Broccoli florets contain low levels of 3-methylsuphinylpropyl and 4-methylsulphinylbutyl glucosinolates. Following tissue disruption, these glucosinolates are hydrolysed to the corresponding isothiocyanates (ITCs), which have been associated with anticarcinogenic activity through a number of physiological mechanisms including the induction of phase II detoxification enzymes and apoptosis. In this paper, we describe the development of ITC-enriched broccoli through the introgression of three small segments of the genome of Brassica villosa, a wild relative of broccoli, each containing a quantitative trait locus (QTL), into a broccoli genetic background, via marker-assisted selection and analysis of glucosinolates in the florets of backcross populations. Epistatic and heterotic effects of these QTLs are described. The ITC-enriched broccoli had 80-times the ability to induce quinone reductase (a standard assay of phase II induction potential) when compared to standard commercial broccoli, due both to an increase in the precursor glucosinolates and a greater conversion of these into ITCs.

Aliphatic glucosinolates are thioglucosides synthesized by genera within the Capparales including Arabidopsis and Brassica. They have been shown to mediate pest or pathogen interactions and to reduce the feeding quality of rapeseed meal. Their biological activity is largely dependent upon the structure of the side chain which determines the nature of hydrolysis products produced following tissue damage. A generalized model of the biosynthesis of aliphatic glucosinolates is proposed and tested with reference to the genetic regulation of side chain length by analysing recombinant populations of B. napus and A. thaliana developed from parental lines which varied in their glucosinolate content. The results of the B. napus studies were consistent with a model in which alleles at a single locus (Gsl-pro) regulate the presence or absence of propyl glucosinolates, and those at two other loci (Gsl-elong-C and Gsl-elong-A) (which map onto a pair of homoeologous linkage groups, one from the C genome and one from the A genome) regulate side chain elongation of the amino acid derivative which results in the production of butyl and pentyl glucosinolates. As null alleles do not occur at the Gsl-elong-A locus, the proportion of propyl glucosinolates is limited to below 30 per cent of total aliphatic glucosinolates. Alleles at a single locus in A. thaliana (GsIelong-Ar), which maps 1.3 cM from the RFLP locus m291 on chromosome 5, regulate side chain elongation of aliphatic glucosinolates in this species. It is suggested that the Gsl-elong-Ar gene is homologous to the Gsl-elong-A and Gsl-elong-C genes and, if cloned, could be used to downregulate the endogenous Gsl-eiong genes in B. napus.

The process of cleavage during the syncytial blastoderm stage of the Drosophila embryo was studied in fixed whole-mounts using a triple-staining technique . Plasmalemma was stained with Concanavalin A conjugated to tetramethylrhodamine isothiocyanate, the underlying cortical F-actin with a fluorescein derivative of phalloidin, and nuclei with 4',-6 diamidine-2-phenylindole dihydrochloride . The surface caps, which overlie the superficial nuclei at this stage, were found to be rich in F-actin as compared with the rest of the cortex. After the caps formed, they extended over the surface and flattened . Whilst this was occurring the F-actin network within the caps became more diffuse . By the end of the expansion process F-actin had become concentrated at both poles of the caps. The caps then split in two . The cleavage was not accompanied by the formation of any apparent contractile ring of microfilaments across the cap, rather the break region was depleted in F-actin . The cortical actin associated with each half of the old cap then became reorganized around a nucleus to form a new daughter cap, and the cycle began again .The development of the Drosophila embryo consists of an initial stage when nuclei cleave rapidly within the egg but no cell membranes are formed (6). After the ninth cleavage, -400 nuclei migrate to the surface. Between 10 and 20 nuclei located at the posterior tip become incorporated into pole cells, which are the progenitors of the germ cell line. The remainder become associated with cytoplasmic caps or protrusions that bulge from the surface (4,13,16,21). These caps are surface structures only, being specializations of the cortex. This stage is known as the syncytial blastoderm. It lasts for -1 h, during which the nuclei and associated caps undergo four further cleavages. The caps go through cycles of expansion and flattening, taking in the whole of the surface prior to dividing and rounding up again (16). After this stage the whole of the embryo surface becomes cellularized simultaneously .The syncytial blastoderm has several useful features for structural studies of cleavage and mitosis . Because the caps are surface structures and the nuclei are <5 lm from the plasmalemma it was possible to observe clearly these structures with epifluorescence microscopy. Divisions occur rapidly between 8 and 20 min apart, the earlier ones cleaving more rapidly (16). Furthermore, in a proportion of the embryos cleavage is not synchronous but occurs in gradient-like fashion, with various different stages present in a single embryo (21). As a result it was not difficult to find embryos with 156 caps at all stages ofdivision .In a previous report (17) the distribution of F-actin microfilaments was described during the process of blastoderm cellularization using a fluorescein derivative ofphalloidin (FLphalloidin)' as a specific stain for F-actin. This paper examines the organization of cortical F-actin during the preceding syncytial blastoderm stage. MATERIALS AND METHODSEmbryos of the desired stage ...

The inheritance of aliphatic glucosinolates was studied in crosses between synthetic B. napus lines and oilseed rape cultivars. Six unlinked loci are described which determine the aliphatic glucosinolate profile of B. napus. One locus regulates the presence or absence of propyl glucosinolates, while another regulates the expression of pentyl glucosinolates. Two loci regulate the removal of the terminal H3CSgroup from the amino acid derivative to produce alkenyl glucosinolates as opposed to methylthioalkyl and methylsulphinylalkyl glucosinolates, regardless of the length of the alkyl chain. Likewise, another two loci regulate the hydroxylation of both butenyl and pentenyl glucosinolates. The functional alleles at one of the hydroxylation loci results in significantly more hydroxylation than those at the other locus. The large number of aliphatic glucosinolates which have been described in Brassica thus results from an interaction between genes which regulate side chain elongation and genes which modify the structure of the side chain, regardless of its length. The implications of this study for the biosynthesis of aliphatic glucosinoiates, the origin of B. napus and the potential to manipulate the leaf and seed glucosinolate profile of oilseed rape are discussed.

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