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Malate, oxalate and mustard oils were analysed in zinc‐resistant and zinc‐sensitive ecotypes of Silene cucubalus Wib., Rumex acetosa L., Thlaspi alpestre L. and Agrostis tenuis Sibth. The effect of zinc on the activities of carbonic anhydrase and peroxidase in Siiene cucubalus was tested. Carbonic anhydrase of the zinc‐resistant ecotypes was stimulated by addition in vivo of high amounts of zinc. The high activity of peroxidase in the non‐zinc‐resistant ecotypes after the addition of zinc documented a poisoning of the sensitive plants by zinc. The amount of oxalate differed greatly between ecotypes. There was, however, no direct correlation between zinc‐resistance and oxalate. When applying zinc to the nutrient medium, the synthesis of oxalate was inhibited in zinc‐sensitive, but stimulated in zinc‐resistant ecotypes of Silene cucubalus and Rumex acetosa. In Thlaspi alpestre high concentrations of mustard oil glucosides were found. Zinc‐resistant plants produced twice as much glucosides as sensitive ones. A possible role of mustard oils in zinc‐resistance is discussed. In the content of malate there were great quantitative differences between zinc‐resistant and zinc‐sensitive plants. All zinc‐resistant ecotypes of all the species contained much higher concentrations in their green organs than the sensitive ones. It is assumed that malate is a major factor in the evolution of zinc‐resistance. Malate may act as a complexing agent for zinc within the plasma, whereas oxalate and mustard oils may function as “terminal acceptors” of large amounts of zinc. The role of malate may be extended by a special transport mechanism, by which zinc is eliminated from the plasma into the vacuole.

The in Ditro and in vivo effects of copper, zinc, cadmium, nickel, cobalt, and manganese on nitrate reductase, malate dehydrogenase, isocitrate dehydrogenase, and glucose-6-phospbate dehydrogenase of zinc-, copper-and non-resistant populations of Silene cucubalus were investigated. During the in vitro experiments no resistant enzyme could be detected; enzymes of resistant and non-resistant ecotypes had a similar sensibility to al! the metals. Nitrate reductase was the most sensitive enzyme. During the in vivo experiments remarkable differences were found. Tbe nitrate reductase and the isocitrate dehydrogenase of the zinc-resistant population were activated when adding zinc to the culture medium, especially the nitrate reductase showed high activities at zinc concentrations where the nitrate reductase of the non-zinc-resistant populations was nearly completely inhibited. Tbe zinc-resistant ecotype bad a real need for zinc.

Cyanobacteria are pathogenic prokaryotes and known for producing a high variety of cyclic hepatotoxic peptides in fresh and brackish water. Prominent members of these toxins are microcystin LR (MC LR) and nodularin (Nod), which are under suspicion to cause cancer. Various analytical methods have been reported for the detection of these cyclopeptides, and these are mainly based on liquid chromatography combined with mass spectrometric techniques. Here, we introduce a new approach based on the direct coupling of high-performance thin-layer chromatography (HPTLC) with infrared matrix-assisted laser desorption/ionization orthogonal time-of-flight mass spectrometry (IR-MALDI-o-TOF MS) using the liquid matrix glycerol. The analysis of the cyclopeptides involves the application of three complementary methods: (i) HPTLC separation of MC LR and Nod, (ii) their detection and quantification by UV spectroscopy at lambda = 232 nm, and (iii) direct identification of separated analytes on the HPTLC plate by IR-MALDI-o-TOF MS. Calibration curves exhibited a linear relationship of amount of analyte applied for HPTLC and UV absorption (R(2) > 0.99). The limits of detection were 5 ng for UV spectroscopy and 3 ng for mass spectrometric analysis of individual peptides. This novel protocol greatly improves the sensitive determination of toxins from pathogenic cyanobacteria in complex water samples. It was successfully applied to the detection and quantification of MC LR and Nod in a spiked, processed environmental water sample.

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