N-terminal domain including conserved flg22 is required for flagellin-induced hypersensitive cell death in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Flagellin in Pseudomonas syringae is a potent elicitor of defense responses including hypersensitive cell death in dicot plants. The oligopeptides flg22 consisting of 22 conserved amino acids near the N-terminus of flagellins is reported to induce plant defense responses. Because glycosylation of the central domain of flagellin affects its elicitor activity, we investigated whether any peptide sequence in addition to flg22 is required for flagellin-induced hypersensitive reaction. A study of recombinant flagellin polypeptides indicated that the N-terminal domain including the conserved flg22 is required for flagellin-induced hypersensitive cell death in Arabidopsis thaliana.     

AlgU contributes to the virulence of <Emphasis Type="Italic">Pseudomonas syringae</Emphasis> pv. <Emphasis Type="Italic">tomato</Emphasis> DC3000 by regulating production of the phytotoxin coronatine

Pseudomonas syringae pv. tomato DC3000 (Pst DC3000), which causes bacterial speck disease of tomato, has been used as a model pathogen to investigate the molecular basis of plant–pathogen interactions. The function of many potential virulence factors encoded in the Pst DC3000 genome and their modes of action are not fully understood. P. syringae is known to produce the exopolysaccharide alginate. Although AlgU, a sigma factor, is known to regulate the expression of genes such as algD related to alginate biosynthesis, the molecular mechanisms of AlgU in the virulence of Pst DC3000 is still unclear. To investigate the function of AlgU and alginate in plant–bacterial pathogen interactions, we generated ΔalgU and ΔalgD mutants. After inoculation with ΔalgU but not ΔalgD, host plants of Pst DC3000 including tomato and Arabidopsis had milder disease symptoms and reduced bacterial populations. Expression profiles of Pst DC3000 genes revealed that AlgU can regulate not only the expression of genes encoding alginate biosynthesis, but also the expression of genes related to type III effectors and the phytotoxin coronatine (COR). We also demonstrated that the ΔalgU mutant showed full virulence in the Arabidopsis fls2 efr1 double mutant, which is compromised in the recognition of PAMPs. Further, the application of COR was able to restore the phenotype of the ΔalgU mutant in the stomatal response. These results suggest that AlgU has an important role in the virulence of Pst DC3000 by regulating COR production.     

Acibenzolar-S-methyl efficacy against bacterial brown stripe caused by Acidovorax avenae subsp. avenae in creeping bentgrass

Journal of General Plant Pathology - Bacterial brown stripe caused by Acidovorax avenae subsp. avenae (Aaa) causes serious damage on creeping bentgrass on golf course greens. However, there are few...     

Defense responses of Arabidopsis thaliana inoculated with Pseudomonas syringae pv. tabaci wild type and defective mutants for flagellin (ΔfliC) and flagellin-glycosylation (Δorf1)

Flagellin, an essential component of the bacterial flagellar filament, is capable of inducing a hypersensitive response (HR), including cell death, in a nonhost plant. A flagellin-defective mutant (ΔfliC) of Pseudomonas syringae pv. tabaci lacks both the flagellar filament and motility, whereas a flagellin-glycosylation-defective mutant (Δorf1) retains the flagellar filament but lacks the glycosyl modification of flagellin protein. To investigate the role of flagellin protein and its glycosylation in the interaction with its nonhost Arabidopsis thaliana, we analyzed plant responses after inoculation with these bacteria. Inoculation with wild-type P. syringae pv. tabaci induced HR, with the generation of reactive oxygen species and cell death. In contrast, inoculation with either ΔfliC or Δorf1 mutant induced a low level of HR, and inoculated leaves developed a disease-like yellowing. These mutant bacteria multiplied better than the wild-type bacteria in A. thaliana. These results indicate that A. thaliana expresses a defense reaction in response to the bacterial flagellin with its glycosyl structure.     

Bacterial DNA activates immunity in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

To initiate defense responses against invasion of pathogenic organisms, animals and plants must recognize microbe-associated molecular patterns (MAMPs). In this study, the elicitor activity of bacterial DNA on the model plant Arabidopsis thaliana was examined. EcoRI-digested plasmid DNA induced defense responses such as generation of reactive oxygen species and deposition of callose, whereas SmaI- and HapII-digested plasmid DNA and EcoRI-digested herring DNA did not remarkably induce these responses. Further, methylation of the CpG sequence of plasmid DNA and Escherichia coli DNA reduced the level of the defense responses. The endocytosis inhibitors wortmannin and amantadine significantly inhibited DNA-induced defense responses. These results suggest that non-methylated CpG DNA, as a MAMP, induced defense responses in Arabidopsis and that non-methylated DNA seems to be translocated into the cytoplasm by endocytosis.     

Geochemistry of sediments in three sectors of Trincomalee Bay,Sri Lanka: provenance,modifying factors and present environmental status

Purpose

The geochemical compositions of sediments from three sectors in Trincomalee Bay (Koddiyar Bay, Thambalagam Bay and the Inner Harbour) in Sri Lanka were examined to determine fluvial and marine contributions and the effects of sorting and heavy mineral concentration. The present environmental status of the bay was also assessed.

Materials and methods

Forty-nine sediment samples were collected from Trincomalee Bay and analysed by X-ray fluorescence, yielding data for the major elements and 17 trace elements. Mean grain size and sorting were also measured. Data were compared with the compositions of sediments from the lower Mahaweli River, which supplies most of the clastic detritus to Trincomalee Bay.

Results and discussion

Sediments in the three sectors differ significantly in chemical composition, according to position relative to the Mahaweli River delta source, depositional environment, heavy mineral concentration and marine influences. According to accepted sediment quality guidelines, some As contamination may have occurred in the Inner Harbour and Thambalagam Bay and Cr contamination in all three sectors.

Conclusions

Proximal Koddiyar Bay sediments compare closely with Mahaweli River bedload. Although the clastic component in the more distal Thambalagam Bay and the Inner Harbour is also derived from the Mahaweli River, compositions are modified significantly by marine contributions. High concentrations of elements including Ti, Zr, Ce, Nb and Y in NW Koddiyar Bay are consistent with heavy mineral concentration by winnowing in high-energy zones. Some decoupling of Fe–Ti- and Zr-bearing heavy mineral assemblages may occur within the bay. Al-normalized metal enrichment factors and contour maps show that apparent contamination by As and Cr is spurious and is caused by locally high background levels from Mahaweli River detritus. This illustrates the importance of establishing local background levels of elements during environmental studies.     

Arsenic extractability with phosphate and citrate from peat collected in Bangladesh

Abstract

Arsenic extractability with various solutions from peat samples collected in Deuli Village, Bangladesh, was investigated to reveal the leaching mechanisms of arsenic in sediments to groundwater. Peat layer was distributed at the depth of 7–8 m in the sediments, and the peat samples collected and used in this experiment contained 137 mg kg^?1 arsenic. A wide range of pH values and concentrations of phosphoric acid and trisodium citrate was used for the extracting solutions. Arsenic extractability with Hel (25–1,000 mM) or NaOH (20–500 mM) at different pH values ranged for 30 to 60% in strong acid or alkali, while was less than 0.1% in the neutral pH range against the total content. Extraction of arsenic with 100 mM phosphoric acid and 100 mM trisodium citrate was about 20% even at a neutral pH, while the extractability with these solutions at concentrations below 1 mM was similar to that with distilled water. These results suggest that competitive exchange and / or chelating action are / is the prior possible mechanism for arsenic leaching from peat. However, the experimental conditions such as pH value or phosphate anion concentration differed from those in the study area where the pH of groundwater was almost neutral and the phosphate anion concentration was only 0.01 mM. Moreover, since the experiment was conducted using a batch system under oxidative conditions and not using a continuous flow system, the importance of the oxidation-reduction potential in the sediments and organic matter content in the groundwater should be investigated.