Mathematical modeling of allelopathy: Biological response to allelochemicals and its interpretation

Allelochemicals are assumed to possess specific biological properties and responses of an organism are external expressions of such properties. Based on this assumption, a mathematical model has been constructed to interpret the characteristic responses of an organism to allelochemicals. Several sets of experimental data have been compared with the model predictions; good agreement between the model and data is observed.     

Roles of amino acids,protein, and fiber in leaf-feeding resistance of corn to the fall armyworm

The free amino acids have been shown by isolational work and choice bioassays to be more important than all other factors evaluated in defining leaf-feeding resistance of corn (Zea mays L.) to fall armyworm (FAW) [(Spodoptera frugiperda J.E. Smith)] larvae. 6-MBOA (6-methoxybenzoxazolinone) and maysin, toxins present in corn, were shown not to be significant factors for leaf-feeding resistance to first-instar FAW larvae because of their low concentrations in the whorl. Amino acid analysis showed that while the ratios of the essential amino acids in susceptible (S) and resistant (R) lines were similar, there were differences in the nonessential amino acids, particularly aspartic acid, which was higher in R lines. Also, the ratio of essential amino acids to nonessential amino acids was important, being too low in expressed whorl leaf juice (obtained from V₈–V₁₀ growth stage plants) to support larval growth, although juice was stimulatory in choice tests. The total protein content of whorls in S lines was about 15% higher than in R lines, but the significance of this difference is uncertain, because nutritional tests showed that larval growth increased with total protein only up to 12% protein. Sugars were only slightly stimulatory. Thus, the amino acids along with higher hemicellulose content of R lines, established by us earlier, appear to explain much of the basis of resistance in corn to larval leaf-feeding of the FAW.     

Enzymatic adaptations of herbivorous insects and mites to phytochemicals

A variety of oxidases, reductases, esterases, epoxide hydrolases, and group transferases in herbivorous insects and mites detoxify and facilitate the excretion of toxic phytochemicals (allelochemicals). Current theory indicates that the cytochrome P-450-dependent mixed-function oxidases (MFOs) are by far the most important enzymes because they have many attributes that are essential for an effective detoxification system. Data presented here on the midgut microsomal MFO activity of larvae of the gypsy moth,Lymantria dispar, are discussed in the light of previous work and support the theory. In the gypsy moth, the MFO levels exhibit a parallel trend with changes in specific feeding rates, and changes in the specific activity of the enzyme appear to be regulated ontogenetically and by inductive effect of chemicals in the diet. The specific activity of the MFOs rises more sharply on leaves of a highly preferred type-1 plant, the pin oak, than on an artificial wheat germ diet; the increase from mid-second instar to mid-fifth is 4.5- and 1.8-fold, respectively. The relationship of food consumption rate to increase in body mass (W) was slightly in excess of a 11 ratio for both pin oak and the artificial diet, indicating that the feeding rate surpasses the increase in W (a rare phenomenon in insects). Moreover, the surface-to-volume ratios are fairly constant for combined data of gut lumen and epithelium in second to fifth instars, because the volume occupied by the epithelial cells is much larger than in older ones. Thus, it is concluded that greater specific activity of the MFO is necessary with larval advancement to higher instars in order that they may process dietary allelochemicals with an efficiency comparable to younger larvae. Additional data suggest that MFO level increases reflect further adaptation to: (1) normal, seasonal changes in plants' allelochemical composition and concentration; (2) increase in allelochemical concentration in response to leaf damage; and (3) the risk faced by dispersing larvae of encountering a greater amount and variety of allelochemicals on suboptimal/ less suitable plants. Evidence also has emerged recently for MFO-catalyzed metabolism/deactivation of numerous plant allelochemicals, including compounds that induce the enzyme. MFOs are further adapted for participation in the biogenesis of substances physiologically important to insects. Moreover, the catalytic center of the MFO system, cytochrome P-450, occurs in multiple forms; the significance of this important feature is discussed.Paper presented at the Symposium Bioorganic Chemistry of Communication Systems, at the NERM-15 ACS meeting, SUNY College at New Paltz, New York, June 1985.     

高效毛细管电泳法测定酶法合成阿莫西林反应体系

建立了用高效毛细管电泳法对酶法合成阿莫西林反应体系中5种物质[阿莫西林(Amox),D-对羟基苯甘氨酸甲酯(D-HPGM),D-对羟基苯甘氨酸(D-HPG),6-氨基青霉烷酸(6-APA),苯乙酸(PAA)]进行定量测定的分析方法. 以0.1%苯甲酸为内标,在电压25 kV、波长214 nm、柱温25℃、进样压力3.45 kPa、进样时间5 s的条件下,以pH 9.0、聚乙二醇(PEG)4000含量为6 mg/mL、浓度为50 mmol/L的硼酸-硼砂缓冲溶液为流动相,5种物质与内标实现了基线分离. D-HPGM, D-HPG, Amox, 6-APA和PAA分别在0.1~0.6, 0.1~1.6, 0.1~1.0, 0.1~2.0和0.1~2.0 mg/L浓度范围内,样品浓度与样品峰面积/内标峰面积的比值线性关系良好,回收率分别为101.45%, 97.5%, 101.5%, 99.9%和101.3%,相对标准偏差分别为1.33%, 1.69%, 2.44%, 1.27%, 0.35%. 该方法简单、快速、准确、重现性好,可取代高效液相色谱用于定量检测酶法合成阿莫西林的反应体系中物质的变化.     

酶法及半仿生法提取杜仲叶中绿原酸和黄酮

为优选杜仲叶中绿原酸和黄酮提取最佳工艺,以绿原酸和黄酮含量为考察指标,通过正交实验对半仿生法和酶法两种提取方法进行了优化。半仿生法的工艺条件为:杜仲叶为原料,以磷酸氢二钠-柠檬酸的缓冲溶液作为提取液,m(杜仲叶)∶m(提取液)=1∶20,提取液pH分别为2.0,7.5,8.3,在70℃,每次提取1 h,提取3次;在此条件下,绿原酸的得率达1.44%,黄酮得率达0.044%。果胶酶提取的工艺条件为:杜仲叶为原料,以磷酸氢二钠-柠檬酸的缓冲溶液作为提取液,m(杜仲叶)∶m(提取液)=1∶15,果胶酶酶解温度为60℃;提取液pH为3.6;每5 g杜仲叶中加入质量分数为0.5%果胶酶1.5 mL,酶解2 h后,升温至80℃,每次1 h,提取3次;在此条件下,绿原酸的得率达1.29%,黄酮得率达0.043%。     

Plant strategies of manipulating predatorprey interactions through allelochemicals: Prospects for application in pest control

To understand the role of allelochemicals in predator-prey interactions it is not sufficient to study the behavioral responses of predator and prey. One should elucidate the origin of the allelochemicals and be aware that it may be located at another trophic level. These aspects are reviewed for predator-prey interactions in general and illustrated in detail for interactions between predatory mites and herbivorous mites. In the latter system there is behavioral and chemical evidence for the involvement of the host plant in production of volatile allelochemicals upon damage by the herbivores with the consequence of attracting predators. These volatiles not only influence predator behavior, but also prey behavior and even the attractiveness of nearby plants to predators. Herbivorous mites disperse away from places with high concentrations of the volatiles, and undamaged plants attract more predators when previously exposed to volatiles from infested conspecific plants rather than from uninfested plants. The latter phenomenon may well be an example of plant-to-plant communication. The involvement of the host plant is probably not unique to the predator-herbivore-plant system under study. It may well be widespread since it makes sense from an evolutionary point of view. If so, prospects for application in pest control are wide open. These are discussed, and it is concluded that crop protection in the future should include tactics whereby man becomes an ally to plants in their strategies to manipulate predator-prey interactions through allelochemicals.     

Effects of cotton plant allelochemicals and nutrients on behavior and development of tobacco budworm

Female moths of the tobacco budworm,Heliothis virescens (F.), oviposit in the terminals of the cotton plant,Gossypium hirsutum (L.). The hatched larvae migrate to the terminal area and then to small squares (buds), on which they feed, finally burrowing into the anthers where they grow and develop. They attempt to avoid gossypol glands as they feed. Chemically related evidence explains, in part, these observations. The calyx crown of resistant lines (which is avoided) is high in the terpenoid aldehydes (TAs) including gossypol. HPLC data showed that the gossypol content of both susceptible and resistant glanded lines is equal, while the hemigossypolone and heliocides H₁ and H₂ are greatly increased in resistant lines and presumably are more closely associated with resistance. Analysis for total amino acids in cotton square tissues showed that there was a gradation from the calyx and calyx crown, which were lowest, to the anthers, the site of final insect development, which were highest. Synthetic diets mimicking amino acid distribution in anthers were found to be successful for larval growth and development.     

Rhodanese in insects

Forty-four species of insects were assayed for the presence of rhodanese, an enzyme generally considered to be responsible for the detoxification of cyanide. Rhodanese was found to be widely distributed in both adults and larvae and was not restricted to those species which encounter exogenous cyanide through feeding on cyanogenic plants. These results indicate that cyanide detoxification is unlikely to be the primary role for rhodanese in insects.     

Effect of oviposition deterrents from elderberry on behavioral responses byHeliothis virescens to host-plant volatiles in flight tunnel

In flight-tunnel assays, mated femaleHeliothis virescens (F.) moths responded by positive anemotaxis to volatiles from extracts of two host plants (cotton and tobacco), but they did not fly to an extract from elderberry (Sambucus simpsonii Rehd.), a nonhost that contains an oviposition deterrent forH. virescens. When the elderberry extract was mixed with extract from either cotton or tobacco, the flight response by moths to volatiles emanating from the extract blends was reduced significantly at most doses when compared to the positive response to extracts from either host alone. The number of landings (including brief contacts) and landings that resulted in oviposition on the substrates treated with extract blends also were reduced significantly in most tests.This article reports the results of research only. Mention of a proprietary product does not constitute an endorsement or the recommendation of its use by USDA.     

Hemicellulose is an important leaf-feeding resistance factor in corn to the fall armyworm

The fall armyworm,Spodoptera frugiperda (J. E. Smith), (FAW) is a major pest of corn,Zea mays L., in the southeastern United States. The damage to pretassel corn is caused by larvae feeding primarily on immature inner whorls. In this study, resistant lines were found to contain more crude fiber in whorls, mostly hemicellulose and cellulose. While hemicellulose, chiefly an arabinoxylan, was higher in resistant (R) lines than in susceptible (S) lines, the distribution of constituent neutral sugars was very similar in the lines. Both lines also containedp-coumaric and ferulic acids. These phenolic acids are known to occur both in the free state and in the cell wall as complexes bound by ester linkages to the arabinose moiety of the arabinoxylan.¹³C NMR data showed that the intensity of the carbonyl carbon (184 ppm) in resistant hemicellulose was stronger, indicating a greater degree of cross-linking. Thus, resistant hemicellulose is both structurally different from susceptible hemicellulose and present in greater quantities. In two of three laboratory dietary tests, FAW larval weight gains were significantly higher on diets with (S) hemicellulose incorporated at the same level as (R) hemicellulose. Therefore, resistance to the FAW appears to be correlated with both a greater amount and a higher degree of cross-linking of the hemicellulose of (R) lines.Mention of a trademark, proprietary product, or vendor does not constitute a guarantee of warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products or vendors that may also be suitable.     

Role of Detoxification of Plant Secondary Compounds on Diet Breadth in a Mammalian Herbivore, Trichosurus vulpecula

Theory predicts that mammalian herbivores detoxify different classes of plant secondary compounds via separate metabolic pathways and that generalist herbivores maintain broad diet breadth to avoid overloading individual detoxification pathways. We tested the hypothesis that a generalist marsupial herbivore, the common brushtail possum, Trichosurus vulpecula, can maintain a higher intake of food when allowed to select from two diets containing different profiles of secondary compounds (phenolics and terpenes) than when given access to the diets individually. Diets consisted of a fruit and vegetable mash to which was added ground leaves of either Eucalyptus melliodora or E. radiata. E. melliodora and E. radiata differ in their concentrations and types of secondary compounds. Brushtail possums include these eucalypt species as part of their natural diet. We measured food consumption and detoxification metabolites of possums on these diets. Consistent with the hypothesis, animals presented with a choice of both diets consumed more food than animals given diets singly. One of the two indicators of detoxification, acid load in urine, differed significantly between diets while the other, glucuronic acid, did not. These results provide partial support for the hypothesis that diet breadth is governed by detoxification abilities.     

Response of generalist and specialist insects to qualitative allelochemical variation

We examined the effects of a set of four biosynthetically related iridoid glycosides, aucubin, catalpol, loganin, and asperuloside, on larvae of a generalist,Lymantria dispar (Lymantriidae), the gypsy moth, and an adapted specialist, the buckeye,Junonia coenia (Nymphalidae). In general,L. dispar grew and survived significantly less well on artificial diets containing iridoid glycoside, compared to a control diet without iridoid glycosides. In choice tests, previous exposure to a diet containing iridoid glycosides caused larvae subsequently to prefer iridoid glycoside-containing diets even though they were detrimental to growth and survival. In contrast,J coenia larvae grew and survived better on diets with aucubin and catalpol, the two iridoid glycosides found in the host plantPlantago lanceolata (Plantaginaceae), than on diets with no iridoid glycoside or with loganin and asperuloside. The results of choice tests of diets with and without iridoid glycosides and between diets with different iridoid glycosides reflected these differences as well. These results are discussed in terms of (1) differences between generalists and specialists in their response to qualitative variation in plant allelochemical content, (2) the induction of feeding preferences, and (3) the evolution of qualitative allelochemical variation as a plant defense.     

Interactions oftrans-cinnamic acid,its related phenolic allelochemicals,and abscisic acid in seedling growth and seed germination of lettuce

Phenolic compounds have been identified as the most common allelochemicals produced by higher plants. Inhibitions of cinnamic acid, its related phenolic derivatives, and abscisic acid (ABA) on seedling growth and seed germination of lettuce were studied.trans-Cinnamic acid, ando-,m-, andp-coumaric acids inhibited the growth of etiolated seedlings of lettuce at concentrations higher than 10^–4 M and seed germination above 10^–3 M. Coumarin inhibited seedling growth and seed germination at 10^–5 M or above. Chlorogenic acid inhibited seedling growth above 10^–4 M, but did not inhibit seed germination at 10^–5–5×10^–3 M. Low concentrations (below 10^–3 M) of caffeic and ferulic acids promoted the elongation of hypocotyls, but higher concentrations (over 10^–3 M) inhibited seedling growth and seed germination. These phenolic compounds and abscisic acid had additive inhibitory effects both on seedling growth and seed germination. The inhibition on lettuce was reversed by caffeic and ferulic acids at concentrations lower than 10^–3 M except for the inhibition of germination by coumarin. These results suggest that in naturetrans-cinnamic acid,o-, m-, p-coumaric acids, coumarin, and chlorogenic acid inhibit plant growth regardless of their concentration. However, caffeic and ferulic acids can either promote or inhibit plant growth according to their concentration.     

Fate of photosensitizing furanocoumarins in tolerant and sensitive insects

The fate of [¹⁴C]xanthotoxin (8-methoxypsoralen) was studied in larvae of insect species that are tolerant (Papilio polyxenes Stoll) or sensitive (Spodoptera frugiperda J.E. Smith) to the phototoxic effects of photosensitizing psoralens. Both insects metabolize xanthotoxin by oxidative cleavage of the furan ring, but the detoxification occurs at a much more rapid rate inP. polyxenes in which >95% of an oral 5 g/g xanthotoxin dose is metabolized within 1.5 hr after treatment. The detoxification of psoralens byP. polyxenes appears to occur primarily in the midgut tissue prior to absorption, with the result that the intact phototoxin does not reach appreciable levels in body tissues. Studies with an angular furanocoumarin indicated that isopsoralens are metabolized byP. polyxenes at a somewhat slower rate than observed for psoralens; however, a reduced rate of metabolic detoxification of isopsoralens probably does not explain the fact that psoralen tolerance inP. polyxenes does not extend to the isopsoralen series.     

Lack of predictability in terpenoid function Multiple roles and integration with related adaptations in soft corals

Terpenoids are commonly found in alcyonacean soft corals of the Great Barrier Reef (Coelenterata, Octocorallia), but they are highly variable in their distribution within this order. Such secondary metabolites in these organisms vary widely in type, concentration, and function. Thus far, they have been found to play roles in predator defense, competitor defense, anti-fouling, and reproduction. The effectiveness of compounds derived from individual species also varies widely with respect to interactions with other members of the community. These chemical characters function in concert with other morphological, physiological, behavioral, or developmental adaptations that have similar functions. Integration of these adaptations is highly species-specific. The multiple functions of terpenoid compounds and the high degree of species specificity in their ecological roles greatly reduces the ability to predict either the presence or absence of a terpenoid from other related characters. In addition, simple indicators of terpenoid function appear not to exist. If such indicators do exist, they are more likely to be found at higher levels of taxonomic resolution (within families or genera).Australian Institute of Marine Science Contribution.     

Detoxification of cereal plant allelochemicals by aphids: Activity and molecular weights of glutathioneS-transferase in three species of cereal aphids

The activity and molecular weights of glutathioneS-transferase were studied in three species of cereal aphid:Metopolophium dirhodum, Sitobion avenae, andRhopalosiphum padi. The highest level of glutathioneS-transferase activity was recorded in extracts fromM. dirhodum and the lowest fromS. avenae, and extracts of larvae were more active than those from adults. The activity of this enzyme was higher in extracts ofS. avenae andR. padi previously fed on a moderately resistant wheat variety than on a susceptible variety. Gel filtration followed by SDS-PAGE revealed three protein bands in the active fractions. The first had a molecular weight of 28,500 and the second of 27,500 and were present in all three species of aphid. The third protein differed in the three species, having a molecular weight of 26,000 inS. avenae, 25,500 inM. dirhodum, and 24,000 inR. padi.     

Interactive Effects of Genotype, Environment, and Ontogeny on Resistance of Cucumber (Cucumis sativus) to the Generalist Herbivore, Spodoptera exigua

Host-plant genotype, environment, and ontogeny all play a role in determining plant resistance to herbivory, yet little is known about the nature of the interactions among these factors. We investigated resistance of cucumber plants Cucumis sativus to the generalist herbivore Spodoptera exigua in a manipulative experiment involving three factors. In particular, we tested the effects of bitter (cucurbitacins present) vs. sweet (cucurbitacins absent) plants (genotype), with or without previous herbivory (environment), and cotyledons vs. true leaves (ontogeny). Contrary to our expectations, S. exigua growth was 54% higher on bitter plants than on sweet plants; growth was 63% higher, however, on undamaged plants compared to damaged plants, and 59% higher on true leaves compared to cotyledons. Moreover, all two-way interaction terms between genotype, environment, and ontogeny were significant. For example, S. exigua performance was higher on bitter than on sweet plants; however, this effect was strongly influenced by whether the tissue consumed was a cotyledon or true leaf and also whether it had been previously damaged. An examination of leaf nutritional chemistry revealed that some of our results could be explained by genotypic, environmental, and ontogenic differences in foliar nitrogen content. In contrast, the cucurbitacin content of plants did not appear to affect caterpillar growth. Our results provide evidence for the importance of interactions between genotype, environment, and ontogeny in determining herbivory and illustrate the value of manipulative experiments in revealing the complexities of these interactions.     

Iridoid glycosides and host-plant specificity in larvae of the buckeye butterfly,Junonia coenia (Nymphalidae)

Larvae of the buckeye,Junonia coenia (Nymphalidae) feed primarily on plants in four families: Scrophulariaceae, Plantaginaceae, Verbenaceae, and Acanthaceae. These plant families have in common the presence of a group of plant secondary compounds, the iridoid glycosides. Larvae were reared on three plant species and two artificial diets, one with and one without iridoid glycosides.Larvae grew poorly and had low survivorship on the artificial diet without iridoid glycosides, while growth and survival on the artificial diet with iridoid glycosides was comparable to that on plants. Choice tests using artificial diets with and without iridoid glycosides showed that larvae: (1) chose diets with iridoid glycosides (in the form of a crude extract or pure compound) over a diet without; (2) showed no preference between the diet with the crude extract and that with pure iridoid glycoside, and (3) preferred the artificial diet with ground leaves of the host plant,Plantago lanceolata, over the diet with pure iridoid glycosides. The artificial diet that larvae had been reared on prior to these tests had no effect on subsequent larval preferences in the choice tests.     

Feeding behavior of graminivorous grasshoppers in response to host-plant extracts,alkaloids, and tannins

Secondary metabolites exhibit the potential to direct food selection by grass-feeding (graminivorous) grasshoppers. We examined the effects of plant extracts and representative secondary metabolites on the feeding behavior of two such grasshoppers,Ageneotettix deorum (Scudder) andPhoetaliotes nebrascensis (Scudder). Three alkaloids and two tannins were bioassayed for their activity as feeding deterrent allelochemicals, as were extracts from the foliage of the graminoids commonly eaten by these grasshoppers:Agropyron smithii Rydb.,Andropogon hallii Hack.,Andropogon scoparius Michx.,Bouteloua gracilis (H. B. K) Lag. ex Griffiths,Carex heliophila Mack. andStipa comata Trin. & Rupr. Alkaloids strongly deterred feeding but tannins only exhibited a weak effect, even when present at four times the concentration of total phenolics typical for these graminoids. Host-plant extracts also exhibited weak effects, such that we found no evidence for either strong deterrence or phagostimulation. Our results for alkaloids and host-plant extracts are consistent with the view that grass-feeding grasshoppers may be restricted to graminoids because of: (1) the presence of deterrents in nonhosts and (2) the absence of deterrents in hosts. However, our data for tannins show that these are unlikely to be effective barriers to herbivory by these grasshoppers.     

Mitochondrial adaptations to oxidative stress confer resistance to apoptosis in lymphoma cells

Acquired resistance to drugs commonly used for lymphoma treatment poses a significant barrier to improving lymphoma patient survival. Previous work with a lymphoma tissue culture model indicates that selection for resistance to oxidative stress confers resistance to chemotherapy-induced apoptosis. This suggests that adaptation to chronic oxidative stress can contribute to chemoresistance seen in lymphoma patients. Oxidative stress-resistant WEHI7.2 cell variants in a lymphoma tissue culture model exhibit a range of apoptosis sensitivities. We exploited this phenotype to test for mitochondrial changes affecting sensitivity to apoptosis in cells made resistant to oxidative stress. We identified impaired release of cytochrome c, and the intermembrane proteins adenylate kinase 2 and Smac/DIABLO, indicating inhibition of the pathway leading to permeabilization of the outer mitochondrial membrane. Blunting of a glucocorticoid-induced signal and intrinsic mitochondrial resistance to cytochrome c release contributed to both points of resistance. The level of Bcl-2 family members or a difference in Bim induction were not contributing factors. The extent of cardiolipin oxidation following dexamethasone treatment, however, did correlate with apoptosis resistance. The differences found in the variants were all proportionate to the degree of resistance to glucocorticoid treatment. We conclude that tolerance to oxidative stress leads to mitochondrial changes that confer resistance to apoptosis.