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JXB Advance Access published online on August 16, 2005
Journal of Experimental Botany, doi:10.1093/jxb/eri255
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© The Author [2005]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved. For Permissions, please e-mail: journals.permissions@oupjournals.org
Received March 8, 2005
Accepted July 4, 2005

RESEARCH PAPER

Functional role of red (retro)-carotenoids as passive light filters in the leaves of Buxus sempervirens L.: increased protection of photosynthetic tissues?

Koldobika Hormaetxe 1, José María Becerril 1, Isabel Fleck 2, Marta Pintó 2, and José Ignacio García-Plazaola 1*

1 Department of Plant Biology and Ecology, University of the Basque Country/EHU, Apdo 644, 48080 Bilbao, Spain
2 Unitat de Fisiologia Vegetal, Departament de Biologia Vegetal, Facultat de Biologia, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain

* To whom correspondence should be addressed.
José Ignacio García-Plazaola, E-mail: gvpgaplj{at}lg.ehu.es


  Abstract

Red (retro)-carotenoids accumulate in chloroplasts of Buxus sempervirens leaves during the process of winter leaf acclimation. As a result of their irregular presence, different leaf colour phenotypes can be found simultaneously in the same location. Five different colour phenotypes (green, brown, red, orange, and yellow), with a distinct pattern of pigment distribution and concentration, have been characterized. Leaf reddening due to the presence of anthocyanins or carotenoids, is a process frequently observed in plant species under photoinhibitory situations. Two main hypotheses have been proposed to explain the function of such colour change: antioxidative protection exerted by red-coloured molecules, and green light filtering. The potential photoprotective role of red (retro-) carotenoids as light filters was tested in Buxus sempervirens leaves. In shade leaves of this species the upper (adaxial) mesophyll of the lamina was replaced by the equivalent upper part of a different colour phenotype. These hybrid leaves were exposed to a photoinhibitory treatment in order to compare the photoprotective effect exerted by adaxial parts of phenotypes with a different proportion of red (retro)-carotenoids in the lower mesophyll of a shade leaf. The results indicated that the presence of red (retro)-carotenoids in the upper mesophyll did not increase photoprotection of the lower mesophyll when compared with chlorophyll, and the best protection was achieved by an upper green layer. This was due to the fact that the extent of photoinhibition was proportional to the amount of red light transmitted by the upper mesophyll and/or to the chlorophyll pool located above. These results do not exclude a protective function of carotenoids in the upper leaf layer, but imply that, at least under the conditions of this experiment, the accumulation of red pigments in the outer leaf layers does not increase photoprotection in the lower mesophyll.

Keywords: Common box; leaf reddening; photoinhibition; photoprotection; retro-carotenoids; winter acclimation.
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