Glutathione is an important antioxidant and redox buffer in plants. It fulfills many important roles during plant development, defense and is essential for plant metabolism. Even though the compartment specific roles of glutathione during abiotic and biotic stress situations have been studied in detail there is still great lack of knowledge about subcellular glutathione concentrations within the different leaf areas at different stages of development. In this study a method is described that allows the calculation of compartment specific glutathione concentrations in all cell compartments simultaneously in one experiment by using quantitative immunogold electron microscopy combined with biochemical methods in different leaf areas of Arabidopsis thaliana Col-0 (center of the leaf, leaf apex, leaf base and leaf edge). The volume of subcellular compartments in the mesophyll of Arabidopsis was found to be similar to other plants. Vacuoles covered the largest volume within a mesophyll cell and increased with leaf age (up to 80% in the leaf apex of older leaves). Behind vacuoles, chloroplasts covered the second largest volume (up to 20% in the leaf edge of the younger leaves) followed by nuclei (up to 2.3% in the leaf edge of the younger leaves), mitochondria (up to 1.6% in the leaf apex of the younger leaves), and peroxisomes (up to 0.3% in the leaf apex of the younger leaves). These values together with volumes of the mesophyll determined by stereological methods from light and electron micrographs and global glutathione contents measured with biochemical methods enabled the determination of subcellular glutathione contents in mM. Even though biochemical investigations did not reveal differences in global glutathione contents, compartment specific differences could be observed in some cell compartments within the different leaf areas. Highest concentrations of glutathione were always found in mitochondria, where values in a range between 8.7mM (in the apex of younger leaves) and 15.1mM (in the apex of older leaves) were found. The second highest amount of glutathione was found in nuclei (between 5.5mM and 9.7mM in the base and the center of younger leaves, respectively) followed by peroxisomes (between 2.6mM in the edge of younger leaves and 4.8mM in the base of older leaves, respectively) and the cytosol (2.8mM in the edge of younger and 4.5mM in the center of older leaves, respectively). Chloroplasts contained rather low amounts of glutathione (between 1mM and 1.4mM). Vacuoles had the lowest concentrations of glutathione (0.01mM and 0.14mM) but showed large differences between the different leaf areas. Clear differences in glutathione contents between the different leaf areas could only be found in vacuoles and mitochondria revealing that glutathione in the later cell organelle accumulated with leaf age to concentrations of up to 15mM and that concentrations of glutathione in vacuoles are quite low in comparison to the other cell compartments.

Plant ascorbate and glutathione metabolism counteracts oxidative stress mediated, for example, by excess light. In this review, we discuss the properties of immunocytochemistry and transmission electron microscopy, redox-sensitive dyes or probes and bright-field microscopy, confocal microscopy or fluorescence microscopy for the visualization and quantification of glutathione at the cellular or subcellular level in plants and the quantification of glutathione from isolated organelles. In previous studies, we showed that subcellular ascorbate and glutathione levels in Arabidopsis are affected by high light stress. The use of light-emitting diodes (LEDs) is gaining increasing importance in growing indoor crops and ornamental plants. A combination of different LED types allows custom-made combinations of wavelengths and prevents damage related to high photon flux rates. In this review we provide an overview on how different light spectra and light intensities affect glutathione metabolism at the cellular and subcellular levels in plants. Findings obtained in our most recent study demonstrate that both light intensity and spectrum significantly affected glutathione metabolism in wheat at the transcriptional level and caused genotype-specific reactions in the investigated Arabidopsis lines.

The three-dimensional (3D) morphology of the stomata in leaves of Pinus canariensis is described with respect to the spatial arrangement of guard cells, subsidiary cells, polar and lateral cells. Serial semi-thin sections of the stomatal apparatus were digitally reconstructed and analysed with regard to the position, shape and size of the cell types involved. The stomatal complex consists of 16 cells with uniquely shaped polar and lateral cells. The polar cells form a kind of roof above the epistomatal chamber thereby reducing the surface aperture. The structural features of the stomatal complex differ from other Pinus species and are presumed to be an adaptation to extreme environmental conditions.