Raymond Yang

Adaptation of Arabidopsis to nitrogen limitation involves induction of anthocyanin synthesis which is controlled by the NLA gene

Plants can survive a limiting nitrogen (N) supply by developing a set of N limitation adaptive responses. However, the Arabidopsis nla (nitrogen limitation adaptation) mutant fails to produce such responses, and cannot adapt to N limitation. In this study, the nla mutant was utilized to understand further the effect of NLA on Arabidopsis adaptation to N limitation. Grown with limiting N, the nla mutant could not accumulate anthocyanins and instead produced an N limitation-induced early senescence phenotype. In contrast, when supplied with limiting N and limiting phosphorus (Pi), the nla mutants accumulated abundant anthocyanins and did not show the N limitation-induced early senescence phenotype. These results support the hypothesis that Arabidopsis has a specific pathway to control N limitation-induced anthocyanin synthesis, and the nla mutation disrupts this pathway. However, the nla mutation does not affect the Pi limitation-induced anthocyanin synthesis pathway. Therefore, Pi limitation induced the nla mutant to accumulate anthocyanins under N limitation and allowed this mutant to adapt to N limitation. Under N limitation, the nla mutant had a significantly down-regulated expression of many genes functioning in anthocyanin synthesis, and an enhanced expression of genes involved in lignin production. Correspondingly, the nla mutant grown with limiting N showed a significantly lower production of anthocyanins (particularly cyanidins) and an increase in lignin contents compared with wild-type plants. These data suggest that NLA controls Arabidopsis adaptability to N limitation by channelling the phenylpropanoid metabolic flux to the induced anthocyanin synthesis, which is important for Arabidopsis to adapt to N limitation.

Isolation of deoxynivalenol-transforming bacteria from the chicken intestines using the approach of PCR-DGGE guided microbial selection.

BackgroundContamination of grains with trichothecene mycotoxins, especially deoxynivalenol (DON), has been an ongoing problem for Canada and many other countries. Mycotoxin contamination creates food safety risks, reduces grain market values, threatens livestock industries, and limits agricultural produce exports. DON is a secondary metabolite produced by some Fusarium species of fungi. To date, there is a lack of effective and economical methods to significantly reduce the levels of trichothecene mycotoxins in food and feed, including the efforts to breed Fusarium pathogen-resistant crops and chemical/physical treatments to remove the mycotoxins. Biological approaches, such as the use of microorganisms to convert the toxins to non- or less toxic compounds, have become a preferred choice recently due to their high specificity, efficacy, and environmental soundness. However, such approaches are often limited by the availability of microbial agents with the ability to detoxify the mycotoxins. In the present study, an approach with PCR-DGGE guided microbial selection was developed and used to isolate DON -transforming bacteria from chicken intestines, which resulted in the successful isolation of several bacterial isolates that demonstrated the function to transform DON to its de-epoxy form, deepoxy-4-deoxynivalenol (DOM-1), a product much less toxic than DON.ResultsThe use of conventional microbiological selection strategies guided by PCR-DGGE (denaturing gradient gel electrophoresis) bacterial profiles for isolating DON-transforming bacteria has significantly increased the efficiency of the bacterial selection. Ten isolates were identified and isolated from chicken intestines. They were all able to transform DON to DOM-1. Most isolates were potent in transforming DON and the activity was stable during subculturing. Sequence data of partial 16S rRNA genes indicate that the ten isolates belong to four different bacterial groups, Clostridiales, Anaerofilum, Collinsella, and Bacillus.ConclusionsThe approach with PCR-DGGE guided microbial selection was effective in isolating DON-transforming bacteria and the obtained bacterial isolates were able to transform DON.

An epimer of deoxynivalenol: purification and structure identification of 3-epi-deoxynivalenol

In an investigation of deoxynivalenol (DON)-transformation products by Devosia mutans 17-2-E-8, the major product was identified as 3-epi-DON. This DON-transformation product was analysed by liquid chromatography and identified by congruent retention time and UV/Vis spectrum, as well as mass spectrometric data. Nuclear magnetic resonance (NMR) experiments including correlation spectroscopy (COSY), heteronuclear single quantum coherence (HSQC) and nuclear overhauser effect (NOE) were conducted for structural characterisation of 3-epi-DON. High-speed counter-current chromatography (HSCCC) was applied to scale up the separation of 3-epi-DON from DON in a D. mutans 17-2-E-8 culture. From the culture where 100 mg DON was applied, 56 mg of 3-epi-DON (purity of 96.8%) was obtained from the HSCCC. The purified 3-epi-DON will be used for toxicological characterisation studies of this chemical.

In vitro antifungal activity and mode of action of selected polyphenolic antioxidants on Botrytis cinerea

Six selected antioxidants (catechin, quercetin-3-galactoside, cyanidin-3-glucoside, pelargonidin-3-glucoside, ellagic and gallic acids) were evaluated in vitro for their antifungal activities and mode of action on Botrytis cinerea Pers., one of the most important pathogens of strawberries. Inhibitory effects were found for all the tested antioxidants, but varied at different fungal developmental stages. Catechin and quercetin-3-galactoside showed linear inhibitory effects on germ tube elongation, with the highest suppression ratios of 54.8% and 58.8% respectively. No significant effect was found on spore germination between treatments and control. Gallic acid showed very strong and linear inhibition on spore germination (r = −0.95), but the effect diminished after spore germination. Cyanidin-3-glucoside and pelargonidin-3-glucoside provided effective control on the fungi as concentrations increased. The arresting effect of ellagic acid on development of B. cinerea was quadratic. Ellagic acid inhibited germ tube elongation and mycelial growth at its highest and lowest concentrations, while no effects were observed at its medium concentration used in this study.

Purification of patulin from Penicillium expansum culture: high-speed counter-current chromatography (HSCCC) versus preparative high-performance liquid chromatography (prep-HPLC).

Patulin is a mycotoxin produced by species of Penicillium and Aspergillus and is toxic to a wide range of organisms, including humans and livestock. To produce large amount of pure patulin for research purposes, high-speed counter-current chromatography (HSCCC) and preparative high-performance liquid chromatography (prep-HPLC) were applied to the purification of patulin. Apple juice was inoculated with P. expansum and containing 0.5 mg patulin per ml was used as a starting material for separation. For HSCCC, a biphasic solvent system consisted of ethyl acetate–hexane–pH 4 acetic acid (7.5:2.5:10, v/v/v) was used. For prep-HPLC, the separation was carried out in a C18 reversed-phase preparative column with a mobile phase containing acetonitrile–pH 4 acetic acid (5:95, v/v). Fractions containing patulin were collected and analysed by analytical HPLC and identified by congruent retention time and ultraviolet/visible (UV–VIS) spectrum of the standard. The structure of the purified patulin was confirmed by mass spectrometry and nuclear magnetic resonance. HSCCC produced 21.9 mg of patulin from 50 ml apple juice culture whereas the prep-HPLC yielded 18.1 mg. HSCCC also produced purer patulin than the prep-HPLC (98.6 versus 96.3%) and higher recovery (86.2 versus 71.3%). In addition, the HSCCC method is advantageous for its lower cost and a simpler procedure compared with the prep-HPLC. This one-step HSCCC method can potentially provide a simple, effective and environmentally friendly tool for obtaining gram-level pure patulin for toxicology, detoxification and many other patulin-related studies.