Cyanogenic Plants Research Articles

Functional characterization of Arabidopsis hydroxynitrile lyase in response to abiotic stress and the regulation of flowering time.

Hydroxynitrile lyases (HNLs) are a class of hydrolytic enzymes from a wide range of sources, which play crucial roles in the catalysis of the reversible conversion of carbonyl compounds derived from cyanide and free cyanide in cyanogenic plant species. HNLs were also discovered in non-cyanogenic plants, such as Arabidopsis thaliana, and their roles remain unclear even during plant growth and reproduction. The pattern of expression of the HNL in A. thaliana (AtHNL) in different tissues, as well as under abiotic stresses and hormone treatments, was examined by real-time quantitative reverse transcription PCR (qRT-PCR) and an AtHNL promoter-driven histochemical β-glucuronidase (GUS) assay. AtHNL is highly expressed in flowers and siliques, and the expression of AtHNL was dramatically affected by abiotic stresses and hormone treatments. The overexpression of AtHNL resulted in transgenic A. thaliana seedlings that were more tolerance to mannitol and salinity. Moreover, transgenic lines of A. thaliana that overexpressed this gene were less sensitive to abscisic acid (ABA). Altered expression of ABA/stress responsive genes was also observed in hnl mutant and AtHNL-overexpressing plants, suggesting AtHNL may play functional roles on regulating Arabidopsis resistance to ABA and abiotic stresses by affecting ABA/stress responsive gene expression. In addition, the overexpression of AtHNL resulted in earlier flowering, whereas the AtHNL mutant flowered later than the wild type (WT) plants. The expression of the floral stimulators CONSTANS (CO), SUPPRESSOR OF OVER EXPRESSION OF CO 1 (SOC1) and FLOWERING LOCUS T (FT) was upregulated in plants that overexpressed AtHNL when compared with the WT plants. In contrast, expression of the floral repressor FLOWERING LOCUS C (FLC) was upregulated in AtHNL mutants and downregulated in plants that overexpressed AtHNL compared to the WT plants. This study revealed that AtHNL can be induced under abiotic stresses and ABA treatment, and genetic analysis showed that AtHNL could also act as a positive regulator of abiotic stress and ABA tolerance, as well as flowering time.

De novo genome assembly of white clover (Trifolium repens L.) reveals the role of copy number variation in rapid environmental adaptation

BackgroundWhite clover (Trifolium repens) is a globally important perennial forage legume. This species also serves as an eco-evolutionary model system for studying within-species chemical defense variation; it features a well-studied polymorphism for cyanogenesis (HCN release following tissue damage), with higher frequencies of cyanogenic plants favored in warmer locations worldwide. Using a newly generated haplotype-resolved genome and two other long-read assemblies, we tested the hypothesis that copy number variants (CNVs) at cyanogenesis genes play a role in the ability of white clover to rapidly adapt to local environments. We also examined questions on subgenome evolution in this recently evolved allotetraploid species and on chromosomal rearrangements in the broader IRLC legume clade.ResultsIntegration of PacBio HiFi, Omni-C, Illumina, and linkage map data yielded a completely de novo genome assembly for white clover (created without a priori sequence assignment to subgenomes). We find that white clover has undergone extensive transposon diversification since its origin but otherwise shows highly conserved genome organization and composition with its diploid progenitors. Unlike some other clover species, its chromosomal structure is conserved with other IRLC legumes. We further find extensive evidence of CNVs at the major cyanogenesis loci; these contribute to quantitative variation in the cyanogenic phenotype and to local adaptation across wild North American populations.ConclusionsThis work provides a case study documenting the role of CNVs in local adaptation in a plant species, and it highlights the value of pan-genome data for identifying contributions of structural variants to adaptation in nature.

Plant Cyanogenic-Derived Metabolites and Herbivore Counter-Defences.

The release of cyanide from cyanogenic precursors is the central core of the plant defences based on the cyanogenesis process. Although cyanide is formed as a coproduct of some metabolic routes, its production is mostly due to the degradation of cyanohydrins originating from cyanogenic glycosides in cyanogenic plants and the 4-OH-ICN route in Brassicaceae. Cyanohydrins are then hydrolysed in a reversible reaction generating cyanide, being both, cyanohydrins and cyanide, toxic compounds with potential defensive properties against pests and pathogens. Based on the production of cyanogenic-derived molecules in response to the damage caused by herbivore infestation, in this review, we compile the actual knowledge of plant cyanogenic events in the plant-pest context. Besides the defensive potential, the mode of action, and the targets of the cyanogenic compounds to combat phytophagous insects and acari, special attention has been paid to arthropod responses and the strategies to overcome the impact of cyanogenesis. Physiological and behavioural adaptations, as well as cyanide detoxification by β-cyanoalanine synthases, rhodaneses, and cyanases are common ways of phytophagous arthropods defences against the cyanide produced by plants. Much experimental work is needed to further understand the complexities and specificities of the defence-counter-defence system to be applied in breeding programs.

Investigation of Levels of Cyanide in Cassava Tubers Marketed in Kampala

Cassava is one of the cyanogenic plants poisonous to humans once consumed in unprocessed state. Cassava is characterized by a cyanogenic glycoside, linamarin and hydrolyzed to cyanohydrin by an enzyme called linamarase, cyanohydrin is hydrolyzed to a toxic hydrogen cyanide (HCN). This study purposed investigation of the levels of cyanide in the sweet cassava subspecies marketed in various markets within Kampala City. The mean concentration levels of cyanide in cassava samples from markets within Nakawa Division were 50.83±2.93, 53.54±2.46, 52.25±2.64, 52.20±2.45 and 47.25±3.12 ppm for Nakawa Market, Kisasi Market, Banda Market, Kirombe Market and Bugolobi Local Market respectively. The mean concentration levels of cyanide in cassava samples from markets within Kawempe Division were 56.25± 3.43, 54.52± 2.84 and 61.08± 3.32 ppm for Kalerwe Market, Mperewe Market and Kawempe Market respectively. The mean concentration levels of cyanide in cassava samples from markets within Rubaga Division were 59.69±2.41, 57.83±2.96 and 61.55±2.52 ppm for Busega Market, Kawala Market and Nakulabye Market respectively. The mean concentration levels of cyanide in cassava samples from markets within Makindye Division were 58.41±2.51, 52.58±2.43, 54.53±2.76 and 54.41±2.93 ppm for Gaaba Market, Kabalagala Market, Kansanga Vendor Market and Bunga Market respectively. All samples analyzed for cyanide in cassava gave values higher than 10ppm which is WHO’s recommended level of cyanide in cassava. This article gives vital information on the levels of cyanide in cassava from the various markets in Kampala City.

Cyanogenesis, a Plant Defence Strategy against Herbivores.

Plants and phytophagous arthropods have coevolved in a long battle for survival. Plants respond to phytophagous feeders by producing a battery of antiherbivore chemical defences, while herbivores try to adapt to their hosts by attenuating the toxic effect of the defence compounds. Cyanogenic glucosides are a widespread group of defence chemicals that come from cyanogenic plants. Among the non-cyanogenic ones, the Brassicaceae family has evolved an alternative cyanogenic pathway to produce cyanohydrin as a way to expand defences. When a plant tissue is disrupted by an herbivore attack, cyanogenic substrates are brought into contact with degrading enzymes that cause the release of toxic hydrogen cyanide and derived carbonyl compounds. In this review, we focus our attention on the plant metabolic pathways linked to cyanogenesis to generate cyanide. It also highlights the role of cyanogenesis as a key defence mechanism of plants to fight against herbivore arthropods, and we discuss the potential of cyanogenesis-derived molecules as alternative strategies for pest control.

Assessing the Benefits and Costs of the Hydrogen Cyanide Antiherbivore Defense in Trifolium repens.

Understanding the evolution of plant defenses against herbivores requires identifying the benefits and costs of defense. Here, we tested the hypothesis that the benefits and costs of hydrogen cyanide (HCN) defense against herbivory on white clover (Trifolium repens) are temperature dependent. We first tested how temperature affected HCN production in vitro, and then examined how temperature influenced the efficacy of HCN defense of T. repens against a generalist slug (Deroceras reticulatum) herbivore using no-choice and choice feeding trial assays. To understand how temperature affected the costs of defense, plants were exposed to freezing, and HCN production, photosynthetic activity, and ATP concentration were quantified. HCN production increased linearly from 5 °C to 50 °C, and cyanogenic plants experienced reduced herbivory compared to acyanogenic plants only at warmer temperatures when fed upon by young slugs. Freezing temperatures induced cyanogenesis in T. repens and decreased chlorophyll fluorescence. Cyanogenic plants experienced lower ATP levels than acyanogenic plants due to freezing. Our study provides evidence that the benefits of HCN defense against herbivores are temperature dependent, and freezing may inhibit ATP production in cyanogenic plants, but the physiological performance of all plants recovered quickly following short-term freezing. These results contribute to understanding how varying environments alter the benefits and costs of defense in a model system for the study of plant chemical defenses against herbivores.

Isolation and Quantification of Mandelonitrile from Arabidopsis thaliana Using Gas Chromatography/Mass Spectrometry.

Mandelonitrile is a nitrogen-containing compound, considered an essential secondary metabolite. Chemically, it is a cyanohydrin derivative of benzaldehyde, with relevant functions in different physiological processes including defense against phytophagous arthropods. So far, procedures for detecting mandelonitrile have been effectively applied in cyanogenic plant species such as Prunus spp. Nevertheless, its presence in Arabidopsis thaliana , considered a non-cyanogenic species, has never been determined. Here, we report the development of an accurate protocol for mandelonitrile quantification in A. thaliana within the context of A. thaliana -spider mite interaction. First, mandelonitrile was isolated from Arabidopsis rosettes using methanol; then, it was derivatized by silylation to enhance detection and, finally, it was quantified using gas chromatography-mass spectrometry. The selectivity and sensitivity of this method make it possible to detect low levels of mandelonitrile (LOD 3 ppm) in a plant species considered non-cyanogenic that, therefore, will have little to no cyanogenic compounds, using a small quantity of starting material (≥100 mg).

ACTION OF CYANOGENIC SUBSTANCES AND MAGNETIC FIELD IN THE REDUCTION OF NEOPLASMS

Cancer treatment has been constantly improved to cause the least possible harm to the patient. New therapies are being researched, many of them having as object of scientific-academic and pharmacological research the use of cyanogenic plants and their antitumor chemical compounds that can bring benefits to human health, having the potential to be associated with the magnetic Field and thus achieve a better benefit and with reduced adverse effects in cancer treatment. This study aimed to review the effect of cyanogenic substances and magnetic Field on tumor evolution in the literature. The integrative review of the literature was carried out in the databases EMBASE, PUBMED, LILACS, VHL, SCOPUS and MEDLINE. A final sample of 14 scientific articles, published from 2011 to 2020, was obtained, highlighting that cyanogenic substances and the magnetic Field can help reduce tumors. The most common studies were on the magnetic Field, and the studies were carried out mainly in vitro, with a frequency of 50 Hz that stood out from the others. Among the cyanogenic substances, the most prevalent was tonsillin, with the most used dosage of 10mg / ml. It was possible to conclude that both the magnetic Field and cyanogenic substances can reduce tumors.

What’s your poison? Cyanide production regulated by a bHLH transcription factor inLotus japonicus

Humans hold a love–hate relationship with cyanogenic plants. Preferentially selected for domestication due to their heightened pest resistance, they can nevertheless threaten both human and livestock health if not consumed in moderation or adequately processed. Over 20% of crops are cyanogenic due to the stable accumulation of cyanogenic glucosides (CNglcs) and, while the biochemical pathways of these specialized metabolites are known, the same cannot be said regarding their underlying molecular pathways. In a comprehensive study, Chen et al. (2022) characterized a basic helix–loop–helix (bHLH) transcription factor that is responsive to methyl jasmonate and directly induces expression of the key CNglc biosynthetic gene in the model species Lotus japonicus.

The Effect of Cooking on the Goitrogenic (cyanogenic glycosides and glucosinolates) Content of Pumpkin Leaves (Telfairia occidentalis) and Spinach Leaves (Spinacia olairaceae)

Fresh ugwu (Telfairia occidentalis) and spinach (Spinacia olairaceae) leaves play important roles in human nutrition. Leafy vegetables including Telfairia occidentalis and Spinacia olairaceae are considered as agents of transmission of goitrogens which interfere with iodine uptake thus causing goiter. Cyanogenic glycosides are naturally occurring goitrogens found in staple foods in the tropics. Thiocyanate and isothiocyanate have been demonstrated as the goitrogenic principles of cyanogenic plants Thiocyanate ion acts as a goitrogen when present at high concentration especially when the iodine content of the diet is low. Thiocyanate inhibits the uptake of iodine by the iodide pump of the thyroid gland thus acting as a goitrogen which suppresses thyroid function leading to goiter. This study examined the effect of cooking on the goitrogenic potential of Ugwu and Spinach leaves. A total of (10g) of fresh/ andraw ugwu and spinach leaves were randomly collected and cooked. All samples were examined according to standard methods for detection of goitrogens. The cyanogenic glycosides content of rawand fresh ugwu leaves were 1. 6mg /kg - 1. 82mg/ kg while that of cooked leaves were 0. 004mg/ kg - 0. 0 l3mg/ kg. The glucosinolates content for raw and fresh Ugwu leaves were15.7mg/kg-17.28mg/kg, while that of cooked Ugwu leaves were 11.18mg/kg- 12.51mg/kg . For Spinach the cyanogenic glycosides content for raw and fresh were 0.24mg/kg-1.28mg/kg, while that of cooked spinach were 0.013mg/kg- 0.00Smg/kg. The glucosinolates content for raw and fresh spinach were 4.0mg/kg-2.64mg/kg while those of the cooked leaves were 2.52mg/kg-1.82mg/kg. there was a significant diference (P=0.085) in the level of reduction of glucosinolate content between raw and cooked Ugwu leaves and Spinach. There is also a significant difference (p=3.04) in the concentration of glucosinolates between Ugwu leaves and Spinach. Ugwu leaves had a higher concentration of glucosinolates than spinach in both fresh (raw) and cooked conditions respectively. These findings provide evidence that the risk of acquiring goiter from the consumption of ugwu and spinach leaves is reduced when cooked.
 Keywords: Ugwu leaves, Spinach leaves, Cooking, Goitrogens, Cyanogenic glycosides, Glucosinolates

Structural and functional characterization of β-cyanoalanine synthase from Tetranychus urticae

Tetranychus urticae is a polyphagous spider mite that can feed on more than 1100 plant species including cyanogenic plants. The herbivore genome contains a horizontally acquired gene tetur10g01570 (TuCAS) that was previously shown to participate in cyanide detoxification. To understand the structure and determine the function of TuCAS in T. urticae, crystal structures of the protein with lysine conjugated pyridoxal phosphate (PLP) were determined. These structures reveal extensive TuCAS homology with the β-substituted alanine synthase family, and they show that this enzyme utilizes a similar chemical mechanism involving a stable α-aminoacrylate intermediate in β-cyanoalanine and cysteine synthesis. We demonstrate that TuCAS is more efficient in the synthesis of β-cyanoalanine, which is a product of the detoxification reaction between cysteine and cyanide, than in the biosynthesis of cysteine. Also, the enzyme carries additional enzymatic activities that were not previously described. We show that TuCAS can detoxify cyanide using O-acetyl-L-serine as a substrate, leading to the direct formation of β-cyanoalanine. Moreover, it catalyzes the reaction between the TuCAS-bound α-aminoacrylate intermediate and aromatic compounds with a thiol group. In addition, we have tested several compounds as TuCAS inhibitors. Overall, this study identifies additional functions for TuCAS and provides new molecular insight into the xenobiotic metabolism of T. urticae.

Fate and toxicity of ferric ferrocyanide with cyanogenic and non-cyanogenic plant species

Iron cyanide complexes are common contaminants at former manufactured gas plant sites. Although combined forms of cyanide have low toxicity, iron cyanide complexes can be decomposed to HCN through photolysis. This experiment was designed to evaluate the efficiency of phytoremediation and investigate potential toxic effect for iron cyanide complexes (i.e., ferric ferrocyanide) using the cyanogenic and non-cyanogenic plants in soil. Results showed that Sorghum (a cyanogenic plant) had the highest cyanide degradation in the root zone with the removal of approximately 32% while Switchgrass (a non-cyanogenic plant) and Flax (a cyanogenic plant) had 21% and 17% removal, respectively, with 4% dissipation in unvegetated soil. It was found that roots had higher cyanide concentrations than plant shoots. Water-soluble cyanide and the weak acid dissociable (WAD) fraction in the soil had increased at the end of the experiment, suggesting that plant may enhance the mobility and bioavailability of cyanide by root exudation. The risk associated with the leaching of cyanide compounds was assessed with the toxicity assay (Microtox). However, results indicated that the leachate from the pots was not toxic.

Screening of natural product extracts for fly repellent and larvicide

Fly is one of the vectors of foodborne pathogenic vectors and causes myiasis in humans and animals. To prevent the contamination of food and myiasis, various chemical products are commonly used. However, eco-friendly is now a trend all over the world so natural products are the alternative ways to reduce the chemical residue in the environment. The present study was screened the 12 natural products in 4 groups; the essential oil plants, the alkaloid plants, the cyanogenic plant, and the inorganic compounds which use a simple extraction on the fly repelling and larvicide. The fly repelling efficacy with 2 criteria consist of the time of the first swarm and percent repelling (PR) in the first 15 min. The larvicidal efficacy was determined by the mortality rate within 24 h. The Kaffir lime peels aqueous crude extract exhibited the best result on fly repelling from both criteria with no significant difference. The bamboo shoots aqueous crude extract gave the best result on larvicide with significantly different from other groups (P < 0.001) which was faster than the positive control group (Coumaphos & Propoxur). Moreover, the high mortality rate reached 73.33 ± 15.28% within 24 h, higher than the positive control group. The present study indicates the power of common natural products on fly repellent and larvicide that may apply for fly repellant to reduce the food contamination especially fresh materials and prevention or treatment of animal and human myiasis in rural areas

Lowered sensitivity of bitter taste receptors to β-glucosides in bamboo lemurs: an instance of parallel and adaptive functional decline in TAS2R16?

Bitter taste facilitates the detection of potentially harmful substances and is perceived via bitter taste receptors (TAS2Rs) expressed on the tongue and oral cavity in vertebrates. In primates, TAS2R16 specifically recognizes β-glucosides, which are important in cyanogenic plants' use of cyanide as a feeding deterrent. In this study, we performed cell-based functional assays for investigating the sensitivity of TAS2R16 to β-glucosides in three species of bamboo lemurs (Prolemur simus, Hapalemur aureus and H. griseus), which primarily consume high-cyanide bamboo. TAS2R16 receptors from bamboo lemurs had lower sensitivity to β-glucosides, including cyanogenic glucosides, than that of the closely related ring-tailed lemur (Lemur catta). Ancestral reconstructions of TAS2R16 for the bamboo-lemur last common ancestor (LCA) and that of the Hapalemur LCA showed an intermediate sensitivity to β-glucosides between that of the ring-tailed lemurs and bamboo lemurs. Mutagenetic analyses revealed that P. simus and H. griseus had separate species-specific substitutions that led to reduced sensitivity. These results indicate that low sensitivity to β-glucosides at the cellular level—a potentially adaptive trait for feeding on cyanogenic bamboo—evolved independently after the Prolemur–Hapalemur split in each species.

Suspected cyanide toxicity in cattle associated with ingestion of laurel - a case report

BackgroundCyanide is one of the most rapidly acting toxins affecting cattle, with poisoning typically occurring following ingestion of cyanogenic plants. Laurel (Prunus laurocerasus), is one such potentially toxic cyanogenic plant. This case report details fatalities in an Irish herd following the ingestion of laurel and aims to raise awareness of the potential risk that access to laurel hedges poses to farm animals.Case presentationOver a twelve-day period, the death occurred of 36 dairy-cross weanlings; the majority (22 weanlings) died over a two-day period. Two days following entry to a field bounded by a laurel hedge, the weanlings displayed signs of lethargy and profuse green diarrhoea. In the majority of animals there was a limited response to treatment with antimicrobials, vitamin B complex and fluid therapy. Recumbency and death ensued. Cyanosis was noted terminally. Two weanlings were submitted for post mortem examination. Laurel leaves were identified in the rumen contents of one weanling. Post mortem findings and additional test results on cohort animals suggested a number of pathological processes may have been involved in the animals, possibly complicating/exacerbating the effects of laurel ingestion. However, cyanide was considered a factor in a least some of the casualties and arrangements were made to test for cyanide on blood samples from a random selection of seven cohort animals. Although collected one week after exposure to the laurel hedge, toxic cyanide levels were recorded in a sample from one animal, which subsequently died.ConclusionsThe large fatality rate serves as a timely reminder to include plant poisoning as a differential diagnosis when dealing with large numbers of rapid fatalities. Failure to thoroughly examine rumen contents and collect a detailed history in this case, could easily have allowed death to be attributed to other causes and the involvement of cyanide toxicity to be missed. In cases of individual or group fatalities, history is invaluable and recent entry to new grazing areas or any potential diet change or access to garden plants should be thoroughly investigated.

Plant Poisoning Containing Hydrocyanic Acid in Cattle in Southern Brazil

Background: Cyanogenic plants accumulate cyanogenic glycosides and release hydrocyanic acid (HCN). In Brazil, there have been reports of several plants that cause HCN poisoning in animals and lead to a fast death with few clinical signs and lesions on post-mortem examination. Some cultivars of Cynodon spp. grasses cause HCN poisoning in cattle in Brazil. The objectives of this work were to report the occurrence of deaths by HCN poisoning in cattle as diagnosed by the veterinary pathology laboratory, describe the quantity of HCN in some cultivars of Cynodon spp., as well as, to describe one cultivar of genus Cynodonnever reported as poisonous.Materials, Methods & Results: The archives of the Veterinary Pathology Laboratory (LPV) at the Concórdia Campus of the Instituto Federal Catarinense (IFC) were reviewed, seeking cases with a diagnosis of hydrocyanic acid poisoning in cattle after post mortem examination. The amount of HCN present in some cultivars of the Cynodon genus was quantified due to the high frequency of poisoning cases. From the 1,235 post mortem examinations of cattle 28 (2.27%) were diagnosed with spontaneous hydrocyanic acid poisoning, 17 cases (60.7%) due to ingestion of Prunus sp. or Manihot sp., and 11 cases (39.3%) of Cynodon dactylon ingestion. Most animals were found dead, normally having presented no clinical signs. Macroscopic evaluation mainly showed a severe amount of unchewed and undigested leaves or grass mixed in the ruminal content presenting a bitter almond odor. It was possible to infer that, among cultivars of the Cynodon genus, Florakirk showed the highest levels of HCN compared (P < 0.05) with Star of Puerto Rico, Tifton 68, Tifton 44, and Coast-Cross. Furthermore, Tifton 85 and Jiggs showed undetected levels of HCN. Leaves showed the highest HCN levels when comparing different parts of the plant. Regarding conservation methods, hay showed undetectable levels of HCN.Discussion: To the best of our knowledge, this work is the first description of HCN poisoning in cattle due to ingestion of Cynodon dactylon cultivar Florakirk. This condition is described with a fast-clinical course, with animals found dead with no premonitory clinical signs. Poisoned animals did not develop macroscopic or microscopic specific lesions. Poisoning can be suspected when animals die suddenly, with absence of lesions under necropsy, and large amounts of unchewed and undigested leaves or grass inside their forestomaches. The diagnosis can be established performing the Picrosodic paper test, either in the pasture, or in the ruminal content. Occasionally however, HCN can go undetected when this chemical compound volatilizes between death and necropsy after several hours. Of all the Cynodon cultivars evaluated, Florakirk was the most dangerous for animals. In contrast, Tifton 85 and Jiggs released no HCN. Leaves were the part of the plant presenting the highest concentration of HCN. This is a defense mechanism that the plant develops against the ingestion by animals. This condition can cause great economic losses to farmers with the loss of animals and the need for prevention by using cultivars without HCN or hay, as 2.27% (28) of deaths diagnosed by the Veterinary Pathology Laboratory in the west of Santa Catarina, Brazil, were due to HCN poisoning. Notably, Florakirk cultivar was identified as the most dangerous cultivar tested, with higher levels compared with Tifton 68. The Star of Puerto Rico cultivar showed similar levels of HCN as Tifton 68. Both cultivars are commonly cultivated in many farms in the south of Brazil.

Cyanogenic glycosides and plant-herbivore interactions

Cyanogenic glycosides are nitrogen containing secondary metabolites which offer plant defense mechanism against herbivores while recently various insects have developed ability to detoxify, sequester and synthesize these cyanogenic compounds. Dhurrin was the first identified and isolated CNGs from young leaves of sorghum, Sorghum vulgare. The presence of CNGs were confirmed in few species of Chilopods, Diplopods, Heteropterans, Coleopterans and Lepidopterans. Linamarin and Lotaustralin were the major CNGs distributed in Lepidopterans. They have developed an ability to de novo synthesize CNGs and detoxify them with the help of β-cyanoalanine synthase and rhodonase. This may be due to the course of insect evolution or the genes responsible for the synthesis of CNGs may get transferred from plants to insects. In future, the responsive genes in these arthropods should be silenced and expansion of transgenic cyanogenic plants may encouraged to ensure plant defense mechanism.

NATURAL TOXIN SUBSTANCES IN EVERYDAY FOOD

Natural toxins are present in a wide variety of plants. Some of these plants are commonly consumed as food. These toxic substances when ingested in significant amount or when they are not processed appropriately can be potentially harmful to human health causing food poisoning. This study conducted by the Centre for Food Safety of the Food and Environmental Hygiene Department aimed to review natural toxins in food plants commonly consumed in Hong Kong and the measures that can be employed to prevent poisoning from consumption of these food plants. Laboratory study of two natural toxins, glycoalkaloids and cyanogenic glycosides, was carried out to determine the levels of these toxins in food plants commonly consumed in Hong Kong. The effects of preparation and cooking on the reduction of the toxin levels were also studied. Results showed that glycoalkaloid contents varied among the different types of the fresh potatoes tested which ranged from 26-88 mg/kg (average 56 mg/kg). This was within the normal range of glycoalkaloid contents in potatoes of 20 - 100 mg/kg, which JECFA considered that consumptions on a daily basis were not of concern. The highest concentrations of glycoalkaloids were found in potato sprouts. Cyanide was detected in bitter apricot seed, bamboo shoot, cassava, and flaxseed samples in their raw state at levels of 9.3 mg/kg to 330 mg/kg. Cyanide contents were found to be higher in bitter cassava than sweet cassava. Cyanide concentration was found to be highest at the tip portion of bamboo shoot, followed by the middle portion, then the base portion. Cutting cyanogenic food plants into small pieces and cooking them in boiling water reduced cyanide contents of the food commodities by over 90%. Dry heat could not reduce cyanide contents effectively and only reduced around 10% of the cyanide contents in flaxseeds following oven-heating for 15 minutes. Consumers should avoid buying or eating potatoes that show signs of sprouting, greening, physical damage or rotting since glycoalkaloids are not decomposed by cooking. Cutting the cyanogenic plants into smaller pieces and cooking thoroughly in boiling water help release toxic hydrogen cyanide before consumption. When the cooking method chosen is heating under dry-heat or at low moisture contents, limit the intake of the cyanogenic plants to only small amounts. KEY WORDS: glycoalkaloids, cyanogenic

Possible mechanism of bamboo shoots (Bambusa balcooa) induced thyroid disruption - An in vitro study.

Endemic goitre and associated iodine deficiency disorders (IDDs) are a major concern in public health even in the period of post salt iodization in many regions. Among others the consumption of cyanogenic plants found responsible for the persistence of such diseases. Bamboo shoots (BS) is one such cyanogenic plant food that caused disruption of certain thyroid hormone synthesizing regulatory element as has already been reported in our earlier study. In this investigation the possible mechanism of thyrocytes disruption along with interruption of thyroid hormone biosynthesis by BS has been worked out. Commonly consumed BS, Bambusa Balcooa Roxb (BBR) water extract was analysed by GC MS; three doses below IC50 were administered to thyrocytes in culture with and without iodine. Expressions of thyroglobulin (Tg), pendrin (PDS) and monocarboxylate transporter 8 (MCT8) were evaluated in thyrocytes with cell cycle analysis, reactive oxygen species (ROS) generation, DNA oxidation and apoptotic regulation through Bax, Bcl-2 and p53. Phytochemical analysis of BBR extract revealed the presence of precursors and metabolic end products of cyanogenic glycosides. Dose dependent decrease in expression of Tg and PDS with concomitant decrease in gene expression of these with MCT8 were observed. Increased ROS, DNA oxidation and associated imbalance were found through increased Bax and p53 with decreased Bcl-2 that perturbed thyrocytes cell cycle. Cyanogenic constituents of BBR generates ROS associated oxidative changes in thyrocytes with DNA damage and oxidation and cell cycle disruption followed by inhibition of thyroid hormone synthesizing regulatory elements; addition of extra iodine showed partial prevention.

High-throughput in-field bioprospecting for cyanogenic plants and hydroxynitrile lyases

Hydroxynitrile lyases (HNLs) are sought-after, stereo-selective biocatalysts used in the agrochemical, pharmaceutical and fine chemical industries to produce cyanohydrin enantiomers. There are several approaches for the discovery of HNLs, most of which are methodologically demanding and not suitable for high-throughput. Bioprospecting studies to date have also been constrained/limited to commercialised plants or botanical gardens, leaving a vast majority of plant species untested for HNL activity or cyanogenesis. To increase the rate of discovery of HCN liberating plants, we devised a Feigl-Anger microfuge tube that is portable and capable of high throughput detection of naturally cyanogenic plants. A workflow suitable for detecting plant candidates containing extractable, novel HNLs was subsequently applied. In this study, we screened over 600 plants for cyanogenic activity as well as the ability to degrade racemic mandelonitrile. We detected 33 plants able to degrade racemic mandelonitrile, of which, 25 were identified to the species level. Six of these plants were found to be naturally cyanogenic. Protein extracts from 5 of the naturally cyanogenic plants retained the ability to degrade racemic mandelonitrile pointing to five yet undescribed enzymes in the species Achyranthes aspera, Davallia trichomonoides, Morus mesozygia, Polypodium aureum “Mandaianum”, and Thelypteris confluens. In contrast, although Acalypha glabrata was found to be naturally cyanogenic, the protein extract did not break down racemic mandelonitrile. Here, we used racemic mandelonitrile as substrate and detected enzymes with mandelonitrile lyase activity, however, any cyanohydrin could be used as part of the approach taken here to detect novel HNLs specific to the substrate utilised.