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WHOLE PLANT AND ECOPHYSIOLOGY

De Novo Synthesis and Degradation of Lx and V Cycle Pigments during Shade and Sun Acclimation in Avocado Leaves¹

School of Biochemistry and Molecular Biology, Australian National University, Canberra, Australian Capital Territory 0200, Australia

The photoprotective role of the universal violaxanthin cycle that interconverts violaxanthin (V), antheraxanthin (A), and zeaxanthin (Z) is well established, but functions of the analogous conversions of lutein-5,6-epoxide (Lx) and lutein (L) in the selectively occurring Lx cycle are still unclear. We investigated carotenoid pools in Lx-rich leaves of avocado (Persea americana) during sun or shade acclimation at different developmental stages. During sun exposure of mature shade leaves, an unusual decrease in L preceded the deepoxidation of Lx to L and of V to A+Z. In addition to deepoxidation, de novo synthesis increased the L and A+Z pools. Epoxidation of L was exceptionally slow, requiring about 40 d in the shade to restore the Lx pool, and residual A+Z usually persisted overnight. In young shade leaves, the Lx cycle was reversed initially, with Lx accumulating in the sun and declining in the shade. De novo synthesis of xanthophylls did not affect - and β-carotene pools on the first day, but during long-term acclimation -carotene pools changed noticeably. Nonetheless, the total change in - and β-branch carotenoid pools was equal. We discuss the implications for regulation of metabolic flux through the - and β-branches of carotenoid biosynthesis and potential roles for L in photoprotection and Lx in energy transfer to photosystem II and explore physiological roles of both xanthophyll cycles as determinants of photosystem II efficiency.

² Present address: School of Biochemistry and Molecular Biology, Australian Research Council Centre of Excellence in Plant Energy Biology, Linnaeus Way, Building 41, Australian National University, Canberra, Australian Capital Territory 0200, Australia.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Britta Förster (britta.forster{at}anu.edu.au).

www.plantphysiol.org/cgi/doi/10.1104/pp.108.131417

^* Corresponding author; e-mail britta.forster{at}anu.edu.au.

Received October 16, 2008; accepted December 1, 2008; published December 5, 2008.

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