Comparative Effects of Heterocyclic Compounds on Inhibition of Lettuce Fruit Germination

The molecules of many biologically active plant constituentscontain heterocyclic ring systems. Inhibitory effects of a numberof heterocyclic compounds and their alicyclic and open-chainanalogues on lettuce (Lactuca sativa L. cv. Great Lakes) germinationwere therefore determined under specified conditions. The mostobvious property which correlates chemical structure with biologicalactivity is lipophilicity, as was found in previous studies.However, other less obvious factors play a part. The inhibitoryactivity of coumarin, for instance, is much greater than wouldbe expected in comparison with compounds of related structures.In general, substitution of a carbon atom in a ring structureby oxygen or nitrogen has either little effect or a loweringeffect on activity, unless the increased solubility in waterallows an inhibitory concentration to be reached which did notoccur with the carbocyclic compound. However, introduction ofunsaturation increases activity markedly, especially with someof the indole compounds. Key words: Heterocyclic compounds, inhibitory compounds, lettuce germination     

Comparative Effects of Aromatic Compounds on Inhibition of Lettuce Fruit Germination

Germination of lettuce (Lactuca sativa L. cv. Great Lakes) wasinhibited by aromatic alcohols, aldehydes and carboxylic acidsin a way similar to that by aliphatic members. Increased lipophilicityusually leads to increased inhibitory activity. Thus methylationincreased activity while hydroxylation decreased it. Exceptionswere seen with ortho-hydroxylated compounds and other exceptionsindicated the presence of unrecognized factors. Many of thephenolic compounds often quoted as inhibitors were shown tobe not particularly activeagainst lettuce germination when comparedwith, for instance, abscisic acid or coumarin.     

Inhibitory effects of monoterpenes on seed germination and seedling growth

Monoterpenes, the chemical constituents of essential oils found in plants, are known biologically active compounds. The present study was conducted to investigate the inhibitory effects of 30 monoterpenes including monoterpene hydrocarbons and oxygenated monoterpenes on seed germination and seedling growth of Amaranthus retroflexus, Chenopodium album and Rumex crispus under laboratory conditions. The monoterpenes were applied at contents of 10 and 20 microl for liquid compounds and 10 and 20 microg for solid compounds. The results show that most of the monoterpenes significantly inhibited seed germination and seedling growth of the tested plants. Oxygenated monoterpenes including beta-citronellol, nerol and terpinen-4-ol completely inhibited seed germination and seedling growth of all tested plants. Their inhibitory effects were also stronger than that of the herbicide 2,4-D. In general, monoterpenes were less effective against seed germination and seedling growth of C. album as compared with R. crispus and A. retroflexus. Phytotoxic effects of monoterpene hydrocarbons were found to be lower than those of oxygenated monoterpenes. The alcohol derivatives of oxygenated monoterpenes were also found to be more phytotoxic as compared with their acetate derivatives. Based on the present results, it can be concluded that the oxygenated monoterpenes can be used as potential bio-herbicides.     

Inhibitory effects of some esters of 2- and 3-substituted alkoxyphenylcarbamic acids on photosynthetic characteristics

The inhibitory effect of 23N-alkyl-4-piperidylesters (alkyl = ethyl-butyl) (APEA) and 8N-ethyl-2-pyrrolidinylmethylesters (EPMEA) of 2- and 3-substituted alkoxyphenylcarbamic acids (alkoxy = butoxy-heptyloxy-) on photosynthetic Hill reaction activity of spinach chloroplasts and on chlorophyll (Chl) synthesis in green algaeChlorella vulgaris was investigated. Inhibitory activities of these compounds were strongly connected with the lipophilicity of the whole molecule. A lower inhibitory activity of 2-alkoxy-substituted derivatives in relation to the corresponding 3-substituted ones was confirmed. Electron spin resonance (ESR) spectra of spinach chloroplasts demonstrated that the studied compounds affected the structure of photosystem (PS) 2 with the release of Mn²⁺ ions into interior of thylakoid membranes.     

Effects of Sulphur-containing Compounds on Lettuce Fruit Germination

The germination of Lactuca sativa L. cv. Arctic King fruit ona 0.5 per cent agar substrate was inhibited in light at temperaturesabove 31?C (? 1.0?). This precisely repeatable value, termedthe upper temperature cut-off point, is characteristic for thislettuce variety. The position of this cut-off point is raisedby the presence of thiourea (500–1000 mg/1) and a numberof other thiol compounds. This effect is not shown by all thiolcompounds and is dependent on the configuration of the restof the molecule. The presence of a hydroxyl group in the testcompound often results in the temperature cut-off point beinglowered but again this effect depends on the configuration ofthe rest of the molecule. It is postulated that the stimulatingeffects of active thiol compounds are related to hydrophobicinteractions with a macro-molecule involved in the initiationof germination.     

Comparative Effects of Aliphatic Compounds on Inhibition of Lettuce Fruit Germination

Germination of lettuce (Lactuca sativa L. cv. Great Lakes) fruitswas inhibited by alcohols, aldehydes and ketones. Inhibitoryactivity increased with increasing length of the carbon chain,being lower for the branched chain isomers. Additional hydroxylgroups decreased inhibitory activity. Allyl alcohol and acro-lcinwere markedly inhibitory but usually unsaturation in the chainhad little effect. Although the main structure-activity correlationwas with lipophilic properties some other structural featuresmodified the action. A comparison was made between these findingsand effects recorded in the literature on membrane perturbationsespecially in connection with mitochondrial activity.     

Shoot Dry Weight, Chlorophyll and UV-B-absorbing Compounds as Indicators of a Plant's Sensitivity to UV-B Radiation

When studying the effects of ultraviolet-B (UV-B) radiationon plants, a good measure of UV-B sensitivity is a decreasein dry weight, since this reflects the cumulative effect ofmany small disruptions in plant function. Measurements of chlorophyllconcentration and the level of UV-absorbing compounds are alsoused to gauge plant health during and after UV-B exposure. Whena variety of vegetable crop plants were screened for UV-tolerance,it was found that the levels of chlorophyll and UV-absorbingcompounds did not correlate with sensitivity. Biomass accumulationwas, however, correlated with UV-sensitivity; plants that accumulatedmore biomass over a 2-week period were more likely to be UV-Bsensitive. This suggests that a rapid growth rate renders plantsmore sensitive to the injurious effects of UV-B radiation. Copyright2000 Annals of Botany Company UV-B radiation, UV-absorbing compounds, chlorophyll, biomass production, UV-B sensitivity, Capsicum frutescens,Cucurbita pepo , Chicorium endivia, Lactuca sativa, Phaseolus vulgaris, Solanum melongena, Spinacia oleracea, Sinapis alba     

Phenolic Growth Inhibitors Isolated from Dormant Buds of Sugar Maple (Acer saccharum Marsh)

Phenolic growth-inhibiting substances were isolated from dormantbuds of sugar maple (Acer saccharurn Marsh) by paper chromatographyof their aqueous methanolic extracts. Inhibition was determinedin germination bioassays using lettuce (Lactuca sativa var.Grand Rapids) seeds. An inhibition of some 20% was attributedto four major phenolics identified as ferulic, vanillic, p-coumaric,and caffeic acids. Quercetm was also present and caused a weakstimulation of growth. Fractionation of the extract with acidic, neutral, and basicgroups indicated that more phenolic compounds were in the acidicgroup than in the neutral, while none were in the basic group. On a seasonal basis, autumn buds had a higher phenolic contentthan winter and spring buds. The results presented are not inconsistentwith the view that growth-inhibitory phenolic compounds couldcontribute to dormancy in sugar maple buds.     

Interaction of Moisture Stress and Three Phenolic Compounds on Lettuce Seed Germination

No interactions between water stress and three phenolic acids(p-coumaric, caffeic and ferulic acids) on lettuce (Lactucasativa L. var. Grand Rapids) seed germination were found. Probitanalysis indicated that mechanisms of action of water stressand the phenolic inhibitors were similar. The relative effectivenessof the compounds was p-coumaric > ferulic > caffeic. Nointeraction was found between p-coumaric and ferulic acid, whereasantagonism was found between caffeic acid and each of the othertwo phenolic acids. Lactuca sativa L., lettuce, germination, phenolic compounds, moisture stress, allelopathy, seed     

Photosynthetic Electron Transport Inhibition by 3-Acyl-2,4,6-trihydroxybenzamide Derivatives

A series of 3-acyl-2,4,6-trihydroxybenzamides was synthesized, and the compounds’ PET inhibitory activities were examined in isolated chloroplasts. In general, the PET inhibitory activity was found to depend on the overall lipophilicity of the molecule. Low activities of the mono and dihydroxy derivatives indicated that the three hydroxyl groups on the nucleus were essential for high activity. The PET inhibition study, on chloroplasts isolated from an atrazine resistant biotype of Brassica napus and using thermoluminescence analysis, suggested that the trihydroxybenzamide derivatives would be classified as a urea type rather than a phenol type of PET inhibitor. However the trihydroxybenzamide derivatives, like the phenol type of PET inhibitor, showed a lag time before inhibition started, which was followed by constant activity. These results indicate that the binding domain for the trihy-droxybenzamide derivatives overlapped with those of both the urea type and phenol type of PET inhibitors.     

Intraspecific Variation in Oil Components ofBoronia megastigmaNees. (Rutaceae) Flowers

Intraspecific variation in the oil composition ofBoronia megastigmaNees.(Rutaceae) was examined. Boronia absolute is extracted fromblossom primarily for use as a food additive. A major componentis ß-ionone andB. megastigmais one of the commercial,natural sources of this compound. Genotypes superior in productionof ß-ionone and low in monoterpene hydrocarbons weresought from natural populations in the south west of WesternAustralia as part of a breeding programme. Flowers were collectedfrom 25 plants in each of 29 different populations. Blossomwas extracted with ethanol and analysed using a gas liquid chromatographfitted with ionisation detectors. The contents of ß-ionone,dodecyl acetate, -pinene, ß-pinene and limonene inthe oil extract were compared. Intra-population variation wasas great as inter-population variation and no distinct chemotypeswere found. Considerable variation existed in the content ofcomponents. The highest ß-ionone content was 1787mg g^-1f. wt. Some genotypes contained all five components analysed,others lacked one or more of the monoterpenes: -pinene, ß-pineneor limonene. Principle components analysis indicated that contentsof ß-ionone and dodecyl acetate were associated andthat they were distinct from the content of the monoterpenes,which were associated with each other. Natural shading was associatedwith lower levels of monoterpenes but other oils were unaffected.Young plants contained less pinenes than older plants and oldplants contained the most dodecyl acetate. Vigorous plants producedmore pinenes. Red flowers contained the least ß-iononeand dodecyl acetate.Copyright 1999 Annals of Botany Company Boronia megastigma,boronia, Rutaceae, oil, -pinene, ß-pinene, limonene, ß-ionone, dodecyl acetate, monoterpenes, chemotypes.     

Effects of substituted aryloxyaminopropanols on photosynthesis and photosynthesizing organisms

The inhibitory activity of 22 substituted aryloxyaminopropanols having beta-lytic and local anaesthetic properties was studied from the view-point of their influences on photosynthesis in plant chloroplasts as well as growth and synthesis of chlorophyll in algae and wheat plants. The inhibitory activity increased significantly with the increasing length of alkyl-substituents of the aryloxyaminopropanol molecule. Less pronounced dependences were found with respect to the position of the substituent chain on benzene ring. The inhibitory activity was found to correlate well with the lipophilicity of the compounds studied.     

Design,synthesis, antibacterial activity and physicochemical parameters of novel N-4-piperazinyl derivatives of norfloxacin

We report herein the synthesis of some N-Mannich bases in addition to different N-4 substituents of norfloxacin. The antibacterial activities of the newly synthesized compounds were evaluated and correlated with their physicochemical properties. Results revealed that some of the tested compounds exhibited better inhibitory activities than the reference antibiotic norfloxacin against Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumonia and Staphylococcus aureus strains. Correlation results showed that there is no single physicochemical parameter that can determine the effect of N-4 piperazinyl group on the activity of these fluoroquinolones, where lipophilicity, molecular mass and electronic factors may influence the activity.     

A New Histochemical Method for Localization of the Site of Monoterpene Phenol Accumulation in Plant Secretory Structures

A new method is reported for the histochemical localizationof monoterpene phenols in essential oil secretory structures.The method was adapted from a spot test originally devised forin vitro detection of phenolic compounds in organic analyses.Plant subjects were the Lamiaceae species Thymus vulgaris L.,Oreganum vulgare L. and Mentha x piperita L., which accumulateessential oil in glandular trichomes. A reagent consisting of4-nitrosophenol in conc. H₂SO₄was applied to sample leaves ofeach species. A positive test for phenol was indicated by theproduction of coloured indophenols. Using this method, monoterpenephenols were identified in the trichomes of T. vulgaris(thymol)and O. vulgare(carvacrol), indicated by colour changes to redand green respectively. No phenol was detected in trichomesof M. x piperita. Results were confirmed by GC-MS analysis ofleaf volatile extracts from each species, and in vitro testswith thymol and carvacrol. The method could be used in fieldsurveys for rapid identification of potential medicinal plantsand bioactive compounds. Copyright 2001 Annals of Botany Company Histochemistry, secretory structures, glandular trichomes, Lamiaceae, Thymus vulgaris, Oreganum vulgare, Mentha x piperita, essential oil, aromatic monoterpenes     

Synthesis and anti-HSV activity of tricyclic penciclovir and hydroxybutylguanine derivatives

A series of tricyclic penciclovir (PCV) and hydroxybutylguanine (HBG) derivatives have been prepared with enhanced lipophilicity following an efficient synthetic route. All the novel tricyclic derivatives were evaluated for inhibitory activity against herpes simplex virus 1 and 2 (HSV-1, HSV-2) and thymidine kinase deficient (ACV resistant) HSV-1. The tricyclic HBG derivatives were devoid of inhibitory activity however several of the tricyclic PCV derivatives showed promising antiviral activity, in particular 9g (R?=?4-MeO-C₆H₄) displayed good inhibitory activity (HSV-1 EC₅₀ 1.5?μM, HSV-2 EC₅₀ 0.8?μM) and retained inhibitory activity in HSV-1 TK^? cells (EC₅₀ 0.8?μM). Computational docking experiments supported the biological data observed and this preliminary study provides useful data for further development of tricyclic acyclic nucleoside derivatives with improved lipophilicity and retention of activity in HSV-1 TK deficient strains. Also, the new tricyclic derivatives were evaluated against a broad range of other DNA and RNA viruses, but were found to be inactive at subtoxic concentrations. In addition, weak to moderate cytostatic effect was observed for the new compounds.     

pH Restraints on Lettuce Fruit Germination

The effects of buffers with a range of pH values and of concentrationslow enough to exert negligible osmotic stress on germinationof lettuce (Lactuca saliva L. cv. Arctic King) fruits were examined.No restraints were noted except at extremes of pH. Furthermoreinhibition in hydrochloric acid or potassium hydroxide solutionswas not evident below concentrations of about 0.05 M. Aceticacid or ammonium hydroxide were very much more inhibitory buttheir salt, ammonium acetate, only inhibited when its concentrationreached a sufficiently high level to operate by osmotic stress.Inhibition by a series of organic acids and bases showed a positivecorrelation with the lipophilie nature of the molecule althoughthere were some unexplained exceptions. In contrast with previouscases of germination inhibition the effect was not producedby a lowering of the upper temperature cut-off point but byan overall lowering of total germination at all temperatures.This is taken to indicate a toxic effect of pH extremes ratherthan a true inhibition.     

The Role of Nitrate in the Osmoregulation of Lettuce (Lactuca sativa L.) Grown at Different Light Intensities

Blom-Zandstra, M. and Lampe, J. E. M., 1985. The role of nitratein the osmoregulation of lettuce (Lactuca sativa L.) grown atdifferent light intensities.—J. exp. Bot. 36: 1043–1052. The effect of different light intensities on the nitrate accumulationvis-à-vis the concentration of other solutes in plantsap expressed from lettuce leaves was studied. After growinglettuce plants under constant environmental conditions for 52d, they were transferred to different light intensities andharvested periodically. A quantitative analysis of componentsin solution in the expressed plant sap showed a decrease innitrate concentration and an increase in the organic acids (mainlymalate) and sugars (mainly glucose) with increasing light intensity.The light intensity only slightly increased the osmolarity ofthe expressed plant sap. The measured osmolarity correspondedvery well with the value estimated from the quantitative analysesimplying that all osmotically active compounds had been accountedfor. The decrease in nitrate concentration in the expressedplant sap was fully compensated for by an increase in the dissociatedorganic acids that partly dissociate twofold to sustain electroneutralityand by an increase in both organic acids and sugars to maintainthe osmolarity. The suggestion is supported that nitrate mayserve as osmoticum at low light conditions to compensate forthe shortage of carbohydrates resulting from suboptimal photosynthesis. Key words: Nitrate accumulation, osmoregulation, Lactuca saliva L.     

卷蛾分索赤眼蜂和拟澳洲赤眼蜂对小菜蛾利他素各成分的嗅觉反应

卷蛾分索赤眼蜂Trichogrammatoidea bactrae Nagaraja和拟澳洲赤眼蜂Trichogramma confusum Viggiani是小菜蛾Plutella xylostella (L.)的优势寄生蜂。本研究利用“Y”型管测定了2种赤眼蜂对小菜蛾P. xylostella利他素-卵表和腹部鳞片13种饱和烷烃的嗅觉反应。结果显示: 卷蛾分索赤眼蜂交配雌蜂进入2, 6, 10, 14-四甲基十五烷、正十五烷、正十七烷处理区的百分数分别为80.65%, 68.75%和66.67%, 表明这3种烷烃对卷蛾分索赤眼蜂交配雌蜂有显著的吸引作用, 其他10种饱和烷烃对卷蛾分索赤眼蜂雌蜂无明显作用。拟澳洲赤眼蜂进入2, 6, 10, 14-四甲基十五烷、正三十五烷和正十五烷处理区的数目分别占84.38%, 70%和62.16%, 表明其对拟澳洲赤眼蜂交配雌蜂起着显著的吸引作用, 而另外10种烷烃对拟澳洲赤眼蜂雌蜂无作用。卷蛾分索赤眼蜂和拟澳洲赤眼蜂未交配雄蜂进入13种烷烃处理区和对照区的时间均无显著差异, 表明利他素各组分对2种赤眼蜂未交配雄蜂均无吸引作用。