Amanitin-induced variable cytotoxicity in various cell lines is mediated by the different expression levels of OATP1B3.

Amanita phalloides is one of the deadliest mushrooms worldwide, causing most fatal cases of mushroom poisoning. Among the poisonous substances of Amanita phalloides, amanitins are the most lethal toxins to humans. Currently, there are no specific antidotes available for managing amanitin poisoning and treatments are lack of efficacy. Amanitin mainly causes severe injuries to specific organs, such as the liver, stomach, and kidney, whereas the lung, heart, and brain are hardly affected. However, the molecular mechanism of this phenomenon remains not understood. To explore the possible mechanism of organ specificity of amanitin-induced toxicity, eight human cell lines derived from different organs were exposed to α, ß, and γ-amanitin at concentrations ranging from 0.3 to 100 µM. We found that the cytotoxicity of amanitin differs greatly in various cell lines, among which liver-derived HepG2, stomach-derived BGC-823, and kidney-derived HEK-293 cells are most sensitive. Further mechanistic study revealed that the variable cytotoxicity is mainly dependent on the different expression levels of the organic anion transporting polypeptide 1B3 (OATP1B3), which facilitates the internalization of amanitin into cells. Besides, knockdown of OATP1B3 in HepG2 cells prevented α-amanitin-induced cytotoxicity. These results indicated that OATP1B3 may be a crucial therapeutic target against amanitin-induced organ failure.

Glycosides from the leaves of Fraxinus Hubeiensis.

Fraxinus hubeiensis is a plant endemic to China and widely used as folk medicine to treat various diseases. However, its chemical constituents have never been reported sufficiently. Thus, the primary objective of this study was to investigate the phytochemical constituents and biological activities of F. hubeiensis leaves. Hence, combined column chromatographic and spectroscopic techniques were used to identify and characterize the secondary metabolites such as a pair of 3-keto-glycoside epimers (1) and (2), along with five known compounds (3 ~ 7). The results of α-glucosidase inhibitory activity exhibited that 1 and 2 had moderate activity with IC50 values of 359.50 and 468.43 µM, respectively, compared to a positive control acarbose with the IC50 value of 164.08 µM. However, Compounds 1-6 were shown to be inactive against the tested microbes.

An Exploration of the Effect of the Kleier Model and Carrier-Mediated Theory to Design Phloem-Mobile Pesticides Based on Researching the N-Alkylated Derivatives of Phenazine-1-Carboxylic Acid-Glycine.

The Kleier model and Carrier-mediated theory are effective for molecularly designing pesticides with phloem mobility. However, the single Kleier model or Carrier-mediated theory cannot achieve a reliable explanation of the phloem mobility of all exogenous substances. A detailed investigation of the two models and the scope of their applications can provide a more accurate and highly efficient basis for the guidance of the design and development of phloem-mobile pesticides. In the present paper, a strategy using active ingredient-amino acid conjugates as mode compounds is developed based on Carrier-mediated theory. An N-alkylated amino acid is used to improve the pesticide's physicochemical properties following the Kleier model, thus allowing the conjugates to fall on the predicted and more accessible transportation region of phloem. Moreover, the influence of this movement on phloem is inspected by the Kleier model and Carrier-mediated theory. To verify this strategy, a series of N-alkylated phenazine-1-carboxylic acid-glycine compounds (PCA-Gly) were designed and synthesized. The results related to the castor bean seeds (R. communis L.) indicated that all the target compounds (4a−4f) had phloem mobility. The capacity for phloem mobility shows that N-alkylated glycine containing small substituents can significantly improve PCA phloem mobility, such as 4c(i-C3H7-N) > 4a(CH3-N) ≈ 4b(C2H5-N) > 4d (t-C4H9-N) > PCA-Gly > 4e(C6H5-N) > 4f(CH2COOH-N), with an oil−water partition coefficient between 1.2~2.5. In particular, compounds 4a(CH3-N), 4b(C2H5-N), and 4c(i-C3H7-N) present better phloem mobility, with the average concentrations in phloem sap of 14.62 µΜ, 13.98 µΜ, and 17.63 µΜ in the first 5 h, which are 8 to 10 times higher than PCA-Gly (1.71 µΜ). The results reveal that the Kleier model and Carrier-mediated theory play a guiding role in the design of phloem-mobile pesticides. However, the single Kleier model or Carrier-mediated theory are not entirely accurate. Still, there is a synergism between Carrier-mediated theory and the Kleier model for promoting the phloem transport of exogenous compounds. Therefore, we suggest the introduction of endogenous plant compounds as a promoiety to improve the phloem mobility of pesticides through Carrier-mediated theory. It is necessary to consider the improvement of physicochemical properties according to the Kleier model, which can contribute to a scientific theory for developing phloem-mobile pesticides.

Study on the selectivity and phloem mobility of Fenoxaprop-P amino acid ester conjugates on rice and barnyard grass.

To improve the selectivity of the fenoxaprop herbicide to rice and barnyard grass, a series of fenoxaprop-P-ethyl-amino acid ester conjugates were designed and synthesized, and tested for biological activity as well as their phloem mobility. The bioassay results indicated that the target compounds possessed better activity against barnyard grass (Echinochloa crusgalli) than rape (Brassica campestris L.) at the concentration of 0.5 mmol/L. Compounds 3h and 3i, showed more than 70% control efficiency against barnyard grass, while less than 30% for rape. The compounds showed less impact on rice after spray treatment than in the germination test. Compounds 3i, 3j, and 3k showed excellently herbicidal activities against barnyard grass and low phytotoxicity to rice. Compound 3k showed 6.1% phytotoxicity to rice at a spray concentration of 0.25 mmol/L, better than fenoxaprop-P-ethyl (61.6%) at the same concentration. The selectivity results of the target compounds revealed that most of compounds obviously reduced phytotoxicity to rice while retaining herbicidal activity of barnyard grass. The herbicidal activity of compound 3d compared to FPE was increased by 50%, while its safety on rice was also increased by 50%. The concentration of the compounds in barnyard grass roots was higher than in rice roots, showing greater phloem mobility. In particular, the concentration of compound 3d on barnyard grass exhibited 142.72 mg/kg which was 3 times as much as Fenoxaprop, while its concentration on rice exhibited 3.65 mg/kg, the results revealed that the difference of phloem mobility might be the important reason for causing the selectivity.

Fungicidal Action of the Triphenylphosphonium-Driven Succinate Dehydrogenase Inhibitors Is Mediated by Reactive Oxygen Species and Suggests an Effective Resistance Management Strategy.

Succinate dehydrogenase (SDH) is an effective target of SDH inhibitor (SDHI) fungicides which received more and more attention in recent years. However, there is no good solution to their rapidly growing drug resistance caused by frequent use. In this study, three triphenylphosphonium (TPP)-conjugated boscalid analogues were synthesized and tested for antifungal activities. They all, especially 2c, exhibited enhanced fungicidal activity and broader spectra compared to boscalid. The action mechanism study revealed that 2c was also an SDH inhibitor acting on the Qp site. However, the rapid accumulation of 2c in mitochondria because of TPP-targeting triggered reactive oxygen species burst in mitochondria, resulting in irreversible damage to the mitochondrial structure and function. Thus, 2c made the fungicidal activity output mode changing from mainly relying on ATP production inhibition (as traditional SDHIs) to significant damage of the cell structure and functions. This mechanism change made it difficult for plant pathogenic fungi to develop resistance to 2c and its analogues, which was of great significance for the increasingly challenging management of field resistance to SDHI fungicides.

Synthesis and insecticidal activity of the fluorinated galegine analogues.

The introduction of fluorine atom can increase the biological activities of the target compounds remarkably. To find more safe and efficient insecticides, natural product galegine as lead compound, a series of novel fluorinated galegine analogues were designed and synthesized. The bioassay results indicate that all the target compounds have moderate to high insecticidal activities against Hyalopterus pruni Geoffroy and Aphis gossypii Glover, in particular, compounds IIa-05, IId-02 and IIe-03 show the best insecticidal activities against Hyalopterus pruni with the mortality of 100%, 100% and 96.6%, respectively. And compounds IIa-02, IId-02, IId-04, IIc-01, IIc-02 and IId-01 show 0.6-7 times insecticidal activities against Aphis gossypii as Imidacloprid with their LC50 values are 0.28 mg/L, 0.38 mg/L, 0.33 mg/L, 0.09 mg/L, 0.03 mg/L and 0.12 mg/L, respectively The analysis of structure-activity relationship indicates that the compounds with difluoro-substituted benzene ring have more potent insecticidal activities than the single fluoro-substituted compounds.

Effect of introducing amino acids into phenazine-1-carboxylic acid on phloem mobility.

To develop new phenazine carboxylic acid derivatives with better phloem mobility, five novel 7-amino acid substituted phenazine-1-carboxylic acids were synthesised by introducing amino acids into PCA at the 7-position. The phloem mobility experiments in Ricinus communis seedlings showed that retaining the carboxyl group of PCA and conjugating amino acids to its phenazine ring can also endow PCA with phloem mobility. Comparing our previous research, we found the amino acids substituted at 7-position on phenazine ring of PCA could clearly enhance the phloem mobility of PCA than that of amino acids conjugated with carboxyl group. Especially, the phloem transport concentration of the compound 7-L-isoleucine substituted PCA (7d) was 21 times higher than PCA-L-isoleucine conjugate (8d). These data suggest that the introduction of amino acids at different structural sites on the phenazine ring could effectively enhance the phloem mobility of PCA and it is worth a further study.

Design and synthesis of novel hydrocarbylidene nitrohydrazinecarboximidamides against aphids based on natural product galegine.

A series of novel hydrocarbylidene nitrohydrazinecarboximidamides were designed and synthesized using an insecticidal natural product Galegine as a lead compound. The bioassay results show that the target compounds exhibited moderate to good insecticidal activities against Hyalopterus pruni Geoffroy at a concentration of 200 mg/L, and most compounds show excellet insecticidal activities against Aphis gossypii Glover. In particular, compounds IIc-01, IIc-03, IIe-02 and IIf-01 show the equal activities to a commercial pesticide Imidacloprid with their LC50 values are 0.21 mg/L, 0.27 mg/L, 0.12 mg/L and 0.24 mg/L, respectively, and compounds IIc-02 and IIe-05 show 10 times insecticidal activities as much as Imidacloprid with their LC50 values both are 0.02 mg/L. Structure-activity relationship and 3D-QSAR analyses indicate that the introduction of fluorine atom is useful for increasing the insecticidal activity of target compounds.

Synthesis and fungicidal activity of phenazine-1-carboxylic triazole derivatives.

A total of 15 novel-substituted 3-(benzylsulfanyl)-1H-1,2,4-triazol-5-ylamine and 10 novel-substituted 3-benzylmercapto-1,2,4-triazol derivatives were synthesized based on the natural product phenazine-1-carboxylic acid (PCA). Their structures were confirmed by 1H-NMR, 13C-NMR, HRMS, and X-ray. Most substituted 3-benzylmercapto-1,2,4-triazol derivatives displayed very strong fungicidal activity against one or multiple plant pathogens in vitro and in vivo. Compounds 8b, 8h, and 8i showed a broad spectrum of fungicidal activity. Further field experiments indicated that compounds 8b, 8c, and 8h displayed better efficacy against rice blast (Pyricularia oryzae) than PCA. These data demonstrate that compounds 8b, 8c, and 8h are promising fungicidal candidates, deserving further studies.[Formula: see text].

Chemical Composition and Attractant Activity of Volatiles from Rhus potaninii to The Spring Aphid Kaburagia rhusicola.

Rhus potaninii Maxim, a type of sumac, is an economically important tree widely cultivated in mountainous areas of western and central China. A gall, called the bellied gallnut, induced by the aphid, Kaburagia rhusicola Takagi, is important in the food, medical, and chemical industries in China. Volatiles from R. potaninii were found to attract K. rhusicola, but little is known about them. The chemical composition of these volatiles was investigated using GC-MS analysis and Y-tube olfactometer methods. Twenty-five compounds accounting for 55.3% of the volatiles were identified, with the highest proportion of 1-(4-ethylphenyl)ethanone (11.8%), followed by 1-(4-hydroxy-3-methylphenyl)ethanone (11.2%) and p-cymen-7-ol (7.1%). These findings provide a theoretical basis for the preparation of attractants and could eventually lead to increased bellied gallnut yield.

Synthesis and herbicidal activity against barnyard grass of novel diarylmethanone O-(2,6-bis((4,6-dimethoxypyrimidin-2-yl)oxy)benzoyl)oximes.

BACKGROUND: Pyribenzoxim is an excellent herbicide that can effectively control barnyard grass. However, there are few reports of its structural analogs and structure-activity relationship (SAR), which makes pyribenzoxim an isolated case. Here, a series of diarylmethanone oxime esters characterized by pyridine heterocycles were designed and synthesized for herbicidal screening and SAR investigation against barnyard grass. RESULTS: At greenhouse treatment concentrations of 1.17-37.5 µg mL-1 , the title compounds showed a positive dose-toxicity correlation toward barnyard grass plants, with the damage becoming progressively more serious over time. At a concentration of 18.75 µg mL-1 and above, obvious damage was observed in 3 days, most plants died in 7 days, and all died in 14 days. Different degrees of damage were also seen when the concentration was lower than 9.38 µg mL-1 . The selected compounds 5-20 and 5-21 showed excellent control against Echinochloa crusgalli (L.) Beauv., Leptochloa chinensis (L.) Nees, Cyperus difformis L. and Lindernia procumbens (Krock.) Philcox in paddy fields, which was slightly better than that of pyribenzoxim. CONCLUSION: SAR analysis of greenhouse data revealed that the type and position of substituents on aromatic rings greatly influenced the activity of the compounds, although log P values showed no obvious correlation with activity. Combined with compounds 5-20 and 5-21, which showed moderate and excellent activity in greenhouse experiments, and excellent activity in controlling barnyard grass in the field, we conclude that pyribenzoxim analogs probably act as prodrugs, and this could be a focus of attention in future studies on structural optimization of the herbicide. © 2020 Society of Chemical Industry.

Chemical Constituents from Fraxinus hupehensis and Their Antifungal and Herbicidal Activities.

The phytochemical investigation of Fraxinus hupehensis led to the isolation and characterization of ten compounds which were identified as fraxin (1), fraxetin (2), esculetin (3), cichoriin (4), euphorbetin (5), kaempferol-3-O-ß-rutinoside (6), oleuropein (7), linoleic acid (8), methyl linoleate (9), and ß-sitosterol (10). Structures of the isolated constituents were characterized by 1H NMR, 13C NMR and HRMS. All the compounds, except compounds 3 and 4, were isolated for the first time from this plant. Further, this was the first report for the occurrence of compound 5 in the Fraxinus species. Antifungal activity evaluation showed that compound 2 exhibited significant inhibitory effects against Bipolaris maydis, Sclerotium rolfsii, and Alternaria solani with EC50 values of 0.31 ± 0.01 mmol/L, 10.50 ± 0.02 mmol/L, and 0.40 ± 0.02 mmol/L respectively, compared to the positive control, Carbendazim, with its EC50 values of 0.74 ± 0.01 mmol/L, 1.78 ± 0.01 mmol/L and 1.41 ± 0.00 mmol/L. Herbicidal activity tests showed that compounds 8-10 had strong inhibitory effects against the roots of Echinochloa crus-galli with EC50 values of 1.16 ± 0.23 mmol/L, 1.28 ± 0.58 mmol/L and 1.33 ± 0.35 mmol/L respectively, more potently active than that of the positive control, Cyanazine, with its EC50 values of 1.56 ± 0.44 mmol/L. However, none of the compounds proved to be active against the tested bacteria (Erwinia carotovora, Pseudomonas syringae, and Ralstonia solanacearum).

Synthesis and bioactivities of phenazine-1-carboxylic piperazine derivatives.

Phenazine-1-carboxylic acid (PCA) as a natural product which has significant inhibition effects against many soil-borne fungal phytopathogens in agricultural application and has been registered in China as the fungicide against rice sheath blight. In order to find new higher fungicidal activities lead compounds and develop new eco-friendly agrochemicals, we introduced substructure piperazines which also have high biological activity into PCA, designed and synthesized a series of phenazine-1-carboxylic piperazine derivatives, and their structures were confirmed by 1H NMR and HRMS. Most compounds exhibited certain in vitro fungicidal activities. In particular, Compounds 5r exhibited the activity against all the tested pathogenic fungi, such as Rhizoctonia solani, Alternaria solani, Fusarium oxysporum, Fusarium graminearum, Pyricularia oryzac Cavgra, with the EC50 value of 24.6µM, 42.9µM, 73.7µM, 73.8µM, 34.2µM, respectively, more potent activities than PCA (33.2µM, 81.5µM, 186.5µM, 176.4µM, 37.3µM). This result provided a highly active lead compound for the further structure optimization design.

Screening Effective Antifungal Substances from the Bark and Leaves of Zanthoxylum avicennae by the Bioactivity-Guided Isolation Method.

Abstract: To find good antifungal substances by the bioactivity-guided isolation method, we tracked down the effective antifungal substances in the bark and leaves of Zanthoxylum avicennae, and isolated three antifungal compounds 1, 2, and 3. The structures were identified as xanthyletin, luvangetin, and avicennin by 1H-NMR, 13C-NMR, and HRMS spectra. Particularly, compound 2 had several isomers, and the 1H-NMR spectra of 2 in different solvents showed a significant difference. To determine the stereo structure of 2, a single crystal was prepared and identified by X-ray diffraction as Luvangetin. Moreover, the difference of 1H-NMR data of 2 between in solvent dimethyl sulfoxide-d6 (DMSO-d6) and deuterated chloroform (CDCl3), and other reported isomers were discussed for the first time. The bioassay results indicated that the three compounds 1, 2, and 3 displayed low to high antifungal activities against tested phytopathogenic fungi. In particular, all compounds 1, 2, and 3 showed excellent antifungal activities against Pyricularia oryzae and Z. avicennae, with the values of half maximal effective concentration (EC50) ranging from 31 to 61 mg/L, and compound 3 was also identified as a more potent inhibitor against Fusaium graminearum (EC50 = 43.26 ± 1.76 mg/L) compared with fungicide PCA (phenazine-1-carboxylic acid) (EC50 = 52.34 ± 1.53 mg/L). The results revealed that compounds 1, 2, and 3 were the main antifungal substances of Z. avicennae, and can be used as lead compounds of a fungicide, which has good development value and prospect.

The influence of steric configuration of phenazine-1-carboxylic acid-amino acid conjugates on fungicidal activity and systemicity.

BACKGROUND: Conjugating an amino acid onto existing fungicidal parent structures has been demonstrated to be an effective way to endow non-phloem mobile fungicides with phloem mobility. To alter the systemicity of the fungicide PCA (phenazine-1-carboxylic acid), 10 amino acids derivatives of this fungicide were designed and synthesized, and their synthesis, characterization, phloem and xylem mobility in Ricinus communis L, and their fungicidal activity in vitro are described. RESULTS: The systemicity experiments in Ricinus communis system demonstrated that all conjugates exhibited obvious phloem mobility compared with non-phloem-mobile PCA, and the introduction of an L-amino acid to PCA more greatly enhanced the phloem mobility. The five D-amino acid conjugates exhibited higher xylem mobility than that of PCA and of each corresponding L-amino acid conjugate. Most conjugates were found to exhibit moderate in vitro fungicidal activities against six pathogenic fungi, which were lower than that of PCA. The results of the bioassay showed fungicidal activities of PCA-amino acid conjugates associated not only with different amino acids, but also with their conformation. Conjugation with D-amino acid contributed to the in vitro fungicidal activities of PCA-amino acid conjugates. CONCLUSIONS: The current research offers a new strategy for enhancing the systemicity of non-phloem-mobile fungicides and presents some useful information on the effects of introducing amino acids of different steric configurations on the fungicidal activity, phloem and xylem mobility of the parent fungicide. © 2019 Society of Chemical Industry.

Synthesis and bioactivities of diamide derivatives containing a phenazine-1-carboxamide scaffold.

Taking natural product phenazine-1-carboxamide (PCN) as a lead compound, a series of novel phenazine-1-carboxylic acid diamide derivatives were designed and synthesised. Their structures were confirmed by 1H-NMR and HRMS. The bioassays showed that some of the target compounds exhibited promising in vitro fungicidal activities, and exhibited excellent and selective herbicidal activities. Particularly, compounds c, h, o and s displayed root length inhibition activities against barnyard grass with the rate of more than 80%. Compound c exhibited the best activity among all the target compounds against barnyard grass stalk length with the IC50 value of 0.158 mmol/L, and compound o exhibited the best and wide spectrum inhibition against barnyard grass root length and rape in both root length and stalk length herbicidal activities with its IC50 values of 0.067, 0.048 and 0.059 mmol/L respectively. The analysis of preliminary Structure-Activity Relationships provides the theoretical basis for further design of phenazine-1-carboxylic acid.

Synthesis and antifungal evaluation of PCA amide analogues.

To improve the physical and chemical properties of phenazine-1-carboxylic acid (PCA) and find higher antifungal compounds, a series of PCA amide analogues were designed and synthesized and their structures were confirmed by 1H NMR, HRMS, and X-ray. Most compounds showed some antifungal activities in vitro. Particularly, compound 3d exhibited inhibition effect against Pyriculariaoryzac Cavgra with EC50 value of 28.7 µM and compound 3q exhibited effect against Rhizoctonia solani with EC50 value of 24.5 µM, more potently active than that of the positive control PCA with its EC50 values of 37.3 µM (Pyriculariaoryzac Cavgra) and 33.2 µM (Rhizoctonia solani), respectively.

Design, synthesis and biological activity of hydroxybenzoic acid ester conjugates of phenazine-1-carboxylic acid.

We prepared 16 novel hydroxybenzoic acid ester conjugates of phenazine-1-carboxylic acid (PCA) and investigated their biological activity. Most of the synthesized conjugates displayed some level of fungicidal activities in vitro against five phytopathogenic fungi. Nine conjugates 5b, 5c, 5d, 5e, 5h, 5i, 5m, 5n and 5o (EC50 between 3.2 µg/mL and 14.1 µg/mL) were more active than PCA (EC50 18.6 µg/mL) against Rhizoctonia solani. Especially conjugate 5c showed the higher fungicidal activity against Rhizoctonia solani which is 6.5-fold than PCA. And the results of the bioassay indicated that the fungicidal activity of conjugates was associated with their LogP, and the optimal LogP values of the more potent fungicidal activities within these conjugates ranged from 4.42 to 5.08. The systemic acquired resistance induced by PCA-SA ester conjugate 5c against rice sheath blight disease in rice seedlings was evaluated. The results revealed that PCA-SA ester conjugate 5c retained the resistance induction activity of SA against rice sheath blight.

Design, Synthesis, Phloem Mobility, and Bioactivities of a Series of Phenazine-1-Carboxylic Acid-Amino Acid Conjugates.

Developing fungicides with phloem mobility that can be applied to leaves to control root or vascular pathogens has long been desirable. To achieve this goal, an efficient and economical strategy involves introducing an amino acid into the existing highly active parent pesticide molecule. Hence, 12 L-phenazine-1-carboxylic acid (PCA)-amino acid conjugates 4a⁻l were designed and synthesized via a simple synthetic route. In vitro bioassays results showed that all synthesized compounds 4a⁻l exhibited certain fungicidal activities against six tested fungi. Compound 4c exhibited relatively good fungicidal activity against Rhizoctonia solani, and the EC50 value was 0.084 ± 0.006 mmol/L. The phloem mobility experiments revealed that introducing an amino acid to PCA could effectively endow PCA with phloem mobility in R. communis L. Among them, nine conjugates were found in phloem sap, and L-PCA-Valine 4d exhibited the highest phloem mobility. Analysis results from the prediction of the Kleier model indicated that an active carrier-mediated mechanism may be involved in L-PCA-amino acid conjugates-a result that needs to be confirmed and complemented with further tests. The current research provides useful data for modifying non-phloem-mobile fungicidal molecules to phloem-mobile types.

Synthesis, fungicidal activity and phloem mobility of phenazine-1-carboxylic acid-alanine conjugates.

Phenazine-1-carboxylic acid (PCA) is a natural product that has been proven effective against a number of soil-borne fungal phytopathogens and registered for biofungicide against rice sheath blight in China. In order to improve the phloem mobility of phenazine-1-carboxylic acid (PCA), four PCA derivatives were designed and synthesized by conjugating PCA with l-alanine methyl ester, d-alanine methyl ester, l-alanine and d-alanine respectively. In vitro and planta bioassays results showed that conjugates L-PAM and D-PAM exhibited higher fungicidal activities against Rhizoctonia solani Kuhn than PCA while L-PA and D-PA were less active than PCA. The concentration of conjugates in Ricinus communis phloem sap was determined by HPLC. The results showed that only L-PA exhibited phloem mobility among these conjugates, and its concentration in Ricinus communis phloem sap increased with the increase of time (the maximum concentration was 12.69µM within 5h). However, the results of pot experiments showed that L-PA and other conjugates didn't exhibited the inhibition for the growth of Rhizoctonia solani Kuhn in the lower leaves after treatment in the upper leaves of rice seedlings. This may be due to the poor plant absorbility for them or their too little amount of accumulation in the lower leaves.