Toxic Plant Substances Research Articles

Silencing of Cytochrome P450 Gene AgoCYP6CY19 Reduces the Tolerance to Host Plant in Cotton- and Cucumber-Specialized Aphids, Aphis gossypii.

Cytochrome P450 monooxygenases play important roles in insect metabolism and detoxification of toxic plant substances. However, the function of CYP6 family genes in degrading plant toxicants in Aphis gossypii has yet to be elucidated. In this study, AgoCYP6CY19, an A. gossypii CYP gene that differentially expresses in cotton- and cucumber-specialized aphids, was characterized. Spatiotemporal expression profiling revealed that AgoCYP6CY19 expression was higher in second instar nymph and 7 day old adults than in other developmental stages. Although the expression of AgoCYP6CY19 was significantly higher in cotton-specialized aphids, AgoCYP6CY19 silencing significantly increased larval and adult mortality and reduced total fecundity in both cotton- and cucumber-specialized aphids. What is more, the expression of AgoCYP6CY19 was significantly induced after the cotton-specialized and cucumber-specialized aphids fed on epigallocatechin gallate (EGCG) and cucurbitacin B (CucB), respectively. These findings demonstrate that AgoCYP6CY19 plays a pivotal role in toxic plant substance detoxification and metabolism. Functional knowledge about plant toxicity tolerance genes in this major pest can provide new insights into insect detoxification of toxic plant substances and insecticides and offer new targets for agricultural pest control strategies.

Disruption of the cytochrome P450 CYP6BQ7 gene reduces tolerance to plant toxicants in the red flour beetle, Tribolium castaneum

In insects, the cytochrome P450 CYP6B family plays key roles in the detoxification of toxic plant substances. However, the function of CYP6 family genes in degrading plant toxicants in Tribolium castaneum, an extremely destructive global storage pest, have yet to be elucidated. In this study, a T. castaneum CYP gene, TcCYP6BQ7, was characterized. TcCYP6BQ7 expression was significantly induced after exposure to essential oil of the plant Artemisia vulgaris (EOAV). Spatiotemporal expression profiling revealed that TcCYP6BQ7 expression was higher in larval and adult stages of T. castaneum than in other developmental stages, and that TcCYP6BQ7 was predominantly expressed in the brain and hemolymph from the late larval stage. TcCYP6BQ7 silencing by RNA interference increased larvae mortality in response to EOAV from 49.67% to 71.67%, suggesting that this gene is associated with plant toxicant detoxification. Combined results from this study indicate that the CYP6 family gene TcCYP6BQ7 likely plays a pivotal role in influencing the susceptibility of T. castaneum to plant toxicants. These findings may have implications for the development of novel therapeutics to control this agriculturally important pest.

Abnormal Development of Hyalomma Marginatum Ticks (Acari: Ixodidae) Induced by Plant Cytotoxic Substances.

The increasing application of toxic plant substances to deter and fight ticks proves the need for investigations focused on the elucidation of their impact on the developmental stages and populations of these arthropods. We examined the course of embryogenesis and egg hatch in Hyalomma marginatum ticks under the effect of cytotoxic plant substances. The investigations demonstrated that the length of embryonic development of egg batches treated with 20 μL of a 0.1875% colchicine solution did not differ significantly from that in the control group. Colchicine caused the high mortality of eggs (16.3%) and embryos (9.7%), disturbances in larval hatch (8.1%), and lower numbers of normal larval hatches (65.6%). In 0.2% of the larvae, colchicine induced anomalies in the idiosoma (67.6%) and gnathosoma (22.5%) as well as composite anomalies (8.5%). The study demonstrates that cytotoxic compounds with an effect similar to that of colchicine can reduce tick populations and cause teratological changes, which were observed in the specimens found during field studies. Since there are no data on the toxic effects of active plant substances on other organisms and the risk of development of tick resistance, a strategy for the use of such compounds in tick control and the management of plant products should be developed.

Physiological responses of Broussonetia papyrifera to manganese stress, a candidate plant for phytoremediation

Effective phytoremediation of Mn contaminated soil requires the selection of a species with good manganese tolerance. Broussonetia papyrifera is an important economic plant and pioneer species, it could be well adapted to drought and saline-alkali environment. In order to understand the effect of Mn stress on B. papyrifera, the effects of different concentrations of Mn (0–50 mmol/L) stress on the growth, morphology, Mn tolerance and physiological indexes of the plant were explored. The results showed that the biomass, surface area, length, root volume, tips, forks, and crossings of B. papyrifera reached the maximum at the Mn concentration of 1 mmol/L. Mn content in the tissue and TF in plants increased with the increase of concentration, while the BCF increased first and then decreased, and the maximum BCF was 0.154 at 10 mmol/L. The accumulation of Mn lead to cell membrane lipid peroxidation, which increased toxic substances in plants, resulting in the increase of MDA and PRO, and affected the synthesis of chlorophyll. However, B. papyrifera could effectively alleviate oxidative stress by increasing the activities of antioxidant enzymes (SOD, POD, CAT), protein and soluble sugar. The results suggested that B. papyrifera had a good oxidative stress mechanism to Mn stress and could be used as candidates for remediation of pollution in mining areas.

The low prevalence of female smoking in the developing world: gender inequality or maternal adaptations for fetal protection?

Background: Female smoking prevalence is dramatically lower in developing countries (3.1%) than developed countries (17.2%), whereas male smoking is similar (32% vs 30.1%). Low female smoking has been linked to high gender inequality. Alternatively, to protect their offspring from teratogenic substances, pregnant and lactating women appear to have evolved aversions to toxic plant substances like nicotine, which are reinforced by cultural proscriptions. Higher total fertility rates (TFRs) in developing countries could therefore explain their lower prevalence of female smoking.Objective: To compare the associations of TFR and gender inequality with national prevalence rates of female and male smoking.Methods: Data from a previous study of smoking prevalence vs gender inequality in 74 countries were reanalysed with a regression model that also included TFR. We replicated this analysis with three additional measures of gender equality and 2012 smoking data from 173 countries.Results: A 1 SD increase in TFR predicted a decrease in female smoking prevalence by factors of 0.58–0.77, adjusting for covariates. TFR had a smaller and unexpected negative association with male smoking prevalence. Increased gender equality was associated with increased female smoking prevalence, and, unexpectedly, with decreased male smoking prevalence. TFR was also associated with an increase in smoking prevalence among postmenopausal women.Conclusions: High TFR and gender inequality both predict reduced prevalence of female smoking across nations. In countries with high TFR, adaptations and cultural norms that protect fetuses from plant toxins might suppress smoking among frequently pregnant and lactating women.

Climate change, invasive species and toxic plant substances in soil and water

Climate change, invasive species and toxic plant substances in soil and water

Climate change, invasive species and toxic plant substances in soil and water

This article was submitted without an abstract, please refer to the full-text PDF file.

Effects of two bitter substances on olfactory conditioning in the moth Heliothis virescens

In nature, moths encounter nutritious and toxic substances in plants, and thus have to discriminate between a diversity of tastants. Whereas olfactory learning allowing memory of nutritious plants is well demonstrated, little is known about learning and memory of toxic items in adult lepidopterans. Moths may use bitter substances to detect and possibly learn to avoid noxious plants. We have studied the physiological and behavioural effects of two bitter substances, quinine and sinigrin, on the moth Heliothis virescens. Electrophysiological recordings showed responses to both compounds in gustatory receptor neurons on the antennae. The response patterns suggested a peripheral discrimination between quinine and sinigrin. We evaluated their putative aversive effect in an appetitive conditioning context where the moths learned to associate an odour with sucrose. We first aimed at enhancing olfactory conditioning of the proboscis extension response by testing the effect of the sucrose concentration on acquisition, retention and extinction. 2 mol l(-1) and 3 mol l(-1) sucrose concentration gave similar acquisition, retention and extinction performances. Experiments involving pre-exposure or facilitated extinction with an odour paired with quinine, sinigrin or no tastant showed a latent inhibitory effect, as well as an aversive effect of quinine and, to a lesser extent, of sinigrin. The results suggested that the two tastants may act as negative reinforcers in H. virescens.

Laccase-type phenoloxidase in salivary glands and watery saliva of the green rice leafhopper, Nephotettix cincticeps

The activity and composition of leafhopper saliva are important in interactions with the host rice plant, and it may play a physiological role in detoxifying toxic plant substances or ingesting sap. We have characterized diphenoloxidase in the salivary glands of Nephotettix cincticeps, its activity as a laccase, and its presence in the watery saliva with the objective of understanding its function in feeding on rice plants. Nonreducing SDS-PAGE of salivary gland homogenates with staining by the typical laccase substrate 2,2′-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), hydroquinone or syringaldazine revealed a band at a molecular mass of approximately 85 kDa at pH 5. A band also appeared at a molecular mass of approximately 200 kDa when the gels were treated with dopamine, L-3,4-dihydroxyphenylalanine (DOPA) or catechol at pH 7. The ABTS-oxidizing activity of the homogenates was drastically inhibited by N-hydroxyglycine, a specific inhibitor of laccase. However, the dopamine-oxidizing activity was not inhibited by N-hydroxyglycine, while it was inhibited by phenylthiourea (PTU). Thus, the salivary glands of N. cincticeps contain two types of phenoloxidases: a laccase (85 kDa) and a phenoloxidase (200 kDa). Laccase activity was detected in a holidic sucrose diet that was fed on for 16 h by two females, but only a trace of catechol oxidase activity was observed, suggesting that the laccase-type phenoloxidase was the predominant phenoloxidase secreted in watery saliva. The laccase exhibited an optimum pH of 4.75–5 in McIlvaine buffer and had a PI of 4.8. Enzyme activity was histochemically localized in V cells of the posterior lobe of the salivary glands. It remained at the same level throughout the adult stage from 2 days after eclosion. A possible function of N. cincticeps salivary laccase may be rapid oxidization of potentially toxic monolignols to nontoxic polymers during feeding on the rice plant. This is the first report proving that laccase occurs in the salivary glands of Hemiptera species and is secreted in the watery saliva.

GC analysis of essential oils in the rumen fluid after incubation of Thuja orientalis twigs in the Rusitec system

Methods for the chemical analysis of toxic plant substances in the rumen of ruminants are of importance for the diagnosis of intoxications with poisonous plants. The present work establishes a method to estimate monoterpene components of the essential oil of thuja ( Thuja orientalis, Cupressaceae) in these types of samples. α-Thujone, which is regarded as the toxic principle, is present at a concentration of 50–60% in the essential oil. The rumen simulation technique (Rusitec) was used to simulate natural digestion. Chopped twigs of thuja were subjected to rumen content in a closed container with an overflow device. The flow of saliva was simulated by the continuous addition of a buffer solution. Samples for analysis were taken from the overflow at 24 and 48 h. A further sample was taken from the remaining liquid fraction of the rumen content in the container at 48 h. The essential oils were extracted with hexane and concentrated. A quantitative determination was done by capillary gas chromatography. Together in the three fractions analysed this resulted in total mean recoveries of 6.8% for α-thujone, 5.3% for β-thujone, 18.9% for fenchone and 27.8% for camphor. The observation that the thujones were recovered to a lesser extent than other oil components is evidence of their fast decomposition in the rumen medium. Under these circumstances the calculated detection limit is 100–200 g thuja twigs in cows with rumen volumes of 60–100 litres. The main essential oil degradation products found in the rumen fluid of all three fractions in the Rusitec system were discovered to be iso-3-thujanol, neo-3-thujanol, carvomenthol and carvomenthone.

Coevolution of Poisonous Plants and Large Herbivores on Rangelands

Highlight: Early literature generally described toxic plant substances as waste products. However, more recent publications in entomology, plant biochemistry, and other fields suggest that toxic secondary compounds in plants may be defense systems against insects and other herbivores. The pertinence of these discussions to range management is the subject of this paper. If plant poisons have evolved as defense mechanisms, various ways that they might function include: (I) extreme toxicity; (2) poisonous properties linked with palatability; and (3) aversive conditioning, i.e., animals “learn” that a plant will make them ill and avoid that plant. All could reduce consumption of poisonous plants by herbivores, thus making the plants more competitive in natural communities. If plant poisons are defense mechanisms, it would be logical to assume that coevolution has occurred in herbivores to prevent their being poisoned by plants. Some of the possible evolutionary adaptations in large herbivores include: (1) a generalized diet that reduces the probability of eating a toxic amount of any one species; (2) ability to detect and avoid poisonous plants; and (3) ability to detoxify plant poisons. All appear to operate, at least to a degree, in both domestic and wild herbivores. Ability to detect and to detoxify poisons varies among species and appears to be more prevalent in native animals that coevolved with the vegetation than in domestic animals. Native big-game animals are occasionally poisoned by plants but large losses usually occur in overpopulated or overgrazed areas where nonpoisonous species have been depleted.

Do Grazers Maximize Individual Plant Fitness?

The hypothesis of Owen and Wiegert stating that grazers may increase individual plant fitness has been found plausible from a theoretical point of view by analyzing two mathematical models. The technique adapted is to search for evolutionarily stable strategies (or ESS) in a system where the plant's palatability is the only evolutionary variable considered. It is concluded that the fitness of particularly shortlived plant species is enhanced when grazed by animals wasting extensive amounts of clipped vegetation and/or defecating close to the eaten plant. Based on this, several generalizations are stated: The hypothesized form of mutualism is (1) more likely to apply for plants which are r-strategists than K-strategists; (2) more likely to apply in early successional stages than close to climax; and (3) more likely in terrestrial than in aquatic systems. Furthermore (4), a gradient with respect to herbivore defense features as a function of plant life histories is likely to exist only in systems with extensive grazing pressure. From these discussions it is concluded that theories for herbivore population regulation relying on mechanisms such as toxic substances in plants are mainly likely to apply for herbivores feeding on long lived plant species. Lastly it is concluded that further theoretical studies on herbivory might prove rewarding by supplementing such studies on predator-prey interactions.

Toxic substances in plants and the food habits of early man.

The widespread occurrence of toxic substances in plants must have greatly restricted their usefulness as food for primitive man. The development of cooking of plant products is suggested to have been a major evolutionary advance, making a major increase in the vegetable materials palatable to man; this technical advantage apparently occurred only in the most recent 2 percent of the anthropological record.