UV-B-absorbing compounds in modern Cedrus atlantica pollen: The potential for a summer UV-B proxy for Northwest Africa

Abstract

Sporopollenin is a complex biopolymer which is the main component of the pollen grain exine and is partly composed of the aromatic compounds para-coumaric acid (pCA) and ferulic acid (FA). These compounds absorb ultraviolet-B radiation (UV-B, 280-315 nm), and their abundance in pollen and spores has been shown to increase in response to increased UV-B flux. Here, we show that the relative abundance of UV-B-absorbing compounds (UACs) measured using Fourier Transform Infrared Spectrometry (FTIR) in modern pollen of autumn-pollinating Cedrus atlantica trees increases in response to summer UV-B flux. This relationship was observed in native Moroccan samples (r 2 = 0.84, p < 0.0001), but not across a larger environmental gradient including non-Moroccan samples (r 2 = 0.00, p = 0.99). For non-Moroccan samples of known provenance, the abundance of UACs is similar to the abundance of UACs found in samples from their place of origin. The FTIR spectra of these samples also closely resemble the FTIR spectra of samples from their place of origin. This unexpected finding suggests there could be a heritable component to UAC production possibly associated with epigenetic memory, an important adaptive mechanism in conifers. Our results indicate that the relative abundance of UACs in Cedrus atlantica pollen could be used as a proxy to reconstruct historic summer UV-B flux in Northwest Africa during at least the Holocene and Late Glacial period while also highlighting how UV-B proxies should be established using pollen samples from specimens growing in their native range or environment.

Chemotaxonomy of domesticated grasses: a pathway to understanding the origins of agriculture

“…Further enhancements to this approach may be possible by incorporating pollen grain size or surface sculpture information into the classification procedure. As already noted, the size variation across Poaceae pollen grains broadly scales with genome size, with generally larger grains in domesticated types than in wild types (Andersen, 1979;Andersen and Bertelsen, 1972;Bennett, 1972;Beug, 1961Beug, , 2004Bottema, 1992;Firbas, 1937;Tweddle et al, 2005). If combined with chemical data, pollen grain size, along with pore and annulus size, may be useful for improving the classification of wild types and their domesticated descendants.…”

“…Attempts to distinguish among and between wild grasses and their domesticated relatives have relied on a combination of grain size and shape, pore diameter and position, annulus width and thickness, and exine structure and microsculpture (Andersen, 1979;Beug, 1961Beug, , 2004Bottema, 1992;Dickson, 1988;Firbas, 1937;Joly et al, 2007;Köhler and Lange, 1979;Rowley, 1960;Tweddle et al, 2005), although of these various characters grain size has been most commonly relied upon in routine palynological studies (Bottema, 1992). Pollen grain size varies between 30 and 100 µm among Poaceae species and broadly correlates with genome size (Bennett, 1972). Since domesticated grasses are typically polyploid they have larger pollen grains than their wild type relatives, and this has led to a size-based circumscription of a "Cerealia" type (Andersen, 1979;Beug, 1961Beug, , 2004Bottema, 1992;Firbas, 1937;Joly et al, 2007;Tweddle et al, 2005).…”

Chemical variations in Quercus pollen as a tool for taxonomic identification: implications for long-term ecological and biogeographical research

“…Previous studies have suggested plasticity of pollen chemistry to climate and other environmental variables (Zimmermann & Kohler, 2014;Zimmermann et al, 2017). For example, temperature has been connected to changes in protein as well as lipid content in both controlled and field experimental conditions (Lahlali et al, 2014;Zimmermann & Kohler, 2014;Jiang et al, 2015;Zimmermann et al, 2017), whilst the effects of exposure to UV-B radiation on pollen chemistry have gained increasing attention (Rozema et al, 2001;Blokker et al, 2006;Fraser et al, 2011;Willis et al, 2011;Jardine et al, 2017;Bell et al, 2018). Additionally, there may be confounding effects related to local adaptation and hybridisation.…”

“…Additionally, there may be confounding effects related to local adaptation and hybridisation. For example, Bell et al (2018) investigated changes in Cedrus pollen chemistry to UV-B radiation and their results suggest a heritable component in the pollen chemical response to UV-B, from analyses of FTIR spectra of pollen samples from botanic gardens closely resembling their source of origin.…”

“…For example, some of the variation in lipid, protein, and carbohydrate chemistry may be explained by environmental influences such as temperature during pollen maturation (Lahlali et al, 2014;Zimmermann & Kohler, 2014;Jiang et al, 2015;Zimmermann et al, 2017), whilst sporopollenin composition may be influenced by external environmental influences such as the plant exposure to UV-B radiation (Rozema et al, 2001;Blokker, Boelen, Broekman, & Rozema, 2006;Willis et al, 2011;Wesley T. Fraser et al, 2011;P. E. Jardine, Abernethy, Lomax, Gosling, & Fraser, 2017;Bell et al, 2018). As a result, the extent to which variation across larger environmental gradients might override taxonomic differences in chemical composition remains unclear.…”