PARENT SESSION

Symposium S3B Photosynthetic acclimation: Ecophysiology, diverse environments
Tuesday August 31st, 2004 10:20 AM-12:20 PM Room 210A
Chair: Jun Minagawa
Co-Chair: Norm Huner

Multiple mechanisms of zeaxanthin function in thermal dissipation, photoinhibition, and signal transduction. Barbara Demmig-Adams^*,1, Volker Ebbert¹, C Zarter¹, Kristine Bachmann¹, Véronique Amiard¹, Anna Sokolenko², Autar Mattoo³, William Adams¹, ¹ Department of Ecology & Evolutionary Biology, Boulder, Colorado, USA² Department Biologie I, München, Germany³ USDA-ARS Vegetable Laboratory, Beltsville, MD, USA

ABSTRACT- The carotenoid zeaxanthin functions in the protection from excess light via several mechanisms. These include (1) its role in rapidly reversible, pH-dependent dissipation of excess energy as heat facilitated by the PsbS protein. The capacity for rapidly modulated dissipation, PsbS levels, and zeaxanthin levels in the sun were all considerably greater in a perennial model species (Monstera deliciosa) with a low maximal photosynthetic capacity than in spinach or Arabidopsis with high maximal capacities for photosynthesis. The capacity for this flexible form of thermal dissipation is thus species-dependent and greatest in those species that utilize only a small fraction of absorbed light in photosynthesis when grown in the sun. In addition, zeaxanthin is involved in (2) a second form of thermal dissipation associated with photoinhibition and observed in perennials during shade-sun transfer or seasonal transition to cold temperatures. This dissipation process is not rapidly reversible and did not depend on pH; it was associated with strongly increased levels of ELIPs and/or HLIPs in several over-wintering evergreens as well as in shade-grown Monstera deliciosa transferred to high light. This sustained dissipation process was furthermore correlated with an inactivation and sustained phosphorylation of PSII cores and, in an over-wintering conifer (Douglas fir), with increased levels of the cyclophilin-like inhibitor (TLP40) of PSII core protein phosphorylation. It thus appears that the sustained maintenance of high levels of dissipation in photoinhibited leaves, while requiring zeaxanthin, is not facilitated by PsbS but rather by other members of the PsbS family and is closely correlated with an inactivation of PSII photochemistry. Lastly, zeaxanthin may (3) have a function in chloroplast-to-nucleus signaling via modulation of lipid peroxidation. The signal transduction cascade involved in this response will be addressed.

KEY WORDS: Zeaxanthin, Phosphorylation, Photoprotection, PsbS