Toxic or just a nuisance - How mosses cope with heavy metals

Although mosses are frequently used as biomonitors to determine air quality and environmental metal contamination, we still have very little knowledge on the factors and dynamics governing metal adsorption and toxicity to plants. In nature, metals almost always occur in combinations but despite clear indications that such metal combinations and complexation play a crucial role in harmfulness, many studies focus on the exposure to single metals. In this project, we exploit the idea that certain combinations of metals, and complexes thereof, are more harmful than others. Additionally, we investigate the effect of metals on the structure and composition of the plant cell wall which is the first line of defense during metal exposure. We use x-ray scattering and other state-of-the-art imaging techniques to discover metal adsorption, dynamics and speciation in moss plantlets. High resolution microscopy, and biochemical analyses will reveal ultrastructural changes in the cell wall caused by metal exposure. This way, we can visualize the metal distribution and complex formation on the outside of cells and compare it to the minute changes that the metals cause in the cell wall and inside the cell. Combinations of iron, arsenic, manganese, antimony and copper are applied to the sample plants, as they would appear in nature. The pH is also taken into account because it plays an important role in metal complex formation. The major part of the study will be done on the model moss Physcomitrium patens that is grown in sterile culture on metal-spiked agar. But the project is not limited to laboratory experiments. At a former mining site in Austria, the Knappenberg near Vienna, we will collect moss plants and directly compare the metal distribution and adsorption properties with the experimental samples in the lab. These studies will shed light on the effects of different metals and metal compounds to plants and help to understand the underlying mechanisms for metal toxicity and tolerance. The moss surface is very similar to roots of seed plants. The results of this project will therefore expand our knowledge to crops in contaminated environments. Two groups are closely collaborating within this project: Ingeborg Lang, University of Vienna (UNIVIE), is a cell biologist and expert in moss physiology under metal stress. She provides the moss cultures, propagation, labelling and microscopy as well as biochemical characterization of the cell wall. Helga Lichtengger, University of Life Sciences (BOKU), is a biophysicist and expert in x-ray imaging methods and high-resolution synchrotron techniques to image and characterize biological materials including metal distribution and the ultrastructure of plant cell walls. Two PhD positions, one in each group, are funded by the project.