JXB Advance Access originally published online on October 22, 2004
Journal of Experimental Botany 2005 56(411):461-468; doi:10.1093/jxb/eri012
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RESEARCH PAPER |
Slowly reversible de-epoxidation of lutein-epoxide in deep shade leaves of a tropical tree legume may ‘lock-in’ lutein-based photoprotection during acclimation to strong light
1Photobioenergetics Group, Research School of Biological Sciences, Australian National University, Box 475 Canberra, ACT 2601, Australia
2Biosphere 2 Center, Columbia University, Oracle, AZ 85623, USA
3Dipartimento Scientifico e Tecnologico, Università di Verona, Strada Le Grazie 15, 37234 Verona, Italy
¶ Present address and to whom corresponence should be sent: School of Biochemistry and Molecular Biology, Australian National University, Canberra, ACT 0200, Australia. Fax: +61 2 6125 0313. E-mail: barry.osmond{at}anu.edu.au
The kinetics of response to strong light have been examined in deeply shaded leaves of the tropical tree legume (Inga sp.) which have extraordinarily high levels of the 
-xanthophyll lutein-epoxide that are co-located in pigment–protein complexes of the photosynthetic apparatus with the ß-xanthophyll violaxanthin. As in other species, rapidly reversible photoprotection (measured as non-photochemical chlorophyll fluorescence quenching) is initiated within the time frame of sun-flecks (minutes), before detectable conversion of violaxanthin to antheraxanthin or zeaxanthin. Photoprotection is stabilized within hours of exposure to strong light by simultaneously engaging the reversible violaxanthin cycle and a slowly reversible conversion of lutein-epoxide to lutein. It is proposed that this lutein ‘locks in’ a primary mechanism of photoprotection during photoacclimation in this species, converting efficient light-harvesting antennae of the shade plant into potential excitation dissipating centres. It is hypothesized that lutein occupies sites L2 and V1 in light-harvesting chlorophyll protein complexes of photosystem II, facilitating enhanced photoprotection through the superior singlet and/or triplet chlorophyll quenching capacity of lutein.
Key words: Inga sp., lutein-epoxide, photoacclimation, photoprotection, photosynthesis, xanthophyll cycles
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