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Ozone enhances the infection of peach leaves by the rust fungus Tranzschelia pruni-spinosae
No full textAn open-top chamber experiment was performed which highlighted the interactive effect of ozone (O-3) on the diffusion and incidence of the peach rust parasite. Such effect was linearly related to the O-3 cumulative dose received by the exposure variants, while the best fit with the daily 8-h O-3 average concentration was found to be multiplicative. Filtering ambient air reduces in a dramatic way (more than 50%) the rust severity. Stomatal conductance was neither correlated to O-3 levels nor to rust infection. The possible mechanisms involved in the above interaction are discussed herein
Cadmium exposure affects iron acquisition in barley (Hordeum vulgare) seedlings
No full textThis study addresses the question of the interference between Fe nutrition and Cd toxicity at the level
of growth performance, phytosiderophores (PS) release, micronutrient accumulation and expression
of genes involved in Fe homeostasis in barley seedlings, a plant with Strategy II-based response to Fe
shortage. Cd exposure induced responses similar to those of genuine Fe deficiency also in Fesufficient
plants. Most genes involved in PS biosynthesis and secretion (HvNAS3, HvNAS4, HvNAS6,
HvNAS7, HvNAAT-A, HvDMAS1 and HvTOM1) induced by Fe deprivation were also significantly upregulated
in presence of Cd under Fe sufficient conditions. Accordingly, the enhanced expression of
these genes in roots under Cd exposure was accompanied by an increase of PS release. However,
induced expression of HvIRO2 and the down-regulation of HvIDEF1 and HvIRT1, after Cd exposure,
suggested the presence of a pathway that induces HvIRO2-mediated PS biosynthesis under Cd stress,
which probably is not simply caused by Fe deficiency. The down-regulation of HvIRT1 and
HvNramp5 may represent a protective mechanism at transcriptional level against further Cd uptake by
these transporters. These results likely indicate that Cd itself may be able to activate Fe acquisition
mechanism in an Fe-independent manner
Ozone induces a differential accumulation of phenyalanine ammonia-lyase, chalcone synthase and chalcone isomerase RNA transcripts in sensitive and resistant bean cultivars
No full textOn exposure to a realistic ozone dose, an enhanced mRNA accumulation for phenyalanine ammonia-lyase (EC 4.3.1.5), naringenin-chalcone synthase [malonyl-CoA:4-coumaroyl-CoA malonyltransferase (cyclising); EC 2.3.1.74] and chalcone isomerase [flavanone lyase (decyclising); EC 5.5.1.6] genes, whose products are involved in the biosynthesis of phenylpropanoid molecules, flavonoid pigments and isoflavonoid phytoalexins, was observed in primary leaves of the bean (Phaseolus vulgaris L.) cv. Pinto. This cultivar was previously known to be ozone-sensitive on the basis of the appearance of macroscopic foliar injury, but not in coeval leaves of the bean cv. Groffy, known to be ozone-resistant on the basis of the aforementioned criterion. Distinct time patterns were observed in Pinto leaves for the ozone-dependent enhanced mRNA accumulation for the aforementioned genes, which in all cases largely preceded the appearance of visible injury symptoms. These results lend support to the view of ozone as an abiotic elicitor of plant defence responses. By analogy with other case studies, it is also suggested that proneness to develop visible ozone symptoms might rest on a sequence of molecular events similar to that leading to the hypersensitive response during plant-pathogen incompatible interactions
Transcriptional and physiological changes in the S assimilation pathway due to single or combined S and Fe deprivation in durum wheat (Triticum durum L.) seedlings
Full text linkThe effect of iron (Fe) and sulphur (S) deprivation on sulphate uptake and assimilation pathways was investigated in durum wheat by analysing the expression of genes coding for major transporters and enzymes involved in sulphate assimilation and reduction: high-affinity sulphate transporters (TdSultr1.1 and TdSultr1.3), ATP sulphurylase (TdATPSul1 and TdATPSul2), APS reductase (TdAPR), sulphite reductase (TdSiR), O-acetylserine(thiol)lyase (TdOASTL1 and TdOASTL2), and serine acetyltransferase (TdSAT1 and TdSAT2). Further experiments were carried out to detect changes in the activities of these enzymes, together with the evaluation of growth parameters (fresh biomass accumulation, leaf green values, and total S, thiol, and Fe concentrations). Fe shortage in wheat plants under adequate S nutrition resulted in an S deficiency-like response. Most of the genes of the S assimilatory pathway induced by S deprivation (TdATPSul1, TdAPR, TdSir, TdSAT1, and TdSAT2) were also significantly up-regulated after the imposition of the Fe limitation under S-sufficient conditions. However, the differential expression of genes encoding the two high-affinity transporters (TdSultr1.1 and TdSultr1.3) indicates that the mechanisms of sulphate uptake regulation under Fe and S deficiency are different in wheat. Moreover, it was observed that the mRNA level of genes encoding ATPS, APR, and OASTL and the corresponding enzyme activities were often uncoupled in response to Fe and S availability, indicating that most probably their regulation involves a complex interplay of transcriptional, translational, and/or post-translational mechanisms induced by S and/or Fe deficiency
Cloning and characterization of three homoeologous wheat PDI-like genes located on group 5 chromosomes
No full textPDI and PDI-like proteins are responsible for multiple metabolic functions, including secretory protein folding, chaperone activity and redox signalling. In plants the proteins of the PDI family cluster into eight phylogenetic classes, five of them include proteins with two thioredoxin (TRX)-like active domains, whereas the other three classes own a single TRX-like domain. The first class includes the typical PDI, which in cereals may be involved in the folding of secretory proteins during the formation of endosperm protein bodies. The three homoeologous genes coding for the typical PDI and their promoter sequences had previously been isolated and characterized. Their exon/intron structure is highly conserved and includes 10 exons. Recently we reported the characterization of the whole set of nine non-homoeologous PDI-like gene sequences of wheat; since phylogenetic analysis assigned them to the eight plant subfamilies, at least one wheat gene has been cloned for each group. In this study we report the characterisation of the genomic and cDNA sequences of three homoeologous PDI-like genes (TaPDIL5-1A, TaPDIL5-1B and TaPDIL5-1D) of the V phylogenetic group and located in chromosome arms 5AL, 5BL and 5DL of hexaploid wheat. The coding region and the exon/intron structure, consisting of nine exons, of their genomic sequences were highly conserved. The most relevant differences were detected in the length of the second (1393 bp in TaPDIL5-1B, 1076bp in TaPDIL5-1A and 1026 bp in TaPDIL5-1D) and fifth (967 bp in TaPDIL5-1D, 723 bp in both TaPDIL5-1A and TaPDIL5-1B) introns. Their ORFs consisted of 1323 bp, corresponding to polypeptides of 440 aa, with an estimated Mw of 47.2 KDa and pI of 5.3. The three encoded proteins possessed two tandem TRX active domains (a°-a), each containing the typical tetra-peptide site -CGHC-, an inactive TRX b domain at its C-terminus, the signal peptide and a modified NDEL signal for retention in the ER. The comparison of the wheat sequences with the PDI-like genes of the V phylogenetic group from Ararabidopsis, rice and the moss Physcomitrella patens revealed a high level of conservation of their structural features, in terms of intron pattern and exon number, size and position of the active sites. The promoter sequence of the PDI-like gene located in 5A chromosome of bread wheat cv Chinese Spring was cloned using the inverse PCR (IPCR) tecnique. The sequence analysis showed that the fragment cloned by IPCR included about 1400 bp located upstream of the coding sequence. The promoter sequences of the PDI-like genes located in 5B and 5D chromosomes of C. Spring were cloned through PCR amplification using two primer pairs. One of the primers, the same for both pairs, was designed on the basis of a sequence in the distal region of the previously cloned promoter of the 5A chromosome, whereas the second specific primer of each pair was chosen within regions of the
second intron. The search of cis-acting regulatory elements within the promoters of the three genes was performed using the databases of plant promoters PlantCARE and PLACE and the differences between the three sequences will be discussed. Finally, transgenic durum wheat lines (cv Svevo) over-expressing the gene located in 5A chromosome, which was put under the control of the ubiquitin promoter of maize, were produced for the functional characterization of this gene. PCR analyses of 40 plants regenerated from 800 bombarded embryos showed that 5 of them were transgenic for the PDI over-expression construct
Fluctuations in Fe availability are translated into modulation of plant sulfate metabolism at both transcriptional and physiological level in durum wheat
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