Secondary ion mass spectrometry imaging of the fixation of N-15-labelled NO in pollen grains

We used secondary ion mass spectrometry to image cellular targets of nitrog en oxides (widespread air pollutants) in pollen grains of birch (Betula ver rucosa Ehrh.) and cockfoot (Dactylis glomerata L.). The pollen samples were exposed to air supplemented with high doses of (NO)-N-15. The pollen grain s were then fixed, dehydrated using a newly developed 'vapour phase' prepar ation method and embedded in LRW resin. Semithin sections were then analyse d. Imaging was performed in scanning mode. As usual, the two isotopes N-14 and N-15 were imaged as (CN-)-C-12-N-14 and (CN-)-C-12-N-15, respectively. The isotopic percentages of N-15 were quantitatively determined either by i mage processing or by direct analysis. We show that the preferential areas of NO fixation in the pollen cell are the sporoderm and discrete intracytop lasmic structures that we tentatively describe as globoid-like structures s imilar to those encountered in seeds.