PARENT SESSION
Posters P2D Marine photosynthesis and production. Abstracts (711-719)

Physiological interactions of Fe with Mn & Cu in marine diatoms: the role of antioxidant enzymes and electron transport. Graham Peers^*,1, Sarah Quesnel¹, Neil Price¹, ¹ Dept. of Biology, McGill University, Montreal, Quebec, Canada

ABSTRACT- Fe-deficiency increases the growth requirements of marine diatoms for Mn and Cu. An increase in reactive oxygen species (ROS) generation, consistent with impaired electron transport, is observed during Fe-deficient growth. Diatom superoxide dismutase (SOD) contains Mn in vivo, is active only with Mn as a metal cofactor in vitro, and shows decreased activity under Mn-deficient growth. When Fe is limiting SOD is up-regulated to deal with increased ROS and can account for part of the increased Mn requirement. Growth in low Mn and Fe results in low SOD activities, a 3-fold increase in ROS generation, and markedly lower growth rates compared to when only one metal is limiting growth. Additionally, PSII function is inhibited by Mn-deficiency. As shown for other eukaryotes, Cu is required for Fe acquisition, but we find that diatoms isolated from the open ocean have additional requirements for Cu that species isolated from coastal environments do not have. Low-light grown diatoms have increased requirements for Cu suggesting a role for this metal in photosynthesis. However, initial experiments suggest the absence of plastocyanin in oceanic diatoms. We will discuss the role of Cu in the electron transport chains of both photosynthesis and respiration. Our results suggest that Fe-deficient environments, such as those found in the open ocean, increase biochemical requirements for other metals and that this selection pressure may not necessarily result in the simple substitution of one metal for another in functionally equivalent proteins.

KEY WORDS: iron, algae, copper, manganese