Cyanogenesis Research Papers - Academia.edu (original) (raw)

Erratum: In the Figure 9 color key, the labels for prunasin and RuBisCO were reversed. This error will be corrected in the PDF and HTML versions of the article shortly
Abstract: Cyanogenic glycosides (CNglcs) are bioactive plant products derived from amino acids. Structurally, these specialized plant compounds are characterized as α-hydroxynitriles (cyanohydrins) that are stabilized by glucosylation. In recent years, improved tools within analytical chemistry have greatly increased the number of known CNglcs by enabling the discovery of less abundant CNglcs formed by additional hydroxylation, glycosylation, and acylation reactions. Cyanogenesis—the release of toxic hydrogen cyanide from endogenous CNglcs—is an effective defense against generalist herbivores but less effective against fungal pathogens. In the course of evolution, CNglcs have acquired additional roles to improve plant plasticity, i.e., establishment, robustness, and viability in response to environmental challenges. CNglc concentration is usually higher in young plants, when nitrogen is in ready supply, or when growth is constrained by nonoptimal growth conditions. Efforts are under way to engineer CNglcs into some crops as a pest control measure, whereas in other crops efforts are directed toward their removal to improve food safety.Given that many food crops are cyanogenic, it is important to understand the molecular mechanisms regulating cyanogenesis so that the impact of future environmental challenges can be anticipated.

- by Ros Gleadow
- •
- Biochemistry, Natural Products Chemistry, Plant Secondary Metabolites, Cassava

The generalist moth, Spodoptera frugiperda (J. E.
Smith) consists of two genetic subgroups (host strains) that
differ in their distribution among host plant species. The
corn strain prefers crop plants such as corn, sorghum, and
cotton, while the rice strain is found in small grasses such as
Cynodon spp. and rice. Little is known about the physiological
factors that drive this host preference. Here, we report a
feeding study with natural host plants and an artificial diet
containing cyanide. We found that corn, two Cynodon spp.
(bermudagrass C. dactylon (L.) Persoon, ‘NuMex Sahara’,
and stargrass C. nlemfuensis var. nlemfuensis Vanderyst,
‘Florona’), and a hybrid between bermudagrass and stargrass,
‘Tifton 85’, exhibited differences in the concentration
of the cyanogenic precursors or cyanogenic potential
(HCNp) and the release of hydrogen cyanide per unit time
or cyanogenic capacity (HCNc). Corn plants released low
levels of hydrogen cyanide, while stargrass had greater
HCNp/HCNc than bermudagrass and ‘Tifton 85’. Feeding
studies showed that corn strain larvae experienced higher
mortality than the rice strain when fed stargrass or artificial
diet supplemented with cyanide. Also, corn strain
larvae excreted higher levels of cyanogenic compounds
than the rice strain when fed Cynodon spp. These differences
in excretion suggest potential disparities in cyanide
metabolism between the two strains. We hypothesize that
differences in the susceptibility to cyanide levels in various
host plants could play a role in driving strain divergence
and what appears to be the incipient speciation of
this moth.

Hydrogen cyanide (HCN) is a toxic chemical that can potentially cause mild to severe reactions in animals when grazing forage sorghum. Developing technologies to monitor the level of HCN in the growing crop would benefit graziers, so that they can move cattle into paddocks with acceptable levels of HCN. In this study, we developed near-infrared spectroscopy (NIRS) calibrations to estimate HCN in forage sorghum and hay. The full spectral NIRS range (400–2498 nm) was used as well as specific spectral ranges within the full spectral range, i.e., visible (400–750 nm), shortwave (800–1100 nm) and near-infrared (NIR) (1100–2498 nm). Using the full spectrum approach and partial least-squares (PLS), the calibration produced a coefficient of determination (R2) = 0.838 and standard error of cross-validation (SECV) = 0.040%, while the validation set had a R2 = 0.824 with a low standard error of prediction (SEP = 0.047%). When using a multiple linear regression (MLR) approach, the best model (NIR spectra) produced a R2 = 0.847 and standard error of calibration (SEC) = 0.050% and a R2 = 0.829 and SEP = 0.057% for the validation set. The MLR models built from these spectral regions all used nine wavelengths. Two specific wavelengths 2034 and 2458 nm were of interest, with the former associated with C═O carbonyl stretch and the latter associated with C–N–C stretching. The most accurate PLS and MLR models produced a ratio of standard error of prediction to standard deviation of 3.4 and 3.0, respectively, suggesting that the calibrations could be used for screening breeding material. The results indicated that it should be feasible to develop calibrations using PLS or MLR models for a number of users, including breeding programs to screen for genotypes with low HCN, as well as graziers to monitor crop status to help with grazing efficiency.

- by Glen Fox and +1
- •
- Drought, Sorghum, NIR spectroscopy, Cyanogenesis

The purpose of this study was to assess the quality of cassava cultivars, in terms of cyanogenic potential and composition of macro- and micronutrients, sampled from different locations in rural Mozambique. Total cyanide concentrations in fresh cassava tissues were measured using portable cyanide testing kits, and elemental nutrients were later analyzed from dried plant tissue. Variation in cyanogenic potential and nutrient composition occurred both among cultivars and across locations. The majority of cultivars contained >100 ppm total cyanide, fresh weight, and are therefore considered to be dangerously poisonous unless adequately processed before consumption. Leaf cyanogenic and nutrient content varied with plant water status, estimated using carbon isotope discrimination (δ13C). The colonization of roots of all cultivars by arbuscular mycorrhizal fungi was also quantified and found to be high, indicating that mycorrhizas could play a key role in plant nutrient acquisition in these low-input farming systems.

- by Ros Gleadow
- •
- Engineering, Drought, Mozambique, Food and Nutrition
- by Ros Gleadow
- •
- Drought, Food and Nutrition, Food Security, Cassava

Abstract Background: Cyanogenic glucosides are common bioactive products that break down to release toxic hydrogen cyanide (HCN) when combined with specific β-glucosidases. In forage sorghum, high concentrations of the cyanogenic... more

- by Ros Gleadow
- •
- Sorghum, Plant Defence, Cyanogenesis, Freeze Drying

Globally, cassava is the second most important root crop after potatoes and the fifth most important crop overall in terms of human caloric intake. In addition to its growing global importance for feed, fuel, and starch, cassava has long been vital to food security in Sub-Saharan Africa. Climate change is expected to have its most severe impact on crops in food insecure regions, yet little is known about how cassava productivity will respond to climate change. The most important driver of climate change is globally increasing atmospheric CO2 concentration ([CO2]). However, the potential for cassava to enhance food security in an elevated [CO2] world is uncertain as greenhouse and open top chamber (OTC) study reports are ambiguous. Studies have yielded misleading results in the past regarding the effect of elevated [CO2] on crop productivity, particularly in cases where pots restricted sink growth. To resolve these conflicting results, we compare the response of cassava to growth at ambient (ca. 385 ppm) and elevated [CO2] (585 ppm) under field conditions and fully open air [CO2] elevation. After three and half months of growth at elevated [CO2], above ground biomass was 30% greater and cassava root tuber dry mass increased over 100% (fresh weight increased 89%). High photosynthetic rates and photosynthetic stimulation by elevated [CO2], larger canopies, and a large sink capacity all contributed to cassava’s growth and yield stimulation. Cassava exhibited photosynthetic acclimation via decreased Rubisco capacity early in the season prior to root tuber initiation when sink capacity was smaller. Importantly, and in contrast to a greenhouse study, we found no evidence of increased leaf N or total cyanide concentration in elevated [CO2]. All of our results are consistent with theoretical expectations; however, the magnitude of the yield increase reported here surpasses all other C3 crops and thus exceeds expectations.

- by Ros Gleadow and +3
- •
- Cassava, Elevated CO2, Plant Defence, Cyanogenesis
- by DR Uns Tariq
- •
- Toxicology, Cassava, Cyanide, Toxicity
- by Ros Gleadow
- •
- Technology, Gene regulation, Biotechnology, Plant biotechnology

Chemical ecology provides unique perspectives for managing plant/human interactions to achieve food security. Allelochemicals function as chemical defences of crop plants, enhancing yields. While ingested allelochemicals can confer health benefits to humans, at higher concentrations they are often toxic. The delicate balance between their positive and negative effects in crop plants is
influenced by many factors. Some of these—how environment
affects optimal levels of defence, how metabolic interactions with nutrients affect toxicity of ingested allelochemicals— are the province of chemical ecology. These biological factors, however, interact with social factors, and neither can be studied independently. Chemical ecologists must work together with social scientists to understand the overall system. Here, we illustrate such an integrative approach, analysing the interactions between people and the major tropical crop manioc, which contains cyanogenic
glucosides. Polymorphism for cyanogen levels in manioc facilitates analysis of how costs and benefits of crop defences vary among social systems. We first show how people/ manioc interactions diversified in this crop’s Amazonian homeland, then turn to the remarkable cultural adaptations of African farmers since manioc’s introduction 400 years ago. Finally, we evaluate new coevolutionary challenges in parts of Africa where people are still unfamiliar with a potentially dangerous crop. Current environmental and social catastrophes have restricted farmers’ options, resulting in acute problems in health of humans and ecosystems. We show that high cyanogen levels confer important agronomic advantages, but also impose costs and constraints that can only be understood when biology is coupled with analysis of social, cultural and economic factors. Detoxifying manioc technologically requires know-how, time, water and other resources. Detoxifying residual dietary cyanogens metabolically depends on being able to grow, or to buy, the nutrients required for detoxification, primarily sulphur-rich proteins. Solutions that appear adaptive today may not be in the future, as changing climate, rising atmospheric CO2 levels and decreased access to fertilizers affect productivity of crops and the nutrient and allelochemical composition of the foods they are used to produce.

Global food security in a changing climate depends on both the nutritive value of staple crops as well as their yields. Here, we examined the direct effect of atmospheric CO2 on cassava (Manihot esculenta Cranz., manioc), a staple for 750 million people worldwide. Cassava is poor in nutrients and contains high levels of cyanogenic glycosides that break down to release toxic hydrogen cyanide when damaged. We grew cassava at three concentrations of CO2 (Ca: 360, 550 and 710 ppm) supplied together with nutrient solution containing either 1 mM or 12 mM nitrogen. We found that total plant biomass and tuber yield (number and mass) decreased linearly with increasing Ca. In the worst-case scenario, tuber mass was reduced by an order of magnitude in plants grown at 710 ppm compared with 360 ppm CO2. Photosynthetic parameters were consistent with the whole plant biomass data. It is proposed that since cassava stomata are highly sensitive to other environmental variables, the decrease in assimilation observed here might, in part, be a direct effect of CO2 on stomata. Total N (used here as a proxy for protein content) and cyanogenic glycoside concentrations of the tubers were not significantly different in the plants grown at elevated CO2. By contrast, the concentration of cyanogenic glycosides in the edible leaves nearly doubled in the highest Ca. If leaves continue to be used as a protein supplement, they will need to be more thoroughly processed in the future. With increasing population density, declining soil fertility, expansion into marginal farmland, together with the predicted increase in extreme climatic events, reliance on robust crops such as cassava will increase. The responses to CO2 shown here point to the possibility that there could be severe food shortages in the coming decades unless CO2 emissions are dramatically reduced, or alternative cultivars or crops are developed.

- by Ros Gleadow
- •
- Climate Change, Elevated CO2, Cyanogenesis, Linamarin

Cyanogenesis is the process by which plantsrelease hydrogen cyanide (HCN) from endogenous cyanide-containing compounds and is thought to play a role in plant defence against generalist herbivores. Cyanogenesis is poorly understood in natural populations, and has been little studied in tree species. In this paper we present the first systematic survey of cyanogenesis in the economically and ecologically important genusEucalyptus. We document variability in both the concentration of the cyanogenic glycoside, prunasin, and the accompanying degradative b-glucosidase in a woody plant for the first time. Leaves of 96E. cladocalyx F. Muell. trees growing in natural populations on Kangaroo Island, South Australia were analysed. All trees werecyanogenic, containing both cyanogenic glycosides and active b-glucosidase. Cyanogenic glycoside concentration varied by over two orders of magnitude. The b glucosidase activity varied widely as well, but plants high in cyanogenic glycosides did not necessarily have higher enzyme activity. A significant proportion of the variation in cyanogenic glycoside concentration can be accounted for by the variation in leaf nitrogen. Most of the variation,however, appears to be the result of genetic polymorphism, which is inherited independently of the level of activity of the degradative b-glucosidase.

- by Ros Gleadow
- •
- Natural Products, Plant Ecophysiology, Eucalyptus, Plant Defence
- by Ros Gleadow
- •
- Climate Change, Drought, Food Security, Cassava
- by Ros Gleadow
- •
- Soil, Plant Biology, Resource Allocation, Ecology
- by Ros Gleadow
- •
- Climate Change, Carbon Dioxide, Photosynthesis, Plant Biology
- by Ros Gleadow
- •
- Climate Change, Photosynthesis, Global Change Biology, Biological Sciences
- by Ros Gleadow
- •
- Phytochemistry, Plant Systematics, Plant defense mechanisms, Eucalyptus

Plants have evolved a vast array of defence mechanisms to avoid or minimize damage caused by herbi-vores and pathogens. The costs and benefits of defences are thought to vary with the availability of resources, herbivore pressure and plant functional traits. We investigated the resource (nitrogen) and growth cost of deploying cyanogenic glycosides in seedlings of Eucalyptus cladocalyx (Myrta-ceae). To do this, we grew the plants under a range of soil N conditions, from levels that were limiting for growth to those that were saturating for growth, and we measured correlations between foliar chemical and performance attributes. Within each N treatment, we found evidence that, for every N invested in cyanogenic glycosides, additional N is added to the leaf. For the lowest N treatment, the additional N was less than one per cyanogenic glycoside, rising to some two Ns for the other treatments. The interaction between cyanogenic glycosides and both condensed tannins and total phenolic compounds was also examined, but we did not detect correlations between these compounds under constant leaf N concentrations. Finally, we did not detect a correlation between net assimilation rate, relative growth rate and cyanogenic glycoside concentrations under any soil N treatment. We conclude that the growth cost of cyanogenic glycosides was likely too low to detect and that it was offset to some degree by additional N that was allocated alongside the cyanogenic glycosides.

- by Ros Gleadow
- •
- Resource Allocation, Nitrogen, Plant Defence, Cyanogenesis

Cyanogenic glycosides (CNglcs) are bioactive plant products derived from amino acids. Structurally, these specialized plant compounds are characterized as α-hydroxynitriles (cyanohydrins) that are stabilized by glucosylation. In recent years, improved tools within analytical chemistry have greatly increased the number of known CNglcs by enabling the discovery of less abundant CNglcs formed by additional hydroxylation, glycosylation, and acylation reactions. Cyanogenesis—the release of toxic hydrogen cyanide from endogenous CNglcs—is an effective defense against generalist herbi-vores but less effective against fungal pathogens. In the course of evolution, CNglcs have acquired additional roles to improve plant plasticity, i.e., establishment , robustness, and viability in response to environmental challenges. CNglc concentration is usually higher in young plants, when nitrogen is in ready supply, or when growth is constrained by nonoptimal growth conditions. Efforts are under way to engineer CNglcs into some crops as a pest control measure, whereas in other crops efforts are directed toward their removal to improve food safety. Given that many food crops are cyanogenic, it is important to understand the molecular mechanisms regulating cyanogen-esis so that the impact of future environmental challenges can be anticipated.

- by Ros Gleadow
- •
- Environmental Stresses, Cassava, Lotus, Cyanide

Cyanogenic glucosides are present in several crop plants and can pose a significant problem for human and animal consumption, due to their ability to release toxic hydrogen cyanide. Sorghum bicolor L. contains the cyanogenic glucoside dhurrin. A biochemical screen and the reverse genetic technique of Targeted Induced Local Lesions in Genomes (TILLING) were employed to identify mutants with altered hydrogen cyanide potential (HCNp). Characterisation of these plants identified mutations affecting the function or expression of dhurrin biosynthesis enzymes, and the ability of plants to catabolise dhurrin. The main focus in this paper is on acyanogenic or low cyanide releasing lines that contain mutations in CYP79A1, the cytochrome P450 enzyme catalysing the first committed step in dhurrin synthesis. Molecular modelling supports the measured effects on CYP79A1 activity in the mutant lines. Plants harbouring a P414L mutation in CYP79A1 are acyanogenic when homozygous for this mutation and are phenotypically normal, except for slightly slower growth at early seedling stage. Biochemical analyses demonstrate that the enzyme is present in wild-type amounts but is catalytically inactive. Additional mutants capable of producing dhurrin at normal levels in young seedlings but with negligible leaf dhurrin levels in mature plants were also identified. No mutations were detected in the coding sequence of dhurrin biosynthetic genes in this second group of mutants, which are as tall or taller, and leafier than non-mutated lines. The sorghum mutants with reduced or negligible dhurrin content that have been produced may be ideally suited for forage production.

- by Ros Gleadow and +1
- •
- Cyanogenesis

"Cassava products obtained in two major Australian cities, Melbourne and Canberra, were analysed for total cyanide content using the picrate method. In Melbourne in 2010, ready to eat cassava chips were found to contain large amounts of cyanide with a mean value of 91 mg HCN equivalents/kg fresh weight = ppm. In Canberra, similar values were found over a six-year study with cassava chip samples,
except for one sample that gave 7 ppm, which was obtained in 2011 after the introduction by Food Standards Australia and New Zealand of a 10 ppm maximum limit. In Melbourne, the highest value obtained was 262 ppm. A calculation based on this very high cyanide sample and using the lethal dose of cyanide for humans, shows that a child of 20 kg body weight would only need to eat 40–270 g of these
chips to reach the lethal dose. Frozen cassava roots gave a mean value of 52 ppm total cyanide, which is also a cause for concern. In contrast, more highly processed foods contained < 1 ppm total cyanide. 2011 Elsevier Inc. All rights reserved."

- by Howard Bradbury and +1
- •
- Plant-Animal Interactions, Cyanide, Cyanogenesis, Linamarin
- by Ros Gleadow
- •
- Plant defense mechanisms, Eucalyptus, Plant Defence, Cyanogenesis

The purpose of this study was to assess the quality of cassava cultivars, in terms of cyanogenic potential and composition of macro- and micronutrients, sampled from different locations in rural Mozambique. Total cyanide concentrations in fresh cassava tissues were measured using portable cyanide testing kits, and elemental nutrients were later analyzed from dried plant tissue. Variation in cyanogenic potential and nutrient composition occurred both among cultivars and across locations. The majority of cultivars contained >100 ppm total cyanide, fresh weight, and are therefore considered to be dangerously poisonous unless adequately processed before consumption. Leaf cyanogenic and nutrient content varied with plant water status, estimated using carbon isotope discrimination (δ(13)C). The colonization of roots of all cultivars by arbuscular mycorrhizal fungi was also quantified and found to be high, indicating that mycorrhizas could play a key role in plant nutrient acquisition i...

- by constantino cuambe
- •
- Engineering, Drought, Mozambique, Food and Nutrition

Cassava (Manihot esculenta Crantz) is the staple food source for over 850 million people worldwide. Cassava contains cyanogenic glucosides and can be toxic to humans, causing paralysing diseases such as konzo, and even death if not properly processed. Konzo epidemics are often associated with times of drought. This may be due to a greater reliance on cassava as it is drought tolerant, but it may also be due to an increase in cyanogenic glucosides. Episodic droughts are forecast to become more common in many cassava-growing regions. We therefore sought to quantify the effect of water-stress on both yield and cyanogenic glucoside concentration (CNc) in the developing tubers of cassava. Five-month-old plants were grown in a glasshouse and either well watered or droughted for 28 days. A subset of droughted plants was re-watered half way through the experiment. Droughted plants had 45% fewer leaves and lower tuber yield, by 83%, compared with well-watered plants. CNc was 2.9-fold higher in the young leaves of droughted plants, whereas CNc in tubers from droughted plants was 4-fold greater than in tubers from well-watered plants. Re-watered plants had a similar biomass to control plants, and lower CNc than droughted plants. These findings highlight the important link between food quality and episodic drought.

- by Ros Gleadow
- •
- Abiotic stress (Crop Physiology), Drought, Vegetables and Tubers, Cassava

Global food security in a changing climate depends on both the nutritive value of staple crops as well as their yields. Here, we examined the direct effect of atmospheric carbon dioxide on the toxicity of the important pasture crop, Trifolium repens L. (clover). Shoots of T. repens contain cyanogenic glycosides that break down to release toxic hydrogen cyanide when damaged. The ability of animals to tolerate cyanogenic compounds is dependent, in part, on their overall protein intake. We grew T. repens communities at ambient and approximately twice-ambient CO2 in a controlled environment greenhouse experiment. We found that the ratio of total cyanogenic glycosides to total protein ratio was nearly two times higher in leaves of T. repens grown at elevated CO2. This study highlights the importance of assessing the nutritive value of this and other plants in response to rising CO2 so that steps can be taken to address any adverse consequences for herbivores.

- by Ros Gleadow
- •
- Climate Change, Natural Products, Plant Secondary Metabolites, Rhizobium

Plants have evolved a vast array of defence mechanisms to avoid or minimize damage caused by herbivores and pathogens. The costs and benefits of defences are thought to vary with the availability of resources, herbivore pressure and plant functional traits. We investigated the resource (nitrogen) and growth cost of deploying cyanogenic glycosides in seedlings of Eucalyptus cladocalyx (Myrtaceae). To do this, we grew the plants under a range of soil N conditions, from levels that were limiting for growth to those that were saturating for growth, and we measured correlations between foliar chemical and performance attributes. Within each N treatment, we found evidence that, for every N invested in cyanogenic glycosides, additional N is added to the leaf. For the lowest N treatment, the additional N was less than one per cyanogenic glycoside, rising to some two Ns for the other treatments. The interaction between cyanogenic glycosides and both condensed tannins and total phenolic compounds was also examined, but we did not detect correlations between these compounds under constant leaf N concentrations. Finally, we did not detect a correlation between net assimilation rate, relative growth rate and cyanogenic glycoside concentrations under any soil N treatment. We conclude that the growth cost of cyanogenic glycosides was likely too low to detect and that it was offset to some degree by additional N that was allocated alongside the cyanogenic glycosides.

- by Ros Gleadow
- •
- Resource Allocation, Eucalypts, Eucalyptus, Plant Defence
- by Dimuth Siritunga
- •
- Genetics, Plant Biology, Forecasting, Plant Molecular Biology

- by Ros Gleadow
- •
- Plant Biology, Sea Level, Abiotic Stress, Cassava

Rising sea levels are threatening agricultural production in coastal regions due to inundation and contamination of groundwater. The development of more salt-tolerant crops is essential. Cassava is an important staple, particularly among poor subsistence farmers. Its tolerance to drought and elevated temperatures make it highly suitable for meeting global food demands in the face of climate change, but its ability to tolerate salt is unknown. Cassava stores nitrogen in the form of cyanogenic glucosides and can cause cyanide poisoning unless correctly processed. Previous research demonstrated that cyanide levels are higher in droughted plants, possibly as a mechanism for increasing resilience to oxidative stress. We determined the tolerance of cassava to salt at two different stages of development, and tested the hypothesis that cyanide toxicity would be higher in salt-stressed plants. Cassava was grown at a range of concentrations of sodium chloride (NaCl) at two growth stages: tuber initiation and tuber expansion. Established plants were able to tolerate 100 mM NaCl but in younger plants 40 mM was sufficient to retard plant growth severely. Nutrient analysis showed that plants were only able to exclude sodium at low concentrations. The foliar cyanogenic glucoside concentration in young plants increased under moderate salinity stress but was lower in plants grown at high salt. Importantly, there was no significant change in the cyanogenic glucoside concentration in the tubers. We propose that the mechanisms for salinity tolerance are age dependent, and that this can be traced to the relative cost of leaves in young and old plants.

- by Ros Gleadow and +1
- •
- Cassava, Salinity, Reactive Oxygen Species, Cyanogenesis
- by Ros Gleadow
- •
- Plant Systematics, Plant defense mechanisms, Eucalyptus, Plant Defence