(Poly)phenolic compounds in pollen and spores of Antarctic plants as indicators of solar UV-B - A new proxy for the reconstruction of past solar UV-B?

The morphology, size and characteristics of the pollen of the plant species Antarctic hairgrass (Deschampsia antarctica, Poaceae) and Antarctic pearlw ort (Colobanthus quitensis, Caryophyllaceae) are described by scanning elec tron microscopy and light microscopy. Based on the number of pores the poll en of Colobanthus quitensis is classified as periporate or polypantorate, w hile that of Deschampsia antarctica is monoporate. Pollen of Vicia faba plants, exposed to enhanced UV-B (10.6 kJ m(-2) day(-) 1 UV-B-BE) in a greenhouse, showed an increased content of UV-B absorbing c ompounds. There was also an increase of UV-B absorbing compounds in respons e to exposure to UV-A. By sequential chemical extraction three `compartment s' of UV-B absorbance of pollen can be distinguished: a cytoplasmic fractio n consisting of, e.g., flavonoids (acid-methanol extractable), a wall-bound fraction, consisting of, e.g., ferulic acid (NaOH extractable) and aromati c groups in the bioresistant polymer sporopollenin possibly consisting of, e.g., para-coumaric acid monomers (fraction remaining after acetolysis). Th e sporopollenin fraction in the pollen of Helleborus foetidus showed consid erable UV-B absorbance (280-320 nm). There is evidence that enhanced solar UV-B induces increased UV-B absorbance (of sporopollenin) in pollen and spo res of mosses, which may be preserved in the fossil record. As there are no instrumental records of solar UV-B in the Antarctic before 1970 and no ins trumental records of stratospheric ozone over the Antarctic before 1957, th e use of UV-B absorbing polyphenolics in pollen (and spores) as bio-indicat or, or proxy of solar UV-B, may allow reconstruction of pre-ozone hole and subrecent UV-B and stratospheric ozone levels. Pollen and spores from herba rium specimens and from frozen moss banks (about 5000-10 000 years old) in the Antarctic may, therefore, represent a valuable archive of historical UV -B levels.