Multivariate patterns of antioxidative and photoprotective defence compounds in spruce needles at two central European forest sites of different elevation.

In this work we measured a set of antioxidative and photoprotective compounds (chlorophylls, carotenoids, tocopherol, ascorbate and glutathione), which were suggested previously as stress markers in conifer needles, at two spruce forest sites at different elevation in Saxony, Germany. Most variables differed significantly between current and 1-year-old needles, but only the content of the xanthophyll cycle per mg total chlorophyll and the oxidation state of glutathione were significantly different between the sites. We applied principal component analysis (PCA) to address the question if underlying accumulated variables are similar to the ones found in spruce needles across Alpine elevation profiles and/or for pines in Mediterranean ecosystems. Four principal components (accumulated variables, PC) representing 68% of the total variance of the dataset were extracted. PC 1 encompassed total chlorophyll, lutein, and beta-carotene contents, PC 2 combined the epoxidation state of xanthophylls, ascorbate content and redox state, and glutathione content, PC 3 represented the content of xanthophylls and the redox state of glutathione, and PC 4 encompassed the content of alpha-carotene and the epoxidation state of xanthophylls. Only PC 3 was significantly different between sites. The PCA structure shows many similarities to corresponding findings in studies on spruce in mountain forests in the Alps and pines in Mediterranean systems. This corroborates the interpretation of PCs as indicative for underlying physiological processes. However, separation of the two investigated sites by PCs was in the present case study not superior to the separation by single input variables.

A new attempt to study biomineralised silica bodies in Dactylis glomerata L.

The accumulation process of inorganic compounds in animals and plants by biomineralisation is not well understood nowadays, though it may be the key to an environmental-compatible production of modern materials in future. In this paper a new attempt will be made on the investigation of silica accumulation in grasses (especially Dactylis glomerata L.). The silicic acid agglomerates in Dactylis glomerata L. were studied by means of scanning electron microscopy in combination with energy dispersive X-ray spectrometry as well as infrared and micro-RAMAN spectrometry.In particular blades were prepared by critical point drying or shock-freezing for anatomical studies of silica cells and bristles in the plant tissue. SEM imaging and EDX microanalysis for elemental composition were done in the cryostage as well as under variable pressure. The localized silica bodies were examined for their structural properties by means of IR and micro RAMAN spectroscopy. The results are comparable to SiO(2) polytypes such as high disperse silica and opal.

Silica accumulation in Triticum aestivum L. and Dactylis glomerata L.

The silica accumulation in orchard grass (Dactylis glomerata L.) and wheat (Triticum aestivum L.) has been studied in plant samples grown under defined conditions in a pot trial. The plant habit and the quantity of biomineralised silica within the selected Gramineae depend to a remarkable extent on the soil. The plants grew with different soil pH values and silica additives. By means of atomic absorption spectrometry, the silicon enrichment in different plant parts was determined. In dried plant parts the silica bodies can be well distinguished by variable pressure scanning electron microscopy in the back scattering mode. They are located in silica cells below the epidermis and in epidermal appendices (bristles, prickle hairs). The silica bodies showed a defined morphology, structure and composition which was elucidated by the combined performance of scanning electron microscopy in combination with X-ray spectroscopy, solid-state nuclear resonance, X-ray diffraction and Raman spectroscopy. The composition was near to stoichiometric SiO(2) (41 weight% silicon, 56 weight % oxygen), and the SiO(4/2)tetrahedra were arranged preferentially in three-dimensional networks; a smaller proportion was in chains and layers. The silica bodies with an overall amorphous structure contained crystalline precipitates, which could be indexed by alpha-quartz.