(2) Phytodegradation refers to the process that plants degrade pollutants through metabolic processes or decompose foreign pollutants through plant-derived substances such as enzymes. Enzymes that can directly degrade organic pollutants mainly include dehalogenase, nitroreductase, peroxidase, laccase and nitrilase. For some pollutants that are difficult to degrade in plants, such as PCBs, it may be a good method to transfer genes that can degrade these pollutants into plants. This genetic engineering method can not only improve the ability of plants to degrade organic pollutants, but also make plant remediation selective and specific. This is also an important application field of genetic engineering technology.
(3) Plant transformation repair Plant transformation refers to the process of transforming pollutants from one form to another by using the physiological process of plants. The most typical and important thing is that plants absorb carbon dioxide in the atmosphere and release oxygen through photosynthesis. Plant transformation is an important physiological reaction process for plants to protect themselves from pollution. Plant transformation requires the participation of many enzymes in plants, including acetylase, mercaptotransferase, methylase, glucuronosyltransferase and phosphorylase. Plants can not completely degrade organic pollutants into C0: and H: 0, but are isolated in vacuoles or combined with insoluble cell structures such as lignin after certain transformation.
(4) Plant Assimilation and Super Assimilation Repair Plant Assimilation refers to the phenomenon that plants absorb pollutants containing plant nutrients and assimilate them into their own material components to promote their own growth. Hyperassimilated plants can efficiently absorb and assimilate air pollutants containing nutrients needed by plants, such as nitrogen oxides and sulfur oxides, and promote their own growth. This phenomenon can be called hyperassimilation. Polycyclic aromatic hydrocarbons (PAHs) pollutants exist in the form of solid and liquid vapor aerosols in the atmosphere, which can be assimilated by higher plants. The ability of different plants to absorb toxic substances in the atmosphere is very different. 3.4 Effects of air pollution on plants
3.4. 1 Influence of air pollution on plant physiological mechanism Environmental pollution is threatening the stability of the whole earth ecosystem and human health. As an important member of the ecosystem, plants are also threatened. Plants can't move by themselves, and they can't choose to escape environmental pollution like animals, so they are good materials for studying the impact of environment on organisms. The response of plants after air pollution is various, including changes in physiology, biochemistry, physical characteristics and external characters. Air pollution will damage the cells and organelles of plants. Under the action of air pollution, the permeability of cell membrane system is destroyed, resulting in imbalance of water molecules and ions and metabolic disorder. When the injury is serious, the intracellular separation disappears and the organelles collapse, leading to final death. Among them, membrane lipid is a major point of action of pollutants. For example, O3 can make membrane lipids undergo peroxidation and interfere with their biosynthesis. When the dose of O3 causes tobacco to have injury symptoms, it will promote respiration and hinder photosynthesis. The damage of SO2 is also related to membrane lipid peroxidation: under the joint action of O3 and SO2, the membrane structure of chloroplasts is also destroyed. In polluted leaves, the most common tissue changes include cell plasma wall separation, granulation or disintegration of cell contents, atrophy or disintegration of cells and pigment deposition of damaged tissues. The harm of air pollution to plant tissues and organs is mainly manifested in tissue necrosis and organ shedding. The symptoms of acute damage caused by air pollutants to plants are leaf spot disease, leaf spot disease and leaf tissue necrosis. Stomatal is the channel through which plants breathe through leaves, so the stomata of plants will change correspondingly under polluted conditions to adapt to the environment. Air pollution can also affect the enzyme system of plants. After pollutants enter plants, on the one hand, they undergo metabolic transformation under the catalysis of enzymes; On the other hand, they also lead to changes in enzyme activity, which will lead to changes in a series of metabolic reactions in plants. For example, fluoride is an inhibitor of many enzymes, especially enolase, an important component of sugar alcohol degradation pathway; Another example is that O3 and peroxyacetyl nitrate are strong oxidants, which can oxidize the protein of many enzymes and lose their activity. Yang Cheng and others found that the representative vegetable oil tea, Pinus massoniana, Cunninghamia lanceolata, Rhizoma Cibotii and Dictyophora dictyophylla in Kaili were polluted by air, which led to the decrease of catalase activity and the accumulation of proline. Li Hailiang and others found that air pollution seriously affected the physiological activities of Sophora japonica, a common greening tree species in Lanzhou, such as chlorophyll degradation, decreased sugar synthesis, decreased PH value of leaf cell fluid, increased membrane permeability of leaves, proline accumulation in plants, changes in SOD activity and changes in plant cell metabolic activity, thus affecting the structure and function of fine cells.