Hughes, Nicole M. , Smith, William K. .
Why undersides of leaves are sometimes red: contrasting the functional significance of abaxial anthocyanin in sun and shade species.
Red/purple coloration of lower (abaxial) leaf surfaces is commonly observed, though its functional significance is not yet understood. Here we examine leaf optics and ecophysiology of two classes of abaxially anthocyanic plants: species adapted to the deeply-shaded understory, and species which frequently encounter high-abaxial irradiance. We test the hypothesis that abaxial anthocyanin enhances light capture in understory species by increasing internal reflectance of red/purple light, while in high-light plants it protects abaxial cells from photoinhibition by absorbing blue-green light incident on abaxial surfaces. For shade species, microscopic chlorophyll fluorescence profiles were derived for anthocyanic and acyanic Saintpaulia ionantha and Begonia spp. under red, blue, and green incident light, to spatially quantify photosynthesis within the leaf lamina. For high-light species, Fv/Fm of anthocyanic and acyanic Galax urceolata surfaces were compared during and following exposure to photoinhibitory conditions (high light, cold temperatures). Spectral scans were also derived for all species to observe leaf absorptive and reflective properties. In anthocyanic shade species, photosynthesis under red light did not differ between anthocyanic and acyanic plants, but photosynthesis under green light was substantially reduced for anthocyanic Begonia leaves. In response to high-light stress, red surfaces of G. urceolata exhibited significantly decreased photoinhibition (as evidenced by higher Fv/Fm during and following the light stress) than leaves lacking anthocyanin, supporting the photoprotection hypothesis. Spectral scans showed that anthocyanic morphotypes of all species had significantly higher absorptance of blue-green wavelengths compared to acyanic morphotypes, but did not differ in reflectance of red light. In summary, while a photoprotective function was supported for abaxial anthocyanin in high-light species, the hypothesis that anthocyanins back-scatter red light in shade species was not. We suggest instead that abaxial anthocyanin may be functioning in photoprotection in shade plants as well, reducing photodamage from internal scattering of blue-green light caused by high-intensity sunflecks.
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1 - Wake Forest University, Biology, Winston Hall 136, Winston-Salem, NC, 27109, USA
2 - Wake Forest University, Department of Biology, PO Box 7325, 226 Winston Hall, Winston-Salem, North Carolina, 27109-7325, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Williford C/Hilton
Date: Wednesday, July 11th, 2007
Time: 9:00 AM