Micro-PIXE in plant sciences

Full text: Studies of the role played by elements in fundamental processes in physiology, nutrition, elemental deficiency and toxicity as well as environmental pollution require accurate, quantitative methods with good spatial resolution. the problem of proper measurements of elemental balances and elemental transfers between various levels of biological organisation (from abiotic to biotic systems; along the food chains; within organs and cells) becomes essential for understanding the mechanisms influencing the selection, interaction, distribution and transport of elements. Highly sensitive techniques for bulk elemental analysis are mostly used in these investigations. These techniques usually offer adequate sensitivity, but without spatial resolution. On the other hand, advanced studies of elemental distribution at a cellular level are mostly conducted using techniques with high spatial resolution, but low sensitivity. Ideally, these studies should be conducted on organs and tissues of sizes as far down as the cellular and sub-cellular level. This applies to e.g. future directions in ionomics and metallomics and opens up new, exciting possibilities of studies of trace metal role. The micro-PIXE has been applied in plant sciences for more than thirty years and has reached a high level of maturity. This is one of the few microanalytical, multielemental techniques capable of quantitative studies of elemental distribution at ppm level with with ability to perform quantitative elemental mapping and easy quantification of data extracted from selected micro-areas. Preparation of biological specimens is undoubtedly the crucial and most difficult part of analysis, and only cryotechniques are recommended presently for ali types of microanalytical studies. Established sample preparation protocols will be presented. Most of results are obtained for cryofixed and freeze-dried material but analysis of samples in frozen-hydrated state brings important advantage. Recent applications in plant sciences will be presented to illustrate multidisciplinary research where close collaboration between biologists and physicists is a key to success. (author)