Unveiling the shade nature of cyanic leaves: a view from the ‘blue
absorbing side’ of anthocyanins
Abstract
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.