Behavioural and chemosensory responses of the turnip root fly (Delia floralis) to glucosinolates

This study investigates the behavioural and neural mechanisms involved in the oviposition behaviour of the turnip root fly,Delia floralis (Fallen). Behavioural studies showed that glucosinolates modulated the oviposition behaviour of the flies on artificial leaves as well as the number of eggs laid in the soil at the base of these leaves. Electrophysiological responses to glucosinolates were obtained from type A and type D sensilla on the prothoracic and mesothoracic tarsi, as well as from the long contact sensilla on the labellum. The neural responses from these sensilla were positively correlated with the oviposition behaviour of the flies and with the number of eggs laid. Of the eleven glucosinolates tested in the behavioural and electrophysiological tests, the flies were most responsive to glucobrassicanapin, gluconapin and glucobrassicin. The type D tarsal sensilla were more responsive to the glucosinolates than either the type A tarsal sensilla or the labellar sensilla. The structure-activity investigations showed that slight modifications to the chemical composition of the glucosinolates resulted in changes in neural activity.     

Oviposition and chemosensory stimulation of the root flies Delia radicum and D. floralis in response to plants and leaf surface extracts from resistant and susceptible Brassica genotypes

In Brassica crops differences in susceptibility to root fly attack can be largely attributed to antixenotic resistance. Plants of four genotypes (two swedes and two kales) with widely differing resistance in field trials, were compared in laboratory choice assays for their susceptibility to oviposition by the root flies Delia radicum (L.) and D. floralis (Fallen) (Diptera, Anthomyiidae). For both species the preference among the genotypes corresponded to the susceptibility of the genotypes in the field. The preference ranking in response to surrogate leaves treated with methanolic surface extracts of the four genotypes was identical to the preference among potted plants, demonstrating that chemical factors on the leaf surface mediate host preference for oviposition in these species.For both species of fly, glucosinolates are major oviposition stimulants and for D. radicum an additional, nonglucosinolate oviposition stimulant, presently called CIF, is known. We describe a procedure for chromatographic separation of glucosinolates from CIF in leaf surface extracts. In oviposition-choice assays with D. radicum, the CIF-fractions of the two swede genotypes applied to surrogate leaves received a 1.8 and 4.6 times higher proportion of eggs than the respective glucosinolate-fractions, confirming the major importance of CIF as an oviposition stimulant. The genotype of swede that was preferred by both fly species in tests with plants and methanolic leaf surface extracts, also stimulated oviposition more in tests with the glucosinolate-fractions or the CIF-fractions derived from the surface extracts, respectively. Thus, glucosinolates and CIF together account for the observed preference among the genotypes and may also be responsible for their susceptibility under field conditions. In the two kale genotypes the preference for plants or surface extracts differed from the preference among the corresponding glucosinolate- and CIF-fractions, indicating that additional, as yet unknown chemical factors may also be involved.For both groups of stimulants tarsal chemoreceptors allow electrophysiological monitoring of glucosinolate- and CIF-activity in fractionated surface extracts. For D. radicum the chemosensory activity of both glucosinolate- and CIF-fractions corresponded to the respective behavioural activity in the oviposition preference tests, suggesting that preference for oviposition among genotypes can be predicted from the electrophysiological activity of their fractions. The chemosensory response of D. floralis, in particular to the CIF-fractions, was less pronounced than the response of D. radicum, indicating interspecific differences in the perception of the major oviposition stimulants. We discuss the potential application of electrophysiological techniques in support of other screening methods used in breeding for root fly resistance in Brassica crops.     

Comparison of the egg-laying behaviour and electrophysiological responses of Delia radicum and Delia floralis to cabbage leaf compounds

Abstract.  The behaviour and the sensitivity of adult cabbage root fly, Delia radicum and turnip root fly, Delia floralis are compared with host-plant extracts and isolated crucifer compounds previously identified as oviposition stimulants for D. radicum . The oviposition behaviour of both species is similar; 7–10-day-old females are stimulated to lay eggs by the methanol extract of cauliflower leaves that contains thia-triaza-fluorenes (CIF) as well as glucosinolates. The glucosinolate fraction is mainly composed of glucobrassicin, which alone stimulate both fly species to lay eggs. The C₅ and D_3,4 sensilla on the prothoracic tarsae of newly-emerged D. radicum contain neurones sensitive to the glucosinolate fractions tested and to glucobrassicin, whereas the CIF specifically stimulate a neurone in the C₅ sensillum. By contrast, newly-emerged D. floralis respond less to glucosinolates, especially to glucobrassicin, and have sensitive neurones to CIF in other sensilla than D. radicum . Recordings are also made from the longest sensilla present on the labellum because they are apparently sensitive to glucosinolates. By contrast to earlier investigations, no remarkable phasic-tonic responses of these neurones are seen. The two species are difficult to discriminate visually, have the same host plants, show identical host-selection behaviour, apparently respond to the same physical and chemical properties of their host-plants, but have a clearly different distribution of receptor neurones in the tarsal sensilla.     

Glucosinolate profiling of Brassica rapa cultivars after infection by Leptosphaeria maculans and Fusarium oxysporum

The glucosinolate contents of two different cultivars of Brassica rapa (Herfstraap and Oleifera) infected with Leptosphaeria maculans and Fusarium oxysporum were determined. Infection triggered the accumulation of aliphatic glucosinolates (gluconapin, progoitrin, glucobrassicanapin and gluconapoleiferin) and indole glucosinolate (4-hydroxy-glucobrassicin) in Herfstraap and of two indole glucosinolates (glucobrassicin and 4-hydroxy-glucobrassicin) in Oleifera. While total and aliphatic glucosinolates decreased significantly in Oleifera, a large increase was observed in Herfstraap after fungal infection. The indole glucosinolate glucobrassicin accumulated in Oleifera at a higher rate than Herfstraap especially after infection with F. oxysporum. Apparently the interaction between fungus and B. rapa is cultivar and fungal species specific.     

Flavonoids from cabbage are feeding stimulants for diamondback moth larvae additional to glucosinolates: Chemoreception and behaviour

In caterpillars two styloconic contact chemoreceptors on the maxillary galea are assumed to contain the main taste receptors involved in host plant selection. The diamondback moth, Plutella xylostella L. is a specialist feeder of plants in the Brassicaceae, a plant family characterized by the biosynthesis of glucosinolates. We used pea (Pisum sativum L., Leguminosae) as a neutral non-host for a dual-choice leaf disc assay to quantify feeding stimulation by glucosinolates and flavonoids. Increasing concentrations of sinigrin resulted in significant preferences for sinigrin-treated leaf discs, with a threshold between 1 and 3 M. Millimolar concentrations of four of the five flavonol triglucosides likewise elicited a significant preference for flavonoid-treated leaf discs. A mixture of four flavonoids and sinigrin was significantly preferred over sinigrin-treated leaf discs alone. Vigorous unicellular electrophysiological responses of medial maxillary styloconic taste sensilla were observed in response to five glucosinolates (glucocapparin, sinigrin, glucobrassicin, glucoiberin, and gluconasturtiin). This medial taste neuron responded in a dose-dependent manner to a concentration series of sinigrin, with a threshold of response of ca. 1 M. The lateral sensillum styloconicum contained a neuron sensitive to sucrose, glucose, and fructose. However, no responses in the two types of maxillary styloconic sensilla to the phagostimulatory flavonoids could be detected, suggesting that other taste organs mediate chemoreception of flavonoids. We conclude that diamondback moth larvae employ a combination of biosynthetically distinct categories of feeding stimulants which allows for a higher degree of discriminatory ability than when this would be based on glucosinolates alone.     

Tarsal contact chemoreceptor response to glucosinolates and cardenolides mediating oviposition in Pieris rape

Abstract. Water-soluble extracts of a host crucifer (Brassica oleracea L.) and non-host crucifer (Erysimum cheiranthoides L.) and isolated pure cardenolides and glucosinolates were tested on Pieris rapae L. (Lepidoptera: Pieridae) butterflies in oviposition assays and by electrophysiological recordings from the contact-chemoreceptor sensilla of the prothoracic tarsi. Ten different glucosinolates stimulated oviposition to varying degree when put on non-host plant leaves. The most active compounds were glucobrassiein and gluconasturtiin (methylindole and phenylethyl aglycone), whereas glucocapparin, sinalbin. glucotropaeolin, sinigrin and glucoalyssinin had intermediate activity. Glucocheirolin, glucoerucin and glucoiberin (sulphur-containing aglycone) were significantly less active. Of eight cardenolides applied to host-plant leaves (100 μg each), four glycosides deterred oviposition strongly (erysimoside, erychroside, cymarin and K-strophanthin-β). Erycordin, helveticoside, digitoxin and strophanthidin had little or no deterrent activity. Sensilla located laterally on the prothoracic tarsi of female butterflies contained one receptor cell sensitive to sucrose. None of the tested extracts or pure compounds stimulated any cell in these sensilla. In contrast, the cells in the medial sensilla showed little or no sensitivity to sucrose. One cell was found to be sensitive to cardenolide glycosides. The threshold for one of the most active compounds, erychroside, was about 0.1 μg/ml (1.5 times 10^-7 M). Two receptor cells, characterized by spikes of differing amplitude, were sensitive to glucosinolates. One of these, with larger amplitude spikes, seemed to be the same as the cell sensitive to cardenolides. The threshold for the most active glucosinolates, glucobrassicin and gluconasturtiin was estimated to be below 0.1 mg/ml (2 times 10^-4 M). The neural activity of both classes of compounds, cardenolides and glucosinolates, was significantly correlated with their behavioural activity as deterrents or stimulants.     

Preference for plants damaged by conspecific larvae in ovipositing cabbage root flies: influence of stimuli from leaf surface and roots

In laboratory dual-choice assays females of the cabbage root fly, Delia radicum, prefer for oviposition plants with roots damaged by conspecific larvae to undamaged controls. Cauliflower and kale plants were inoculated with root fly eggs (25 per plant) and the hatching larvae were allowed to feed on the roots for various periods of time (1–17 days). After 4 (cauliflower) or 5 (kale) days of larval feeding the oviposition preference was most pronounced and flies laid between 64% and 68% of their eggs near plants with damaged roots. Later, with increasing damage but fewer surviving, and thus actively feeding, larvae, the magnitude of the preference declined. The preference for plants already damaged by conspecific larvae may contribute to the previously observed aggregated distribution of D. radicum eggs in Brassica crop fields.Further experiments revealed that the sensory cues inducing this oviposition preference originate from the complex consisting of the damaged roots, the surrounding substrate (soil) and associated microbes, rather than from the aerial plant parts. In choice assays using the root-substrate complex of damaged and control plants (aerial parts removed), the observed preference for damaged roots was similar to that found for the entire plant but was more pronounced. The damaged roots alone, compared to control roots, received up to 72% (cauliflower) and 75% (kale) of the eggs. By contrast, surrogate leaves sprayed with methanolic leaf surface extracts from the most preferred plants which had been damaged were not discriminated from surrogate leaved sprayed with extracts of the respective control plants. Analysis of glucosinolate levels in methanolic leaf surface extracts revealed that root damage resulted in enhanced concentrations of indole-glucosinolates on the leaf surface in kale but not in cauliflower. Although indole-glucosinolates are oviposition stimulants for the cabbage root fly, the induced changes were apparently too small to influence oviposition behaviour.     

Tarsal chemoreceptors and oviposition behaviour of the cabbage root fly (Delia radicum) sensitive to fractions and new compounds of host-leaf surface extracts

Abstract. Contact chemoreception plays a decisive role in host selection and oviposition behaviour of the cabbage root fly, Delia radicum L. (Diptera, Anthomyiidae). Glucosinolates (mustard oil glucosides) are known to be perceived by the flies, and when sprayed on paper leaf-models induce oviposition. Recently it has become clear that other non-volatile types of compounds must also be involved in host selection.
A pair of ventro-medial C sensilla on die fifth tarsomere respond strongly to a novel compound called tentatively 'cabbage identification factor' (CIF), but not to sucrose, glucose, fructose and proline. CDF is a new non-glucosinolate oviposition stimulant. A single neurone in each sensillum is activated by this compound and the same is true for glucosinolates. In some flies a mixture of bom types of stimuli evoked an apparent mononeural spike train, whereas in odiers spikes of two separate cells were activated. The significance of this variability is not yet clear.
The new stimulant, CIF, does not evoke responses in glucosinolate receptors in the D sensilla. The involvement of the C₃ sensilla in the detection of host-specific compounds constitutes the first known function for C sensilla in D. radicum. CIF appears to be present in leaf surface extracts from the host-plant Brassica oleracea in quantities as low as 1 ng per gram leaf. In spite of this low level, it stimulates oviposition significantly better than glucobrassicin at higher concentrations, which up till now was known as the most powerful stimulant for D.radicum.     

Reciprocal interactions between the cabbage root fly (Delia radicum) and two glucosinolate phenotypes of Barbarea vulgaris

The cabbage root fly, Delia radicum L. (Diptera: Anthomyiidae), has a life cycle with spatially separated components: adults live and oviposit above ground, whereas larvae feed and pupate below ground. Oviposition choice is affected by shoot glucosinolates. However, little is known about below‐ground plant defence against D. radicum. Here, we investigate the effect of glucosinolates on oviposition preference and performance of D. radicum, using two naturally occurring heritable chemotypes of Barbarea vulgaris R. Br. (Brassicaceae) with different glucosinolate profiles: BAR‐type plants (the most common and genetically dominant glucosinolate profile, dominated by glucobarbarin) and NAS‐type plants (the recessive phenotype, dominated by gluconasturtiin). Performance was studied by applying 10 neonate D. radicum larvae per plant and measuring pupal biomass after 18 days. There was no difference in retrieval, but pupae had a higher biomass after development on BAR‐type plants. On average, BAR‐type plants received 1.8 times more eggs than NAS types, but this difference was not statistically significant. In a separate experiment, we compared the physiological response of both chemotypes to D. radicum feeding. Infestation reduced root and shoot biomass, root sugar and amino acid levels, and shoot sugar levels. Except for shoot sugar levels, these responses did not differ between the two chemotypes. Shoot or root glucosinolate profiles did not change on infestation. As glucosinolate profiles were the only consistent difference between the chemotypes, it is likely that this difference caused the reduced biomass of D. radicum pupae on NAS‐type plants. In an experimental garden, plants were heavily infested by root flies, but we found no differences in the percentage of fallen‐over flower stalks between the chemotypes. Overall, we found more pupae in the soil near BAR‐type plants, but this was not statistically significant. The results of the performance experiment suggest that BAR‐type plants may be more suitable hosts than NAS‐type plants.     

Arabidopsis thaliana leaf-surface extracts are detected by the cabbage root fly (Delia radicum) and stimulate oviposition

Abstract. Oviposition of the cabbage root fly, Delia radicum (Diptera, Anthomyiidae) is stimulated by leaf‐surface extracts of Arabidopsis thaliana (L.) Heynh. (Brassicaceae) ecotype Columbia. The leaf surface of A. thaliana, similar to that of many other crucifers, contains glucosinolates and CIF (‘cabbage identification factor’; 1,2‐dehydro‐3‐thia‐4,10,10b‐triaza‐cyclopenta[.a.]fluorene‐1‐carboxylic acid). These compounds stimulate receptor neurones of the tarsal sensilla of D. radicum whereas additional, unknown compounds are detected by other receptor neurones.     

Oviposition behavior of the cabbage root fly,Delia radicum (L.), influenced by host plant extracts

An ethanolic extract of cabbage leaves (Brassica oleraceavar. capitata,Golden Acre)and derived fractions were tested on natural and surrogate leaves in order to study the oviposition behavior of the cabbage root fly Delia radicum(Diptera: Anthomyiidae). On surrogate plastic leaves coated with a thin layer of paraffin wax and treated with 0.1 gram leaf equivalent (gle) of an ethanolic raw cabbage extract, the females displayed the same sequence of behavioral patterns as on a natural host plant. The quantified oviposition behavior correlated well with the actual number of eggs laid. The extract-treated surrogate leaves received at least as many eggs as natural leaves with a similar surface area. Previous exposure to surrogate or natural leaves seemed not to induce a specific preference. The three fractions (hexane, butanol, and water) of the raw extract stimulated the oviposition behavior. This was taken as evidence for the presence of a multicomponent mixture or a chemical pattern in the cabbage leaves stimulating oviposition. At the tested concentration each fraction alone could stimulate in some individuals the complete behavior. No effect of volatile components of the raw extract could be detected. This is thought to be due to the extraction procedure, which limits the production of attractive, volatile compounds, such as isothiocyanates.     

Quantification of glucosinolates in leaves of leaf rape (Brassica napus ssp. pabularia) by near-infrared spectroscopy

The potential of near-infrared spectroscopy (NIRS) for screening the total glucosinolate (t-GSL) content, and also, the aliphatic glucosinolates gluconapin (GNA), glucobrassicanapin (GBN), progoitrin (PRO), glucoalyssin (GAL), and the indole glucosinolate glucobrassicin (GBS) in the leaf rape (Brassica napus L. ssp. pabularia DC), was assessed. This crop is grown for edible leaves for both fodder and human consumption. In Galicia (northwestern Spain) it is highly appreciated for human nutrition and have the common name of "nabicol". A collection of 36 local populations of nabicol was analysed by NIRS for glucosinolate composition. The reference values for glucosinolates, as they were obtained by high performance liquid chromatography on the leaf samples, were regressed against different spectral transformations by modified partial least-squares (MPLS) regression. The coefficients of determination in cross-validation (r2) shown by the equations for t-GSL, GNA, GBN, PRO, GAL and GBS were, respectively, 0.88, 0.73, 0.81, 0.78, 0.37 and 0.41. The standard deviation to standard error of cross-validation ratio, were for these constituents, as follows: t-GSL, 2.96; GNA, 1.94; GBN, 2.31; PRO, 2.11; GAL, 1.27, and GBS, 1.29. These results show that the equations developed for total glucosinolates, as well as those for gluconapin, glucobrassicanapin and progoitrin, can be used for screening these compounds in the leaves of this species. In addition, the glucoalyssin and glucobrassicin equations obtained, can be used to identify those samples with low and high contents. From the study of the MPLS loadings of the first three terms of the different equations, it can be concluded that some major cell components as protein and cellulose, highly participated in modelling the equations for glucosinolates.     

Quantification of plant surface metabolites by matrix‐assisted laser desorption–ionization mass spectrometry imaging: glucosinolates on Arabidopsis thaliana leaves

The localization of metabolites on plant surfaces has been problematic because of the limitations of current methodologies. Attempts to localize glucosinolates, the sulfur‐rich defense compounds of the order Brassicales, on leaf surfaces have given many contradictory results depending on the method employed. Here we developed a matrix‐assisted laser desorption–ionization (MALDI) mass spectrometry protocol to detect surface glucosinolates on Arabidopsis thaliana leaves by applying the MALDI matrix through sublimation. Quantification was accomplished by spotting glucosinolate standards directly on the leaf surface. The A. thaliana leaf surface was found to contain approximately 15 nmol of total glucosinolate per leaf with about 50 pmol mm^?2 on abaxial (bottom) surfaces and 15–30 times less on adaxial (top) surfaces. Of the major compounds detected, 4‐methylsulfinylbutylglucosinolate, indol‐3‐ylmethylglucosinolate, and 8‐methylsulfinyloctylglucosinolate were also major components of the leaf interior, but the second most abundant glucosinolate on the surface, 4‐methylthiobutylglucosinolate, was only a trace component of the interior. Distribution on the surface was relatively uniform in contrast to the interior, where glucosinolates were distributed more abundantly in the midrib and periphery than the rest of the leaf. These results were confirmed by two other mass spectrometry‐based techniques, laser ablation electrospray ionization and liquid extraction surface analysis. The concentrations of glucosinolates on A. thaliana leaf surfaces were found to be sufficient to attract the specialist feeding lepidopterans Plutella xylostella and Pieris rapae for oviposition. The methods employed here should be easily applied to other plant species and metabolites.     

Constitutive and herbivore-inducible glucosinolate concentrations in oilseed rape (Brassica napus) leaves are not affected by Bt Cry1Ac insertion but change under elevated atmospheric CO2 and O3

Glucosinolates are plant secondary compounds involved in direct chemical defence by cruciferous plants against herbivores. The glucosinolate profile can be affected by abiotic and biotic environmental stimuli. We studied changes in glucosinolate patterns in leaves of non-transgenic oilseed rape (Brassica napus ssp. oleifera) under elevated atmospheric CO₂ or ozone (O₃) concentrations and compared them with those from transgenic for herbivore-resistance (Bacillus thuringiensis Cry1Ac endotoxin), to assess herbivory dynamics. Both elevated CO₂ and O₃ levels decreased indolic glucosinolate concentrations in transgenic and non-transgenic lines, whereas O₃ specifically increased the concentration of an aromatic glucosinolate, 2-phenylethylglucosinolate. The herbivore-inducible indolic glucosinolate response was reduced in elevated O₃ whereas elevated CO₂ altered the induction dynamics of indolic and aliphatic glucosinolates. Herbivore-resistant Bt plants experienced minimal leaf damage after target herbivore Plutella xylostella feeding, but exhibited comparatively similar increase in glucosinolate concentrations after herbivory as non-transgenic plants, indicating that the endogenous glucosinolate defence was not severely compromised by transgenic modifications. The observed differences in constitutive and inducible glucosinolate concentrations of oilseed rape under elevated atmospheric CO₂ and O₃ might have implications for plant–herbivore interactions in Brassica crop-ecosystems in future climate scenarios.     

Indole glucosinolate breakdown and its biological effects

Most species in the Brassicaceae produce one or more indole glucosinolates. In addition to the parent indol-3-ylmethylglucosinolate (IMG), other commonly encountered indole glucosinolates are 1-methoxyIMG, 4-hydroxyIMG, and 4-methoxyIMG. Upon tissue disruption, enzymatic hydrolysis of IMG produces an unstable aglucone, which reacts rapidly to form indole-3-acetonitrile and indol-3-ylmethyl isothiocyanate. The isothiocyanate, in turn, can react with water, ascorbate, glutathione, amino acids, and other plant metabolites to produce a variety of physiologically active indole compounds. Myrosinase-initiated breakdown of the substituted indole glucosinolates proceeds in a similar manner to that of IMG. Induction of indole glucosinolate production in response to biotic stress, experiments with mutant plants, and artificial diet assays suggest a significant role for indole glucosinolates in plant defense. However, some crucifer-feeding specialist herbivores recognize indole glucosinolates and their breakdown products as oviposition and/or feeding stimulants. In mammalian diets, IMG can have both beneficial and deleterious effects. Most IMG breakdown products induce the synthesis of phase 1 detoxifying enzymes, which may in some cases prevent carcinogenesis, but in other cases promote carcinogenesis. Recent advances in indole glucosinolate research have been fueled by their occurrence in the well-studied model plant Arabidopsis thaliana. Knowledge gained from genetic and biochemical experiments with A. thaliana can be applied to gain new insight into the ecological and nutritional properties of indole glucosinolates in other plant species.     

Hydrolysis products of glucosinolates in Brassica napus tissues as inhibitors of seed germination

Enzymatic hydrolysis of glucosinolates, a class of compounds found in Brassica species, results in a number of products with potential to inhibit seed germination. To investigate the impact of both volatile and water-soluble allelochemicals, germination bioassays using Lactuca sativa seeds were conducted with root and combined leaf and stem tissues of Brassica napus. Tissues in which glucosinolates were hydrolyzed to remove volatile glucosinolate degradation products were compared with intact tissues and water controls. Only tissues containing glucosinolates produced volatiles that inhibited germination. Volatiles were trapped and identified using GC-MS. Volatiles produced in greater quanitity from intact tissues than from tissues without glucosinolates were almost exclusively glucosinolate hydrolysis products. Water-soluble components also inhibited germination. Chemical analysis of extracts confirmed the presence of glucosinolate hydrolysis products, but indicated the involvement of additional allelochemicals, especially in leaf and stem tissues. Results support the proposal that glucosinolate-containing plant tissues may contribute to reductions in synthetic pesticide use if weed seeds are targeted.Abbreviations ITC isothiocyanates - CN organic cyanides - OZT oxazolidinethione - iRoot intact root tissue - iL&S intact leaf and stem tissue - hRoot hydrolyzed root tissue - hL&S hydrolyzed leaf and stem tissue     

Interaction of cruciferous phytoanticipins with plant fungal pathogens: indole glucosinolates are not metabolized but the corresponding desulfo-derivatives and nitriles are

Glucosinolates represent a large group of plant natural products long known for diverse and fascinating physiological functions and activities. Despite the relevance and huge interest on the roles of indole glucosinolates in plant defense, little is known about their direct interaction with microbial plant pathogens. Toward this end, the metabolism of indolyl glucosinolates, their corresponding desulfo-derivatives, and derived metabolites, by three fungal species pathogenic on crucifers was investigated. While glucobrassicin, 1-methoxyglucobrassicin, 4-methoxyglucobrassicin were not metabolized by the pathogenic fungi Alternaria brassicicola, Rhizoctonia solani and Sclerotinia sclerotiorum, the corresponding desulfo-derivatives were metabolized to indolyl-3-acetonitrile, caulilexin C (1-methoxyindolyl-3-acetonitrile) and arvelexin (4-methoxyindolyl-3-acetonitrile) by R. solani and S. sclerotiorum, but not by A. brassicicola. That is, desulfo-glucosinolates were metabolized by two non-host-selective pathogens, but not by a host-selective. Indolyl-3-acetonitrile, caulilexin C and arvelexin were metabolized to the corresponding indole-3-carboxylic acids. Indolyl-3-acetonitriles displayed higher inhibitory activity than indole desulfo-glucosinolates. Indolyl-3-methanol displayed antifungal activity and was metabolized by A. brassicicola and R. solani to the less antifungal compounds indole-3-carboxaldehyde and indole-3-carboxylic acid. Diindolyl-3-methane was strongly antifungal and stable in fungal cultures, but ascorbigen was not stable in solution and displayed low antifungal activity; neither compound appeared to be metabolized by any of the three fungal species. The cell-free extracts of mycelia of A. brassicicola displayed low myrosinase activity using glucobrassicin as substrate, but myrosinase activity was not detectable in mycelia of either R. solani or S. sclerotiorum.     

Seasonal variation in glucosinolate content in Brassica oleracea crops grown in northwestern Spain

Brassica oleracea L. crops including kales, cabbages, and Tronchuda cabbages are widely grown in northwestern Spain and Portugal but little information is available on leaf glucosinolate content of these crops. The objectives were to determine the diversity for the total glucosinolate content and profile on leaves in a collection of 153 kales, 26 cabbages, and three Tronchuda cabbages varieties grown at two growing seasons and to determine the seasonal variation of glucosinolates in cabbages and Tronchuda cabbage varieties. Sinigrin, glucoiberin, and glucobrassicin were the major glucosinolates found in kales. Glucoiberin was the most common glucosinolate in Tronchuda cabbages in both planting seasons and in cabbages sown in fall season whereas glucobrassicin and glucoiberin were the most common glucosinolates in cabbages in spring season. In kales the total glucosinolate content ranged from 11.0 to 53 micromol g(-1) dw, with a mean value of 26.3 micromol g(-1) dw. Four kale varieties (MBG-BRS0468, MBG-BRS0476, MBG-BRS0060 and MBG-BRS0223) showed the highest total sinigrin or glucobrassicin contents. So, they could be good candidates for future breeding programs. In cabbages, the total glucosinolate content ranged from 10.9 to 27 g(-1) dw. Total glucosinolate concentration during spring sowing (22 micro mg(-1) dw) was higher than those in fall sowing (13 micro mg(-1) dw). Regarding both high glucosinolate content and the agronomic value, MBG-BRS0057 and MBG-BRS0074 could be good sources of beneficial glucosinolates. The presence of high concentrations of sinigrin, glucoiberin, and glucobrassicin warrant further search into their potential use to enhance the level of these important phytochemicals in these edible crops.