Cyanogenesis In Plants Research Articles

Host plant cyanotype determines degree of rhizobial symbiosis

AbstractPlants with nitrogen‐fixing bacteria, such as legumes with rhizobia, can tap the atmospheric nitrogen pool to obtain resources for defense compounds. Cyanogenesis, a nitrogen‐based plant defense against herbivores, increases in response to rhizobial colonization, but depends on plant genotype. Here, we tested whether genotypic differences in host plant cyanogenesis influence symbiotic reliance on nitrogen‐fixing rhizobia. Using thin, clear soil containers, we counted nodules on live root systems of distinct high (HC) and low (LC) lima bean (Phaseolus lunatus) cyanotypes across the duration of an eight‐week study. We measured changes in cyanogenic potential (HCNp) and protein content to reveal quantitative interactions between nodule number and both leaf traits. High cyanogenic plants maintained consistently twice as many nodules as LC plants. Including both cyanotypes, nodule number correlated positively with HCNp, but negatively with foliar protein content. However, within‐cyanotype interactions between nodule number and plant traits were not significant except for foliar protein in HC plants, which decreased with increasing nodule number. Our results imply that while genotypes with higher levels of nitrogen‐based defense invest more in the rhizobial partner, the costs involved in maintaining the symbiosis may cause resource allocation constraints in the plants' primary nitrogen metabolism.

A free cyanohydrin as arms and armour of Marasmius oreades.

Cyanogenic plants and fungi are widespread in nature. Although the origin of hydrocyanic acid in plants has been studied in detail, little is known about its origin in fungi. Here, we report the identification of the cyanohydrin of glyoxylic acid as the precursor of hydrocyanic acid in the fungus Marasmius oreades and several other cyanogenic fungi. Moreover, a feeding experiment revealed glycine as biosynthetic precursor of the cyanohydrin of glyoxylic acid. Thus, the cyanogenesis of M. oreades and other fungi is fundamentally different from cyanogenesis in plants.

Jasmonic acid enhances plant cyanogenesis and resistance to herbivory in lima bean.

Jasmonic acid (JA) is a natural plant hormone ubiquitously distributed in plants and centrally involved in the induction of direct and indirect plant defenses. Defenses up-regulated by this hormone include trichomes--a direct, mechanical defense--and alkaloids--a direct chemical defense--as well as two indirect chemical defenses: volatile organic compounds (VOCs) and extrafloral nectar (EFN). Plant cyanogenesis--the release of toxic hydrogen cyanide (HCN) from preformed cyanogenic precursors in fruits, leaves, and seeds of many plants--is recognized as a direct, constitutive plant defensive trait, and is among the most widely distributed of all direct chemical plant defenses. The cyanogenic system in plants is composed of three parameters: The cyanogenic potential (HCNp; concentration of cyanogenic precursors), β-glucosidase activity, and cyanogenic capacity (HCNc; release of gaseous hydrogen cyanide). Here, we demonstrated that experimental application of aqueous solutions of JA ranging from 0.001 to 1.0 mmol L(-1), as well as insect herbivory significantly enhanced HCNc via the induction of β-glucosidase activity in wild lima bean (Phaseolus lunatus L.). In choice feeding trials with JA induced and damaged leaves, adult Mexican bean beetles--natural herbivores of lima bean--rejected leaves with enhanced β-glucosidase activity and HCNc. Our findings suggest that jasmonic acid plays a critical role in regulating activity of β-glucosidases, which determines the rate of cyanogenesis, and thus mediates direct plant defense against herbivores.

Chemical defense lowers plant competitiveness.

Both plant competition and plant defense affect biodiversity and food web dynamics and are central themes in ecology research. The evolutionary pressures determining plant allocation toward defense or competition are not well understood. According to the growth-differentiation balance hypothesis (GDB), the relative importance of herbivory and competition have led to the evolution of plant allocation patterns, with herbivore pressure leading to increased differentiated tissues (defensive traits), and competition pressure leading to resource investment towards cellular division and elongation (growth-related traits). Here, we tested the GDB hypothesis by assessing the competitive response of lima bean (Phaseolus lunatus) plants with quantitatively different levels of cyanogenesis-a constitutive direct, nitrogen-based defense against herbivores. We used high (HC) and low cyanogenic (LC) genotypes in different competition treatments (intra-genotypic, inter-genotypic, interspecific), and in the presence or absence of insect herbivores (Mexican bean beetle, Epilachna varivestis) to quantify vegetative and generative plant parameters (above and belowground biomass as well as seed production). Highly defended HC-plants had significantly lower aboveground biomass and seed production than LC-plants when grown in the absence of herbivores implying significant intrinsic costs of plant cyanogenesis. However, the reduced performance of HC- compared to LC-plants was mitigated in the presence of herbivores. The two plant genotypes exhibited fundamentally different responses to various stresses (competition, herbivory). Our study supports the GDB hypothesis by demonstrating that competition and herbivory affect different plant genotypes differentially and contributes to understanding the causes of variation in defense within a single plant species.

The multiple strategies of an insect herbivore to overcome plant cyanogenic glucoside defence.

Cyanogenic glucosides (CNglcs) are widespread plant defence compounds that release toxic hydrogen cyanide by plant β-glucosidase activity after tissue damage. Specialised insect herbivores have evolved counter strategies and some sequester CNglcs, but the underlying mechanisms to keep CNglcs intact during feeding and digestion are unknown. We show that CNglc-sequestering Zygaena filipendulae larvae combine behavioural, morphological, physiological and biochemical strategies at different time points during feeding and digestion to avoid toxic hydrolysis of the CNglcs present in their Lotus food plant, i.e. cyanogenesis. We found that a high feeding rate limits the time for plant β-glucosidases to hydrolyse CNglcs. Larvae performed leaf-snipping, a minimal disruptive feeding mode that prevents mixing of plant β-glucosidases and CNglcs. Saliva extracts did not inhibit plant cyanogenesis. However, a highly alkaline midgut lumen inhibited the activity of ingested plant β-glucosidases significantly. Moreover, insect β-glucosidases from the saliva and gut tissue did not hydrolyse the CNglcs present in Lotus. The strategies disclosed may also be used by other insect species to overcome CNglc-based plant defence and to sequester these compounds intact.

Hydroxynitrile lyases with α/β-hydrolase fold: two enzymes with almost identical 3D structures but opposite enantioselectivities and different reaction mechanisms.

Hydroxynitrile lyases (HNLs) catalyze the cleavage of cyanohydrins to yield hydrocyanic acid (HCN) and the respective carbonyl compound and are key enzymes in the process of cyanogenesis in plants. In organic syntheses, HNLs are used as biocatalysts for the formation of enantiopure cyanohydrins. We determined the structure of the recently identified, R-selective HNL from Arabidopsis thaliana (AtHNL) at a crystallographic resolution of 2.5 Å. The structure exhibits an α/β-hydrolase fold, very similar to the homologous, but S-selective, HNL from Hevea brasiliensis (HbHNL). The similarities also extend to the active sites of these enzymes, with a Ser-His-Asp catalytic triad present in all three cases. In order to elucidate the mode of substrate binding and to understand the unexpected opposite enantioselectivity of AtHNL, complexes of the enzyme with both (R)- and (S)-mandelonitrile were modeled using molecular docking simulations. Compared to the complex of HbHNL with (S)-mandelonitrile, the calculations produced an approximate mirror image binding mode of the substrate with the phenyl rings located at very similar positions, but with the cyano groups pointing in opposite directions. A catalytic mechanism for AtHNL is proposed, in which His236 from the catalytic triad acts as a general base and the emerging negative charge on the cyano group is stabilized by main-chain amide groups and an α-helix dipole very similar to α/β-hydrolases. This mechanistic proposal is additionally supported by mutagenesis studies.

Comparing responses of generalist and specialist herbivores to various cyanogenic plant features

AbstractPlants are obliged to defend themselves against multiple generalist and specialist herbivores. Whereas plant cyanogenesis is considered an efficient defence against generalists, it is thought to affect specialists less. In the present study, we analysed the function of various cyanogenic features of lima bean [Phaseolus lunatus L. (Fabaceae)] during interaction with different herbivores. Three cyanogenic features were analysed, i.e., cyanogenic potential (HCNp; concentration of cyanogenic precursors), β‐glucosidase activity, and cyanogenic capacity (HCNc; release of cyanide per unit time). In no‐choice and free‐choice feeding trials, five lima bean accessions were offered to generalist desert locust [Schistocerca gregaria Forskål (Orthoptera: Acrididae)] and specialist Mexican bean beetle [Epilachna varivestis Mulsant (Coleoptera: Coccinellidae)]. The HCNc was the most important parameter determining host plant selection by generalists, whereas choice behaviour of specialists was strongly affected by HCNp. Although locusts were effectively repelled by high HCNc, this cue was misleading for the detection of suitable host plants, as extensive consumption of low HCNc plant material resulted in strong intoxication of locusts. Balancing cyanide in consumed leaf area, the quantitative release of gaseous cyanide during feeding, and cyanide in faeces suggested that specialists metabolized significantly lower rates of cyanide per consumed leaf material than generalists. We hypothesize that specialists are able to avoid toxic concentrations of cyanide by using HCNp rather than HCNc as a cue for host plant quality, and that they exhibit mechanisms that reduce incorporation of host plant cyanide.

ChemInform Abstract: Cyanogenesis in Plants and Arthropods

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Cyanogenesis in plants and arthropods

Cyanogenic glucosides are phytoanticipins known to be present in more than 2500 plant species. They are regarded as having an important role in plant defense against herbivores due to bitter taste and release of toxic hydrogen cyanide upon tissue disruption, but recent investigations demonstrate additional roles as storage compounds of reduced nitrogen and sugar that may be mobilized when demanded for use in primary metabolism. Some specialized herbivores, especially insects, preferentially feed on cyanogenic plants. Such herbivores have acquired the ability to metabolize cyanogenic glucosides or to sequester them for use in their own defense against predators. A few species of arthropods (within diplopods, chilopods and insects) are able to de novo biosynthesize cyanogenic glucosides and some are able to sequester cyanogenic glucosides from their food plant as well. This applies to larvae of Zygaena (Zygaenidae). The ratio and content of cyanogenic glucosides is tightly regulated in Zygaena filipendulae, and these compounds play several important roles in addition to defense in the life cycle of Zygaena. The transfer of a nuptial gift of cyanogenic glucosides during mating of Zygaena has been demonstrated as well as the involvement of hydrogen cyanide in male attraction and nitrogen metabolism. As more plant and arthropod species are examined, it is likely that cyanogenic glucosides are found to be more widespread than formerly thought and that cyanogenic glucosides are intricately involved in many key processes in the life cycle of plants and arthropods.

Quantitative Effects of Cyanogenesis on an Adapted Herbivore

Plant cyanogenesis means the release of gaseous hydrogen cyanide (HCN) in response to cell damage and is considered as an effective defense against generalist herbivores. In contrast, specialists are generally believed not to be affected negatively by this trait. However, quantitative data on long-term effects of cyanogenesis on specialists are rare. In this study, we used lima bean accessions (Fabaceae: Phaseolus lunatus L.) with high quantitative variability of cyanogenic features comprising cyanogenic potential (HCNp; concentration of cyanogenic precursors) and cyanogenic capacities (HCNc; release of gaseous HCN per unit time). In feeding trials, we analyzed performance of herbivorous Mexican bean beetle (Coleoptera: Coccinellidae: Epilachna varivestis Mulsant) on selected lines characterized by high (HC-plants) and low HCNp (LC-plants). Larval and adult stages of this herbivore feed on a narrow range of legumes and prefer cyanogenic lima bean as host plant. Nevertheless, we found that performance of beetles (larval weight gain per time and body mass of adult beetles) was significantly affected by lima bean HCNp: Body weight decreased and developmental period of larvae and pupae increased on HC-plants during the first generation of beetles and then remained constant for four consecutive generations. In addition, we found continuously decreasing numbers of eggs and larval hatching as inter-generational effects on HC-plants. In contrast to HC-plants, constantly high performance was observed among four generations on LC-plants. Our results demonstrate that Mexican bean beetle, although preferentially feeding on lima bean, is quantitatively affected by the HCNp of its host plant. Effects can only be detected when considering more than one generation. Thus, cyanide-containing precursors can have negative effects even on herbivores adapted to feed on cyanogenic plants.

Source characteristics of oxygenated volatile organic compounds and hydrogen cyanide

Airborne trace gas measurements from Transport and Chemical Evolution over the Pacific (TRACE‐P), Pacific Exploratory Mission (PEM)‐Tropics B, and Intercontinental Chemical Transport Experiment‐North America (INTEX‐NA) experiments are analyzed to examine the major source factors contributing to the observed variabilities of oxygenated volatile organic compounds and cyanides. The positive matrix factorization method is applied to coincident measurements of 11 chemicals including CH3OH, CH3COCH3, CH3CHO, C2H2, C2H6, i‐C5H12, CO, CH3Cl, and CHBr3. Measurements of HCN and CH3CN are available for TRACE‐P and INTEX‐NA. We identify major source contributions from the terrestrial biosphere, biomass burning, industry/urban regions, and oceans. Spatial and back trajectory characteristics of these factors are examined. On the basis of TRACE‐P and PEM‐Tropics B data, we find a factor that explains 80–88% of the CH3OH variability, 20–40% of CH3COCH3, 7–35% of CH3CHO, and 41% of HCN, most likely representing the emissions from terrestrial biosphere. Our analysis suggested that biogenic emissions of HCN may be significant. Cyanogenesis in plants is likely a major emission process for HCN, which was not fully accounted for previously. Larger contributions than previous global estimations to CH3COCH3 and CH3CHO by biomass burning and industry/urban sources likely reflect significant secondary production from volatile organic compound oxidation. No evidence was found for large emissions of CH3COCH3 from the ocean. The oceanic CH3CHO contribution implies large regional variations.

Oviposition Choice of Mexican Bean Beetle (Epilachna varivestis) Depends on Host Plants Cyanogenic Capacity

The choice of insect females as to where to lay their eggs strongly affects progeny survival and, thus, fitness. We conducted choice experiments with female Mexican bean beetles, which were offered lima bean plants differing in their cyanogenic capacity (HCNc), i.e., in the intensity of hydrogen cyanide release per time unit from damaged plant tissue. Females preferred to lay their eggs on plants with low HCNc. In contrast, the mere concentration of cyanide-containing precursors (the cyanogenic potential, HCNp) did not affect oviposition choices. Plant cyanogenesis occurs after tissue damage, which brings specific beta-glucosidases in contact with their substrates, cyanogenic glycosides, from which they are separated by compartmentation in the intact plant tissue. Plants commonly store toxic compounds in an inactive form. Our results demonstrate that for cyanogenesis, which is widespread in plants, it is the toxic product itself rather than the precursor that affects oviposition choices of a specialized herbivore.

Frequency of cyanogenesis in tropical rainforests of far north Queensland, Australia.

Plant cyanogenesis is the release of toxic cyanide from endogenous cyanide-containing compounds, typically cyanogenic glycosides. Despite a large body of phytochemical, taxonomic and ecological work on cyanogenic species, little is known of their frequency in natural plant communities. This study aimed to investigate the frequency of cyanogenesis in Australian tropical rainforests. Secondary aims were to quantify the cyanogenic glycoside content of tissues, to investigate intra-plant and intra-population variation in cyanogenic glycoside concentration and to appraise the potential chemotaxonomic significance of any findings in relation to the distribution of cyanogenesis in related taxa. All species in six 200 m(2) plots at each of five sites across lowland, upland and highland tropical rainforest were screened for cyanogenesis using Feigl-Anger indicator papers. The concentrations of cyanogenic glycosides were accurately determined for all cyanogenic individuals. Over 400 species from 87 plant families were screened. Overall, 18 species (4.5 %) were cyanogenic, accounting for 7.3 % of total stem basal area. Cyanogenesis has not previously been reported for 17 of the 18 species, 13 of which are endemic to Australia. Several species belong to plant families or orders in which cyanogenesis has been little reported, if at all (e.g. Elaeocarpaceae, Myrsinaceae, Araliaceae and Lamiaceae). A number of species contained concentrations of cyanogenic glycosides among the highest ever reported for mature leaves-up to 5.2 mg CN g(-1) d. wt, for example, in leaves of Elaeocarpus sericopetalus. There was significant variation in cyanogenic glycoside concentration within individuals; young leaves and reproductive tissues typically had higher cyanogen content. In addition, there was substantial variation in cyanogenic glycoside content within populations of single species. This study expands the limited knowledge of the frequency of cyanogenesis in natural plant communities, includes novel reports of cyanogenesis among a range of taxa and characterizes patterns in intra-plant and intra-population variation of cyanogensis.

Phenotypic Plasticity of Cyanogenesis in Lima Bean Phaseolus lunatus—Activity and Activation of β-Glucosidase

Cyanogenesis, the release of toxic HCN from damaged plant tissues, is generally considered as a constitutive plant defense. We found phenotypic plasticity of cyanogenesis in young leaves of lima bean Phaseolus lunatus based on increased activity of the beta-glucosidase in response to herbivore attack. Two aspects of plant cyanogenesis have to be considered in ecological analyses: (1) the cyanogenic potential (HCNp), which indicates the total amount of cyanide-containing compounds present in a given tissue, and (2) the cyanogenic capacity (HCNc), representing the release of HCN per unit time. This release is catalyzed by specific beta-glucosidases, whose activity is a crucial parameter determining overall toxicity. Enzymatic activity of beta-glucosidase-and, in consequence, the rate of HCN release-was increased significantly after 72 hr of incubation with spider mites as compared to non-infested leaves. Feeding by L1 larvae of Mexican bean beetles also led to enhanced enzymatic activity, whereas mechanical damage of leaf tissue had no effect on beta-glucosidase activity and the release of HCN. The results place plant cyanogenesis in the group of induced resistance traits, whose degree of activity depends on the feeding by a particular herbivore.

Plant Cyanogenesis of Phaseolus lunatus and its Relevance for Herbivore–Plant Interaction: The Importance of Quantitative Data

Quantitative experimental results on the antiherbivorous effect of cyanogenesis are rare. In our analyses, we distinguished between the total amount of cyanide-containing compounds stored in a given tissue [cyanogenic potential (HCNp)] and the capacity for release of HCN per unit time (HCNc) from these cyanogenic precursors as a reaction to herbivory. We analyzed the impact of these cyanogenic features on herbivorous insects using different accessions of lima beans (Phaseolus lunatus L.) with different cyanogenic characteristics in their leaves and fourth instars of the generalist herbivore Schistocerca gregaria Forskål (Orthoptera, Acrididae). Young leaves exhibit a higher HCNp and HCNc than mature leaves. This ontogenetic variability of cyanogenesis was valid for all accessions studied. In no-choice bioassays, feeding of S. gregaria was reduced on high cyanogenic lima beans compared with low cyanogenic beans. A HCNp of about 15 micromol cyanide/g leaf (fresh weight) with a corresponding HCNc of about 1 micromol HCN released from leaf material within the first 10 min after complete tissue disintegration appears to be a threshold at which the first repellent effects on S. gregaria were observed. The repellent effect of cyanogenesis increased above these thresholds of HCNp and HCNc. No repellent action of cyanogenesis was observed on plants with lower HCNp and HCNc. These low cyanogenic accessions of P. lunatus were consumed extensively--with dramatic consequences for the herbivore. After consumption, locusts showed severe symptoms of intoxication. Choice assays confirmed the feeding preference of locusts for low over high cyanogenic leaf material of P. lunatus. The bioassays revealed total losses of HCN between 90 and 99% related to the estimated amount of ingested cyanide-containing compounds by the locusts. This general finding was independent of the cyanogenic status (high or low) of the leaf material.

Negative-ion CIMS: analysis of volatile leaf wound compounds including HCN

Chemical-ionization mass spectrometry (CIMS) using flow-reactor mass spectrometers has flourished as a sensitive, on-line method of analyzing trace volatile organic compounds (VOCs) in air. In this work, the OH− anion is explored as the ionizing reagent in a flowing-afterglow selected ion flow tube (FA-SIFT) instrument for its utility in detecting VOCs and HCN released by cut and wounded plant material. Reaction rate coefficients and products for reactions between OH− anion and 17 plant VOCs and some structural isomers are reported. These results are also compared to reactions between H3O+ and these same VOCs. Fragmentation products from collision-induced dissociation (CID) of the [M−1]− anion of each species are also given to aid in ion identification. H/D exchange was successfully used to distinguish ionized aldehyde/ketone products that are structural isomers for two different isomeric aldehyde/ketone pairs. Simultaneous emissions of acetone, butanone, and HCN were observed from several plants and the emissions of acetone and butanone were confirmed from one plant using H/D exchange. The utility of this technique as a screening tool for cyanogenesis in plants is discussed.

Cyanogenic polymorphism in Eucalyptus polyanthemos Schauer subsp. vestita L. Johnson and K. Hill (Myrtaceae)

Plant cyanogenesis, the release of cyanide from endogenous cyanide-containing compounds, is an effective herbivore deterrent. This paper characterises cyanogenesis in the Australian tree Eucalyptus polyanthemos Schauer subsp. vestita L. Johnson and K. Hill for the first time. The cyanogenic glucoside prunasin ((R)-mandelonitrile beta-D-glucoside) was determined to be the only cyanogenic compound in E. polyanthemos foliage. Two natural populations of E. polyanthernos showed quantitative variation in foliar prumasin concentration, varying from zero (i.e. acyanogenic) to 2.07 mg CN g(-1) dry weight in one population and from 0.17 to 1.98 mg CN g(-1) dry weight in the other. No significant difference was detected between the populations with respect to the mean prunasin concentration or the degree of variation in foliar prunasin, despite significant differences in foliar nitrogen. Variation between individuals was also observed with respect to the capacity of foliage to catabolise prunasin to form cyanide. Moreover, variation in this capacity generally correlated with the amount of prunasin in the tissue, suggesting genetic linkage between prunasin and beta-glucosidase. (C) 2002 Elsevier Science Ltd. All rights reserved.

Cyanogenesis, herbivory and plant defense in Turnera ulmifolia on Jamaica

Field surveys of eight populations of Turnera ulmifolia L., a Jamaican weed exhibiting quantitative genetic variation for cyanogenesis, were undertaken to assess the effectiveness of cyanogenesis as a plant defense. Populations known to be characteristically acyanogenic, cyanogenic or to exhibit within-population variation were surveyed for cyanogenesis, plant size, and the presence and identity of invertebrate plant visitors. A developmental series of 10 leaves from a shoot of each surveyed plant was analyzed, using image analysis techniques, for the type and extent of damage present. We also surveyed two additional plant populations for the presence of plants with eggs or larvae of Euptoieta hegesia Cramer, a Nymphalid butterfly that is potentially the most damaging herbivore of T. ulmifolia, and a paired comparison analysis of cyanogenesis in plants with the herbivore versus plants without the herbivore was conducted. We found that T. ulmifolia are attacked by a reasonably diverse insect fauna, but a relatively small suite of specialist herbivores that are seemingly undeterred by cyanogenesis inflicts most of the leaf damage. Cyanogenesis does appear to play a role in determining the types, numbers, and presence of generalist herbivores found within and between populations. Tissue loss sustained by plants varies both within and between populations; however, the proportion of leaf tissue lost due to herbivory is low, ranging from only 1-9% on average, and does not appear to be correlated with cyanogenesis in a consistent way. An analysis of covariance did, however, reveal that cyanogenesis has a significant effect on both plant height and number of shoots per plant. These results suggest that cyanogenesis might afford protection against herbivory from generalizing herbivores.

Variation in cyanogenesis in plants with season and insect pressure

Cyanogenesis of 800 plant specimens (108 species) growing on a sandy tract of land between the sea and an inner lagoon 400 m distant was found to increase with insect density and, hence, with distance from the seashore and seasonal variation towards summer.

A survey for cyanogenesis in ferns and gymnosperms

298 species of ferns and 48 species of gymnosperms were tested for cyanogenic activity. 5% of the fern species examined gave positive results, but these showed no correlation with taxonomic groupings. None of the gymnosperms surveyed gave a positive result. The limitations of a survey of this type for detecting cyanogenesis in plants is discussed.