Fate and impact on microorganisms of rice allelochemicals in paddy soil

Allelopathic rice can release allelochemicals from roots to inhibit neighboring plant species, but little is currently known about their fate and impact on microorganisms in paddy soil. This study showed that allelopathic rice PI312777 released much higher concentrations of allelochemical (5,7,4'-trihydroxy-3',5'-dimethoxyflavone) than non-allelopathic rice Liaojing-9 in field. When quantitative 5,7,4'-trihydroxy-3',5'-dimethoxyflavone was added into soil, flavone gave a short half-life of 18.27 +/- 2.32 h (r(2) = 0.94) and could easily be degraded into benzoic acid. Benzoic acid with a half-life of 29.99 +/- 2.19 h (r(2) = 0.96) was more resistant toward degradation in paddy soil. Furthermore, both the culturable microbial population and the entire microbial community structure of soil incubated with flavone and benzoic acid were evaluated using the soil dilution plate method and phospholipid fatty acid (PLFA) analysis, respectively. It appeared from the results that flavone could reduce microorganisms especially for fungi present in paddy soil, while benzoic acid could induce a higher response for soil microorganisms especially for bacteria. Consequently, flavone would be responsible for the dynamics of soil microorganisms during the early period, and any observed effect during the late period would be very likely due to its degradation product benzoic acid rather than flavone itself. These results suggested that allelopathic rice varieties could modify soil microorganisms to their advantage through the release of allelochemicals. The concentration and fate of discriminating 5,7,4'-trihydroxy-3',5'-dimethoxyflavone between allelopathic and non-alleloparhic varieties tested in rice soil would result in the different patterns of microbial population and community structure in paddy ecosystems.     

Urease,invertase, dehydrogenase and polyphenoloxidase activities in paddy soil influenced by allelopathic rice variety

Allelopathic rice variety can release allelochemicals from roots to soil in which interfere with neighboring plant and microbial species, but little is currently known about their effect on enzyme activities of paddy soils. This study showed that enzyme activities and concentrations of allelochemicals in paddy field varied with rice varieties, growth stages and moisture regime. Allelopathic rice variety PI312777 paddy fields had higher levels of soil urease, invertase, dehydrogenase and polyphenoloxidase activities when compared to non-allelopathic rice variety Liaojing-9. Furthermore, allelopathic PI312777 released much higher concentrations of allelochemical 5,7,4′-trihydroxy-3′,5′-dimethoxyflavone than non-allelopathic Liaojing-9 during the whole growth stages. Both rice root exudates and the flavone changed soil enzyme activities, but their effects could be distinguished by allelopathic PI312777 and non-allelopathic Liaojing-9 varieties tested. There was a correlation with concentrations of the flavone and enzyme activities in rice soil. The flavone increased enzyme activities, but all test enzyme activities were less responsive to the flavone in flooded soil than in non-flooded soil. The flavone given the short half-life easily degraded in rice soil, but the flavone was more resistant toward degradation in non-flooded soil. These results suggest that the urease, invertase, dehydrogenase and polyphenoloxidase activities of paddy soils may be positively influenced by allelopathic rice variety through the release of allelochemicals.     

Release and activity of allelochemicals from allelopathic rice seedlings

3-Isopropyl-5-acetoxycyclohexene-2-one-1 (1), momilactone B (2), and 5,7,4'-trihydroxy-3',5'-dimethoxyflavone (3) were isolated and identified from an allelopathic rice accession PI312777. These three compounds at low concentrations could inhibit the growth of weeds Echinochloa crusgalli and Cyperus difformis associated with rice, especially mixtures of the compounds had stronger inhibitory activity than did individual compounds. Studies with hydroponic culture, continuous root exudates trapping system (CRETS), and direct resin adsorption methods showed that a total of 7.6 n moles 1, 2, and 3 were exuded from living roots of each seedling into the environment at 10 days after seedlings were transplanted. Furthermore, 1, 2, and 3 were found in the soil growing PI312777 seedlings at day 15 after seedlings emergence and reached a total of 39.5 microg/g soil at day 30. The results indicated that PI 312777 seedlings could release sufficient quantities of 1, 2, and 3 into the environment to act as allelochemicals inhibiting the growth of associated weeds. Investigations on the distribution of 1, 2, and 3 in PI 312777 plant, and its root exudates showed that the levels of 1, 2, and 3 were significantly higher in the shoots and root exudates than in the roots, and only trace 1 was observed in the roots. The results suggest that the roots of rice seedlings are not major site of synthesis or accumulation 1, 2, and 3, but a pathway for their release into the environment. The levels of 1, 2, and 3 in the root exudates were over 2-folds higher under direct resin adsorption than under hydroponic culture and CRETS, and hence, it is the preferred method to collect and identify active allelochemicals in rice exudates in future studies on rice allelopathy.     

Impact of allelochemical exuded from allelopathic rice on soil microbial community

Allelopathic rice releases allelochemicals from its roots to paddy soils at early growth stages to inhibit neighboring weeds. However, little is currently known about the effects of allelochemicals on soil microbes. In this study, we show that allelopathic rice can have great impact on the population and community structure of soil microbes. Allelopathic rice PI312777 seedlings reduced the culturable microbial population and total PLFA when compared to non-allelopathic rice Liaojing-9. Similar results were observed when, instead of growing seedlings, soils were incubated with plant root exudates. This result demonstrates that the composition of root exudates from the rice varieties tested contributes to the soil microbial community. Further experiments showed that the microbial community was affected by the allelochemical 5,4′-dihydroxy-3′,5′-dimethoxy-7-O-β-glucopyranosylflavone exuded from allelopathic rice roots, through immediately hydrolyzing glucose with stimulation on soil bacteria and aglycone (5,7,4′-trihydroxy-3′,5′-dimethoxyflavone) with inhibition on soil fungi. This result indicates that the flavone O-glycoside can provide carbon and interact with soil microbes. PC analysis of the fatty acid data clearly separated the allelopathic PI312777 and the non-allelopathic Liaojing-9 variety (PC1 = 46.4%, PC2 = 20.3%). Similarly, the first principal component (PC1 = 37.4%) together with the second principal component (PC2 = 17.3%) explained 54.7% of the variation between the allelopathic and non-allelopathic root exudates. Furthermore, the canonical correlation between allelopathic root exudates and the flavone O-glycoside was statistically significant (Canonical R = 0.889, χ² (25) = 69.72, p = 0.0041). Although the data generated in this study were not completely consistent between culturable microbes and PLFA profile, it is a fact that variation in soil microbial populations and community structures could be distinguished by the allelopathic and non-allelopathic rice varieties tested. Our results suggest that individual components of rice root exudates, such as allelochemicals from allelopathic rice, can modify the soil microbial community.     

Prenylated flavanones isolated from flowers of Azadirachta indica (the neem tree) as antimutagenic constituents against heterocyclic amines

Four prenylated flavanones were isolated from the methanol extract of the flowers of Azadirachta indica (the neem tree) as potent antimutagens against Trp-P-1 (3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole) in the Salmonella typhimurium TA98 assay by activity-guided fractionation. Spectroscopic properties revealed that those compounds were 5,7,4'-trihydroxy-8-prenylflavanone (1), 5,4'-dihydroxy-7-methoxy-8-prenylflavanone (2), 5,7,4'-trihydroxy-3',8-diprenylflavanone (3), and 5,7,4'-trihydroxy-3',5'-diprenylflavanone (4). All isolated compounds were found for the first time in this plant. The antimutagenic IC(50) values of compounds 1-4 were 2.7 +/- 0.1, 3.7 +/- 0.1, 11.1 +/- 0.1, and 18.6 +/- 0.1 microM in the preincubation mixture, respectively. These compounds also similarly inhibited the mutagenicity of Trp-P-2 (3-amino-1-methyl-5H-pyrido[4,3-b]indole) and PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine). All of the compounds 1-4 strongly inhibited ethoxyresorufin O-dealkylation activity of cytochrome P450 1A isoforms, which catalyze N-hydroxylation of heterocyclic amines. However, compounds 1-4 did not show significant inhibition against the direct-acting mutagen NaN(3). Thus, the antimutagenic effect of compounds 1-4 would be mainly based on the inhibition of the enzymatic activation of heterocyclic amines.     

不同化感潜力水稻化感效应与产量的关系

本研究探讨了连续3年5种不同化感潜力水稻田间抑草效应、产量及其之间相互关系。结果表明,不同种植时间,不同化感潜力水稻田间种植过程中伴生杂草总生物量以非化感水稻"Lemont"最大,化感水稻"PI-1"最小。化感潜力分析结果表明,不同化感潜力水稻以化感水稻"PI-1"化感抑草潜力最强,非化感水稻"Lemont"最弱。水稻产量分析结果表明,不除草条件下,不同种植时间均以化感水稻"PI-1"产量最高,非化感水稻"Lemont"产量最低。除草条件下,依然以化感水稻"PI-1"产量最高,化感水稻"IAC47"产量最小。杂草生物量、水稻化感潜力与水稻产量的相关性分析结果表明,不同化感潜力水稻产量的大小与田间杂草生物量存在极显著负相关,与化感潜力大小存在极显著正相关。     

Isolation and characterization of structurally novel antimutagenic flavonoids from spinach (Spinacia oleracea).

Thirteen compounds, isolated from spinach (Spinacia oleracea), acted as antimutagens against the dietary carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline in Salmonella typhimurium TA 98. The antimutagens were purified by preparative and micropreparative HPLC from a methanol/water (70:30, v/v) extract of dry spinach (commercial product) after removal of lipophilic compounds such as chlorophylls and carotenoids by solid-phase extraction (SPE). Pure active compounds were identified by instrumental analysis including FT-IR, (1)H and (13)C NMR, UV-vis spectroscopy, and mass spectrometry. All of these compounds were flavonoids and related compounds that could be attributed to five groups: (A, methylenedioxyflavonol glucuronides) 5,3'-dihydroxy-4'-methoxy-6,7-methylenedioxyflavonol 3-O-beta-glucuronide (compound 1), 5,2',3'-trihydroxy-4'-methoxy-6,7-methylenedioxyflavonol 3-O-beta-glucuronide (compound 2), 5-hydroxy-3',4'-dimethoxy-6,7-methylenedioxyflavonol 3-O-beta-glucuronide (compound 3); (B, flavonol glucuronides) 5,6,3'-trihydroxy-7,4'-dimethoxyflavonol 3-O-beta-glucuronide (compound 4), 5,6-dihydroxy-7,3',4'-trimethoxyflavonol 3-O-beta-glucuronide (compound 5); (C, flavonol disaccharides) 5,6,4'-trihydroxy-7,3'-dimethoxyflavonol 3-O-disaccharide (compound 6), 5,6,3',4'-tetrahydroxy-7-methoxyflavonol 3-O-disaccharide (compounds 7 and 8); (D, flavanones) 5,8,4'-trihydroxyflavanone (compound 9), 7,8,4'-trihydroxyflavanone (compound 10); (E, flavonoid-related compounds) compounds 11, 12, and 13 with incompletely elucidated structures. The yield of compound 1 was 0.3%, related to dry weight, whereas the yields of compounds 2-13 ranged between 0.017 and 0.069%. IC(50) values (antimutagenic potencies) of the flavonol glucuronides ranged between 24.2 and 58.2 microM, whereas the flavonol disaccharides (compounds 7 and 8), the flavanones (compounds 9 and 10), and the flavonoid-related glycosidic compounds 11-13 were only weakly active. The aglycons of compounds 7 and 8, however, were potent antimutagens (IC(50) = 10.4 and 13.0 microM, respectively).     

Separation and purification of tricin from an antioxidant product derived from bamboo leaves

Tricin (5,7,4'-trihydroxy-3',5'-dimethoxyflavone) occurs in its glycosidic form in rice bran and other grass species such as wheat, barley, and maize. Tricin is considered sufficiently safe for clinical development as a cancer chemopreventive agent, therefore it can be used for cancer prevention. This study established a new method for the preparation of tricin from bamboo leaves as an alternative to traditional methods such as chemical synthesis via the Baker-Venkata-Raman reaction between acetylsyringic acid and phloroacetophenone. Tricin was prepared from an antioxidant product that was derived from bamboo leaves (AOB) by extraction with aqueous ethanol. A concentrated solution of this product was obtained and then processed by polystyrene (AB-8) resin column chromatography and preparative high-performance liquid chromatography (HPLC) with 30% (v/v) acetonitrile in 1% (v/v) acetic acid as the mobile phase. The collected tricin-rich fraction was further sequentially purified by dialysis membrane separation and drowning-out crystallization methods. The purity was assessed by analytical HPLC with 25% (v/v) acetonitrile in 1% (v/v) acetic acid as the mobile phase, and the chemical confirmation was evaluated by infrared, mass, nuclear magnetic resonance, and ultraviolet spectroscopies. Tricin (3.09 g) was prepared from 174 g of a crude column chromatography fraction obtained from 5 L of AOB concentrated solution. The present method is appropriate for preparing quantities of pure tricin, which can be used for the quantification of tricin in various plant herbs and further for pharmaceutical/biomedical applications and evaluation.     

绰墩遗址古水稻土孢粉学特征初步研究

自1998年以来,绰墩遗址发现了大量的马家浜时期的水稻田.对遗址Ⅵ工作区两个剖面P01和P03进行植硅体和孢粉分析,P01的植硅体分析结果显示在马家浜文化中晚期、马桥文化时期、宋代直至现代,研究点都有水稻生长.孢粉分析还显示,在植硅体浓度较高土壤沉积物中,水生植物花粉在整个孢粉谱中所占比例较小,与现代水田相似.这表明,在新石器时代,人类在种植水稻过程中可能已将杂草除去.绰墩遗址孢粉分析的结果可能为判断古水稻土提供一个有效的方法.     

Effect of phytocompounds from the heartwood of Acacia confusa on inflammatory mediator production

Acacia confusa Merr. (Leguminosae) is traditionally used as a medicinal plant in Taiwan. In the present study, anti-inflammatory activity of extracts from the heartwood of A. confusa were investigated for the first time. Results demonstrated that ethanolic extracts of A. confusa heartwood strongly suppressed NO production in lipopolysaccharide (LPS)-activated RAW 264.7 macrophages. Among all fractions derived from ethanolic extracts, the EtOAc fraction exhibited the best inhibitory activity. Following column chromatography and reverse-phase high-performance liquid chromatography, 13 specific phytocompounds including 5 new flavonoids (i.e., 7,8,3',4'-tetrahydroxy-4-methoxyflavan-3-ol, 7,8,3',4'-tetrahydroxyflavone, 7,8,3'-trihydroxy-3,4'-dimethoxyflavone, 7,3',4'-trihydroxyflavone, and 7,3',4'-trihydroxy-3-methoxyflavone) were isolated and identified from the EtOAc fraction. In addition, melanoxetin (3,7,8,3',4'-pentahydroxyflavone), a major compound in the EtOAc fraction, markedly suppressed LPS-induced NO and prostaglandin E 2 (PGE 2) production. Moreover, melanoxetin completely suppressed gene expression of inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) at 50 and 100 microM, respectively. This is the first report to identify the inhibitory bioactivities of melanoxetin on iNOS and COX-2.     

Antioxidant polyphenols from tart cherries (Prunus cerasus).

Montmorency and Balaton tart cherries were lyophilized and sequentially extracted with hexane, ethyl acetate, and methanol. Methanolic extracts of dried Balaton and Montmorency tart cherries (Prunus cerasus) inhibited lipid peroxidation induced by Fe(2+) at 25 ppm concentrations. Further partitioning of this methanol extract with EtOAc yielded a fraction that inhibited lipid peroxidation by 76% at 25 ppm. Purification of this EtOAc fraction afforded eight polyphenolic compounds, 5,7,4'-trihydroxyflavanone (1), 5,7, 4'-trihydroxyisoflavone (2), chlorogenic acid (3), 5,7,3', 4'-tetrahydroxyflavonol-3-rhamnoside (4), 5,7,4'-trihydroxyflavonol 3-rutinoside (5), 5,7,4'-trihydroxy-3'methoxyflavonol-3-rutinoside (6), 5,7,4'-trihydroxyisoflavone-7-glucoside (7), and 6, 7-dimethoxy-5,8,4'-trihydroxyflavone (8), as characterized by (1)H and (13)C NMR experiments. The antioxidant assays revealed that 7-dimethoxy-5,8,4'-trihydroxyflavone (8) is the most active, followed by quercetin 3-rhamnoside, genistein, chlorogenic acid, naringenin, and genistin, at 10 microM concentrations.     

Effect of different ecological conditions on the mud snail (Cipangopaludina japonica) in submerged paddy soil

Summary The effects of environmental factors, such as the nature of paddy soil, the presence of rice plants and weeds and applications of compost and weed-killers, on the behavior, growth and reproduction of the mud snail (Cipangopaludina japonica, an important paddy-soil dweller in Japan) were studied. The types of water-soluble substances in the soil and the softness of the mud make paddy soil a suitable habitat for this snail. The snail avoids soils that bear rice plants and weeds, preferring soils without higher plants. Feeding experiments revealed that the snail consumes a great deal of bacterial materials, such as detritus and sludge compost, suggesting that the sewage sludge produced from wastewater-treatment installations can be decreased by the snail if it is applied to paddy fields as sludge compost.     

Antimutagens in gaiyou (Artemisia argyi levl. et vant.)

Antimutagens from gaiyou (Artemisia argyi Levl. et Vant., Compositae) were examined. The methanol extract prepared from aerial parts of this plant strongly reduced the mutagenicity of 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), when Salmonella typhimurium TA98 was used in the presence of the rat liver microsomal fraction. The antimutagens were purified chromatographically while monitoring the antimutagenic activity against Trp-P-2 with a modified Ames test employing a plate method. This purification resulted in the isolation of four strong antimutagens, 5,7-dihydroxy-6,3',4'-trimethoxyflavone (eupatilin), 5, 7,4'-trihydroxy-6,3'-dimethoxyflavone (jaceosidin), 5,7, 4'-trihydroxyflavone (apigenin) and 5,7, 4'-trihydroxy-3'-methoxyflavone (chrysoeriol) from the methanol extract. These antimutagenic flavones exhibited strong antimutagenic activity against not only Trp-P-2 but also against other heterocyclic amines, such as 3-amino-1,4-dimethyl-5H-pyrido[4, 3-b]indole (Trp-P-1), 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), 2-amino-3, 8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-3-methyl-9H-pyrido[2,3-b]indole (MeA(alpha)C) in S. typhimurium TA98. In contrast, they did not exhibit antimutagenic activity against benzo[a]pyrene (B[a]P), 4-nitroquinoline-1-oxide (4-NQO), 2-aminofluorene (2-AF), 2-nitrofluorene (2-NF) or furylfuramide (AF-2) in S. typhimurium TA98, or B[a]P, 4-NQO, 2-NF, AF-2, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) or sodium azide (SA) in Salmonella typhimurium TA100, whereas they decreased the mutagenicity caused by aflatoxin B(1) (AFB(1)) and 2-aminoanthracene (2-AA) in both of these tester strains. Regarding the structure-activity relationship, the tested flavones had distinct differences in the intensities of their antimutagenic activities according to the differences of their substitution patterns. Namely, the intensity of antimutagenic activities against Trp-P-2 decreased in the order of: 5,7,3',4'-tetrasubstituted flavones (IC(50): <0.1 mmol/plate), 5,7,4'-trisubstituted flavones (IC(50): 0.120-0.260 mmol/plate), 5,6,7,3',4'-pentasubstituted flavones (IC(50): 0.440-0. 772 mmol/plate). The four isolated flavones were also studied regarding their antimutagenic mechanisms with preincubation methods of the modified Ames test and emission spectroscopic analysis. The results suggested that all isolated flavones were desmutagens which directly inactivated Trp-P-2 or inhibited its metabolic activation.     

Identification of 5,7,3',4'-tetramethoxyflavone metabolites in rat urine by the isotope-labeling method and ultrahigh-performance liquid chromatography-electrospray ionization-mass spectrometry

5,7,3',4'-Tetramethoxyflavone (TMF), one of the major polymethoxyflavones (PMFs) isolated from Kaempferia parviflor , has been reported possessing various bioactivities, including antifungal, antimalarial, antimycobacterial, and anti-inflammatory activities. Although several studies on the TMF have been reported, the information about the metabolism of TMF and the structures of TMF metabolites is still not yet clear. In this study, an isotope-labeling method was developed for the identification of TMF metabolites. Three isotope-labeled TMFs (5,7,3',4'-tetramethoxy[3'-D(3)]flavone, 5,7,3',4'-tetramethoxy[4'-D(3)]flavone, and 5,7,3',4'-tetramethoxy[5,4'-D(6)]flavone) were synthesized and administered to rats. The urine samples were collected, and the main metabolites were monitored by ultrahigh-performance liquid chromatography-electrospray ionization-mass spectrometry. Five TMF metabolites were unambiguously identified as 3'-hydroxy-5,7,4'-trimethoxyflavone, 7-hydroxy-5,3',4'-trimethoxyflavone sulfate, 7-hydroxy-5,3',4'-trimethoxyflavone, 4'-hydroxy-5,7,3'-trimethoxyflavone, and 5-hydroxy-7,3',4'-trimethoxyflavone.     

田间旱育条件下不同化感潜力水稻根际土壤酚酸类和萜类物质分析

酚酸类和萜类是水稻化感作用研究中研究较多、争议较大的2大类化感物质,但目前有关水稻根系分泌物的研究多在实验室条件下进行。本文以国际公认的强化感水稻‘PI312777’和弱化感水稻‘Lemont’为材料,以未种植水稻的土壤为对照,研究了其在田间旱育条件下,不同土壤水分状态(旱地和湿地)时,根际土壤酚酸类和萜类物质的差异。结果表明,不同水分条件下不同化感潜力水稻品种和对照根际土壤中酚酸类物质和萜类物质的组成较为相似,但各物质含量存在一定差异。适度旱胁迫下,各处理根际土壤中所检测到的咖啡酸、对羟基苯甲酸、香草酸、阿魏酸和肉桂酸5种酚酸类物质及总量均有提高,其中强化感水稻‘PI312777’根际土壤中5种酚酸类物质提高最显著,比CK湿地处理提高2.84倍;在各处理根际土壤共检测到的27种萜类物质中,17种是含氧单萜;干旱胁迫导致各处理根际土壤单萜烯、含氧单萜、含氧倍半萜和总萜变化程度和变化趋势不同,单萜烯相对含量在强化感水稻‘PI312777’根际土壤中明显提高,而在弱化感水稻‘Lemont’和对照根际土壤中则降低。本文在此基础上讨论了由此导致2种水稻田间化感抑草效果差异的原因与机制。     

Enzymatic dehydrogenative polymerization of urushiols in fresh exudates from the lacquer tree, Rhus vernicifera DC

Fresh exudates from the lacquer tree, Rhus vernicifera DC, were extracted with acetone and the solution was chromatographed to isolate monomer, dimer, trimer, and oligomer fractions of urushiols. Constituents of the monomeric and dimeric fractions were then identified by two-dimensional (2D) 1H-13C heteronuclear multiple quantum coherence (HMQC) and heteronuclear multiple bond coherence (HMBC) NMR spectroscopic techniques. The results showed that the monomeric fraction contained 3-[8'Z,11'E,13'Z-pentadecatrienyl]catechol (1), 3-[8'Z,11'Z,14'-pentadecatrienyl]catechol (2), and 3-pentadecanyl]catechol (3), which was verified by HPLC analysis. The dimeric fraction contained 8'-(3' ',4' '-dihydroxy-5' '-alkenyl)phenyl-3-[9'E,11'E,13'Z-pentadecatrienyl]catechol (4), 14'-(3' ',4' '-dihydroxy-5' '-alkenyl)phenyl-3-[8'Z,10'E,12'E-pentadecatrienyl]catechol (5), 2-hydroxyl-3- or -6-alkenylphenyl ethyl ether (6), 14'-(3' ',4' '-dihydroxy-2' '-alkenyl)phenyl-3-[8'Z,10'E,12'E-pentadeca-trienyl]catechol (7), 15'-(2' '-hydroxy-3' '- or -6' '-alkenyl)phenyloxy-3-[8'Z,11'Z,13'E)-pentadecatrienyl]catechol (8), 14'-(2' ',3' '-dihydroxy-4' '-alkenyl)phenyl-3-[8'Z,10'E,12'E-pentadecantrienyl]catechol (9), 1,1',2,2'-tetrahydroxy-6,6'-dialkenyl-4,3'-biphenyl (10), 1,1',2,2'-tetrahydroxy-6,6'-dialkenyl-4,4'-biphenyl (11), 1,1',2,2'-tetrahydroxy-6,6'-dialkenyl-5,4'-biphenyl (12), and 1,2,1'-trihydroxy-6,6'-dialkenyldibenzofuran (13) as constituents. In addition, dimeric ethers and peroxides, such as compounds 14 and 15, were produced by autoxidation of monomeric urushiols in atmospheric air. The possible reaction mechanisms for the dehydrogenative polymerization of urushiols by Rhus laccase present in the fresh raw exudates under the atmospheric oxygen are discussed on the basis of structures identified. This is of primary importance because the use of the urushi exudates as coating materials does not involve organic solvents and is an environmentally friendly process.     

Characterization of ammonia oxidizing bacteria associated with weeds in a Japanese paddy field using amoA gene fragments

Abstract

Ammonia oxidizing bacteria (AOB) are important microorganisms in rice paddy field ecosystems because they play a key role in the nitrogen (N) cycle by converting ammonia (NH₃) to nitrite (NO^? ₂). In this study, we investigated AOB associated with three types of weeds in a Japanese paddy field (semi-aquatic Echinochloa oryzicola Vasing, floating Lemna paucicostata Hegelm and submerged Najas graminea Delile) using molecular techniques polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and DNA sequencing targeting ammonia monooxygenase (amoA) gene. This work confirmed that rice paddy weeds harbor AOB and that the community composition is different for each type of weed. However, all AOB sequences associated with the tested weeds were closely related to known species of Nitrosospira-like AOB isolated from soil, suggesting that AOB associated with weeds were not specific to weeds and can also be found in the soil. Nitosomanas-like AOB were not detected on any of the weeds tested. In addition, the most dominant AOB strains present in the tested weeds were closely related to Nitrosospira sp. Ka3 and Nitrosospira sp. CT2F. The phylogenetic tree revealed that most of the AOB detected in the present study belonged to amoA cluster 1.     

5-(2,6-difluorobenzyl)oxymethyl-5-methyl-3-(3-methylthiophen-2-yl)- 1,2-isoxazoline as a useful rice herbicide

5-(2,6-difluorobenzyl)oxymethyl-5-methyl-3-(3-methylthiophen-2-yl)-1,2-isoxazoline derivative was synthesized, and its herbicidal activity was assessed under glasshouse and flooded paddy conditions. 5-(2,6-Difluorobenzyl)oxymethyl-5-methyl-3-(3-methylthiophen-2-yl)-1,2-isoxazoline demonstrated good rice selectivity and potent herbicidal activity against annual weeds at 125 g of a.i. ha(-1) under greenhouse conditions. Soil application of this compound showed complete control of barnyard-grass to the fourth leaf stage at 250 g of a.i. ha(-1). Field trials indicated that this compound controlled annual weeds rapidly with a good tolerance on transplanted rice seedlings by post-emergence and soil application. This compound showed a low mammalian and environmental toxicity in various toxicological tests.     

Evaluation of allelopathic potential and quantification of momilactone A,B from rice hull extracts and assessment of inhibitory bioactivity on paddy field weeds

Rice (Oryza sativa L.) hull extracts were used in a bioassay to evaluate the allelopathic potential of rice on the germination and growth of barnyard grass (Echinochloa crus-galli P. Beauv. var. oryzicola Ohwi), to quantify momilactone A and B levels in rice hull germplasm and to assess the inhibitory bioactivity of momilactone A and B as a potential natural source of herbicide for weed control in paddy fields. Four varieties of weeds including E. crus-galli P. Beauv. var. oryzicola Ohwi, Monochoria vaginalis var. plantaginea, Scirpus juncoides, and Eleocharis kuroguwai were tested in the paddy field. Of 99 rice varieties, the top five including Noindari exhibited inhibition effects greater than 50% in average inhibition of dry weight (AIDW). Noindari among them exerted the strongest effect (55.6%). The next five in the ranking exhibited inhibition effects of greater than 40%. Also, 46 varieties had inhibition effects between 20 and 40%, and 29 varieties had inhibition effects greater than 10%. Fourteen varieties had very low inhibitory effects (less than 10%), the lowest of which was Heunbe (4.7%). These varieties showed a mean inhibition of 19.8% for germination rate (GR), 9.9% for germination percentage (GP), 16.6% for leaf dry weight (LDW), 38.9% for straw dry weight (SDW), and 26.8% for root dry weight (RDW). Rice varieties were classified into six categories based on their total momilactones (TMs) (momilactone A + momilactone B). The highest level of momilactone A was found in the Baekna rice variety (34.7 microg g(-1)), and Baekgwangok contained the highest level of momilactone B (37.8 microg g(-1)). In allelopathic potential with genetic properties and morphological characteristics, the total inhibition rate (TIR) was 18.3% for Korean rice varieties, 19.0% for middle maturing varieties, 17.8% for colorless hull varieties, 18.3% for awn varieties, and 19.0% for colorless awn varieties. In addition, Korean varieties showed higher TMs (4.5 microg g(-1)) as compared with varieties that were late maturing (4.4 microg g(-1)), had colorless hulls (4.1 microg g(-1)), awns (4.7 microg g(-1)), and colorless awns (4.8 microg g(-1)). Momilactone A levels were generally higher than momilactone B levels. Total inhibition rates on barnyard grass correlated with average inhibitions of germination (AIG) (r2 = 0.62***), AIDW (r2 = 0.92***), and were affected by the inhibition rate of GP (r2 = 0.57***). Regions of origin for rice varieties correlated with the AIG (r2 = -0.23***), and maturing time showed a positive correlation with SDW (r2 = 0.15**) and RDW (r2 = 0.19**). Levels of momilactones were also correlated with the region of origin (r2 = -0.32***), maturing time (r2 = 0.13***), and awns (momilactone A, r2 = 0.23***; momilactone B, r2 = 0.14**), suggesting that rice varieties with awns, Korean varieties, and varieties with later maturing times contain higher levels of momilactone. Also, the investigation of the momilactone A and B bioactivity (0, 250, 500, 1000, 2000, and 4000 g a.i./ha) for weed control in paddy fields indicated that momilactones A and B exhibited no toxicity (0 in all concentrations) against rice plants, and the inhibitory bioactivity on weeds with momilactone A was higher than that of momilactone B. When compared with no momilactone control, the highest inhibitory effect (50%) on E. crus-galli P. Beauv. var. oryzicola Ohwi was shown on the 14th day after the application of momiactone A. The inhibitory effect increased with the concentration of the compound from 250 to 4000 g a.i./ha. Furthermore, momilactone A showed greater suppression than momliactone B toward toward E. crus-galli P. Beauv. var. oryzicola Ohwi, M. vaginalis var. plantaginea, S. juncoides, and E. kuroguwai. In broad weed species, momilactone A showed the highest inhibitory effect (90% in 4000 g a.i./ha) on S. juncoides, 14 days after the application as compared with no momilactone control. Further studies on allelopathic effects and momilactones from the germplasm of rice varieties using genetic properties and morphological characteristics may facilitate the development of rice varieties with higher allelopathic potential. Momilactones A and B present in rice hulls may serve as a potential natural herbicide source for weed control in paddy fields reducing the dependence on synthetic herbicides.     

水稻节水栽培的生态和环境效应

综述了节水栽培对稻田生态条件及温室气体生成和排放、肥料流失污染、稻田矿质营养平衡与水肥耦合效应以及病虫草害发生动态等方面的影响。在此基础上,提出了今后应加强水稻节水栽培对农田生态的综合效应、水稻节水栽培的高效灌溉指标及水肥耦合效应、水稻节水栽培对农田病虫草害发生的影响、对土壤中盐分运移及再分布的影响以及无公害可降解的地膜覆盖旱作配套栽培技术等方面的研究