Browsing by Subject "SCREENING PIGMENTS"

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  • Viljanen, Martta L. M.; Nevala, Noora E.; Calais-Grano, Cecilia L.; Lindstrom, K. Magnus W.; Donner, Kristian (2017)
    The eyes of two glacial-relict populations of opossum shrimp Mysis relicta inhabiting the different photic environments of a deep, dark-brown freshwater lake and a variably lit bay of the Baltic Sea differ in their susceptibility to functional depression from strong light exposures. The lake population is much more vulnerable than the sea population. We hypothesized that the difference reflects physiological adaptation mechanisms operating on long time scales rather than genetically fixed differences between the populations. To test this, we studied how acclimation to ultra-slowly increased illumination (on time scales of several weeks to months) affected the resilience of the eyes to bright-light exposures. Light responses of whole eyes were measured by electroretinography, the visual-pigment content of single rhabdoms by microspectrophotometry and the structural integrity of photoreceptor cells by electron microscopy (EM). Slow acclimation mitigated and even abolished the depression of photoresponsiveness caused by strong light exposures, making a dramatic difference especially in the lake animals. Still, acclimation in the sea animals was faster and the EM studies suggested intrinsic differences in the dynamics of microvillar membrane cycling. In conclusion, we report a novel form of physiological adaptation to general light levels, effective on the time scale of seasonal changes. It explains part but not all of the differences in light tolerance between the lake and sea populations.
  • Seddon, Alistair W. R.; Festi, Daniela; Nieuwkerk, Mayke; Gya, Ragnhild; Hamre, Borge; Kruger, Linn Cecilie; Ostman, Silje A. H.; Robson, T. Matthew (2021)
    Research indicates that phenolic compounds (e.g. para-coumaric acid) found within pollen grains may be useful as a proxy to reconstruct the UV-B radiation received at the Earth's surface in the geological past. However, application of this method to the plant-fossil record currently relies on a series of untested assumptions surrounding the ecological factors driving the response of pollen grains in the contemporary environment. Here, we investigate the relationship of Pinus spp. pollen to UV-B radiation using individuals of five populations sampled from three elevation gradients across Europe. We develop a novel radiation-modelling approach, which allows us to estimate the UV-B radiation dose of individual trees, weighted by different UV-B action spectra. We then use linear mixed-effects modelling to investigate: (a) whether the variations in UV-B-absorbing compounds in Pinus pollen are best described by models using coarser (subgenus) or finer (population) taxonomic levels; and (b) the duration of the period of accumulation of UV-B-absorbing compounds in pollen, ranging from 8 to 28 days. Our results demonstrate an overall positive relationship between para-coumaric acid and UV-B radiation, best described by applying a UV-B-accumulation period spanning 12-19 days. However, we also show clear evidence for population-level factors influencing this relationship across the study locations. Synthesis. Our multidisciplinary approach, which combines expertise from palaeoecology, plant physiology and atmospheric physics, provides clear evidence that pollen-grain chemistry is subject to population-level variations. We suggest that quantitative reconstructions of long-term changes in springtime UV-B radiation are still achievable using fossil reconstructions, but only with careful consideration of the factors leading to pollen representation in sediments. Future improvements are dependent on mechanistic understanding of the local factors which mediate the UV-B response across different populations, and on upscaling knowledge at the plant level to incorporate longer-term chemical variations represented within sediment samples.