Brassica Napus Seedlings Research Articles

Iron triggers a rapid induction of ascorbate peroxidase gene expression in Brassica napus

In plants, only ferritin gene expression has been reported to be iron-dependent. Here it is demonstrated that an iron overload of Brassica napus seedlings causes a large and rapid accumulation of ascorbate peroxidase transcripts, a plant-specific hydrogen peroxide-scavenging enzyme. This result documents a novel link between iron metabolism and oxidative stress. The ascorbate peroxidase mRNA abundance was not modified by reducing agents like N-acetyl cysteine, glutathione and ascorbate or by pro-oxidants such as hydrogen peroxide or diamide. Furthermore, the iron-induced ascorbate peroxidase mRNA accumulation was not antagonized by N-acetyl cysteine. Abscisic acid had no effect on the ascorbate peroxidase gene expression. Taken together these results suggest that iron-mediated expression of ascorbate peroxidase gene occurs through a signal transduction pathway apparently different from those already described for plant genes responsive to oxidative stress.

Analysis of the native forms of the 90 kDa heat shock protein (hsp90) in plant cytosolic extracts.

A polyclonal antibody, R2, was raised against a fusion protein consisting of a portion of plant hsp90 fused to the trpE protein of Escherichia coli. This antibody was found to be specific towards plant hsp90, showing little or no cross-reactivity with mouse and human hsp90 proteins. The R2 antibody identified an 83 kDa protein as the hsp90 homologue in cytosolic extracts of several dicot and monocot plants. Two-dimensional gel electrophoresis indicated that at least two different isoforms of hsp90 are expressed in Brassica napus seedlings. An examination of the native state of hsp90 by non-denaturing gel electrophoresis showed that this protein exists as a monomer, dimer and as a high-molecular-mass complex of ca. 680 kDa in cell extracts of spinach cotyledons and leaves, B. napus seedlings and wheat germ. Native gel analysis and cross-linking studies of purified hsp90 showed that plant hsp90 exists predominantly as a monomer. When 35S-labelled B. napus cytosolic extracts were immunoprecipitated with the R2 antiserum, hsp90 and two additional proteins with approximate molecular masses of 49 and 45 kDa were detected in the immunoprecipitates. These results are consistent with the idea that hsp90:protein heterocomplexes exist in plant cells.

Response of oilseed Brassica cultivars to ozone

Cultivars of four oilseed Brassica species were exposed to acute levels of ozone (0.31 or 0.47 μL L−1) at the seedling stage. Brassica hitra ’BHL-926’ was the most sensitive to ozone followed by B. juncea ’Newton’ and B. rapa ’Torch.’ Brassica napus seedlings exhibited very little foliar injury (0 – 4%) after 24 h exposure to 0.31 μL L−1 ozone. Key words: Ozone, foliar injury, rapeseed, mustard

Hydrophilic Photosystem II Inhibitors: Cyanoacrylate Thiolate Salts

Cyanoacrylate thiolate salts such as the sodium salt of ethoxyethyl-3-p-chlorobenzylthio-2-cyano-3-mercapto acrylate have been shown to be relatively slow binding, potent inhibitors of photosynthetic electron transport, that are equally active against thylakoids isolated from atrazine-susceptible and atrazine-resistant Brassica napus seedlings. It has been suggested that their mode of binding involves the substituted benzyl group interacting with the membrane lipids and the thiolate ion interacting in the region of the histidine215 residue of the D1 peptide, close to the non-heme Fe centre. This, together with their slow rate of binding, has led to the thiolate salts being classified as phenol type inhibitors.

Spatial patterns of gene expression in Brassica napus seedlings: identification of a cortex-specific gene and localization of mRNAs encoding isocitrate lyase and a polypeptide homologous to proteinases.

We investigated the spatial expression of three genes that are expressed during seed germination and postgerminative development in Brassica napus L. using in situ hybridization procedures. Two of the mRNAs encode isocitrate lyase and a predicted polypeptide that is homologous to cysteine proteinases. We reported previously that the mRNAs are prevalent primarily in cotyledons of seedlings and accumulate with similar kinetics during postgerminative growth. Here, we show that the two mRNAs are detected in several seedling tissues, but they display different distribution patterns in both cotyledons and root-shoot axes. The third mRNA is abundant in seedling axes and accumulates specifically in the ground meristem and mature cortex of hypocotyls and roots. Distribution of the mRNA in root meristems suggests that the gene product participates in an early event in cortical cell differentiation. Our results provide insight into the physiological processes that characterize seedlings.

Spatial Patterns of Gene Expression in Brassica napus Seedlings: Identification of a Cortex-Specific Gene and Localization of mRNAs Encoding Isocitrate Lyase and a Polypeptide Homologous to Proteinases

Spatial Patterns of Gene Expression in Brassica napus Seedlings: Identification of a Cortex-Specific Gene and Localization of mRNAs Encoding Isocitrate Lyase and a Polypeptide Homologous to Proteinases