PARENT SESSION
Posters P6C Photosynthesis, respiration and alternative electron sinks. Abstracts (660-680)

Changes in expression of cyanobacterial terminal oxidases (PTOX and cyd bd) during acclimation to high light. Allison McDonald¹, Sasan Amirsadeghi^*,1, Greg Vanlerberghe¹, ¹ Departments of Life Sciences and Botany, Toronto, Ontario, Canada

ABSTRACT- Genome sequencing projects have revealed the presence of plastoquinol terminal oxidase (PTOX) in four different cyanobacteria. We have confirmed the presence and expression of PTOX in Anabaena variabilis PCC 7120 (Plant Mol. Biol. 53: 865-876, 2003). A. variabilis is thought to contain two quinol oxidases, the plant-like PTOX, and the bacterial-like cytochrome bd oxidase (cyd bd). Toward understanding the role of these oxidases in photosynthetic and respiratory metabolism, we examined temporal changes in gene expression in response to shifts in light intensity. As expected, a shift to higher light caused increased expression of the PSII D1 protein (psbA2), decreased expression of a PS I core protein (psaA) and moderately increased expression of the Rubisco large subunit (rbcL). These changes are interpreted as an upregulation of protection against photodamage and CO₂ fixation capacity and a downregulation of photosystem contents. Interestingly, the shift also caused a rapid increase in PTOX expression while that of cyd bd (A subunit) was little effected. We also describe results following shifts to darkness and experiments that utilize inhibitors (e.g. DCMU) to establish whether changes in the reduction state of particular electron transport chain components may signal these gene expression changes.

KEY WORDS: light acclimation, plastoquinol terminal oxidase, cyanobacteria, gene expression