Constituents of the tapetosomes and elaioplasts in Brassica campestris tapetum and their degradation and retention during microsporogenesis

In Brassica anthers during microsporogenesis, the tapetum cells contain two abundant lipid-rich organelles, the tapetosomes possessing oleosins and triacylglycerols (TAGs), and the elaioplasts having unique polypeptides and neutral esters. B. campestris, for its simplicity of possessing only the AA genome and one predominant oleosin of 45 kDa, was studied. In the developing anthers, the lipids and proteins of the tapetosomes and elaioplasts were concomitantly accumulated but selectively degraded or retained. Upon incubation of isolated tapetosomes in a pH-5 medium, the predominant 45 kDa oleosin underwent selective enzymatic proteolysis to a 37 kDa fragment, which was not further hydrolyzed upon prolonged incubation. The unreacted 45 kDa oleosin was retained in the organelles, whereas the 37 kDa fragment was released to the exterior. The fragment would become the predominant 37 kDa polypeptide in the pollen coat. Isolated tapetosomes did not undergo hydrolysis of the TAGs upon incubation in media of diverse pHs. An alkaline lipase in the soluble fraction of the anther extract was presumed to be the enzyme that would hydrolyze the tapetosome TAGs, which disappeared in the anthers during development. The tapetum elaioplasts contained several unique polypeptides of 31-36 kDa. The gene encoding a 32 kDa polypeptide was cloned, and its deduced amino acid sequence was homologous to those of two proteins known to be present on the surface of fibrils in chromoplasts. Upon incubation of isolated elaioplasts in media of diverse pHs, the organelle polypeptides were degraded completely and most rapidly at pH 5, whereas the neutral esters remained unchanged; these neutral esters would become the major lipid components of the pollen coat. The findings show that the constituents of the two major tapetum organelles underwent very different paths of degradation, or modification, and transfer to the pollen surface.

Molecular cloning of a cDNA encoding a pollen extracellular protein as a potential source of a pollen allergen in Brassica rapa

A polyclonal antiserum was raised against the extracellular pollen proteins of Brassica rapa and used for screening the expression cDNA libraries made from immature anthers. We obtained five groups of cDNA clones, including cDNAs similar to PCP1, thioredoxin, and lipid transfer protein (LTP). Recombinant protein of the cDNA clone showing sequence similarity to LTP was demonstrated to bind IgE of a patient allergic to Brassica pollen. The cDNA clone reported here, therefore, represents a novel pollen allergen of Brassica rapa.

Two jasmonate-inducible myrosinase-binding proteins from Brassica napus L. seedlings with homology to jacalin

Two homologous but different cDNAs encoding a 97-kDa and a 70-kDa protein from Brassica napus L. seedlings have been characterized. Both proteins contain sequence motifs with high homology to the IgA binding lectin, jacalin, and the deduced 97-kDa protein contains the peptide sequences of myrosinase-binding protein. The 70-kDa and the 97-kDa protein can both be isolated as a complex containing myrosinase, indicating they indeed are myrosinase-binding proteins. We provide evidence that the 70-kDa protein binds IgA in vitro, and therefore classify the protein as a jacalin-type lectin. Both the 97-kDa and the 70-kDa proteins are encoded by a small number of genes in the Brassica genome. The mRNA for the 97-kDa protein is detected in both light- and dark-grown seedlings, whereas the mRNA for the 70-kDa protein is mainly detected in etiolated seedlings. The transcript levels for both proteins are transient and are rapidly increased by methyl jasmonate. The 70-kDa protein is synthesized de novo during germination and accumulates mainly in the hypocotyl and in the root. By immunogold labeling we show that a few cells scattered in the cotyledons of young seedlings (approx. 5% of total cells), contain protein-body-like structures with the 70-kDa protein. These bodies are present in a 10,000 g pellet from which the 70-kDa protein can be extracted by sodium carbonate. In addition, the 70-kDa protein is detected in the amorphous structures of the vacuole in a few cells of the cotyledon, the hypocotyl and the root.

Identification of volatile organic compounds emitted in the field by oilseed rape (Brassica napus ssp. oleifera) over the growing season

BACKGROUND

Oilseed rape has been associated by rural dwellers with seasonal symptoms, such as sneezing, coughing, headache and eye irritation, during its flowering season, for a number of years. This study was performed to identify the volatile chemicals emitted from oilseed rape in the field.

OBJECTIVE

The objective of this study was to establish which volatile chemicals may be causative factors of oilseed rape allergy/toxicity.

METHODS

The volatile organic compounds were sampled over the flowering period using a modified entrainment technique for headspace analysis under field conditions. These volatiles were then identified using thermal desorption-gas chromatography-mass spectrometry.

RESULTS

The major constituents identified were the monoterpenes limonene, sabinene, beta-myrcene, and cis-3-hexen-l-ol acetate, a 'green leaf' volatile. The minor constituents included monoterpenes, sesquiterpenes, short chain aldehydes and ketones, other 'green leaf' volatiles and organic sulphides including the respiratory irritant, dimethyl disulphide.

CONCLUSIONS

This report highlights the diversity of volatile chemicals emitted by oilseed rape and confirms field emissions to be broadly similar to those found previously in laboratory studies. A review is carried out on the scientific literature already published on oilseed rape flower headspace analysis.

Project of conveyer-type space greenhouse for cosmonauts' supply with vitamin greenery

Design and advantages of conveyer-type growth chamber PHYTOCYCLE with a cylindrical crop surface are featured. Based on the results of testing, an experimental prototype of conveyer-type vegetable greenhouse VITACYCLE for space vehicles is being developed at the SSC-IBMP in conjunction with a number of institutions of the Russian space industry to provide space crews with fresh greenery. Rated daily production of the greenhouse is 150 g of eatable biomass with power consumption of 1 kW. The system is to be mounted within the Life support module of international space station Alpha (ISSA). Design of the greenhouse is outlined. Brief description, state-of-the-art, and further plans regarding VITACYCLE elaboration and construction are presented.

Biosynthesis, targeting and processing of oleosin-like proteins, which are major pollen coat components in Brassica napus

The purpose of this study is to characterise the biosynthesis, targeting and processing of some of the major protein components of the pollen coat, or tryphine, of Brassica napus. The authors have N-terminally sequenced 11 of the most abundant pollen coat polypeptides, and nine of these sequences correspond to proteolytically cleaved products of seven oleosin-like genes, i.e. Oln B;1 to Oln B;6 and Oln B;11. The Oln B;11 gene product is co- or post-translationally targeted in vitro to canine microsomal membranes. This implies that the oleosin-like protein is targeted to the endoplasmic reticulum in tapetal cells in vivo. Affinity-purified antibodies raised against a 20-residue domain of Oln B;3 and B;4 gene products cross-reacted with full-length proteins of 45-48 kDa in early developing (< 2 mm to 5 mm) buds and anthers, but recognised truncated proteins of 32-38 kDa at later (4 mm to 7 mm) stages of development. The 45-48 kDa immunoreactive proteins were associated with a floating lipid body fraction obtained from a tapetal/locular fluid extract from maturing anthers and a major 48 kDa polypeptide from this fraction was confirmed by N-terminal sequencing to be a full length product of the Oln B;3 gene. Quantitative immunocytochemical studies showed that the full length 45-48 kDa oleosin-like proteins were specifically localised in the interior of tapetal cytoplasmic lipid bodies where they were associated with a regular hexagonal-like fibrous reticulum. No significant labelling of elaioplasts was observed. The same antibodies specifically labelled 32-38 kDa oleosin-like proteins on the extracellular pollen coat of maturing pollen grains. These results demonstrate for the first time that many of the major pollen coat proteins are derived from an endoproteolytic cleavage of precursor oleosin-like proteins that originally accumulate within the large cytoplasmic lipid bodies of tapetal cells.

Agravitropic behaviour of roots of rapeseed (Brassica napus L.) transformed by Agrobacterium rhizogenes

Transgenic hairy roots of Brassica napus (cv. Omega) have been developed, using Agrobacterium rhizogenes strain AR 25, for use as a model system in the investigation of physiological and morphological differences between transgenic and normal roots. The basic parameters of growth and normal or altered gravitropical behaviour of hairy roots are for the first time presented in this paper together with an ultrastructural and morphological analysis of the root statocytes. The results obtained also represented the basis for the TRANSF0RM-experiment on the IML-2 mission performed onboard the Space Shuttle Columbia. Typical hairy root traits such as hormone-autonomous growth high growth rate, lateral branching, and changed/absence of gravitropism were detected. The transformed nature of the roots was confirmed by Southern blot analyses. The gravitropical behaviour of apices from hairy root cultures of this clone has been compared with root tips from normal seedlings. While the wild type roots curved progressively with increasing stimulation angles, the transformed roots showed no curvature when stimulated at 45 degrees, 90 degrees or 135 degrees on the ground. The morphology and ultrastructure of the root tip regions were examined by light microscopy and transmission electron microscopy. At the ultrastructural level no major differences could be detected between the roots studied. There was, however, a slight reduction in the starch content of most of the amyloplasts of the transgenic root tips, and the root cap was more V-shaped in the transgenic roots than in the wild type. Preliminary results from the Shuttle experiment TRANSFORM show a random distribution of amyloplasts in the root cells of both transformed and wild type root caps after 14 h on a 1xg centrifuge followed by 37 h in microgravity.

Broccoli sprouts: an exceptionally rich source of inducers of enzymes that protect against chemical carcinogens

Induction of phase 2 detoxication enzymes [e.g., glutathione transferases, epoxide hydrolase, NAD(P)H: quinone reductase, and glucuronosyltransferases] is a powerful strategy for achieving protection against carcinogenesis, mutagenesis, and other forms of toxicity of electrophiles and reactive forms of oxygen. Since consumption of large quantities of fruit and vegetables is associated with a striking reduction in the risk of developing a variety of malignancies, it is of interest that a number of edible plants contain substantial quantities of compounds that regulate mammalian enzymes of xenobiotic metabolism. Thus, edible plants belonging to the family Cruciferae and genus Brassica (e.g., broccoli and cauliflower) contain substantial quantities of isothiocyanates (mostly in the form of their glucosinolate precursors) some of which (e.g., sulforaphane or 4-methylsulfinylbutyl isothiocyanate) are very potent inducers of phase 2 enzymes. Unexpectedly, 3-day-old sprouts of cultivars of certain crucifers including broccoli and cauliflower contain 10-100 times higher levels of glucoraphanin (the glucosinolate of sulforaphane) than do the corresponding mature plants. Glucosinolates and isothiocyanates can be efficiently extracted from plants, without hydrolysis of glucosinolates by myrosinase, by homogenization in a mixture of equal volumes of dimethyl sulfoxide, dimethylformamide, and acetonitrile at -50 degrees C. Extracts of 3-day-old broccoli sprouts (containing either glucoraphanin or sulforaphane as the principal enzyme inducer) were highly effective in reducing the incidence, multiplicity, and rate of development of mammary tumors in dimethylbenz(a)anthracene-treated rats. Notably, sprouts of many broccoli cultivars contain negligible quantities of indole glucosinolates, which predominate in the mature vegetable and may give rise to degradation products (e.g., indole-3-carbinol) that can enhance tumorigenesis. Hence, small quantities of crucifer sprouts may protect against the risk of cancer as effectively as much larger quantities of mature vegetables of the same variety.

Comparison of flowering time genes in Brassica rapa, B. napus and Arabidopsis thaliana

The major difference between annual and biennial cultivars of oilseed Brassica napus and B. rapa is conferred by genes controlling vernalization-responsive flowering time. These genes were compared between the species by aligning the map positions of flowering time quantitative trait loci (QTLs) detected in a segregating population of each species. The results suggest that two major QTLs identified in B. rapa correspond to two major QTLs identified in B. napus. Since B. rapa is one of the hypothesized diploid parents of the amphidiploid B. napus, the vernalization requirement of B. napus probably originated from B. rapa. Brassica genes also were compared to flowering time genes in Arabidopsis thaliana by mapping RFLP loci with the same probes in both B. napus and Arabidopsis. The region containing one pair of Brassica QTLs was collinear with the top of chromosome 5 in A. thaliana where flowering time genes FLC, FY and CO are located. The region containing the second pair of QTLs showed fractured collinearity with several regions of the Arabidopsis genome, including the top of chromosome 4 where FRI is located. Thus, these Brassica genes may correspond to two genes (FLC and FRI) that regulate flowering time in the latest flowering ecotypes of Arabidopsis.

Biological activity of purpurogallin

Purpurogallin showed antibacterial activity toward gram-positive bacteria. Strong activity against methicillin-resistant Staphylococcus aureus [minimal inhibitory concentration (MIC) against methicillin of 1600 micrograms/ml] was found, with MIC of 11.0 micrograms/ml. Purpurogallin inhibited the growth of all tested plants and decreased the chlorophyll content in the cotyledons of Brassica campestris subsp. rapa. It showed potent inhibitory activity against prolyl endopeptidase (the 50% inhibitory concentration was 1.6 x 10(-5) M), unlike its analogues, hinokitiol and tropolone.

Selenium-induced growth reduction in Brassica land races considered for phytoremediation

Brassica species considered for use in selenium (Se) phytoremediation need to accumulate large amounts of Se to be successful. Retarded plant growth and impaired protein synthesis are common symptoms for plants grown under seleniferous soils. Selenium accumulation by different land races of Brassica juncea (L.) Czern and Coss and one land race of Brassica carinata was investigated in Se-enriched water and soil cultures containing 2 mg Se kg-1. Effects of Se concentration in the root environment on the assimilation of Se, leaf surface area, dry matter yield, total leaf protein concentration, and free seleno-amino acid concentrations were analyzed for plants grown in Se-laden media. In water culture, shoot Se concentrations among the land races ranged from 501 to 1017 mg Se kg-1 dry matter (DM), and in plants grown in Se-laden soil, concentrations ranged from 407 to 769 mg Se kg-1 DM. Land races grown with Se exhibited decreases in dry matter yields from 12 to 23% and in leaf surface area from 5 to 26% compared to the same land races grown without Se. Protein content was significantly correlated both with shoot Se concentrations (r = 0.746, P < 0.001) and with leaf surface area (r = 0.446, P < 0.01) for all land races grown in Se-enriched water culture. There was also a significant correlation (r = 0.767, P < 0.001) between total Se assimilation and shoot protein for all land races. Free selenomethionine was detected for plants grown with Se and ranged from 92 to 958 ng g-1 DM. Other seleno-amino acids, Se-methyl-selenocysteine and selenocysteine, were not consistently detected as free amino acids in the different land races. Although visual symptoms of Se toxicity were not observed in the Brassica species, dry matter yield, leaf surface, and total shoot protein decreased, depending on the land races tested.

Developmental basis of homeosis in precociously germinating Brassica napus embryos: phase change at the shoot apex

Precociously germinating Brassica napus (oilseed rape) embryos produce extra cotyledons or chimeric organs with sectors of cotyledon and leaf tissue, rather than leaves, at the shoot apex. To investigate this phenomenon in more detail, scanning electron microscopy was used to examine the development of organ primordia at the shoot apex. In situ hybridizations with molecular markers of the embryonic phase were used to assess the status of individual cells in the shoot apex with regard to the transition between embryonic and vegetative phases. The results indicate that, under conditions that support precocious germination, primordia develop at the shoot apex in the mode characteristic of postgerminative growth, i.e. they arise sequentially in a spiral phyllotaxy. Cells in the rest of the embryo, however, can continue to express molecular markers of the embryonic phase for several weeks after the start of culture. When patterns of gene expression and the fate of individual primordia were compared, a strong correlation was found between organ identity and the status of cells in the vicinity of the meristem with regard to phase. Primordia that develop in situations where neighboring cells are in the embryonic phase always produce organs with cotyledon morphology. Primordia that develop in situations where neighboring cells have exited the embryonic phase produce leaves. Based on an examination of situations where chimeric organs are produced, I propose that short range interactions or signalling are likely to be involved in communicating information about phase to developing primordia.

Leaf senescence in Brassica napus: cloning of senescence related genes by subtractive hybridisation

A subtractive hybridisation technique was developed to clone cDNAs representing genes that showed enhanced expression during leaf senescence in Brassica napus. A number of different genes were identified that, when analysed by northern hybridisation, showed different patterns of expression during leaf development but were all expressed at increased levels during senescence. Sequence analysis of these cDNAs showed that several types of genes were found including two different proteases, glutamine synthetase, ATP sulphurylase, catalase, metallothionein, ferritin and an antifungal protein. The possible roles of these gene products in the senescence process are discussed.

Identification, subcellular localization, and developmental studies of oleosins in the anther of Brassica napus

mRNAs encoding putative oleosins have been detected in the tapetum of developing anthers in Brassica and Arabidopsis, but the authentic proteins have not been previously documented. Antibodies against a synthetic 15-residue polypeptide that represents a portion of the putative tapetum oleosins encoded by two cloned Brassica napus genes were raised. Using these antibodies for immunoblotting after SDS-PAGE of the sporophytic extracts of B. napus developing anthers, two oleosins of approximately 48 and 45 kDa were detected. These two oleosins were judged to be the putative oleosins encoded by cloned Brassica genes because of their identical N-terminal sequences. The two oleosins were present in the anthers only during the developmental stage when the tapetum cells were packed with organelles. A fraction of lowdensity organelles was isolated from the developing anthers by flotation centrifugation. The fraction contained plastoglobule-filled plastids and lipid-containing particles. The structures of these two isolated organelles were similar to those in situ in the tapetum cells. Of subcellular fractions of the anther homogenate, the two oleosins were present exclusively in the low-density organelle fraction. They were absent in the surface fractions of the developing microspores and the mature pollen, although fragmented oleosin molecules were earlier reported to be present on the pollen. By immunocytochemistry, immunogold particles were found largely on the periphery of the plastoglobuli inside the plastids in the tapetum cells. The antibodies also detected oleosins on the surface of storage oil bodies inside the maturing microspores. Apparently, the gametophytic microspore oil-body oleosins share common epitopes at the generally non-conserved C-terminal domain with the sporophytic tapetum oleosins.

Floral homeotic gene expression defines developmental arrest stages in Brassica oleracea L. vars. botrytis and italica

Brassica oleracea L. vars, italica (broccoli) and botrytis (cauliflower) both undergo developmental arrests which result in heading phenotypes. We characterized these arrested tissues at the morphological and molecular levels, and defined the developmental changes that ensure after arrest has been broken. We found that the order of floral organ initiation and the positions of resulting floral organ primordia in this species in some respects from that of Arabidopsis, which is a member of the same family, Brassicaceae. We also cloned homologs of the Arabidopsis floral homeotic genes APETALA1 (AP1) and APETALA3 (AP3) from B. oleracea and characterized their expression patterns. We found that the AP1 homolog was expressed in some of the meristems of arrest-stage cauliflower, providing evidence that this tissue is florally determined. In broccoli, both the AP1 and AP3 homologs were expressed. However, the spatial pattern of expression of the broccoli AP1 homolog differed from that of Arabidopsis. In addition we identified a homolog of the CAULIFLOWER (CAL) gene, BoiCAL, from broccoli. The predicted amino acid sequence indicated that the BoiCAL gene product does not contain the mutation thought to be responsible for the early arrest exhibited in cauliflower (Kempin et al. 1995), but contains other changes that might play a role in the broccoli heading phenotype.

[Dormancy characteristic and inner inhibitory substances of fructus Schisandrae]

It has been found for the first time that there is quite a number inhibitory substances in the testa and kernel of dormant Fructus Schisandrae. Differences have alas been found between the inhibitor extracted from the testa and that from the kernel. The fromer is stronger in inhibiting the root elongatain of Brassica sp, whereas the latter is stonger in inhibiting the seeds germination. The result shows that the dormancy of Fructus Schisandrae the inhibitors contained in the testa and kernel.

Photoinduced toxicity of PAHs to the foliar regions of Brassica napus (canola) and Cucumbis sativus (cucumber) in simulated solar radiation

Simulated solar radiation and natural sunlight can enhance polycyclic aromatic hydrocarbon (PAH) toxicity, previously reported in terms of inhibited production of Lemna gibba leaves and diminished growth of Brassica napus seedling roots. This work has been extended to examine the photoinduced impact of PAHs on the foliar regions of terrestrial plants. To carry out these experiments two crop species, B. napus (canola) and Cucumbis sativus (cucumber), were chosen to test the photoinduced toxicity of six PAHs (anthracene, phenanthrene, benzo(a)anthracene, benzo(a)pyrene, flouranthene, and pyrene). Aqueous solutions containing PAHs were sprayed on the foliage of the plants. It was found that all the PAHs tested had negative impacts on the foliage of the plants and the concentrations that induced toxicity were consistent with those observed for inhibition of growth of L. gibba. The impacts were observed as diminished biomass accumulation, induction of chlorosis, and inhibition of photosynthesis. It may be concluded from this work that PAHs in rain and surface waters could be harmful to photosynthetic tissues of terrestrial plants.

GSBF1, a seedling-specific bZIP DNA-binding protein with preference for a 'split' G-box-related element in Brassica napus RbcS promoters

Promoters of RbcS genes may contain a GS-box, which is a cis element with a core sequence related to the G-box, but split by a spacer of about 14 bp. Here we describe GSBF1, a DNA-binding protein that specifically interacts with a GS-box element located proximal to the G-box in the Brassica napus RbcS IV promoter. Sequence analysis of GSBF1 revealed a basic region/leucine zipper (bZIP) domain that displays structural features distinct from that of G-box binding factors (GBFs). Gel shift experiments showed that recombinant GSBF1 does not efficiently bind to the continuous G-box motif. RNA gel blot analysis indicated that GSBF1 transcripts are cotyledon-specific and accumulate to the highest levels during late seedling development in a ligh-dependent manner. During the same time period, RbcS IV transcript levels decreased simultaneously, suggesting that GSBF1 acts as a developmental, stage-specific, negative regulator of RbcS IV gene expression in rape seedlings.

The response to auxin of rapeseed (Brassica napus L.) roots displaying reduced gravitropism due to transformation by Agrobacterium rhizogenes

It has recently been documented that, compared to untransformed controls, the roots of oilseed rape (Brassica napus L. CV CrGC5) seedlings transformed by Agrobacterium rhizogenes A4 show a reduced gravitropic reaction (Legue et al. 1994, Physiol Plant 91: 559-566). After stimulation at 90 degrees C or 135 degrees, the transformed root tips curve. but never reach a vertical orientation. In the present study, we investigated the causes of reduced gravitropic bending observed in stimulated transformed root tips. First, we localized the gravitropic curvature in normal and in transformed roots after 1.5 h of stimulation. The cells involved in root curvature (target cells) corresponded at the cellular level to the apical part of the zone of increasing cell length. In transformed roots grown in the vertical position, these cells showed a reduction in cell length compared to controls. Because auxin is considered to be the gravitropic mediator, the response of normal and transformed roots to exogenous auxin was studied. Indole-3-acetic acid (IAA) was applied along the first 3 mm using resin beads loaded with the hormone. In comparison to normal roots, transformed roots showed reduced bending toward the bead at all points of bead application. Moreover, the cells which responded to IAA corresponded to the target cells involved in the gravitropic reaction. The level of endogenous IAA was lower in transformed roots. Thus, it was concluded that the modified behavior of transformed roots during gravitropic stimulation could be due to differences either in IAA levels or in reactivity of the target cells to the message from the cap.

The behaviour of normal and agravitropic transgenic roots of rapeseed (Brassica napus L.) under microgravity conditions

In the TRANSFORM experiment for IML-2 on the Space Shuttle Columbia, normal (wild type = WT) and genetically transformed agravitropic rapeseed roots were tested under microgravity conditions. The aim of the experiment was to determine if the wild-type roots behaved differently (growth, morphology, gravitropical sensitivity) from the transgenic roots. The appearance of the organelles and distribution of statoliths (i.e. amyloplasts with starch grains) in the gravitropic reactive cells (statocytes) under weightlessness was compared for the two types of roots. Attempts have also been made to regenerate new plants from the root material tested in space. Both the WT and the transgenic root types showed the expected increase in length during 36 h of photorecording. Contrary to the results of the ground controls, no significant difference in elongation rates was found between the WT and transgenic roots grown in orbit. However, there are indications that the total growth both in the WT and the transgenic roots was higher in the ground control than for roots in orbit. After a 60 min 1 x g stimulation of the roots on board the Shuttle, no detectable curvatures were obtained in either the transgenic or the WT roots. However, it cannot be excluded that a minute curvature development occurs in the root tips but was not detected due to technical reasons. The ultrastructure was well preserved in both the WT and the transgenic roots, despite the fact that the tissue was kept in the prefixative for over 3 weeks. No marked differences in ultrastructure were observed between the transformed root statocyte cells and the equivalent cells in the wild type. There were no obvious differences in root morphology during the orbital period. Light micrographs and morphometrical analysis indicate that the amyloplasts of both the wild type and transformed root statocytes are randomly distributed over the cells kept under micro-g conditions for 37 h after a 14 h stimulation on the 1 x g centrifuge. The main scientific conclusion from the TRANSFORM experiment is that the difference in growth found in the ground control between the WT and the transgenic root types seems to be eliminated under weightlessness. Explanations for this behaviour cannot be found in the root ultrastructure or in root morphology.

A gene for Brassica napus extensin is differentially expressed on wounding

We have analysed the expression of the endogenous extensin genes in Brassica napus, using northern hybridisation and dot blotting. In the unstressed plant, the extA gene is only expressed in the root, expression in the leaf, petiole and stem being absent. We have found that wounding dramatically alters this normal pattern of expression. Expression in wounded leaf is seen after 36 h, in wounded petioles after 11 h and in wounded stem after 17 h. Differences in the amount of extensin mRNA accumulated are also seen: wounded petiole accumulating extensin message to a level higher than the leaf or the stem. Inhibitors of ethylene biosynthesis greatly delay the onset of accumulation of extensin mRNA in wounded tissues. Wounding the root causes the level of extensin message to decline with time, until levels below the limit of non-specific hybridisation are reached 11 h after wounding. Thus, application of the wounding stimulus results in the accumulation of extensin gene transcripts to different degrees and at different times in the aerial parts of the plant, and results in a decline in the same transcripts in the roots. Extensin transcript accumulation as a result of wounding is also dependent on the age of the tissue; high levels of message are seen in old wounded leaves, while expression in young wounded leaves is absent.

Leaf senescence in Brassica napus: expression of genes encoding pathogenesis-related proteins

Genes that are expressed during leaf senescence in Brassica napus were identified by the isolation of representative cDNA clones. DNA sequence and deduced protein sequence from two senescence-related cDNAs, LSC94 and LSC222, representing genes that are expressed early in leaf senescence before any yellowing of the leaves is visible, showed similarities to genes for pathogenesis-related (PR) proteins: a PR-1a-like protein and a class IV chitinase, respectively. The LSC94 and LSC222 genes showed differential regulation with respect to each other; an increase in expression was detected at different times during development of healthy leaves. Expression of both genes was induced by salicylic acid treatment. These findings suggest that some PR genes, as well as being induced by pathogen infection, may have alternative functions during plant development, for example in the process of leaf senescence.

Photoinduced effects of polycyclic aromatic hydrocarbons on Brassica napus (Canola) during germination and early seedling development

It has recently been demonstrated that light dramatically enhances the toxicity of polycyclic aromatic hydrocarbons (PAHs) to the duckweed Lemna gibba L. G-3 (L. Ren, X.-D. Huang, B.J. McConkey, D.G. Dixon, and B.M. Greenberg, 1994, Ecotoxicol. Environ. Saf. 28, 160-171). To extend this research to terrestrial plants, Brassica napus L. (oil seed rape) seeds were germinated in the presence of three PAHs; anthracene (ANT), benzo[a]pyrene (BAP), and fluoranthene. The chemicals were applied both in intact form and following photomodification in UV-B radiation; toxicity was assessed in simulated solar radiation (SSR), a light source with a visible light:UV-A:UV-B ratio similar to that of sunlight. Germination efficiency, root and shoot growth, and chlorophyll content, measured after 6 days of exposure, were used as toxicity endpoints. Intact and photomodified PAHs had little impact on shoot fresh weight or chlorophyll content, but markedly inhibited root fresh weight, with the photomodified PAHs having greater impacts than the intact PAHs. The decline in root fresh weight was not attributable to a decline in germination frequency or delayed germination. However, the seedlings produced shorter roots in the presence of either intact or photomodified PAHs. To explore the role of actinic radiation on PAH toxicity, seedlings were incubated in SSR, visible light and darkness with either intact or photomodified PAHs. Inhibition of root growth was only achieved by the intact chemicals if actinic radiation was present. However, with photomodified ANT or photomodified BAP, root fresh weight accumulation was inhibited in SSR, visible light and darkness. Thus, intact PAHs are hazardous to terrestrial plants in the presence of light, but once the compounds are photomodified, actinic radiation is no longer an absolute requirement for phytotoxic activity.

Comparative mapping in Arabidopsis and Brassica, fine scale genome collinearity and congruence of genes controlling flowering time

The model dicotyledonous plant, Arabidopsis thaliana, is closely related to Brassica crop species. It is intended that information concerning the genetic control of basic biological processes in Arabidopsis will be transferable to other species. Genome collinearity and its potential to facilitate the identification of candidate genes in Arabidopsis homologous to genes controlling important agronomic traits in Brassica was investigated. Genetic mapping in B. nigra identified two loci influencing flowering time (FT), with loci on linkage groups 2 and 8 explaining 53% and 12% of the total variation in FT, respectively. The CO gene exerts an important control over FT in A. thaliana, and B. nigra homologues of CO probably also play an important role in regulating FT. B. nigra homologues of CO were identified on linkage groups 2 and 8, the homologue on group 2 was coincident with the major locus controlling FT while the homologue on group 8 was within the 90% confidence interval of the weaker FT gene. The CO homologue on group 2 exhibits abundant allelic variation suggesting that it naturally controls a wide range of flowering times. Fine-scale A. thaliana/B. nigra comparative mapping demonstrated short-range collinearity between the genomes of Arabidopsis and Brassica. Eleven DNA fragments spaced over a 1.5 Mb contig in A. thaliana were used as RFLP probes in B. nigra. Three collinear representations of the A. thaliana contig were identified in B. nigra, with one interrupted by a large chromosomal inversion. Collinearity over this range will allow the resources generated by the Arabidopsis genome project to facilitate map-based cloning in Brassica crops.