacuole solution, protoplasm layer, and extracellular fluid constitute an osmotic system, which flows from high water potential to low water potential.
Changes in volume and water potential components during cell water absorption
Under normal conditions: the pressure potential is greater than 0, under complete tension: the water potential is 0, initial mass wall separation: the pressure potential is equal to 0, severe transpiration: the pressure potential is less than 0
Swelling and water absorption: before the formation of vacuoles, it mainly relies on the lining potential; metabolic water absorption: using the energy of cellular respiration to allow water to enter the cells
2.2.4 Water movement between cells: determined by the water potential difference, and also determines the movement speed
3Moisture transport
3.1 and 3.2
apoplastic pathway
Apoplast: A whole body composed of non-living substances other than the protoplasm, including cell walls, intercellular spaces, intercellular layers, xylem vessels and other non-living substances interconnected with each other. It does not cross membranes and moves quickly.
symplast pathway
Symtoplast: The protoplasts in living cells are formed into a continuous whole through plasmodesmata. Because they need to cross the membrane, the resistance to water movement is large.
3.3 Root water absorption mechanism
Root pressure: active water absorption, definition: the phenomenon of plants absorbing water caused by the physiological activities of the root system itself, and the pressure that causes the liquid flow of the plant root system to rise from the roots; phenomenon: spitting water, hurting the flow
Production mechanism: Osmosis theory, metabolism theory, endothelial jump theory
Transpiration pull: passive water absorption, definition: the transpiration of the above ground causes water absorption by the roots. Motive force is the force of transpiration, which is the force that causes water to rise along the conduit due to a series of water potential gradients generated by transpiration. The magnitude has nothing to do with the vitality of the root system.
3.4 Factors affecting root water absorption
Internal factors: root water potential, heel development, water permeability, etc. External factors: atmospheric factors affect the transpiration rate, thereby indirectly affecting the root water absorption, and soil factors directly affect the root water absorption.
soil moisture status
Key point: temporarily withered, permanently withered
Movement of Soil Moisture: Convergence
4. Transpiration
Significance: 1. The power of plants to absorb and transport water; 2. Material transportation to meet the needs of life; 3. Bottoming of plant body temperature; 4. The opening of stomata is conducive to absorption and assimilation
Part: lenticel transpiration, leaf transpiration: transpiration through the cuticle is cutin transpiration, transpiration through stomata is stomatal transpiration
The transpiration rate from stomata is more than 50 times faster than the transpiration rate from the free water surface of the same area.
Small pore law: The rate at which water vapor diffuses through the surface of a small pore is proportional to the circumference of the small pore.
Stomatal structure: guard cells are composed of adjacent cells or accessory cells; the pores are closed through the expansion of water absorption and shrinkage of water loss by the guard cells.
Basics of movement: starch sugar conversion theory; K ion accumulation theory; malic acid metabolism theory
Factors affecting stomatal movement: light, CO2, temperature, moisture, stomatal oscillation, plant hormones
Indicators of transpiration: Transpiration intensity/rate: the amount of water transpired per unit leaf area within a certain period of time
Ways to reduce transpiration: reduce the transpiration area; reduce the transpiration rate (avoid strong light and high temperature); use anti-transpiration meter
5. Water transport in plants
Transport route: soil, plant atmosphere; speed: apoplast is faster than symplast; power: root pressure in the lower part, transpiration pull in the upper part
6. Moisture application
Reasonable irrigation: maintain the water balance in plants based on a certain water content,
The water critical period of crops: The water critical period refers to the period when the water demand is not necessarily large, but the plants are particularly sensitive to insufficient water and are most vulnerable to damage; the water critical period of general crops is at the stage when vegetative growth turns to reproductive growth
Reasonable irrigation indicators: crop morphology indicators, soil moisture content indicators, physiological indicators of irrigation: leaf water potential, cell leaf potential concentration, stomatal opening