Horseradish is a crop grown for its edible underground parts. The development of new cultivars is hindered by the species' predominant vegetative reproduction, making it essential to evaluate locally cultivated accessions to identify new types suitable for cultivation. To this end, 11 horseradish accessions from family vegetable gardens in Trentino-Alto Adige, Italy were examined using 26 qualitative and six quantitative morphological descriptors and characterized by the five major glucosinolates (GSLs) present in the rhizome compared to a reference cultivar. A wide range of variability was observed for the considered qualitative morphological traits. The rhizome's top and basal diameters were 9.9 and 6.2 cm, respectively, with an average fresh weight of 521 g. Total GSL content ranged between 79.5 and 133.5 μmol/g dry weight (DW), with sinigrin (SIN) being the primary component at an average content of 110.0 μmol/g DW. Differences among the investigated accessions were noted for quantitative traits describing their productive features and for GSL content. A positive correlation was discovered between the biometric traits of the plant's underground parts and the SIN and total GSL content, suggesting a link between the quality and yield of the edible product. According to the multivariate analysis, accessions were grouped into three main clusters: the largest of the reference cultivar and the majority of accessions with similar productive and qualitative traits; another featuring two with good qualitative and productive characteristics. The investigated accessions proved to be a valuable germplasm source for cultivating the species.

This trial was conducted to study the effects of dietary rapeseed cake (RSC) containing high glucosinolates (GLS) on rumen fermentation, nutrient digestion and the rumen microbial community in steers. Eight growing steers and four rations containing RSC (GLS 226·1 μmol/g DM) at 0·00, 2·65, 5·35 and 8·00 % DM were assigned in a replicate 4 × 4 Latin square design. The results indicated that increasing RSC levels increased the ruminal concentration of thiocyanate (SCN) (P < 0·01), decreased the ruminal concentration of ammonia nitrogen (NH3-N) and the molar proportion of isovalerate (P < 0·05), did not affect the ruminal concentration of total volatile fatty acids (P > 0·05), decreased the crude protein (CP) digestibility (P < 0·05) and increased the ether extract (EE) digestibility (P < 0·01). Increasing RSC levels tended to decrease the abundances of ruminal Ruminobacter amylophilus (P = 0·055) and Ruminococcus albus (P = 0·086) but did not affect methanogens, protozoa, fungi and other bacteria (P > 0·05). Increasing RSC levels in the ration did not affect the ruminal bacterial diversity (P > 0·05), but it increased the operational taxonomic units and the bacterial richness (P < 0·05) and affected the relative abundances of some bacteria at the phylum level and genus level (P < 0·05). In conclusion, RSC decreased the ruminal concentration of NH3-N and the CP digestibility, increased the EE digestibility and partly affected the ruminal bacterial community. SCN, as the metabolite of GLS, could be a major factor affecting these indices.

Cruciferous vegetables contain high levels of glucosinolates (GSL) and isothiocyanates (ITC). ITC are known to induce glutathione S-transferases (GST) and thus exert their anticarcinogenic effects. This study explored the combined effects of cruciferous vegetable, GSL and ITC intake and GST polymorphisms on breast cancer risk. A total of 737 breast cancer cases and 756 controls were recruited into this case–control study. OR and 95 % CI were assessed by multivariable logistic regression. Higher cruciferous vegetable, GSL and ITC intakes were inversely associated with breast cancer risk, with adjusted OR of 0·48 (95 % CI 0·35, 0·65), 0·54 (95 % CI 0·40, 0·74) and 0·62 (95 % CI 0·45, 0·84), respectively. Compared with women carrying the GSTP1 rs1695 wild AA genotype and high cruciferous vegetable, GSL or ITC intake, carriers of the AA genotype with low cruciferous vegetable, GSL and ITC intake had greater risk of breast cancer, with adjusted OR of 1·43 (95 % CI 1·01, 1·87), 1·34 (95 % CI 1·02, 1·75) and 1·37 (95 % CI 1·05, 1·80), respectively. Persons with the GSTM1-null genotype and lower intake of cruciferous vegetables, GSL and ITC had higher risk of breast cancer than those with the GSTM1-present genotype and higher intake, with OR of 1·42 (95 % CI 1·04, 1·95), 1·43 (95 % CI 1·05, 1·96) and 1·45 (95 % CI 1·06, 1·98), respectively. Among women possessing the GSTT1-present genotype, low intake of cruciferous vegetables, GSL or ITC was associated with higher risk of breast cancer. But these interactions were non-significant. This study indicated that there were no significant interactions between cruciferous vegetable, GSL or ITC intake and GST polymorphisms on breast cancer risk.

Sulphoraphane originates from glucoraphanin in broccoli and is associated with anti-cancer effects. A preclinical study suggested that daily consumption of broccoli may increase the production of sulphoraphane and sulphoraphane metabolites available for absorption. The objective of this study was to determine whether daily broccoli consumption alters the absorption and metabolism of isothiocyanates derived from broccoli glucosinolates. We conducted a randomised cross-over human study (n 18) balanced for BMI and glutathione S-transferase μ 1 (GSTM1) genotype in which subjects consumed a control diet with no broccoli (NB) for 16 d or the same diet with 200 g of cooked broccoli and 20 g of raw daikon radish daily for 15 d (daily broccoli, DB) and 100 g of broccoli and 10 g of daikon radish on day 16. On day 17, all subjects consumed a meal of 200 g of broccoli and 20 g of daikon radish. Plasma and urine were collected for 24 h and analysed for sulphoraphane and metabolites of sulphoraphane and erucin by triple quadrupole tandem MS. For subjects with BMI >26 kg/m2 (median), plasma AUC and urinary excretion rates of total metabolites were higher on the NB diet than on the DB diet, whereas for subjects with BMI <26 kg/m2, plasma AUC and urinary excretion rates were higher on the DB diet than on the NB diet. Daily consumption of broccoli interacted with BMI but not GSTM1 genotype to affect plasma concentrations and urinary excretion of glucosinolate-derived compounds believed to confer protection against cancer. This trial was registered as NCT02346812.

Although previous studies have investigated the association of cruciferous vegetable consumption with breast cancer risk, few studies focused on the association between bioactive components in cruciferous vegetables, glucosinolates (GSL) and isothiocyanates (ITC), and breast cancer risk. This study aimed to examine the association between consumption of cruciferous vegetables and breast cancer risk according to GSL and ITC contents in a Chinese population. A total of 1485 cases and 1506 controls were recruited into this case–control study from June 2007 to March 2017. Consumption of cruciferous vegetables was assessed using a validated FFQ. Dietary GSL and ITC were computed by using two food composition databases linking GSL and ITC contents in cruciferous vegetables with responses to the FFQ. The OR and 95 % CI were assessed by unconditional logistic regression after adjusting for the potential confounders. Significant inverse associations were found between consumption of cruciferous vegetables, GSL and ITC and breast cancer risk. The adjusted OR comparing the highest with the lowest quartile were 0·51 (95 % CI 0·41, 0·63) for cruciferous vegetables, 0·54 (95 % CI 0·44, 0·67) for GSL and 0·62 (95 % CI 0·50, 0·76) for ITC, respectively. These inverse associations were also observed in both premenopausal and postmenopausal women. Subgroup analysis by hormone receptor status found inverse associations between cruciferous vegetables, GSL and ITC and both hormone-receptor-positive or hormone-receptor-negative breast cancer. This study indicated that consumption of cruciferous vegetables, GSL and ITC was inversely associated with breast cancer risk among Chinese women.

We tested the sulfur-modulated plant resistance hypothesis using potted cabbage (Brassica oleracea var. capitata) plants that were grown without and with increasing levels of sulfur fertilization. Changes in plant chemical traits were assessed and developmental performance of Plutella xylostella, a highly host-specific leaf-chewing insect, was followed. Leaf sulfur concentration gradually increased with growing addition of sulfur in soil; however, there was a generalized saturation response curve, with a plateau phase, for improvements in total leaf nitrogen, defense glucosinolates and insect performance. Plutella xylostella performed better in sulfur-fertilized cabbage probably because of the higher level of nitrogen, despite of the higher content of glucosinolates, which are toxic for many non-specialized insects. Despite the importance of sulfur in plant nutrition and production, especially for Brassica crops, our results showed that sulfur fertilization could decrease plant resistance against insects with high feeding specialization.

Field experiments were conducted near Blackville, SC, and Tifton, GA, in 2004 and 2005, to evaluate the effect of wild radish and rye cover crops on weed control and sweet corn yield when used in conjunction with lower-than-recommended herbicide rates. Cover crop treatments included wild radish, rye, and no cover crop, alone and in conjunction with half and full rates of atrazine (0.84 and 1.68 kg ai ha−1) plus S-metolachlor (0.44 and 0.87 kg ai ha−1) applied before sweet corn emergence. Florida pusley, large crabgrass, spreading dayflower, ivyleaf morningglory, and wild radish infested the test sites. Wild radish and rye cover crops without herbicides reduced total weed density by 35 and 50%, respectively, at 4 wk after planting (WAP). Wild radish in conjunction with the full rate of atrazine plus S-metolachlor controlled Florida pusley, large crabgrass, and ivyleaf morningglory better than rye or no cover crop treated with a full herbicide rate in 2004 at Blackville. In 2005, at Blackville, weed control in sweet corn following wild radish cover crop plots alone was not different from that following rye. Wild radish or rye in conjunction with a half or full rate of atrazine and S-metolachlor controlled > 95% Florida pusley, wild radish, and large crabgrass in sweet corn at Tifton during both years. Ten glucosinolates, potential allelopathic compounds, were identified in wild radish, including glucoiberin, progoitrin, glucoraphanin, glucoraphenin, glucosinalbin, gluconapin, glucotropaeolin, glucoerucin, glucobrassicin, and gluconasturtin. Sweet corn yields at Blackville and Tifton following wild radish or rye cover crops were similar between the half and full rates of atrazine plus S-metolachlor. Sweet corn in wild radish or rye cover crop plots without herbicides produced less-marketable ears than herbicide-treated plots, indicating that a combination of cover crops and herbicides are required to optimize yields and to obtain desirable weed control.

Exotic weeds can interfere with neighboring species by releasing allelochemicals that either directly inhibit growth and distribution of associated species or affect them indirectly by disrupting their interaction with soil organisms, such as arbuscular mycorrhizal fungi (AMF). The allelopathic potential of tall hedge mustard was assessed using aqueous root and shoot extracts in seed germination and radicle growth bioassays. Aqueous tall hedge mustard root and shoot extracts strongly inhibited seed germination and growth of bluebunch wheatgrass, Idaho fescue, and spotted knapweed, but had minimal autotoxicity. Chemical analysis of tall hedge mustard tissues revealed the presence of two major glucosinolates—isopropyl and sec-butyl glucosinolate. The degradation products of these glucosinolates (isopropyl isothiocyanate and sec-butyl isothiocyanate) were identified in dichloromethane extracts of tall hedge mustard aqueous root and shoot extracts. Commercially available isopropyl isothiocyanate and sec-butyl isothiocyanate inhibited seed germination and radicle growth, suggesting their role in the allelopathic potential of tall hedge mustard. Tall hedge mustard aqueous extracts and isothiocyanates incorporated into an agar medium inhibited the spore germination of the AMF, Glomus intraradices. Tall hedge mustard infestations were also found to reduce the AMF inoculum potential of soil under field conditions. The results from this study show that tall hedge mustard produces chemicals that can inhibit the growth of neighboring plant species and their AMF associates.

Wild radish is a prevalent annual weed throughout the cropping regions of southern Australia. Field experiments were conducted at Wagga Wagga, New South Wales, in 1998 and 1999 to determine the effect of various densities and emergence times of wild radish on yield and quality of canola and on wild radish seed production. As few as 4 wild radish m−2 emerging with canola reduced canola yield 9 to 11%, whereas 64 wild radish m−2 reduced canola yield 77 to 91%. Wild radish interference in canola was greatly affected by its time of emergence relative to canola. At 64 wild radish m−2, canola yield was reduced 77, 54, 33, and 19% in 1998 and 91, 65, 56, and 19% in 1999 when wild radish emerged 0, 2, 4, and 7 wk after canola, respectively. Wild radish that emerged 10 wk after canola did not reduce canola yield. Maximum wild radish seed production ranged from 24,183 to 32,167 seed m−2 when they emerged with canola at high densities. Wild radish that emerged later than canola produced much less seed, but some seed production still occurred in one of the 2 yr when it emerged as late as 10 wk after canola. Wild radish did not directly reduce canola quality in either year, but if wild radish seed were not separated from canola seed, the amount of erucic acid and glucosinolates was increased above marketable levels in some cases. The results of this study will be used to advise growers on wild radish control in canola and will aid the development of a multiyear management strategy for this troublesome weed in annual cropping systems.

The allelopathic potential of hoary cress was evaluated by exposing the seeds and the germinated seeds of winter wheat, alfalfa, crested wheatgrass, bluebunch wheatgrass, and hoary cress to a water extract of dried, hoary cress roots under controlled conditions in an environmental chamber. Germination for all species was reduced in the hoary cress root extract when compared with distilled water, with winter wheat and hoary cress being more tolerant than the other species. Root length of all species was reduced by the extract when compared with distilled water. These data show the presence of phytotoxic chemical(s) that may inhibit germination and initial seedling growth in natural environments. Three glucosinolate compounds were identified in hoary cress root extracts.

A greenhouse experiment was conducted to evaluate the herbicidal activity of five aliphatic (ethyl, propyl, butyl, allyl, and 3-methylthiopropyl) and three aromatic (phenyl, benzyl, 2-phenylethyl) isothiocyanates on Texas panicum, large crabgrass, and sicklepod. All isothiocyanates were applied to soil at 0, 10, 100, 1,000, and 10,000 nmol g−1 of soil and incorporated. Weed emergence was generally stimulated at the lower isothiocyanate concentrations, but all isothiocyanates provided 37% or more suppression of each species at the highest concentration. Propyl and allyl isothiocyanate were most effective in suppressing Texas panicum, with 50% effective dose (ED50) values of 345 and 409 nmol g−1 of soil. All aliphatic isothiocyanates reduced Texas panicum density by at least 98%. Allyl and 3-methylthiopropyl isothiocyanate were the most effective aliphatics on large crabgrass, with density reductions of 98 and 100%, respectively. All aromatic isothiocyanates reduced large crabgrass density by 86 to 96%. Sicklepod was generally the most tolerant of the three species evaluated, with ED50 values for ethyl, propyl, and butyl isothiocyanate being greater than the evaluated concentrations. Maximum reduction in sicklepod density was 72, 68, 65, and 62%, which was achieved with allyl, benzyl, 3-methylthiopropyl, and phenyl isothiocyanate, respectively. This research shows that soil-applied and incorporated isothiocyanates are effective in suppressing some important weeds of the southeastern United States, but effectiveness of each isothiocyanate varies among species. Application techniques that minimize loss of volatile isothiocyanates may further improve their potential as an effective means of controlling these and other troublesome weeds.

Weed control in organic onion production is often difficult and expensive, requiring numerous cultivations and extensive hand weeding. Onion safety and weed control with mustard seed meal (MSM) derived from Sinapis alba was evaluated in greenhouse and field trials. MSM applied at 110, 220, and 440 g m−2 severely injured onions and reduced onion stand by 25% or more when applied from planting to the one-leaf stage of onions in greenhouse trials. MSM derived from mustard cultivars ‘IdaGold’ and ‘AC Pennant’ reduced plant dry weight of redroot pigweed with an effective dose that provided 90% weed control (ED90) of 14.5 and 3.2 g m−2, respectively, in greenhouse trials, whereas the ED90 of MSM from a low-glucosinolate cultivar ‘00RN29D10’ was 128 g m−2, suggesting that glucosinolate content and ionic thiocyanate (SCN−) production contribute to phytotoxicity of MSM. In field trials, weed emergence, onion injury, and onion yield were recorded following single or three sequential applications of MSM from 1.1 to 4.5 MT ha−1 beginning at the two-leaf stage of onions in 2008, 2009, and 2010. By 8 wk after treatment (WAT), onion injury following MSM sequential applications was 10% or less in all 3 yr. Combined over 2008 and 2009, 48 and 68% fewer weeds emerged 3 WAT with MSM at 2.2 and 4.5 MT ha−1, respectively. In 2010, MSM at 2.2 and 4.5 MT ha−1 reduced the number of weeds emerged 4 WAT by 91 and 76%, respectively. MSM treatment did not significantly affect onion yield or size in 2008 and 2009, but in 2010 onion total yield was reduced by 29% by three sequential applications of MSM at 2.2 MT ha−1. MSM has potential to be used as a weed-suppressive amendment in organic production systems, but the risk of crop injury is substantial.

A greenhouse experiment was conducted to evaluate the herbicidal activity of five aliphatic (ethyl, propyl, butyl, allyl, and 3-methylthiopropyl) and three aromatic (phenyl, benzyl, and 2-phenylethyl) isothiocyanates (ITCs) on Palmer amaranth, pitted morningglory, and yellow nutsedge. All ITCs were applied to soil at 0, 10, 100, 1,000, and 10,000 nmol g−1 of soil and incorporated. All ITCs had a deleterious effect on Palmer amaranth and pitted morningglory emergence. LC50 values for Palmer amaranth emergence inhibition from aliphatic and aromatic ITCs ranged from a low of 32 nmol g−1 of soil for phenyl ITC to a high of 941 nmol g−1 of soil for propyl ITC. Pitted morningglory was slightly more tolerant than Palmer amaranth to each of the ITCs, with LC50 values for emergence ranging from 347 to 2,855 nmol g−1 of soil for 3-methylthiopropyl and butyl ITC, respectively. Yellow nutsedge was the most tolerant of the three species, with LC50 values for ethyl, butyl, benzyl, and 2-phenylethyl being greater than the highest evaluated concentration of 10,000 nmol g−1 of soil. Phenyl and 3-methylthiopropyl at 10,000 nmol g−1 of soil were the most effective ITCs against yellow nutsedge, reducing emergence by 92%. Effectiveness of the ITCs varied across structure and species, but 3-methylthiopropyl and phenyl ITC were generally the most efficacious for the three species evaluated.

Glucosinolates, phytochemicals found in cruciferous vegetables, are metabolised to bioactive isothiocyanates (ITC) by certain bacteria in the human gut. Substantial individual variation in urinary ITC excretion has been observed in previous cruciferous vegetable-feeding studies. We hypothesised that individual differences in gut microbial community contribute to the observed variation in glucosinolate metabolism, i.e. gut microbiota composition between high- and low-ITC excreters differs. We recruited twenty-three healthy individuals and fed them a standardised meal containing 200 g of cooked broccoli. After the meal, 24 h urinary ITC excretion was measured. Study participants with the highest (n 5) and lowest (n 5) ITC excretion provided faecal samples for ex vivo bacterial cultivation with 50 μm-glucoraphanin, the major glucosinolate found in broccoli. When grown ex vivo, faecal bacteria from the selected high-ITC excreters were able to degrade more glucoraphanin than those from the low-ITC excreters (P = 0·05). However, bacterial fingerprints of faecal and ex vivo culture microbiota revealed no statistically significant differences between the high- and low-ITC excreters in terminal restriction fragment length polymorphism analysis of the bacterial 16S ribosomal RNA gene. In conclusion, glucosinolate degradation by faecal bacteria ex vivo may be associated with in vivo bacterial glucosinolate metabolism capacity, but no direct link to specific bacterial species could be established, possibly due to the complexity and functional redundancy of the gut microbiota.

The cabbage stem weevil (Ceutorhynchus pallidactylus (Mrsh.)) (Col., Curculionidae) is a serious pest of winter oilseed rape (Brassica napus L. var. oleifera Metzg.) in central and northern Europe. Although host-plant resistance is a key tool in integrated pest management systems, resistant genotypes are not yet available for this species. Resynthesized rapeseed lines (B. oleracea L.×B. rapa L.) are broadening the genetic diversity and might have potential as sources of resistance to pest insects. The host quality, of nine resynthesized rapeseed lines and six genotypes of B. napus to cabbage stem weevil, was evaluated in laboratory screening tests and in a semi-field experiment. In dual-choice oviposition tests, female C. pallidactylus laid significantly fewer eggs on five resyntheses and on swede cv ‘Devon Champion’ than on the moderately susceptible oilseed rape cv ‘Express’, indicating a lower host quality of these genotypes. Results of laboratory screenings were confirmed in a semi-field experiment, in which twelve genotypes were exposed to C. pallidactylus females. The number of larvae was significantly lower in two resyntheses and in cv ‘Devon Champion’ than in oilseed rape cv WVB 9. The total, as well as individual, glucosinolate (GSL) content in the leaves differed substantially among the genotypes tested. The amount of feeding by larvae of C. pallidactylus, as measured by a stem-injury coefficient, was positively correlated with the indolyl GSL compounds 3-indolylmethyl and 4-methoxy-3-indolylmethyl, and with the aromatic GSL 2-phenylethyl, whereas it was negatively correlated with 4-hydroxy-3-indolylmethyl. Thus, the composition and concentration of GSL compounds within the plant tissue might be a key factor in breeding for pest resistance in oilseed rape.

Sulforaphane is a naturally occurring isothiocyanate with promising chemopreventive activity. An analytical method, utilising liquid chromatography-MS/MS, which allows the determination of sulforaphane in small volumes of rat plasma following exposure to low dietary doses, was developed and validated, and employed to determine its absolute bioavailability and pharmacokinetic characteristics. Rats were treated with either a single intravenous dose of sulforaphane (2·8 μmol/kg) or single oral doses of 2·8, 5·6 and 28 μmol/kg. Sulforaphane plasma concentrations were determined in blood samples withdrawn from the rat tail at regular time intervals. Following intravenous administration, the plasma profile of sulforaphane was best described by a two-compartment pharmacokinetic model, with a prolonged terminal phase. Sulforaphane was very well and rapidly absorbed and displayed an absolute bioavailability of 82 %, which, however, decreased at the higher doses, indicating a dose-dependent pharmacokinetic behaviour; similarly, Cmax values did not rise proportionately to the dose. At the highest dose used, the rate of absorption constant kab, biological half-life t½ and apparent volume of distribution decreased significantly. It is concluded that in the rat orally administered sulforaphane is rapidly absorbed, achieving high absolute bioavailability at low dietary doses, but dose-dependent pharmacokinetics was evident, with bioavailability decreasing with increasing dose.

Evidence indicates that cruciferous vegetables are protective against a range of cancers with glucosinolates and their breakdown products considered the biologically active constituents. To date, epidemiological studies have not investigated the intakes of these constituents due to a lack of food composition databases. The aim of the present study was to develop a database for the glucosinolate content of cruciferous vegetables that can be used to quantify dietary exposure for use in epidemiological studies of diet–disease relationships. Published food composition data sources for the glucosinolate content of cruciferous vegetables were identified and assessed for data quality using established criteria. Adequate data for the total glucosinolate content were available from eighteen published studies providing 140 estimates for forty-two items. The highest glucosinolate values were for cress (389 mg/100 g) while the lowest values were for Pe-tsai chinese cabbage (20 mg/100 g). There is considerable variation in the values reported for the same vegetable by different studies, with a median difference between the minimum and maximum values of 5·8-fold. Limited analysis of cooked cruciferous vegetables has been conducted; however, the available data show that average losses during cooking are approximately 36 %. This is the first attempt to collate the available literature on the glucosinolate content of cruciferous vegetables. These data will allow quantification of intakes of the glucosinolates, which can be used in epidemiological studies to investigate the role of cruciferous vegetables in cancer aetiology and prevention.

The breakdown of glucosinolates, a group of thioglucoside compounds found in cruciferous plants, is catalysed by dietary or microbial myrosinase. This hydrolysis releases a range of breakdown products among which are the isothiocyanates, which have been implicated in the cancer-protective effects of cruciferous vegetables. The respective involvement of plant myrosinase and gut bacterial myrosinase in the conversion, in vivo, of glucosinolates into isothiocyanates was investigated in sixteen Fischer 344 rats. Glucosinolate hydrolysis in gnotobiotic rats harbouring a whole human faecal flora (Flora+) was compared with that in germ-free rats (Flora−). Rats were offered a diet where plant myrosinase was either active (Myro+) or inactive (Myro−). The conversion of prop-2-enyl glucosinolate and benzyl glucosinolate to their related isothiocyanates, allyl isothiocyanate and benzyl isothiocyanate, was estimated using urinary mercapturic acids, which are endproducts of isothiocyanate metabolism. The highest excretion of urinary mercapturic acids was found when only plant myrosinase was active (Flora−, Myro+ treatment). Lower excretion was observed when both plant and microbial myrosinases were active (Flora+, Myro+ treatment). Excretion of urinary mercapturic acids when only microbial myrosinase was active (Flora+, Myro− treatment) was low and comparable with the levels in the absence of myrosinase (Flora−, Myro− treatment). No intact glucosinolates were detected in the faeces of rats from the Flora+ treatments confirming the strong capacity of the microflora to break down glucosinolates. The results confirm that plant myrosinase can catalyse substantial release of isothiocyanates in vivo. The results also suggest that the human microflora may, in some circumstances, reduce the proportion of isothiocyanates available for intestinal absorption.

Two rapeseed (Brassica napus) meals, RM1 and RM2, with two levels of glucosinolates (GLS; 5 and 41 μmol/g DM respectively) were incorporated at the levels of 300 and 500 g/kg of the diets of juvenile rainbow trout (Oncorhynchus mykiss) in replacement of fish meal, and compared with a fish-meal-based diet. A decrease in the digestibility of the DM, protein, gross energy and P was observed with high-rapeseed meal (RM) incorporation. In trout fed on RM-based diets, growth performance was reduced even after only 3 weeks of feeding. Feed efficiency was adversely affected by RM and GLS intake. Protein and energy retention coefficients were significantly lower in fish fed on the diet containing the higher level of GLS. P retention was significantly lower with all the RM-based diets than with the fish-meal diet. Irrespective of the degree of growth inhibition, fish fed on RM-based diets exhibited similar typical features of hypothyroid condition due to GLS intake, expressed by lower plasma levels of triiodothyronine and especially thyroxine and a hyperactivity of the thyroid follicles. This hypothyroidal condition led to a strong adjustment of the deiodinase activities in the liver, the kidney and the brain. A significant increase of the outer ring deiodinase activities (deiodinases type I and II respectively) and a decrease of the inner ring deiodinase activity (deiodinase type III) were observed. It is concluded that the observed growth depression could be attributed to the concomitant presence of GLS, depressing the thyroid function, and of other antinutritional factors affecting digestibility and the metabolic utilization of dietary nutrients and energy.

Plants use chemical defences to reduce damage from herbivores and the effectiveness of these defences can be altered by biotic and abiotic factors, such as herbivory and soil resource availability. Streptanthus polygaloides, a nickel (Ni) hyperaccumulator, possesses both Ni-based defences and organic defences (glucosinolates), but the extent to which these defences interact and respond to environmental conditions is unknown. S. polygaloides plants were grown on high-Ni and low-Ni soil and concentrations of Ni and glucosinolates were compared with those of the congeneric non-hyperaccumulator, S. insignus spp. insignus, grown under the same conditions. Ni contents were highest (4000 μg g−1 dry tissue) in S. polygaloides plants grown on high-Ni soil. Glucosinolate content was significantly higher in S. insignus than in S. polygaloides suggesting that plants defended by Ni produce a lower concentration of organic defences. In a separate experiment, high-Ni S. polygaloides plants were exposed to simulated herbivory or live folivores to determine the inducibility of Ni-based and organic defences. Contents of Ni were not affected by either herbivory treatment, whereas glucosinolate concentrations were >30% higher in damaged plants. We concluded that the Ni-based defence of S. polygaloides is not induced by herbivory.