Developmental regulation of aldoxime formation in seedlings and mature plants of Chinese cabbage (Brassica campestris ssp. pekinensis) and oilseed rape (Brassica napus): Glucosinolate and IAA biosynthetic enzymes

The first steps in the biosynthesis of glucosinolates and indole-3-acetic acid (IAA) in oilseed rape (Brassica napus L.) and Chinese cabbage (Brassica campestris ssp. pekinensis) involve the formation of aldoximes. In rape the formation of aldoximes from chain-extended amino acids, for aromatic and aliphatic glucosinolate biosynthesis, is catalysed by microsomal flavin-containing monooxygenases. The formation of indole-3-aldoxime from l-tryptophan, the potential precursor of both indole-3-acetic acid and indolyl-glucosinolates, is catalysed by several microsomal peroxidases. The biosynthesis of glucosinolates and indole-3-acetic acid was shown to be under developmental control in oilseed rape and Chinese cabbage. No monooxygenase activities were detected in cotyledons or old leaves of either species. The highest monooxygenase activities were found in young expanding leaves; as the leaves reached full expansion and matured the activities decreased rapidly. The indole-aldoxime-forming activity was found in all of the tissues analysed, but there was also a clear decrease in foliar activity with maturity in leaves of rape and Chinese cabbage. Partial characterisation of the Chinese cabbage monooxygenases showed that they have essentially identical properties to the previously characterised rape enzymes; they are not cytochrome P450-type enzymes, but resemble flavin-containing monooxygenases. No monooxygenase inhibitors were detected in microsomes prepared from either cotyledons or old leaves.Abbreviations DHMet dihomomethionine - FMO flavin-containing monooxygenase - HPhe homophenylalanine - IAA indole-3-acetic acid - l-Phe l-phenylalanine - l-Trp l-tryptophan - MO monooxygenase - IAALD indole-3-acetaldehyde - IAOX indole-3-aldoxime - THMet trihomomethionine     

Involvement of Cytochrome P450 in Glucosinolate Biosynthesis in White Mustard (A Biochemical Anomaly)

One of the first steps in glucosinolate biosynthesis is the conversion of amino acids to their aldoximes. The biochemistry of this process is controversial, and several very different enzyme systems have been described. The major glucosinolate in white mustard (Sinapis alba) is sinalbin, which is derived from tyrosine via its aldoxime, and this conversion is catalyzed by a cytochrome P450 (Cyt P450) monooxygenase. Phenylethyl- and alkenylglucosinolates are also present in white mustard leaves, as are the enzymes catalyzing the relevant aldoxime formation from homophenylalanine and methionine homologs, respectively. These enzymes are similar to those found in Brassica sp. and are distinct from the tyrosine-dependent enzyme in that they contain no heme and are unaffected by Cyt P450 inhibitors. They are instead inhibited by the flavoprotein inhibitor diphenylene iodonium and by Cu2+. In both white mustard and oilseed rape (Brassica napus) methyl jasmonate specifically stimulates indolylglucosinolate biosynthesis and yet has no effect on sinalbin accumulation in either cotyledons or leaves of white mustard. White mustard appears to be unique among crucifers in having a Cyt P450 aldoxime-forming enzyme for biosynthesis of one glucosinolate, although it also contains all of the non-Cyt P450 enzyme systems found in other members of the family. Sinalbin biosynthesis in white mustard is therefore an inappropriate model system for the synthesis of other glucosinolates in crucifers, including canola and oilseed rape.     

Glucosinolate Biosynthesis (Further Characterization of the Aldoxime-Forming Microsomal Monooxygenases in Oilseed Rape Leaves)

The initial steps in glucosinolate biosynthesis are thought to proceed from amino acids, via N-hydroxy amino acids, to aldoximes. We showed previously that microsomes from green leaves of oilseed rape (Brassica napus cv Bienvenu) contain two distinct monooxygenases that catalyze the conversion of homophenylalanine and dihomomethionine to their respective aldoximes. Further characterization of these enzymes has now demonstrated that the latter enzyme catalyzes the NADPH-dependent oxidative decarboxylation of two higher homologs of methionine, in addition to dihomomethionine. No activity was found for either enzyme with L-methionine, DL-homomethionine, L-phenylalanine, L-tyrosine, or L-tryptophan. Both of these rape monooxygenase activities are dependent on O2, not requiring any other O2 species or radical. The presence of an unoxidized sulfur atom and its relative position in the side chain of the aliphatic substrates are important for binding to the active site of the methionine-homolog enzyme. Neither enzyme has any characteristics of a cytochrome P450-type enzyme, and antiserum raised against cytochrome P450 reductase did not significantly inhibit monooxygenase activity.     

Sinapis phylogeny and evolution of glucosinolates and specific nitrile degrading enzymes

Levels of sinalbin (4-hydroxybenzylglucosinolate) and 28 other glucosinolates were determined in leaves and roots of 20 species that were either phylogenetically close to Sinapis alba, Sinapis arvensis, or Sinapis pubescens (tribe Brassiceae, Brassicaceae), or were expected to contain arylalkyl nitrilase activity. Comparison with a molecular phylogenetic tree based on ITS DNA sequences identified two separate occurrences of sinalbin. The first in a group of species related to S. alba (including members of the genera Coincya and Kremeriella); and the second in S. arvensis, nested among sinalbin deficient species. Significant 4-hydroxyphenylacetonitrile degrading enzyme activity was found in both S. alba and S. arvensis, but in S. alba the major product was the corresponding carboxylic acid, while in S. arvensis the major product was the amide. Both investigated enzyme activities, nitrilase and nitrile hydratase, were specific, accepting only certain arylacetonitriles such as 4-hydroxy and 4-methoxyphenylacetonitrile. Only the S. alba enzyme required an oxygen in para position of the substrate, as found in sinalbin. Indole-3-acetonitrile, arylcyanides, and arylpropionitriles were poor substrates. The nitrilase activity of S. alba was quantitatively comparable to that reported in the monocot Sorghum bicolor (believed to be involved in cyanogenic glycoside metabolism). Glucosinolates derived from methionine were found in all Sinapis clades. Glucosinolate patterns suggested a complex evolution of glucosinolates in the investigated species, with several apparent examples of abrupt changes in glucosinolate profiles including chain length variation and appearance of glucosinolates derived from branched-chain amino acids. NMR data for desulfated homosinalbin, 9-methylsulphonylnonylglucosinolate, 3-methylpentylglucosinolate and related glucosinolates are reported, and a facultative connection between sinalbin and specific nitrilases is suggested.     

Phytogeny of Brassica and allied genera based on variation in chloroplast and mitochondrial DNA patterns: molecular and taxonomic classifications are incongruous

Summary Chloroplast DNA (cpDNA) variability of 60 taxa of the genus Brassica and allied genera comprising 50 species was studied. RFLPs for seven enzymes were generated and F values were estimated from five frequently cutting enzymes. Phenetic clusterings indicated a clear division of Brassica coenospecies into two distinct lineages referred to as the Brassica and Sinapis lineages. Two unexplored genera, Diplotaxis and Erucastrum, also exhibited two lineages in addition to the genera Brassica and Sinapis. This finding is inconsistent with the existing taxonomic classification based on morphology. Mitochondrial DNA (mtDNA) variability studied from EcoRI RFLP patterns, by hybridizing total DNA with four cosmid clones containing non-overlapping mtDNA fragments, did not show any congruence with cpDNA variation patterns. However, at the cytodeme level, the patterns of genetic divergence suggested by the cpDNA data could be correlated with mtDNA variation. In the Brassica lineage, Diplotaxis viminea was identified as the female parent of the allotetraploid D. muralis. The chloroplast DNAs of Erucastrum strigosum and Er. abyssinicum were found to be very closely related. In the Sinapis lineage, Brassica maurorum was found to be the diploid progenitor of autotetraploid B. cossoneana. B. amplexicaulis showed a very different cpDNA pattern from other members of the subtribe. Brassica adpressa was closest to Erucastrum laevigatum and could be the diploid progenitor of autotetraploid Er. laevigatum. Based on the close similarity of the cpDNA pattern of Diplotaxis siifolia with that of D. assurgens, we have proposed the retention of this species in the genus Diplotaxis. The taxonomic positions of some other species have also been discussed.     

Effect of Brassica Biofumigant Amendments on Different Stages of the Life Cycle of Phytophthora cinnamomi

The oomycete plant pathogen Phytophthora cinnamomi causes a highly destructive root rot that affects numerous hosts. Integrated management strategies are needed to control P. cinnamomi in seminatural oak rangelands. We tested how biofumigation affects crucial stages of the pathogen's life cycle in vitro, in infested soils under laboratory conditions and in planta. Different genotypes of three potential biofumigant plant species (Brassica carinata, Brassica juncea, Brassica napus) were collected at different phenological stages, analysed for their glucosinolate contents, and subsequently tested. The most effective genotypes against mycelial growth and sporangial production were further tested on the viability of chlamydospores in artificially infested natural soils and in planta on Lupinus luteus, a host highly susceptible to P.cinnamomi. Brassica carinata and B. juncea genotypes inhibited mycelial growth, decreased sporangial production, and effectively inhibited the viability of chlamydospores in soil, but only B. carinata decreased disease symptoms in plants. Effective genotypes of Brassica had high levels of the glucosinolate sinigrin. Biofumigation with Brassica plants rich in sinigrin has potential to be a suitable tool for control of oak root disease caused by P. cinnamomi in Spanish oak rangeland ecosystems.     

Uptake and distribution of sinigrin in microspore derived embryos of Brassica napus L

In Brassica napus, glucosinolates are transported from all parts of the plant into the embryo during seed development. In this study we describe the uptake of the alkenyl glucosinolate sinigrin by microspore derived embryos from high and low glucosinolate genotypes. Microspore derived embryos develop completely isolated from maternal tissues unlike zygotic embryos, which contains glucosinolates transported into the embryo synthesised in the vegetative tissues. The sinigrin in the culture medium was almost completely absorbed by the embryos after three days of culture. The embryos of high and low glucosinolate genotypes were equally capable of absorbing sinigrin from the medium. A significant increase in different alkenyl glucosinolates following feeding of sinigrin suggests induction of biosynthetic enzymes in the embryos. Following excess feeding of sinigrin, we found a strong uptake against a concentration gradient and stable accumulation by the embryos. The glucosinolate was detected in single dissected cotyledons by a photometric test and by HPLC. This test could potentially be useful for screening mutants defective in glucosinolate uptake into the embryo.     

Antioxidant defense system in leaves of Indian mustard (<Emphasis Type="Italic">Brassica juncea</Emphasis>) and rape (<Emphasis Type="Italic">Brassica napus</Emphasis>) under cadmium stress

Plant species capable of hyper-accumulating heavy metals are of considerable interest for phytoremediation, and differ in their ability to accumulate metals from environment. Using two brassica species (Brassica juncea and Brassica napus), nutrient solution experiments were conducted to study variation in tolerance to cadmium (Cd) toxicity based on (1) lipid peroxidation and (2) changes in antioxidative defense system in leaves of both plants (i.e., superoxide dismutase (SOD EC 1.15.1.1), catalase (CAT EC 1.11.1.6), ascorbate peroxidase (APX EC 1.11.1.11), guaiacol peroxidase (GPX EC 1.11.1.7), glutathione reductase (GR EC 1.6.4.2), levels of phytochelatins (PCs), non-protein thiols (NP-SH), and glutathione. Plants were grown in nutrient solution under controlled environmental conditions, and subjected to increasing concentrations of Cd (0, 10, 25 and 50 μM) for 15 days. Results showed marked differences between both species. Brassica napus under Cd stress exhibited increased level of lipid peroxidation, as was evidenced by the increased malondialdehyde (MDA) content in leaves. However, in Brassica juncea treated plants, MDA content remained unchanged. In Brassica napus, with the exception of GPX, activity levels of some antioxidant enzymes involved in detoxification of reactive oxygen species (ROS), including SOD, CAT, GR, and APX, decreased drastically at high Cd concentrations. By contrast, in leaves of Brassica juncea treated plants, there was either only slight or no change in the activities of the antioxidative enzymes. Analysis of the profile of anionic isoenzymes of GPX revealed qualitative changes occurring during Cd exposure for both species. Moreover, levels of NP-SH and PCs, monitored as metal detoxifying responses, were much increased in leaves of Brassica juncea by increasing Cd supply, but did not change in Brassica napus. These results indicate that Brassica juncea plants possess the greater potential for Cd accumulation and tolerance than Brassica napus.     

Flavonol glycosides in Brassica and Sinapis

The 7-glucosides and 3,7-diglucosides of kaempferol and isorhamnetin were identified in leaves and flowers of Sinapis arvensis. Additionally, the 3-sophoroside-7-glucosides of kaempferol, quercetin and isorhamnetin were found in leaves of S. arvensis and Brassica oleracea. Two dimensional surveys of leaf extracts of 27 species and cultivars of Brassica and Sinapis showed that the same pattern occurred in most species. B. tournefortii and S. flexuosa were exceptional in having flavonol 3-monosides and 3-diglycosides instead. The results suggest that it is the glycosidic patterns, rather than the distribution of the flavonol aglycones, which are likely to be of taxonomic value for distinguishing groups of species or genera within the Cruciferae.     

Suppressive Effect of Yamato-mana (Brassica rapa L. Oleifera Group) Constituent 3-Butenyl Glucosinolate (Gluconapin) on Postprandial Hypertriglyceridemia in Mice

We examined the bioactivity of Yamato-mana (Brassica rapa L. Oleifera Group) constituent glucosinolates and found that 3-butenyl glucosinolate (gluconapin) decreased the plasma triglyceride gain induced by corn oil administration to mice. However, phenethyl glucosinolate (gluconasturtiin) had little effect. 2-Propenyl glucosinolate (sinigrin) also reduced the plasma triglyceride level, which suggests that alkenyl glucosinolates might be promising agents to prevent postprandial hypertriglyceridemia.     

Host plant recognition in monophagous weevils: specificity in feeding responses of Ceutorhynchus constrictus and the variable effect of sinigrin

Host plant relations of the monophagous weevil Ceutorhynchus constrictus Marsh. (Coleoptera: Curculionidae: Ceutorhynchinae) feeding on garlic mustard, Alliaria petiolata (Bieb.) Cavara & Grande (Cruciferae) were studied in the laboratory. Most other crucifers were rejected in choice tests using garlic mustard as a reference plant, but Brassica nigra, Sinapis alba and Thlaspi arvense were as acceptable as the host plant. Flowering plants of Descurainia sophia were acceptable while young plants of this species were not. The most important feeding stimulants in extracts of garlic mustard were uncharged, water soluble compounds. The most abundant glucosinolate in garlic mustard, sinigrin, was a feeding stimulant, too. However, the feeding stimulatory activity of sinigrin was only expressed in the presence of still unidentified uncharged compounds from garlic mustard leaves. Host plant relations in monophagous crucifer-feeding insects is discussed in relation to the distinctness of glucosinolate patterns found in their host plants.

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Zusammenfassung Ceutorhynchus constrictus Marsh. (Coleoptera: Chrysomelidae: Ceutorhynchinae) ist ein monophager Rüsselkäfer, der an Knoblauchhederich frisst. Das Wirtswahl-Verhalten dieses Käfers ist im Labor untersucht worden. Die meisten Crucifiren waren im Wahlversuche nicht akzeptiert, wenn Knoblauchhederich als Vergleichspflanze vorhanden war. Von Brassica nigra, Sinapis alba, und Thlaspi arvense wurden im Vergleich gleiche Mengen verzehrt wie von der Wirtspflanze. Blühende Descurainia sophia Pflanzen wurden, im Gegensatz zu Jungpflanzen der gleichen Art, angenommen. Die wichtichsten Phagostimulanten in Extrakten von Knoblauchhederich-Blättern waren ungeladene, wasserlösliche Substanzen. Das häufigste Glukosinolat im Knoblauchhederich, Sinigrin, war auch ein Phagostimulant. Doch war die phagostimulierende Wirkung von Sinigrin nur in Kombinationen mit noch nicht identifizierten, ungeladenen Substanzen aus Knoblauchhederich-Blätter nachweisbar. Wirtspfanzen-Beziehungen von monophagen Insekten werden diskutiert im Zusammenhang mit der Eigenart des Glukosinolat-Inhaltes ihrer Wirtspflanzen.

     

Host plant derived feeding deterrence towards ants in the turnip sawfly Athalia rosae

Larvae of the sawfly Athalia rosae ruficornis Jakovlev (Hymenoptera: Tenthredinidae) feed on several glucosinolate-containing plants and have been shown to sequester the main glucosinolates of different hosts, namely sinalbin (p-hydroxybenzylglucosinolate) from Sinapis alba L., sinigrin (allylglucosinolate) from Brassica nigra (L.) Koch, and glucobarbarin ((S)-2-hydroxy-2-phenylethylglucosinolate) from Barbarea stricta Andrz. (Brassicaceae). These plant metabolites are stored in the haemolymph, which is readily released when larvae are attacked by predators. In a dual-choice bioassay the bio-activity of sawfly haemolymph collected from larvae reared on different host plants (S. alba, B. nigra, and B. stricta) was tested against the ant Myrmica rubra L. (Hymenoptera: Formicidae). The haemolymph had a stronger deterrence effect when the corresponding sawfly larvae were reared on S. alba than when reared on B. nigra and B. stricta. Haemolymph of caterpillars of Pieris rapae L. (Lepidoptera: Pieridae) that had fed on S. alba was not deterrent to the ants. No sinalbin could be detected in their haemolymph. The glucosinolates sinalbin and sinigrin, offered in a concentration comparable to that in the sawfly haemolymph, were deterrent to the ants, but not as strongly as the corresponding haemolymph samples. This suggests, that glucosinolates are not the only compounds involved in the chemical defence of A. rosae. However, the presence of sequestered glucosinolates is already a sufficient defence towards predators such as ants, and their effectiveness is modulated by the host plant chemistry.     

Cofactor-independent oxidases and oxygenases

Whereas the majority of O₂-metabolizing enzymes depend on transition metal ions or organic cofactors for catalysis, a significant number of oxygenases and oxidases neither contain nor require any cofactor. Among the cofactor-independent oxidases, urate oxidase, coproporphyrinogen oxidase, and formylglycine-generating enzyme are of mechanistic as well as medical interest. Formylglycine-generating enzyme is also a promising tool for protein engineering as it can be used to equip proteins with a reactive aldehyde function. PqqC, an oxidase in the biosynthesis of the bacterial cofactor pyrroloquinoline quinone, catalyzes an eight-electron ring-closure oxidation reaction. Among bacterial oxygenases, quinone-forming monooxygenases involved in the tailoring of polyketides, the dioxygenase DpgC found in the biosynthesis of a building block of vancomycin and teicoplanin antibiotics, luciferase monooxygenase from Renilla sp., and bacterial ring-cleaving 2,4-dioxygenases active towards 3-hydroxy-4(1H)-quinolones have been identified as cofactor-independent enzymes. Interestingly, the 3-hydroxy-4(1H)-quinolone 2,4-dioxygenases as well as Renilla luciferase use an α/β-hydrolase architecture for oxygenation reactions. Cofactor-independent oxygenases and oxidases catalyze very different reactions and belong to several different protein families, reflecting their diverse origin. Nevertheless, they all may share the common mechanistic concept of initial base-catalyzed activation of their organic substrate and “substrate-assisted catalysis.”     

Potential taxonomic use of random amplified polymorphic DNA (RAPD): a case study in Brassica

Summary The potential use of RAPDs for taxonomic studies were investigated using Brassica, Sinapis and Raphanus taxa. Principal coordinate analysis of 284 RAPD bands revealed the classical U triangle relationship between diploid and amphidiploid Brassica taxa. Raphanus sativus and S. alba were distinct from the Brassica taxa. It appears that at least ten primers with approximately 100 total bands are needed to adequately portray these relationships. Cultivars of cabbage and cauliflower were separated by RAPDs. Analysis of RAPDs from individual plants of B. carinata cv. dodola resulted in 69 RAPDs, with 91.7% monomorphic and 8.3% polymorphic bands. RAPDs appear to be useful for taxonomic studies at levels ranging from populations to species and perhaps genera.     

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.     

Identification of Glucosinolates in Seeds of Three Brassicaceae Species Known to Hyperaccumulate Heavy Metals

Plants from the Brassicaceae family are known to contain secondary metabolites called glucosinolates. Our goal was to establish by LC/MS the glucosinolate profile of seeds of three Brassicaceae species known to hyperaccumulate heavy metals. We investigated Alyssum fallacinum auct. non Hausskn ., Iberis intermedia Guers ., and Noccaea caerulescens (J. Presl & C. Presl ) F. K. Mey . Our results indicate that A. fallacinum seeds contain glucoiberin and glucoibervirin, which had not been previously identified in this plant. Furthermore, we report for the first time the presence of glucoiberin, glucoibervirin, glucotropaeolin, and sinigrin in I. intermedia. We have detected for the first time glucoconringiin in N. caerulescens. In addition, glucosinalbin, 4‐hydroxyglucobrassicin, and glucomoringin were also detected.     

Glucosinolate degradation by Aspergillus clavatus and Fusarium oxysporum in liquid and solid-state fermentation

Two fungal strains, Aspergillus clavatus II-9 and Fusarium oxysporum @ 149, proved to be capable of degrading sinigrin and sinalbin. During the degradation of sinigrin by whole cells of the Aspergillus strain, allylcyanide accumulated in the liquid incubation mixture. After a maximum concentration had been reached, the concentration of allylcyanide decreased as a result of its instability in the medium used. Incubation of cell-free extracts with sinigrin resulted in accumulation of glucose and allylisothiocyanate, suggesting that myrosinase is involved. Experiments with intact cells and cell-free extracts indicate the formation of an as yet unknown intermediate. When sinigrin was degraded by the Aspergillus strain in mustard seed meal under solid-state fermentation (SSF) conditions, no accumulation of allylcyanide or allylisothiocyanate was measured. Degradation of sinigrin by F. oxysporum @ 149 did not result in accumulation of intermediates, neither in liquid incubation mixtures nor in mustard seed meal under SSF conditions. Sinigrin was not degraded during incubation with cell-free extracts of F. oxysporum @ 149. Degradation of sinalbin by A. clavatus and F. oxysporum was measured during fermentation of yellow mustard seed meal under SSF conditions. Both fungi are useful for laboratory-scale SSF of mustard seed meal, thus opening new perspectives for a cost effective detoxification process for raw feed materials. Correspondence to: J. P. Smits     

Locating a resistance mechanism to the cabbage aphid in two wild Brassicas

Feeding behaviour of the cabbage aphid,Brevicoryne brassicae, was monitored electronically on two resistantBrassica species,B. fruticulosa andB. spinescens, and compared with a susceptible controlB. oleracea var.capitata cv. Offenham Compacta. Aphids, monitored for 10 h on the under side of leaves, performed recognizable feeding behaviour on all species. Electrical Penetration Graphs (EPGs) of aphids on resistant and susceptible plants showed no difference in behaviour for aphids on resistantBrassica species compared to susceptible until stylets penetrated the phloem sieve elements when a large reduction in the duration of passive phloem uptake (E₂ pattern) onB. fruticulosa was indicated. Although feeding behaviour on 6 week-old plants ofB. spinescens was similar to the susceptible controls, behaviour on 10 week-old plants was similar to that recorded forB. fruticulosa. The mechanism of resistance is thought to be located in the sieve element as the normal sieve element salivation (E₁) signal was either quickly terminated by withdrawal of the stylets from the sieve element or continued as a disrupted E₂ pattern. Analysis of secondary plant compounds in the threeBrassica species only identified significant differences in the glucosinolate profile. No reproducible differences were detected in the concentration of phenolics or anthocyanins. The major glucosinolate component ofB. fruticulosa andB. spinescens was gluconapin rather than glucobrassicin and glucoiberin as found in the susceptible host plant. However, both pure glucosinolates and glucosinolate extracts from all three species did not reduce aphid survival on chemically-defined artificial diets. These results suggest that the mechanism of resistance may be a mechanical blocking of the sieve element or stylets rather than a difference in the secondary plant chemistry of glucosinolates and phenolics.     

Distribution of 1-sinapoylglucose: choline sinapoyltransferase activity in the brassicaceae

The occurrence of 1-sinapoylglucose: choline sinapoyltransferase (SCT) in seeds of various members of the Brassicaceae is reported. Within the species and cultivars investigated, a positive correlation was found between extractable levels of enzyme activity and the degree of sinapine accumulation. High enzymatic activities were found in seeds from Brassica, Raphanus and Sinapis, known for their high sinapine content.     

Characterization of a myrosinase cDNA from Brassica parachinensis and its defense role against Plutella xylostella after suppression

Abstract In Brassicaceae, myrosinase catalyzes the hydrolysis of glucosinolate and plays an important role in anti‐herbivore defense. We have cloned and characterized the full‐length complementary DNA of myrosinase gene from Brassica parachinensis that exhibits high sequence identity with myrosinase genes from other Brassica species. To investigate the role of this myrosinase in defense against the diamondback moth (Plutella xylostella), we constructed an RNA‐interference (RNAi) cassette expressing a double‐stranded RNA that targeted myrosinase and transfected it into B. parachinensis. Myrosinase was suppressed in the resulting transgenic plants. Diamondback moth larvae feeding on transgenic plants had lower larval and pupal weights, longer pupal duration, and lower fecundity than those feeding on non‐transgenic plants, suggesting that the diamondback moth has adapted to the glucosinolate‐myrosinase defensive system. Therefore, the suppression of myrosinase is a potential approach for controlling the diamondback moth.