Research progress on the synthesis and metabolic pathways of volatile organic compounds in plants, as well as their release and perception regulation mechanisms
Human activities and biological metabolism produce various volatile organic compounds (VOCs), which can be classified into biogenic volatile organic compounds (BVOCs) and anthropogenic volatile organic compounds (AVOCs) based on their sources. Among them, plants are the main source of biogenic volatile organic compounds (BVOCs) in the atmosphere, which are generally synthesized through the secondary metabolic pathways of plants. In the 1950s and 1960s, the characteristic of plants being able to release BVOCs was first reported, and it has now been found that almost all plants can release BVOCs.

Volatile organic compounds (VOCs) are an important characteristic of plants, which differ from the physical properties of traditional plant terpenes, fatty acids, and phenylalanine/aromatic ring metabolites. They are more widely disseminated and therefore play various important roles in plant life, serving as the main medium for communication between plants and transmitting important plant information to other organisms, mediating various synergistic interactions above and below ground. Numerous studies have found that plant BVOCs have allelopathic effects, which can release allelopathic substances into the surrounding environment through volatilization, thereby affecting the defense response, reproduction, and competition of surrounding plants; Under stressful conditions, plants can alleviate the damage they suffer from biotic or abiotic stress by releasing BVOCs such as isoprene or green leaf volatiles; The synthesis and release of various plant BVOCs from flowers and nutrient parts also have an impact on plant reproduction, usually releasing volatile compounds with certain odors through petals and glands to attract specific pollinating insects for pollination; Plant BVOCs can also directly enhance plant competitiveness through emissions and have negative impacts on receivers, or indirectly regulate plant competition mechanisms by manipulating interactions with other nutrient levels; In addition, plants not only release BVOCs to protect themselves, but also provide early warning to neighboring unaffected plants, making them more defensive against subsequent stress.
BVOCs from plants also play an important role in human life. According to statistics, the annual emissions of BVOCs from plants account for 90% of the global terrestrial non methane volatile organic compound emissions, which have significant impacts on other organisms as well as atmospheric chemistry and physics. The released plant BVOCs, in the presence of sunlight and nitrogen oxides (NOx), increase the levels of O3 and other oxidants in the atmosphere, leading to the formation of tropospheric ozone and promoting the production of secondary organic aerosols; In addition, many plant BVOCs can also provide natural resources for human beings, and are widely used in perfumes, perfume, beverages, flavorings, cosmetics and other industries.
The BVOCs released by plants have a huge impact on plants and even human life. In recent years, research on various plant BVOCs has become a hot topic. BVOCs are produced in different plant organ physiological metabolism, released and enter the surrounding environment, and then re perceived by plants, playing a role in repelling pests, repelling weeds, and spreading information. This article mainly reviews the regulatory mechanisms in the synthesis and metabolism pathways of plant BVOCs, the physiological and physicochemical properties of released cells, and the perception and regulation of BVOCs by plants.

In the past few decades, significant progress has been made in understanding the synthesis and metabolic regulation mechanisms, as well as the regulation of release and perception of BVOCs in plants. However, currently, due to the complexity of terpenoid biosynthesis and metabolic pathways, many enzyme encoded genes have not been clearly defined, and some modifications in the final stage of terpenoid synthesis and metabolism are largely unknown; There are still many gaps in the research on volatile fatty acid metabolites and volatile phenylalanine/aromatic ring metabolites. Further research is needed to identify their key enzymes and related genes in metabolic pathways, as well as how these genes are regulated by transcription factors. In addition, due to the fact that plant BVOCs are released from different cells of plants through multiple barriers (including cytoplasm, plasma membrane, cell wall, stratum corneum, etc.), many researchers have proposed multiple hypotheses on how BVOCs move within and between plant cells, as well as how they are released into the environment. However, there are still many questions and controversies that need to be resolved. At the same time, our research group also found in previous studies that, from the perspective of plant kinship, external factors have a greater impact on the release of plant BVOCs than their own factors, which raises the question of how external factors (such as environmental factors) affect the release of plant BVOCs. In addition, plant BVOCs are perceived and converted into signals by plants after release, thereby inducing specific responses in plant cells. In the future, more precise mechanisms and pathways of perception regulation need to be revealed.