The effects of pollen on dissolved inorganic nitrogen (DIN) compounds in throughfall water are not completely understood. We conducted a 7-day leaching experiment with pollen from silver birch (including a sterilized control), European beech, sessile oak, Scots pine, Corsican black pine and Norway spruce using an immersion medium containing nitrate (11.295 mg N l-1). Within 2 hours, pollen released substantial amounts of potassium (K+), phosphate (PO43-) and organic compounds. Solute concentrations of ammonium (NH4+) were built up over time. In treatments with pollen from birch, oak and beech, nitrate (NO3-) concentrations started to decrease after 24–48 hours, while simultaneously nitrite (NO2-) emerged, but part of the inorganic nitrogen could no longer be detected in solution. For birch, sterilisation of the pollen made no difference, indicating that microorganisms on the pollen played no substantial role in the observed N transformations. Conditions in the samples were oxic (1.82–6.12 mg O2 l-1), rendering microbial denitrification unlikely. Our findings revealed that pollen from broadleaved deciduous trees can transform throughfall NO3- into NO2- and likely also nitric oxide (NO), probably through the nitrate reductase pathway. The synthesis of NH4+ might be part of a natural defence mechanism protecting reproductive organs against pathogens during pollination.

Introduction The IL-33 pathway involved in the development of type-2 airway inflammation is activated in allergic asthma patients. According to the “one airway, one disease” concept, the IL-33 pathway should also be activated in the airways of allergic rhinitis patients. Material and methods We compared the levels of IL-33 and its mRNA precursor, in induced sputum of patients suffering from seasonal allergic rhinitis (n=27) with those measured in patients with seasonal allergic asthma (n=23), and in healthy controls (n=17), in and out of the pollen season. Results IL-33 levels were higher in sputum supernatants of allergic rhinitis (median 9.4 pg.ml-1, range 0 – 51.1 pg.ml-1) and asthma patients (5.2 pg.ml-1, range 0 – 45.4 pg.ml-1) when compared to controls (median 0 pg.ml-1, range 0 – 13 pg.ml-1; p<0.001), and the same was observed with qPCR for IL-33. IL-33 levels were similar in patients suffering from allergic rhinitis (median 4.9 pg.ml-1 vs 7.1 pg.ml-1, p=0.256) or allergic asthma patients (median 3.6 pg.ml-1 vs 3.2 pg.ml-1, p=0.61) in and out of pollen seasons. Conclusion IL-33 is detectable in the lower airways of allergic rhinitis patients, to similar levels than in asthma patients, and appears to be independent of natural variation in allergen exposure. Those findings could reflect a silent epithelial dysfunction in the lower airways of allergic rhinitis patients without asthma, further confirming the «one airway, one disease» theory linking asthma and rhinitis.