Solution culture Solution culture, also known as hydroponics, is a method of growing plants in a solution containing all or part of the nutrients. Containers wrapped in tin foil or opaque containers are often used to prevent light and avoid the growth of algae. The nutrient solution should be replaced frequently and ventilated frequently with an oxygen pump.

Sand-based culture method Sand-based culture method, referred to as sand culture method, is a method of fixing plants with substrates such as washed quartz sand or glass balls, and adding nutrient solution at the same time to cultivate plants.

When studying essential elements of plants, certain elements can be removed or added to the prepared nutrient solution to observe the growth and development and physiological and biochemical changes of plants. If a certain element is removed from the culture medium in which plants grow and develop normally, the plants will grow poorly and develop specific symptoms. When the element is added, the symptoms disappear, it means that the element is an essential element for the plant. On the contrary, if subtracting a certain element has no adverse effect on plant growth and development, it means that the element is not essential for plants.

Conditions of nutrient solution The nutrient solution must meet the following four conditions: ① Contain all nutrients necessary for plant growth; ② Nutrients should be active ingredients, and the quantity and proportion of nutrients can meet the needs of plant growth; ③ During the plant growth period The internal energy can maintain the pH suitable for plant growth. ④ The nutrient solution should be a physiologically balanced solution.

For example, carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur, etc. are components of organic substances such as sugars, lipids, proteins, and nucleic acids.

Essential plant elements serve as enzyme components and enzyme activators, controlling enzymatic reactions; they are components of endogenous physiologically active substances (hormones and vitamins, etc.) and regulate plant metabolism, growth and development.

For example, K*, Na*, CI* and other ions can adjust the osmotic potential of cells and maintain intracellular charge balance; H*, OH*, etc. regulate the pH of cells, and elements such as iron, zinc, copper, nickel, and molybdenum participate in redox reactions.

Such as calcium.

The nitrogen absorbed by plants is mainly inorganic nitrogen, namely ammonium nitrogen (NH4*) and nitrate nitrogen (NO5*). It can also absorb part of organic nitrogen (such as urea)

(1) The main physiological functions of nitrogen The main physiological functions of nitrogen are: ① Nitrogen is the main component of proteins, nucleic acids, and phospholipids, and these three are important components of cellular structural materials such as protoplasm, cell nuclei, and biological membranes; ② Nitrogen It is a component of enzymes, ATP, various coenzymes and prosthetic groups (such as NAD*, NADP, FAD, etc.), which play an important role in material metabolism and energy metabolism; ③ Nitrogen is a component of certain plant hormones (such as auxin and cell division) Vitamins (such as vitamin B, vitamin B, vitamin B, vitamin PP), etc., which regulate life activities; ④ Nitrogen is a component of chlorophyll and is closely related to photosynthesis. It can be seen that nitrogen plays an important role in plant life activities, so nitrogen is also called the element of life.

(2) Symptoms of nitrogen deficiency. When nitrogen is deficient, the synthesis of organic matter is blocked, resulting in short plants, yellow or red leaves, few branches (branching), few flowers, incomplete grains, and reduced yield. Due to the high mobility of nitrogen, compounds in old leaves can be decomposed and transported to young tissues for reuse. Therefore, old leaves show symptoms first when nitrogen is lacking.

(3) The harm of too much nitrogen: When there is too much nitrogen, the leaves of plants will be dark green and the branches and leaves will be leggy. The maturity period is delayed; the mechanical tissue in the stem is underdeveloped, which can easily lead to lodging and infestation by diseases and insect pests. However, appropriately applying more nitrogen fertilizer to leafy vegetable crops is beneficial to increasing yield and improving quality.

Phosphorus is mainly absorbed by plants in the form of H2PO4* or HPO42*.

(1) The main physiological functions of phosphorus: ① Phosphorus is the main component of nucleic acids, nucleoproteins and phospholipids; ② Phosphorus is a component of many coenzymes (such as NAD*, NADP*, etc.), and is also a component of ATP and ADP Ingredients; ③ Phosphorus plays an important role in plant material metabolism, such as participating in the metabolism of sugars, fats and proteins, and can promote the transportation of sugars; ④ Plant cell fluid contains certain acids and salts to form a buffer system, which is harmful to cells The maintenance of osmotic potential plays a certain role.

(2) Symptoms of phosphorus deficiency: When phosphorus is lacking, the plants are thin and small, the tillers or branches are reduced, the leaves are green or purple, the flowering and maturity stages are delayed, the yield is low, and the resistance is weakened. Phosphorus is a reusable element, so when phosphorus is lacking, symptoms will first appear on older leaves.

(3) The harm of too much phosphorus: When there is too much phosphorus, small scorch spots will appear on the leaves, which is caused by the precipitation of calcium phosphate. Excessive phosphorus will also hinder the absorption of silicon by plants, which can easily cause symptoms such as zinc deficiency and calcium deficiency in plants.

Potassium is absorbed by plants in the form of K* and exists in the plant body, and does not participate in the composition of important organic matter

(1) The main physiological effects of potassium The main physiological effects of potassium are: ① Potassium participates in important metabolism in plants as an activator of pyruvate kinase, malate dehydrogenase, fructokinase and other enzymes; ② Potassium can promote protein and The synthesis of sugars and can promote the transportation of sugars; ③Potassium can increase the hydration degree of protoplasts and reduce their viscosity, thereby enhancing the water retention capacity of cells and improving premature resistance; ④Potassium is an important component of cell osmotic potential , participates in the control of physiological processes such as cell water absorption and stomatal movement; ⑤ Potassium is the most important charge balance component in plant cells. It plays a vital role in maintaining the normal life activities of living cells across membranes (plasma membrane, tonoplast membrane, chloroplast membrane, mitochondrial membrane). etc.) plays an irreplaceable role in potential.

(2) Potassium deficiency: When potassium is deficient, plants have reduced early resistance and cold resistance, the plants are weak and prone to lodging, the leaves turn yellow, the leaf edges are scorched, and the growth is slow. Because the middle part of the leaf is still growing faster, the entire leaf will form a cup-like bend or shrink. Potassium is an element that can be reused. When potassium is lacking, symptoms will first appear in older leaves.

(3) The harm of too much potassium. Excessive application of potassium will cause the plant's absorption of calcium and other cations to decrease, leading to "heart rot" in leafy vegetables, "bitter pox" in apples, etc.

Calcium is absorbed by plants in the form of Ca'*

(1) The main physiological functions of calcium. The main physiological functions of calcium are: ① Calcium is an important intracellular messenger. In plant cytoplasm, calcium ions can combine with calmodulin (CaM) to form calcium-calmodulin (Ca*- The CaM) complex participates in signal transduction and plays an important regulatory role in many cellular reactions; ② Calcium is a component of calcium pectate in the intercellular layer of plant cell walls; ③ Calcium participates in the formation of spindles and is therefore related to mitosis; ④ Calcium Ions can serve as a bridge between phosphoric acid in phospholipids and carboxyl groups of proteins, stabilizing the membrane structure; ⑤ Calcium is an activator of ATP hydrolase and phospholipid hydrolase; ⑥ Calcium can form calcium oxalate with oxalic acid in plants , eliminate the poison of excessive oxalic acid to plants; ⑦ Calcium helps the formation of plant callus and also plays a certain role in plant disease resistance.

(2) Calcium deficiency symptoms: In the early stage of calcium deficiency, the terminal buds and young leaves turn light green, and then the leaf tips appear typical hook-shaped, and then become necrotic. Calcium is an element that is difficult to move and can be reused, so humin symptoms first appear on young stems and leaves. For example, when Chinese cabbage is deficient in calcium, the heart leaves turn brown.

Magnesium is absorbed by plants in the form of Mg*.

(1) The main physiological functions of magnesium The main physiological functions of magnesium are: ① Magnesium is a component of chlorophyll, and about 20% of the magnesium in plants exists in chlorophyll; ② Magnesium is a component of many enzymes in photosynthesis and respiration [such as 1,5 -Activator of ribulose diphosphate carboxylase/oxygenase, acetyl-CoA synthetase]; ③The activation of amino acids requires the participation of magnesium. Magnesium can combine the ribosome subunits into a stable structure. If the magnesium concentration is too high, If it is low, the ribosome will disintegrate and the protein synthesis ability will be lost; 4. Magnesium is an activator of DNA polymerase and RNA polymerase, so magnesium is involved in the synthesis of DNA and RNA; 5. Magnesium is also a component of chromosomes. Acts during cell division.

(2) Symptoms of magnesium deficiency. The most obvious symptom of magnesium sensitivity is leaf chlorosis, which is characterized by starting from the lower leaves first. The mesophyll often turns yellow while the veins remain green. This is the main difference from nitrogen deficiency symptoms. Severe magnesium deficiency can cause premature aging and shedding of leaves, eventually causing the entire plant to wither and die.

Sulfur is mainly absorbed by plants in the form of sulfate radical (SO42*).

(1) The main physiological functions of sulfur The main physiological functions of sulfur are: ① Sulfur is a component of cysteine ​​and methionine, and therefore is also a component of protein. -SH and -S-S- between sulfur-containing amino acids in proteins can transform into each other, which not only regulates the redox reaction in plants, but also stabilizes the spatial structure of proteins; ② Sulfur is plant coenzyme A (CoA), The components of thiamine, biotin, etc. are closely related to the metabolism of carbohydrates, proteins, and fats; ③ Sulfur is a component of thioredoxin, iron-sulfur protein, and nitrogenase, and plays a role in plant photosynthesis, nitrogen fixation, and other reactions. plays an important role in.

(2) Symptoms of sulfur deficiency: Sulfur is difficult to move. When deficient, young leaves show symptoms first, and new leaves become evenly chlorotic, yellow and fall off easily. Sulfur deficiency is rarely encountered in crop cultivation practices because there is sufficient sulfur in the soil to meet plant needs.

Silicon is absorbed by plants in the form of H4SiO4

(1) The main physiological effects of silicon The main physiological effects of silicon are: ① Silicon is mainly deposited in the cell wall and intercellular space in the form of amorphous water compounds (SiO2·nH2O), and can also form complexes with polyphenols to become cell wall additives. Thick substances to increase the rigidity and elasticity of cell walls; ② Silicon promotes the formation of reproductive organs and can increase the number of ears, spikelets and single grain quality of cereal crops; ③ Silicon can relieve the stress of various metals (including aluminum and Magnesium) is toxic to plants.

(2) Symptoms of silicon deficiency: When plants are deficient in silicon, their transpiration is accelerated, their growth is stunted, and they are prone to lodging or fungal infection. Especially in rice, the ability to resist diseases, insect pests and lodging is significantly reduced when silicon is deficient.

Nitrogen is absorbed by plants in the form of CI*. Only a very small amount of oxygen is incorporated into the organic matter, of which 4-chloroindoleacetic acid is a natural growth hormone.

(1) The main physiological effects of chlorine The main physiological effects of chlorine are: ① CI* participates in the photolysis of water during photosynthesis; ② CI* is also required for the division of leaf and root cells; ③ CI* regulates cytosolic potential and maintains charge. Plays an important role in balance.

(2) Symptoms of chlorine deficiency: When chlorine is lacking, the leaves will wilt, become chlorotic and necrotic, and finally turn brown. At the same time, the growth of the root system is hindered, becomes thicker, and the root tip becomes rod-shaped.

Iron is mainly absorbed by plants in the form of Fe2^ or chelated iron.

(1) The main physiological functions of iron The main physiological functions of iron are: ① Iron is a prosthetic group for many enzymes, such as cytochrome oxidase, peroxidase, catalase, and ferredoxin. In these enzymes, iron can transfer electrons through the change Fe3* e *=Fe2*. Iron is also a metal component of ferritin and molybdenum ferritin in nitrogenase, which plays a role in biological nitrogen fixation. ②The enzyme that catalyzes chlorophyll synthesis requires activation by Fe2*.

(2) Symptoms of iron deficiency Iron is necessary for the synthesis of chlorophyll, so iron deficiency causes yellowing of leaves. In recent years, it has been discovered that iron affects the structure of chloroplasts and the synthesis of chlorophyll. For example, when the eye algae is deficient in iron, the chloroplasts also disintegrate while the chlorophyll is decomposed.

Iron is an element that is difficult to reuse, so the most obvious symptom of iron deficiency is that the young buds and leaves become chlorotic and turn yellow, or even turn yellow-white, while the lower leaves remain green.

Boron is absorbed by plants in the form of H3BO3

(1) The main physiological functions of boron: ① Boron promotes the construction and development of plant reproductive organs, because boron is conducive to the formation of pollen, and can promote the germination, elongation and fertilization process of pollen; ② Boron Promote the transportation and metabolism of sugar, because boron can combine with free sugar, making the sugar polar, making it easier for sugar to pass through the plasma membrane and promoting its transport; boron can increase the activity of uridine diphosphate glucose (UDPG) pyrophosphorylase Activity, promotes the synthesis of sucrose; ③ Boron participates in the synthesis of hemicellulose and cell materials, promoting cell elongation and division; it is also involved in the synthesis of nucleic acids and proteins, hormone reactions, membrane function, cell division, root development and other physiological processes There is a certain relationship; ④ Boron can inhibit the formation of phenolic acid compounds such as caffeic acid and chlorogenic acid in plants, which may cause root lignification.

(2) Symptoms of boron deficiency: When boron is lacking, anthers and filaments shrink, pollen is underdeveloped, seed setting rate is low, root tips and terminal buds are necrotic, apical dominance is lost, and branches increase.

Manganese is mainly absorbed by plants in the form of Mn2*.

(1) The main physiological effects of manganese The main physiological effects of manganese are: ① Manganese is an activator of many important enzymes, such as hexose phosphokinase, carboxylic acids, dehydrogenating acids, RNA polymerase, some enzymes in fatty acid synthesis, and The activation of nitric acid reducing acid, indole acetic acid (IAA) oxidation, etc. all require the participation of manganese; ② Manganese is a component of the oxygen-evolving complex in photosystem II and participates in the photosynthetic oxygen-emitting reaction. The photolysis of water in photosynthesis requires manganese. Participation ③ Manganese is a component of superoxide dismutase and participates in the scavenging of free radicals in mitochondria.

(2) Symptoms of manganese deficiency: During manganese deficiency, the leaves become chlorotic between the veins, but the veins remain green, and the leaves begin to turn yellow from the leaf edges. This is the main difference between manganese deficiency and iron deficiency. Mn2* is highly mobile in plants. When manganese deficiency occurs, symptoms will generally appear on young leaves to medium-aged leaves, rather than the youngest leaves. Symptoms of manganese deficiency in cereal crops often appear on older leaves.

Sodium is absorbed by plants as Na*

(1) The main physiological effects of sodium. The main physiological effects of sodium are: ① Sodium ions can increase the solute potential, expand cells and promote growth: ② Sodium can catalyze phosphoric acid in C4 plants and Crassulacea acid metabolism (CAM) plants. Regeneration of enolpyruvic acid (PEP); ③Sodium can partially replace the role of potassium and increase the osmotic potential of cells

(2) Symptoms of sodium deficiency: When sodium is deficient, plants will show yellowing and necrosis, and may even be unable to bloom.

Zinc is absorbed by plants in the form Zn2*

(1) The main physiological functions of zinc. The main physiological functions of zinc are: ① Zinc is a component or activator of many enzymes, such as glutamate dehydrogenase, superoxide dismutase, carbonic anhydrase, etc.; ② Zinc is involved in The synthesis of indole acetic acid (IAA) is because the precursor of indole acetic acid is tryptophan, and zinc is an essential component of tryptophan synthase.

(2) Zinc deficiency symptoms: Zinc deficiency will affect auxin synthesis, resulting in stunted growth of young leaves and stems of plants, resulting in leaf diseases and cluster leaf diseases.

In well-aerated soil, copper is absorbed by plants in the form of Cu2*, while in moist and anoxic soil, it is mostly absorbed in the form of Cu2*.

(2) The main physiological functions of copper The main physiological functions of copper are: ① Copper is a component of polyphenol oxidase, ascorbic acid oxidase, laccase and other enzymes, and plays an important role in the redox of respiration; ② Copper is a substance The component of cyanine participates in photosynthetic electron transfer; ③ Copper can improve the ability of potatoes to resist late blight, so spraying copper sulfate has a good effect on preventing and treating the disease.

(2) Symptoms of copper deficiency: During copper deficiency, leaves grow slowly, appear blue-green, and young leaves become chlorotic. When copper deficiency is severe, leaves fall off. In addition, copper deficiency will cause the degeneration of the leaf palisade tissue and the expansion of the substomatal cavity, causing the plant to wilt due to excessive transpiration even when the water supply is sufficient.

Nickel is absorbed by plants in the form Ni2*.

(1) The main physiological functions of nickel The main physiological functions of nickel are: ① Nickel is the metal component of urease, and the function of urease is to catalyze the hydrolysis of urea into carbon dioxide (CO2) and ammonia (NH3), so plants lacking urease will A large amount of urea accumulates in the plant, seriously affecting the germination of seeds; ② Nickel is also one of the components of hydrogenase, which plays a role in generating hydrogen in biological nitrogen fixation; ③ Nickel can activate α-amylase activity in barley seeds.

(2) Symptoms of nickel deficiency: When nickel is lacking, more urea accumulates in the leaf tips, causing the leaves to become abnormal or even necrotic.

Molybdenum is absorbed by plants in the form of MoO24*

(1) The main physiological functions of molybdenum The main physiological functions of molybdenum are: ① Molybdenum is a component of nitrate reductase and plays an electron transfer role ② Molybdenum is a component of molybdenum ferritin in nitrogen-fixing enzyme and plays a role in the nitrogen fixation process; ③ Molybdenum It is an essential component of xanthine dehydrogenase and certain oxidases in the synthesis of abscisic acid.

(2) Symptoms of molybdenum deficiency: When molybdenum is lacking, the leaves are smaller, the leaves are chlorotic between the veins, there are necrotic spots, and the edges of the leaves are scorched and curled inward. When cruciferous plants are deficient in molybdenum, their leaves become curled and deformed, and old leaves become thickened and scorched. When cereal crops are deficient in molybdenum, the grains shrink or fail to form grains.

Soil pH can significantly affect the availability of various mineral elements in the soil. Low pH is conducive to the weathering of minerals and the release of various ions, such as K*, Mg*, Ca*, Mn*, Cu* and AI*. The solubility of various salts such as carbonates, phosphates, and sulfates is also high at low pH. When the pH is 5.0 to 6.0, the absorption and utilization of plants is high, but it is easy to run off or be washed away by rainwater, so in acidic red soil In soil, crops often suffer from deficiencies of phosphorus, potassium, molybdenum, etc. As the alkalinity of the soil gradually increases, elements such as iron, phosphorus, manganese, boron, and zinc gradually turn into insoluble compounds, and the amount of plants absorbing them gradually decreases.

The effect of soil acidity and alkalinity (pH) on the absorption rate of mineral elements varies depending on the ionic properties. Within a certain pH range, in general, the absorption rate of cations increases with the increase of soil pH, while the absorption rate of anions decreases with the increase of pH.

The reason why soil pH has different effects on the absorption rates of bright ions and cations is related to the fact that the proteins that make up the cytoplasm are ampholytes. In an alkaline environment, the amino acids that make up the protein in root cells are positively charged, making it easy for the roots to absorb anions in the external solution; while in an alkaline environment, the amino acids are negatively charged, making it easy to absorb cations.

Generally, the optimal soil pH for plant growth is between 6 and 7, but some plants prefer a slightly acidic environment, such as tea, potatoes, tobacco, etc.; some plants prefer an alkaline environment, such as clematis, beets, etc.

After spraying a solution containing mineral elements on the above ground part of the plant (mainly the leaves), the mineral elements can enter the plant through the stomata or lenticels on the stem surface, or through the cutin on the plant surface. The stratum corneum is a mixture of polysaccharides and lipid compounds distributed on the lateral walls of epidermal cells and is not easily permeable to water. But there are gaps in the stratum corneum, which are tiny pores that allow solutions to pass through. After the solution reaches the lateral wall of the epidermal cells through the stratum corneum pores, it further passes through the epidermal filaments in the cell wall and reaches the plasma membrane of the epidermal cells. The fluid secretions filled with epidermal cell protoplasts in the epidermal filaments extend outward from the protoplast surface through the fine pores in the wall and connect with the apoplast. When the solution reaches the plasma membrane through the epithelia, it is transported into the interior of the cell and finally reaches the phloem in the stems and leaves.

Since plant stems and leaves can only absorb nutrients dissolved in the solution, the longer the solution stays on the leaves, the more nutrients will be absorbed. Therefore, any external environmental factors that can affect liquid evaporation (such as light, wind speed, temperature, atmospheric humidity, etc.) will affect the absorption of nutrients by stem surfaces and leaves. Therefore, in terms of production, extra-root fertilization operations are mostly carried out in cool, windless and high-humidity times (for example, in the evening when it is cloudy).

Extra-root fertilization has the characteristics of low dosage and fast fertilizer effect. In some cases, extra-root fertilization is an effective way to supplement plant nutrients. For example, in the later stages of crop growth, when the root activity decreases and the ability to absorb fertilizer declines, or when the soil lacks available water, soil fertilization cannot be effective, or when certain mineral elements have poor soil fertilization effects (such as iron in alkaline soil). The effectiveness is very low (molybdenum is fixed in acidic soil, etc.), and external topdressing can achieve obvious results. Fertilizers commonly used for crop foliar spraying include urea, potassium dihydrogen phosphate, trace element fertilizers, etc.

The disadvantages of extra-root fertilization are: the fertilization effect is poor on plants with thick cuticles (such as citrus); the spray concentration is too high, which can easily cause leaf damage

There are three types of carrier proteins: unidirectional transporters, co-(co-)porters and anti-(anti)porters. Uniporters can be further divided into passive unidirectional transporters and active unidirectional transporters (such as plasma membrane H*-ATPase). Both symporters and antiporters are involved in active transport

By kinetically analyzing the relationship between transport rate and solute concentration difference, it can be distinguished whether the solute is transported through ion channels or carrier proteins. Transport through ion channels is a simple diffusion process without saturation; while transport through carrier proteins relies on the binding of solutes to specific sites on the carrier. Since the number of binding sites is limited, carrier protein transport has saturation.

The relationship between primary active transport and secondary active transport is: primary active transport hydrolyzes ATP and converts chemical energy into ΔμH* or proton power, while secondary active transport uses ΔμH* or proton power to transport ions or molecules across the membrane. The secondary active transport will weaken ΔμH*. Of course, when ΔμH* decreases, the feedback effect can promote the continuation of the primary active transport. The final result is the consumption of ATP and the active transport of ions and molecules across the membrane.

In fact, plasma membrane ATPase is also a unidirectional transporter, which is an active unidirectional transport that consumes energy. Therefore, one-way transport can be divided into two types: active and passive.