In the present study, a minicolumn of sisal fiber loaded with alizarin fluorine blue is proposed as a preconcentration system for copper determination in tobacco leaf samples by flame atomic absorption spectrometry. During the optimization procedure, a two level full factorial design (2(4)) was used at the preliminary evaluation of four factors, involving the following variables: sampling flow rate, elution flow rate, buffer concentration and pH. Regarding the studied levels, this design has shown that buffer concentration and pH were significant factors. The experimental conditions established in the optimization step were: pH=4.75, buffer concentration of 0.005 mol L(-1) for elution with HCl 1.0 mol L(-1) this system allows the determination of copper content with a detection limit (LD) of 0.018 μg L(-1) and a quantification limit (LQ) of 0.061 μg L(-1) precision expressed as relative standard deviation (R.S.D.) of 4.65 and 5.07%, utilizing concentration of 10 and 2.0 μg L(-1), respectively, and a preconcentration factor of 75, for a sample volume of 50.0 mL. Accuracy was confirmed by copper determination in the standard reference material, NIST SRM 1570 a trace element units in Spinach Leaves and by spike tests with recovery levels ranging from 93 to 100%; the procedure was applied for copper determination in tobacco leaf samples collected in Cruz das Almas City, Bahia, Brazil. The achieved concentrations of the three samples analyzed varied from 0.15 to 0.52 μg g(-1).
Context An obligate biotrophic parasitism with a rust fungus led to gall formation on Byrsonima variabilis. Aims The hypothesis that the host leaf–rust fungi interaction alters the dynamics of plant cell walls and the histochemical profile toward favouring the plant cell-to-fungi cell translocation of metabolites is tested. Methods Gall samples were sectioned and submitted to anatomical, histometric, histochemical, and immunocytochemical techniques to evaluate structural alterations and the detection of primary and secondary metabolites, as well as the epitopes of glycoproteins, pectins, and hemicelluloses. Key results Fungi gall development results in the hypertrophy of the stomatal chamber and the hyperplasia of epidermis and spongy parenchyma. The cell-to-cell translocation of metabolites from plant mesophyll cells toward the rust fungi gall is favoured by the epitopes of homogalacturonans (HGs) and (1 → 5) α-l-arabinans detected in the hyphae passage sites in the pycnial and aecial stages. The arabinogalactan-proteins (AGPs) may favour mycelial nutrition and differentiation, and cell wall adhesion. HGs and arabinans confer porosity to mesophyll cell walls, which favours the traffic of molecules toward the rust fungi gall. Conclusions The unexpected labelling of AGPs, HGs, and arabinans in fungi cell walls is a novelty regarding the plant–fungi interaction. The primary metabolites detected in rust fungi support hyphae growth and spore maturation. Implications The immunolabelling of host plant cell wall components on fungi cell walls indicates the integrative role of some plant cell wall components in the biological process of pathogen colonisation in leaf tissues.
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