Research Progress on Lonicera japonica Thunb. Affected by Environmental Stress

Jinggang LI Longtai JU Lei ZHANG Panpan SUN Min LI Jia LI Yang LIU

Abstract Lonicera japonica Thunb. is widely distributed in China. It has strong adaptability to the environment and can maintain normal growth and development under a variety of stress conditions. It is commonly used as a medicine with its dry flower buds or newly opened flowers， named honeysuckle， and with both economic value and ecological application value. The research progress of L. japonica Thunb. under stress conditions such as temperature， drought， light， salt， heavy metals and diseases， pests and endophytic bacteria was reviewed， and the current research situation of the physiological and biochemical response mechanism， changes of photosynthetic fluorescence and accumulation of secondary metabolites of honeysuckle under different stresses was discussed， so as to provide a reference for deep-level exploring the resistance mechanism of L. japonica Thunb. in the future and lay a theoretical foundation for the high-quality authentic ecological cultivation of L. japonica Thunb.

Key words Honeysuckle; Environmental stress; Stress resistance; Response mechanism

Received： October 21， 2021  Accepted： December 23， 2021

Supported by National Key R&D Program （2017YFC1701503）; National Nature Science Foundation of China （81872963）.

Jinggang LI （1968-）， male， P. R. China， devoted to research about economic forest management and promotion.

*Corresponding author. E-mail： ljytl7172@163.com.

Lonicera japonica Thunb. is a perennial semi-evergreen voluble and stoloniferous shrub， the flower buds or open flowers of which are used as a medicine[1]. The flower buds are cold in nature and sweet in taste， and have the functions of clearing away heat and removing toxic substances， and dispersing wind-heat. They can be used for treating symptoms such as pharyngitiss， carbuncle and furuncle， bloody dysentery， febrile disease and fever. The chemical components in honeysuckle are mainly organic acids， flavonoids， iridoid glycosides， triterpenoid saponins， volatile oils and other components. Modern pharmacological studies have shown that in addition to anti-inflammatory， antibacterial， antiviral， and antioxidant effects， honeysuckle has significant blood sugar-reducing， liver protection， anti-tumor， and blood lipid-lowering effects[2]. It is a commonly used medicinal material and is widely used in clinical treatment of traditional Chinese medicine. According to statistics， about 1/3 of Chinese medicine clinical prescriptions in China use honeysuckle[3]. In addition， it is widely used in food， health care products and other fields.

L. japonica Thunb. is extremely adaptable to the environment. Hillsides and hills， sparse forests and thickets， hillside roads， and the front and back of rural houses are all suitable habitats for L. japonica Thunb. Materia Medica Companion once said that "L. japonica Thunb.  generally grows in fields， or on the walls of gardens". L. japonica Thunb. does not have high requirements for habitat soil， and it can grow in loam， sandy soil and clay soil， even in karst areas in southwest China[4]. In addition， L. japonica Thunb. has excellent cold resistance， drought resistance， salinity resistance and other properties. In recent years， it has also been used in landscaping， windbreak and sand fixation. Chinese researchers have done a lot of research on the response of L. japonica Thunb. to environmental stress， mainly focusing on temperature stress， drought stress， light stress， salt stress， heavy metal stress and biological stress. In order to more deeply and systematically explore the adaptation mechanism of L. japonica Thunb. to adversity， and explore the economic value and ecological application value of L. japonica Thunb.， we reviewed the research progress on the physiological and biochemical response mechanism， photosynthetic fluorescence changes and accumulation of secondary metabolites of L. japonica Thunb. under various environmental stresses. This study aimed to provide a reference for exploring the deep-level mechanism of L. japonica Thunb. resistance in the future， and for the ecological planting of high-quality authentic L. japonica Thunb. as well.

Abiotic Stress

Temperature stress

Temperature stress is generally divided into high temperature stress and low temperature stress. L. japonica Thunb. "does not wither in winter" and has strong adaptability. It can grow in all parts of China except in the alpine regions of the northwest and northeast. Normal growing plants， after being subjected to temperature stress， first appear as yellow and brown leaves and dead spots in appearance. At 5， 15， and 35 ℃， the leaves of L. japonica Thunb. showed chlorosis after 3 d of treatment; after 14 d， frostbite spots appeared in the low temperature group， and in the high temperature group， the leaf margins lost water and curled， and the root color changed from white to tan; and after 25 d， the leaves wilted and fell， and the roots turned dark brown. The contents of chlorophyll and carotenoid in L. japonica Thunb. leaves decreased after temperature stress， and the damage was more obvious in low temperature environment. Meanwhile， temperature stress can destroy the structure of PSII reaction center in leaves and cause a decrease in Fv/Fo and Fv/Fm， resulting in a continuous decrease in light energy conversion efficiency， a reduction in the number of stomatal openings， and limitation of photosynthesis[5]. Temperature stress can also cause changes in plant cell membrane systems. Under low temperature or high temperature treatment， the cell membrane permeability of L. japonica Thunb. leaves will increase to varying degrees[5]. Temperature stress will continuously damage the cell membrane， which leads to extravasation of water-soluble substances in cells， resulting in changes in cell conductivity. The stronger the degree of low temperature stress， the greater the relative conductivity. Meanwhile， temperature stress can cause more ROS to be produced in plants， which in turn leads to oxidative stress and promotes lipid peroxidation， protein oxidation and other reactions. Lipid peroxidation will change the MDA content in plants， and the stronger the cold resistance of plants， the lower the MDA content[6]. Studies have found that with the decrease of temperature below freezing point， the relative conductivity of cell membrane and MDA content in L. japonica Thunb. leaves increased continuously， and the SOD activity first increased and then decreased[7-8]. With the increase of temperature above zero， the content of MDA in the cell membrane of L. japonica leaves first decreased and then increased， and the activity of SOD， POD， CAT， APX and other antioxidant enzymes first increased and then decreased[5]， and reached the maximum at 25 ℃， indicating that temperature stress will damage the membrane system of L. japonica Thunb. and reduce the antioxidant level of leaf cells. In addition， as important osmotic regulators， soluble sugar， soluble protein， and proline are all important indicators to characterize the degree of plant temperature stress. With the decrease of temperature below freezing point， the contents of proline， soluble sugar and soluble protein in leaves all showed a rising trend[9-10]， and different varieties of L. japonica Thunb. had different proline contents at low temperature， indicating different cold resistance[10-11]. Temperature stress can also initiate the molecular response mechanism of L. japonica in vivo. Qiao et al.[12] found that AP2 transcription factor could participate in the low temperature response mechanism of L. japonica Thunb. After low temperature treatment， AP2_7， AP2_24 and AP2_30 had the highest expression levels in leaves， and it was speculated that they might mediate the anti-low temperature expression of leaves expression of low temperature resistance in leaves; AP2_10 had the highest expression level in roots， and it was speculated that it might mediate the anti-low temperature expression of low temperature resistance in roots; and real-time PCR detection results showed that both DREB and RAV genes could respond to low temperature stress， and their expression levels were different in different organs. DREB was concentratedly expressed in leaves and RAV was concentratedly expressed in roots.

Drought stress

With the intensification of global climate change， the phenomenon of plants being subjected to drought stress is becoming more and more normal. Drought and water shortage seriously affect the growth and development of plants. Dang et al.[13] pointed out that the damage caused by drought to plants exceeded the sum of other adversity factors. L. japonica Thunb. is mostly distributed in mountainous and hilly areas， where the soil has poor water holding capacity and vulnerable to drought stress. Under drought conditions， L. japonica Thunb. leaves generally show a decline in water potential， an increase in water saturation deficit[14]， and a continuous decrease in chlorophyll content[15]. Zhao et al.[16] showed that different degrees of drought had different effects on the leaves of L. japonica Thunb.， the water point （RSWCSL-NSL） at which the photosynthesis of L. japonica Thunb. changed from stomatal factor limitation to non-stomatal factor limitation was 29.7%， and the water points for Pn≈0 and plant leaf wilting were both 11.4%， at which the damage degree of photosynthetic mechanism was the greatest. Some scholars have specially studied the changes of chlorophyll fluorescence characteristics under drought conditions[15，17]. After L. japonica Thunb. lacked water， the leaf Fo increased significantly， and Fv/Fm， ETR， and qP decreased significantly， which is consistent with the research results of Zhao et al.[16]. In addition， it was also found that under drought conditions， leaf Fm and Fv/Fo significantly decreased， and qN increased， indicating that the PSII reaction center of L. japonica Thunb. leaves was damaged. In arid environments， L. japonica Thunb. resists drought by regulating protective enzymes and other substances in the body. Huang et al.[18] studied the changes in the physiological characteristics of L. japonica Thunb. seedlings under different PEG-6000 concentrations. The results showed that with the increase of PEG concentration， the MDA content gradually increased， and CAT， SOD， POD， and APX were activated in turn and showed an overall trend of increasing first and decreasing then， and the contents of proline and soluble sugar reached the highest values after 72 h of treatment， indicating that under drought stress， membranous peroxidation in L. japonica Thunb. gradually increased， and L. japonica Thunb. resisted drought stress by increasing the content of proline and soluble sugar and protecting the enzyme system. Meng et al.[19] found that for L. japonica Thunb. in the natural arid environment， the content of proline and soluble sugar increased with the extension of the stress time， the content of MDA increased first and then decreased， and the activity of POD increased first， then decreased and then increased， which is similar to the research results of Ma et al.[20]. Moreover， drought stress will also cause the reduction of nitrate reductase activity and root activity in L. japonica Thunb.[21]， and the quality of flower buds and yield per plant will be significantly reduced[20].

Light stress

As a direct source of energy for plant photosynthesis， light can determine the survival and growth of most plants. Light intensity， light quality and light time all affect the growth and development of plants and the synthesis and accumulation of secondary metabolites in the body of  L. japonica Thunb. is a heliophile， and proper and sufficient light is beneficial to improve the quality of L. japonica Thunb. herbs and increase the size and dry weight of flower buds. Some scholars pointed out that the contents of chlorogenic acid and luteolin reached their maximum under full light conditions[22-23]. If the light is too strong， L. japonica Thunb. will appear photoinhibition， while long-term lack of light and a weak light environment will cause weak light stress on L. japonica. Thunb. under shading conditions， 50% light transmittance was beneficial to the growth of L. japonica Thunb.[24]. With the weakening of light intensity， the length of L. japonica Thunb. buds and the fresh weight of single flower increased first and then decreased， the dry weight of single flower decreased， the content of photosynthetic pigments gradually increased， the Chl a/b value decreased， Pn， Gs， Tr and Ci all showed a downward trend， Ls increased， and MDA content and SOD， CAT and POD activity decreased first and then increased; and with the prolongation of treatment time， the content of MDA increased， while the activity of SOD， CAT and POD increased first and then decreased， which is consistent with the research results of Xue et al.[25]. Meanwhile， the study found that under artificial shading conditions， the shortening of light time was not conducive to the growth of L. japonica Thunb.， and would inhibit the synthesis of leaf photosynthetic pigments， resulting in the reduction of Chl a， Chl b， and Car content in the leaves of L. japonica Thunb.， which in turn caused the reduction of photosynthetic parameters such as Pn， Gs， Tr， and Ci and the increase of Ls. In addition， light also affects the key enzymes of secondary metabolism in L. japonica Thunb. Under different light intensities， the four enzymes PAL， HQT， CHS and CHI in flower buds in the large white period were positively correlated with light intensity， which was consistent with the content change trends of chlorogenic acid and luteolin， and their expression levels were the highest under full light conditions. C4H1 and C3H1 were most abundantly expressed under 65% full light conditions. Among these four enzymes， the expression of CHI was most significantly affected by light intensity[23].

Agricultural Biotechnology2022

Salt stress

Soil salinization has become an important environmental factor restricting the growth of crops. China’s salinized land accounts for about 10% of the global saline soil area. During the evolution process， a large number of plants gradually adapt to the growth of sweet soil and lose their tolerance to high concentrations of salt. As a highly tolerant economic plant， L. japonica Thunb. has strong resistance to salt and alkali. In recent years， it has been gradually promoted in coastal salinized areas. Binzhou， Dongying and other places in Shandong Province have become new production areas of L. japonica Thunb. Studies have shown that L. japonica Thunb. has certain adaptability to low-salt stress[26]. With the increase of salt concentration and the extension of stress time， the photosynthesis and growth and development of L. japonica Thunb. will be inhibited[27]， resulting in leaf wilting and even plant death. Under short-term stress， with the increase of salt concentration， the contents of Chl a and Chl b decreased slightly， while the content of Car increased continuously; in the later stage of stress， the contents of the three photosynthetic pigments continued to increase[28]. Different concentrations of salt stress had different effects on photosynthesis and chlorophyll fluorescence parameters of L. japonica Thunb. When the salt concentration was 0.15%， Ls of L. japonica Thunb. decreased， Pn， Gs， Tr， Ci and WUE increased， Fo and qN of leaves decreased， and Fm， Fv/Fm and qP increased; when the salt concentration was 0.45% and 0.60%， except that Ci first decreased and then increased， Pn， Gs， Tr and WUE of L. japonica Thunb. showed a linear downward trend， which might be due to the decrease in the activity of phosphoenolpyruvate carboxylase （PEPC） and ribulose-1， 5-bisphosphate carboxylase/oxygenase （rubisco） caused by excessive salt[29]. At this time， the main reason for the decrease of Pn was changed from stomatal factor to non-stomatal factor， and Ls first increased and then decreased， while Fo and qN continued to increase， and Fm， Fv and qP continued to decrease[30-31].

In addition， salt stress will disrupt the osmotic balance in plants， which will lead to ion imbalance， nutrient deficiency， and changes in membrane permeability， physiological and biochemical metabolic disorders and accumulation of toxic substances caused by oxidative stress， which ultimately affect plant growth and development. Xu et al.[32] found that when the treatment concentration was greater than 0.4%， the growth of L. japonica Thunb. was severely inhibited. With the increase of salt concentration， the osmotic potential of L. japonica Thunb. leaves gradually decreased， the cell membrane permeability gradually increased， the proline content increased， and the SOD activity gradually increased. Bao et al.[33] also found that the proline content in the leaves of L. japonica Thunb. was positively correlated with the salt concentration， and tree-type L. japonica Thunb. was more sensitive to salt stress and had a stronger osmotic regulation ability than vine-like L. japonica Thunb. Salt stress also affects ion content， ion ratio and related gene expression in various parts of L. japonica Thunb. Huang et al.[34] showed that the Na+ content in each part of L. japonica Thunb. increased significantly with the increase of salinity， the K+ content first increased and then decreased， and the Ca2+ content decreased significantly， but the Mg2+ content in roots and stems did not change significantly， and the Mg2+ content in leaves decrease continuously; the ratios of K+ to Na+， Ca2+ to Na+ and Mg2+ to Na+ in each part decreased rapidly after salt stress， and the higher the salt concentration， the lower the ratios; and the photosynthesis-related genes Cab and rbcL of L. japonica Thunb. were rapidly and highly expressed under short-term salt stress.

In addition， salt stress will affect the primary and secondary metabolism of L. japonica Thunb. in vivo. After salt stress， ROS accumulated in L. japonica Thunb. in vivo， causing a chain reaction of polyunsaturated fatty acids， resulting in the increase in the contents of three endogenous hormones， SA， ABA， and JA in L. japonica Thunb.[35]. YAN et al.[36-37] believed that the accumulation of phenolic substances in leaves was a mechanism for L. japonica Thunb. to adapt to salt stress. Studies have shown that salt stress can promote the synthesis of phenolic compounds in leaves， stimulate the transcription of genes encoding key enzymes for chlorogenic acid synthesis in leaves， and significantly increase the transcription level of the PAL gene family， the activity of phenylalanine ammonia lyase and the concentration of phenols also increase， while moderate salt stress is more conducive to the accumulation of active compounds in L. japonica Thunb. leaves. The content of active ingredients in flower buds is the highest when the salt concentration is 0.5%， and a high-concentration neutral salt environment is most conducive to the accumulation of phenolic acids in flower buds[38].

Heavy metal stress

The rapid development of modern society has caused a great impact on agricultural production， and soil heavy metal pollution has become increasingly prominent. In recent years， with the implementation of the comprehensive prevention and control plan for heavy metal pollution， the overall situation of heavy metal pollution in China’s cultivated land has improved， but the pressure is still ongoing. L. japonica Thunb. has a strong ability to enrich heavy metals and has great potential in the field of remediation of heavy metal pollution. Studies have shown that L. japonica Thunb. has a strong tolerance to Cd and is a Cd hyperaccumulator. After Cd treatment， the Cd content in plants increased， and Cd absorbed by L. japonica Thunb. was mainly concentrated in the roots， showing a distribution pattern of root>stem>leaf[39]. The contents of other elements in L. japonica Thunb. also changed after Cd treatment. With the increase of Cd concentration in soil， Fe content in roots increased， while Mn， Cu， and Zn contents decreased; and Cu content in leaves decreased， while Fe， Mn and Zn contents increased at low concentrations and decreased at high concentrations[40]. Meanwhile， the effect of Cd on plant growth shows a significant dose-effect relationship， which is called hormesis， that is， low concentration promotes， high concentration inhibits. Jia et al.[41] pointed out that the dose range for Cd to produce hormesis on L. japonica Thunb. was 0.5-5.0 mg/L. When the Cd concentration was 5.0 mg/L， the biomass of seedlings increased， the water content and soluble protein content of each part decreased， while the contents of Chl， Car and MDA in leaves and MDA in roots all increased， and SOD activity was significantly enhanced[39-41]. With the increase of Cd concentration， some leaves of L. japonica Thunb. gradually appeared chlorotic symptoms， the contents of chlorophyll and carotenoid in leaves and SOD activity in seedlings decreased[42]， the level of reactive oxygen species continued to increase， and the degree of membrane lipid peroxidation increased， MDA and proline contents increased， and Cd concentration≥150 mg/kg inhibited the normal growth of L. japonica Thunb.， resulting in antagonism[43].

In addition to Cd， L. japonica Thunb. also has strong tolerance to heavy metal elements such as Pb and Cu. The accumulation of Pb in L. japonica Thunb. is mainly in the roots[44]， and the enrichment capacities rank as root>leaf>flower. When the concentration of Pb increased continuously， the yield and biomass of L. japonica Thunb. decreased continuously. When Pb≥800 mg/kg， the contents of proline， soluble sugar and soluble protein increased the most， and when the concentration reached 1 000 mg/kg， the content of MDA reached the maximum value. The study of He[45] also showed that L. japonica Thunb. had strong tolerance to lead and zinc tailings. Cu stress treatment had the effect of promoting at low concentrations and inhibiting at high concentrations on the growth of L. japonica Thunb.[46]， and when the content of Cu was lower than 25 mg/L， L. japonica Thunb. could grow normally.

Biotic Stress

The biotic stress of L. japonica Thunb. mainly comes from diseases， pests and fungal infection. L. japonica Thunb. is very vulnerable to pests and diseases during its growth， which will affect the yield and quality of medicinal materials[47]， and even lead to production failure in severe cases. Pests such as aphids， Xylotrechus grayii White， Holotrichia diomphalia Bates， Tetranychus cinnbarinus and measuring worm are common pests in L. japonica Thunb. cultivation， among which aphids are the most common. The budding stage and flowering stage are the most serious periods of L. japonica Thunb. aphid damage， and the main damage aphids are Amphicercidus sinilonicericola Zhang and Semiaphis heraclei （Takahashi）[48]. After being attacked by aphids， L. japonica Thunb. leaves turn yellow， curled and shrunken， buds shrunken and deform， and yield decreases[49]， and the contents of chlorogenic acid， loganin， caffeic acid， luteolin， neochlorogenic acid and rutin in flower buds are lower than those in the flower buds of normal plants， and the contents of caffeic acid， quercetin， isochlorogenic acid B and isochlorogenic acid C increase[50-51]. After aphids invaded for a long time， the activity of leaf defense enzymes also changed. The activity of POD in leaves first increased and then decreased， the activity of PAL and PPO increased first， then decreased and then increased， and SOD activity showed a wave-like change[49].

L. japonica Thunb. diseases are mostly powdery mildew， brown spot and root rot. In the early stage of the onset of powdery mildew， small brown spots appear on the front of the leaves， and then gradually turn into circular or irregular white powdery lesions， and then the lesions continue to expand and connect into pieces， so that the leaves are covered with white powdery mildew[52].  Chen et al.[53] found that mild powdery mildew could increase the chlorogenic acid content in honeysuckle， and with the aggravation of the disease， the chlorogenic acid content was gradually lower than that of the control. For the brown spot disease of L. japonica Thunb. caused by Phomopsis spp.[54]， small yellow-brown spots appear on the leaves at the early stage of the disease， and gradually merge together in the later stage， appearing as round spots or irregular spots limited by leaf veins， which can lead to falling of all leaves of L. japonica Thunb.[55]. In addition， root rot is becoming more and more serious in L. japonica Thunb. cultivation. According to field surveys， in 2018， the incidence of L. japonica Thunb. root rot in Pingyi County reached 20% to 30%， and the yield was reduced by more than 30%. Studies have shown that the pathogenic fungus Fusarium oxysporum is the main culprit in causing root rot of L. japonica Thunb.， which mostly occurs in plants with pests on the roots， and occurs more heavily in acidified and salinized soils[56].

AM fungi are widely distributed in nature and can form symbionts with about 90% of the plants on the earth. They are one of the most closely related microorganisms found so far[57]. There are various types of AM fungi in the root system of L. japonica Thunb.， with the highest abundance in spring and the lowest in summer， and the abundance is significantly positively correlated with soil available P and total nitrogen， and significantly negatively correlated with soil pH[58]. AM fungal infection can improve the root growth， photosynthesis， physiological metabolic activity and water use efficiency of L. japonica Thunb.， promote the absorption of nutrients by L. japonica Thunb.， and enhance the drought resistance and disease resistance of L. japonica Thunb. After inoculation with AM fungi， the root surface area and volume of L. japonica Thunb. roots increase. Liu et al.[59] found that AM fungi could promote the root growth of L. japonica Thunb. in drought and dry-wet alternating environments by increasing root-shoot ratio， and the effect was more significant in arid environment. Meanwhile， AM fungi could promote the absorption of nutrient elements in L. japonica Thunb.， and the contents of N and P elements in plants after AM infection were significantly higher than those before infection; and the accumulation of K， Ca， and Mg in leaves was enhanced， and Mg among them had the strongest response to AM fungi， and the Mg content could be increased by 3.16 times after inoculation of mycorrhizae with normal watering[60]. In addition， some studies speculated that the increase of Ca content is related to the involvement of Ca2+ as the main signal substance in cell signal transduction after AM fungal infection[61]. In addition， under normal growth conditions， AM fungal infection can increase the Pn， Tr， and Gs of L. japonica Thunb.， while L. japonica Thunb. will appear photosynthetic inhibition after water stress. AM fungi can increase leaf Pn and WUE， reduce Gs， and then improve the growth of L. japonica Thunb.[62].

Summary and Prospect

Medicinal plants are subject to different degrees of environmental stress during their growth. Environmental stress not only affects the photosynthesis， nutrient absorption， physiological and biochemical reactions of plants， but also promotes the formation and accumulation of secondary metabolites in plants， affecting the quality of medicinal materials. The formation of high-quality authentic medicinal materials is inseparable from specific environmental conditions. Pingyi in Shandong， Julu in Hebei and Fengqiu in Henan are the main producing areas of L. japonica Thunb. Their climate is mainly a continental warm temperate monsoon semi-arid climate， and the terrain is mainly plain or low hills. They have sufficient sunlight， more precipitation in summer and autumn， and long frost-free period， all of which directly or indirectly affect the quality of L. japonica Thunb.

At present， the research on the environmental stress of L. japonica Thunb. mainly focuses on the aspects of temperature， drought， light， salt， heavy metals， pests and diseases， endophytes and so on. These stresses are all common types of stress in L. japonica Thunb. cultivation and are the main aspects of traditional botanical research. However， at present， most studies have conducted in-depth research on the apparent morphology， photosynthetic fluorescence response， and physiological and biochemical indicators of L. japonica Thunb.， but there are also many problems.

① The research on the correlation between environmental stress and honeysuckle quality is not in-depth. Environmental stress not only affects the morphogenesis， physiological and biochemical reactions of medicinal plants， but also ultimately affects the formation and accumulation of secondary metabolites in the body. Under the premise of guaranteeing the normal growth of L. japonica Thunb.， exploring the optimal conditions for improving the yield and quality of honeysuckle can provide technical support for the ecological planting of L. japonica Thunb.

② Most studies focus on a single stress， while L. japonica Thunb. is often affected by multiple stresses in actual production. The effects of single stress and compound stress on plant growth and development are very different， and the effects of compound stress on plant growth and development and secondary metabolites cannot be simply inferred from single stress. When multiple stresses act together， there will be synergistic， antagonistic or independent relationships between different stress conditions， and the cross-influence of multiple signaling pathways in plants will make the mechanisms for plants to respond to compound stress extremely complex.  On the basis of simulating the original production environment， exploring the response mechanism of L. japonica Thunb. to compound stress and the change mechanism of secondary metabolites will lay a theoretical foundation for the production of high-quality authentic honeysuckle.

③ Most of the current research focuses on the physiological and biochemical mechanisms of L. japonica Thunb. resistance to stress， while the research on the deep-level stress resistance mechanism， key signaling substances and secondary metabolic gene regulatory network of L. japonica Thunb. is relatively rare. With the rapid development of omics technology， the combined analysis of biological mechanisms by multi-omics has become an indispensable means of botanical research. Through environmental stress experiments， we can understand the molecular mechanism of L. japonica Thunb. in response to stress， excavate the response genes and proteins in L. japonica Thunb. under specific conditions， analyze its molecular and metabolic pathways in response to stress signals， and comprehensively elucidate the stress resistance mechanism of L. japonica Thunb.， so as to provide references for improving the quality of honeysuckle.

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Editor： Yingzhi GUANG  Proofreader： Xinxiu ZHU