Basic Introduction Chinese Name: Aerated Tissue mbth: Aerated Tissue Type: Schizophytic and Lysogenic Common Organisms: Aquatic Plants and Wet Plants Definition: parenchyma with a large number of intercellular spaces: ensuring the metabolic needs of roots, etc. Brief introduction, structural characteristics, main functions, formation process and ecological significance. Ventilation tissue is a parenchyma with a large number of intercellular spaces. Common in aquatic plants and wet plants, such as lotus, rice, POTAMOGETON, etc. There are well-developed aeration tissues in roots, stems and leaves, and their intercellular spaces communicate with each other to form an aeration system, which is conducive to gas exchange and oxygen generated during photosynthesis of leaves entering the roots and giving plants certain buoyancy and support. Under anoxic conditions (such as flooding), the root cortex cells of plants will die and disintegrate, so that the radial cell walls of collapsed cells will gather together to form large cavities. Aerated tissue provides a diffusion path, which reduces the resistance of aerial parts of plants to transport oxygen to flooded or anoxic roots, thus ensuring the metabolic needs of roots, which is of great significance to the growth of hygrophytes and halophytes. Structural features Aerated tissue is a collection of air cells or cavities in parenchyma of plants. Many aquatic and hygrophytic plants form aeration tissue in rhizomes, and other plants (including amphibians and terrestrial plants) also differentiate to produce or accelerate the development of aeration tissue in anoxic environment. The aeration tissue is diverse in form and complex in structure, and the classical view holds that it is the channel for oxygen to transport to the root system. Aeration tissue exists not only in the roots of plants, but also in the peels of leaves and fruits. With the development and application of molecular biotechnology, the formation process of ventilated tissue has been gradually revealed, and its physiological and ecological significance has been paid more and more attention. According to different plant species and formation conditions, the aeration tissue can be divided into schizogenic type and lysogenic type. The former comes from programmed death and dissolution of some living cells, and there are residual cell walls in mature tissues, which are induced by soil flooding or hypoxia stress. It is species-specific, and cells regularly separate and differentiate to form intercellular spaces, which is the basic feature of many aquatic plants, such as rice (Oryza sativa), flooded corn (Zea mays) and wheat (Triticum aestivum), and even exists in some coastal halophytes. The latter originated from programmed death and dissolution of some living cells, and was formed during the process of plant development and differentiation. Cells divide and differentiate regularly to form cavities, and there is no cell wall residue, such as aeration tissue in leaves, leaf sheaths and coleoptiles. Two kinds of aeration tissues can sometimes appear in the same plant at the same time, but lysogenic tissues usually appear in roots and schizogenic tissues often appear in leaves. The main functional ventilation tissue is the characteristic expression of waterlogging tolerance and hypoxia tolerance of plants, which not only provides oxygen transport channels for plants, but also reduces the number of oxygen-consuming cells. The radial partial pressure of oxygen in different parts of reed root was measured by microelectrode. It was found that the partial pressure of oxygen in cortical cells was almost stable except for the low oxygen level in the middle column, and the radial oxygen loss (ROL) above the root tip was gradually reduced or even zero. On the one hand, due to the formation and strengthening of oxygen diffusion barrier (thick-walled cells at the edge of the outer cortex), oxygen escape is reduced; On the other hand, the formation of cortical ventilation tissue can enhance the diffusion of oxygen in the body, maintain the appropriate oxygen level in the tissue, and is conducive to the long-distance transport of oxygen to the root tip to ensure normal physiological functions. The roots of halophytes also have many ventilation channels. The unobstructed ventilation structure can quickly transport the oxygen obtained from the aboveground parts of plants to the roots, and most of the ventilation channels are located inside the protective tissues. According to the position of ventilated tissue, it is speculated that it is related to the availability of oxygen. In addition, plants can release oxygen to rhizosphere by using aeration tissue, which can reduce the toxicity of reducing substances in rhizosphere to plants and play a detoxification role; Ventilating tissue also helps to discharge some harmful metabolic waste gases, such as CH 4, CO 2, N 2 and N 2 O Root aeration tissue is a special form of root cortex tissue during its formation. It can be seen from the fact that the proportion of the ventilation cavity in the post-apical mature area in the root cross section has increased significantly that the ventilation tissue is formed with the decay of root cells. In addition, from the root cortex tissue arranged in rows in the radial direction, the lines between cells are relatively close, but the lines between adjacent cells in the horizontal direction are not recent. As long as the cells in the mesocortex contract, the intercellular space will become a whole, showing a radial airway. Therefore, we speculate that the essence of the formation of ventilated tissue is the combination of root cortex cell decline and cell gap expansion. The roots of Gramineae and Cyperaceae produce aeration tissue through lysogenic mechanism. Taking rice roots as an example, it was observed that the aeration tissue began to differentiate in the elongation zone and formed in the mature zone. The formation process is as follows: (1) The growth of cortical cells stops and the intercellular space increases; (2) Cortical cells autolyse with aging, and the inclusion disintegrates; (3) Disintegration gradually disappeared, and cortical cells began to contract and invaginate. When all the cell contents disappear, the residual cell walls of adjacent cells overlap to form wheel spokes. Ecological significance provides short-distance intercellular diffusion of oxygen needed for root respiration and metabolism, and can provide oxygen needed for aerobic respiration of cells. This intercellular gas diffusion is based on the direct contact between root epidermal cells and external gas. When the contact surface is reduced by flooding, the flooded organ may suffocate. In some plants with good adaptability to flooding, the danger of suffocation can be eliminated through the long-distance gas passage between apoplast and aeration tissue. For example, under the condition of flooding, the aeration tissue that runs through the roots, stems and even leaves of rice continuously provides oxygen for breathing from the aboveground parts to the roots. Besides rice, aerenchyma can also be found in other crops such as wheat and sesame. The results showed that there were obvious genotypic differences in the development degree of aeration tissue or the ability to produce aeration tissue in wheat roots under flooding conditions, which was closely related to the waterlogging tolerance of wheat. The genotype with strong waterlogging tolerance has developed ventilation tissue. The biggest change of rhizosphere environment caused by regulating rhizosphere oxidation potential flooding is that rhizosphere oxygen is gradually exhausted, oxidation potential is reduced, aerobic microbial activity is weakened and anaerobic microbial activity is enhanced. The decrease of rhizosphere oxidation potential and anaerobic microbial activity will lead to the decrease of oxides and the accumulation of plant toxic substances. Some people think that plants with aeration tissue can release oxygen to rhizosphere, thus reducing the toxicity of reducing substances in rhizosphere to plants. The study of rice confirmed that the aeration tissue not only provided oxygen for root tissue respiration and metabolism in anoxic environment, but also the root axis could release oxygen radially to the rhizosphere through the aeration tissue. The amount of oxygen released is positively correlated with the development of ventilated tissue. Although there is no report on the influence of aeration tissue on rhizosphere oxidation potential, it can be inferred that the oxygen released by this root system will inevitably participate in the oxidation of reducing inorganic and organic substances in rhizosphere under the environment of flooding and hypoxia. By removing the tops of several aquatic plants to block the oxygen transport from aeration tissue to rhizosphere, it was found that rhizosphere nitrogen decreased sharply and reducing CH 4 increased, which indirectly proved that oxygen released from aeration tissue could regulate rhizosphere oxidation potential. Under the condition of flooding, the denitrification activity of rice rhizosphere with developed aeration tissue is obviously lower than that of wheat rhizosphere, which further supports the above argument. The gas exchange between aeration tissue and rhizosphere not only shows that plants release oxygen to rhizosphere, but also shows that some metabolic waste gases harmful to plants are discharged through aeration tissue. Researchers' research in rice fields shows that more than 90% of CH 4 produced in rhizosphere soil is released into the atmosphere through aeration tissues, and only a small part of methane is discharged from the water surface through bubbles and diffusion. In addition to the above three functions, the ventilation tissue in leaves can significantly reduce the resistance of photon diffusion, thus affecting the photosynthetic rate of chloroplasts; The aeration tissue in the stems and leaves has a positive effect on increasing the elasticity and buoyancy of aquatic plants and making the leaves perform normal photosynthesis. Aerated tissues are also containers for storing CO2, which is especially important for Sedum plants. Most of these plants have closed stomata during the day and opened stomata at night. Part of CO2 absorbed at night is assimilated into carboxylic acid for photosynthesis, and the other part is directly stored in ventilated tissues for later use.