Probing subcellular distributions of micronutrients and trace elements is a major challenge in biology. High-resolution imaging techniques show great potential to understand biochemical functions and accumulation of elements at the subcellular scale.

The 50nm spatial resolution with a Cs⁺ ion beam on the NanoSIMS has been used to map important negative ions such as CN, P, S, I, and As in a range of biological tissues. Often stable isotopes such as 13C and 15N are also used in labelling strategies. O^- primary ions are known to increase positive secondary ion yield but the practical resolution has been limited to 300-400nm on the NanoSIMS due to lower O^- duoplasmatron ion source brightness.

A brighter RF-plasma O^- ion source (Oregon Physics) has been adapted to achieve similar performance levels of spatial resolution, beam current and density to that of Cs⁺. It improves the capability of NanoSIMS for positive ion detection and opens its potential applications to alkalis, transition metals, rare earths and uranides.

In this poster the source design and principle will be described and we will show beam current/spot size performance. We will illustrate these improvements through two studies of metals in plants:

Certain major and trace metals are important as catalytic and structural cofactors in enzymes as well as second messager which are involved in plant photosynthesis. These are Ca, Mg, Mn, Cu, Fe and Zn. Samples from the plant Arabidopsis thaliana and from the green algae Chlamydomonas reinhardtii are studied at IPREM for subcellular localization of these essential (trace) elements. For both organisms wild type and specific mutants are studied. Essential trace metals were localized in chloroplasts of A. thaliana cells. In C. reinhardtii metals were mainly found in acidocalcisomes. Moreover, for this green algae the influence of the toxic metal Cd on photosynthesis is investigated by analyzing changes in the spatial distribution of essential metals.

Aluminium toxicity to plant roots has been recognised for >100 years and affects about 40% of the world’s arable soils, causing a loss of crop yield, yet the mechanisms remain unknown. It is believed that the toxic effects of Al are related to the strength that it binds to the cell wall. This binding occurs more strongly in the outer cells and prevents root elongation causing root tearing and hence a loss of root function. Determining the Al distribution at a subcellular scale is therefore crucial to understanding its effects and selectively breed crops that are resistant to the effects of Al. High resolution NanoSIMS analysis with the new O^- source will show cell wall localisation of the Al.