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Unveiling the shade nature of cyanic leaves: a view from the ‘blue absorbing side’ of anthocyanins
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  • Marco Landi,
  • Giovanni Agati,
  • Alessio Fini,
  • Lucia Guidi,
  • Federico Sebastiani,
  • Massimiliano Tattini
Marco Landi
University of Pisa
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Giovanni Agati
National Research Council of Italy
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Alessio Fini
University of Milan
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Lucia Guidi
Universita degli Studi di Pisa
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Federico Sebastiani
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Massimiliano Tattini
Department of Biology, Agriculture and Food Sciences, The National Research Council of Italy (CNR), Institute for Sustainable Plant Protection
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Anthocyanins have long been suggested as having great potential in offering photoprotection to plants facing high light irradiance. Nonetheless, their effective ability in protecting the photosynthetic apparatus from supernumerary photons has been questioned in many instances, based upon the inexact belief that anthocyanins almost exclusively absorb green photons, which are instead poorly absorbed by chlorophylls. This suggestion also contrasts with the well-recognized ‘shade syndrome’ displayed by cyanic leaves: shade avoidance responses are activated indeed by excessive green light. Here we focus on the blue light absorbing features of anthocyanins, a neglected issue in anthocyanin research. We offer a comprehensive picture of the suite of molecular events activated in response to low blue-light availability, which we suggest to be responsible for the shade nature of cyanic leaves/individuals. As a corollary, this adds further support to the view of an effective photoprotective role of anthocyanins. We discuss about the morpho-anatomical adjustments imposed by the epidermal anthocyanin shield, mostly devoted at maximizing light harvesting, which make complex the analysis of the photosynthetic performance of cyanic vs acyanic leaves. Finally, we evidence major methodological issues for future research, which may help to draw conclusions on how and how much anthocyanins sustain photoprotection.