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Research progress on regulation mechanism of fruit tree fruit abscission[J]. Plant Science Journal. DOI: 10.11913/PSJ.2095-0837.23054
Citation: Research progress on regulation mechanism of fruit tree fruit abscission[J]. Plant Science Journal. DOI: 10.11913/PSJ.2095-0837.23054

Research progress on regulation mechanism of fruit tree fruit abscission

  • Fruit abscission refers to the process of fruit abscission from the tree, which is a very important stage in the growth and development of fruit trees. During the growth and development of fruit trees, physiological fruit drops usually occur twice. The first time occurs in the young fruit period, which is called the ' June fruit drop '. The second time occurs before maturity, which is called a ' pre-harvest fruit drop '. Fruit abscission usually occurs in the abscission zone, which is roughly divided into four steps: the basal cells of the abscission organ differentiate into primary abscission zone tissue, feel and mediate the shedding stimulation signal, induce the activity of cell wall metabolic enzymes and activate abscission, and close the fracture by differentiating a protective layer on the main side of the abscission zone. The production of the abscission zone and the acceptance of abscission stimulation signals lead to fruit abscission is a regulatory process involving a variety of genes. It is the result of a variety of factors such as cell structure, carbohydrates, cell wall metabolic enzymes, ethylene synthesis, signal transduction processes, and transcription factors. However, the formation of the abscission zone does not necessarily mean that abscission will occur, and specific signal activation is required to cause fruit abscission. At the same time, the abscission zone is extremely sensitive to the shedding of exogenous stimuli. Most of the abscission-induced genes are directly expressed in the abscission zone after isolation and activation, inducing plant organ abscission. Cell wall decomposition and cell separation in the fruit abscission zone are necessary conditions for fruit abscission, in which cell wall metabolic enzymes are the direct cause of fruit abscission. In most cases, pectinase and cellulase work together to hydrolyze pectin and cellulose in the cell wall to make the cell wall lose and cause the cell to expand and round, accelerating fruit abscission. At the same time, shading, binding, and leaf removal of fruit trees will affect sugar metabolism-related genes, thereby reducing the type and content of carbohydrates produced by source organs, blocking the transport system in the plant or inhibiting its transport rate, resulting in a decrease in the level of carbohydrates in the fruit, causing the fruit to fall off. Plant hormones such as ethylene and auxin also play an important role in fruit abscission. Auxin inhibited fruit abscission, ethylene showed antagonism with auxin. After ethylene synthesis, it is necessary to regulate the expression of related genes through ethylene receptor proteins and a series of signal transduction factors, so that plants can produce corresponding physiological and biochemical reactions, which ultimately lead to fruit abscission. At the same time, ethylene can promote the decomposition of auxin, reduce the content of free auxin and inhibit its transfer to the abscission area, and promote fruit abscission. At the same time, transcription factors regulate the expression of fruit abscission-related genes by interacting with specific cis-acting elements to regulate fruit abscission. For example, transcription factors such as NAC, KNOX, HB, and ERF can regulate fruit abscission by controlling the expression of abscission-related genes such as ethylene-related genes and cell wall metabolic enzyme genes. However, the research on the factors affecting fruit abscission is not perfect, the excavation of genes regulating fruit abscission is not comprehensive, and the relationship between the factors needs further study. Fruit abscission has a huge impact on fruit production. On the one hand, appropriate fruit abscission can reduce the labor cost caused by flower and fruit thinning. On the other hand, excessive fruit abscission will affect yield and fruit quality, resulting in a decline in economic value. In the production process of fruit trees, controlling the amount of fruit shedding can not only reduce the production cost of artificial thinning but also improve fruit quality and increase income. Therefore, it is particularly important to analyze the molecular mechanism of fruit abscission for improving fruit tree varieties and fruit quality. Based on this, this paper reviews the formation and structural changes of the abscission zone, the content of carbohydrates, cell wall metabolic enzymes, ethylene, and other substances, and the expression of related genes in the process of fruit abscission, to provide new ideas for the study of fruit abscission mechanism, and also provide the theoretical basis for scientific regulation of fruit abscission, improvement of fruit quality and reduction of loss in fruit tree production.
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