CS29 Phytoplankton & Primary Production
Date: Monday, June 10, 2002
Time: 11:00:00 AM
Location: Oak Bay
 
PeersGS, McGill University, Montreal, Canada, gpeers@bio1.lan.mcgill.ca
Price, N, M, McGIll University, Montreal, Canada, nprice@bio1.lan.mcgill.ca
 
The importance of manganese for the ecology and physiology of iron-limited diatoms
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Vast areas of the world’s oceans are now known to be Fe-limited, but experiments conducted over a decade ago showed that nM additions of Mn also stimulated phytoplankton growth in both the Southern Ocean and the Northeast Pacific Ocean. We have observed that marine diatoms require more Mn to grow when they are Fe-deficient compared to Fe-sufficient. In seawater, containing low concentrations of Fe and Mn like HNLC regions, both resources co-limited growth of phytoplankton cultures. Fe-deficient diatoms had significantly higher internal concentrations of Mn (0.257mM vs 0.191 mM, p<0.05, ANOVA), suggesting that Mn could be substituting for Fe in some metabolic functions. The abundant antioxidant enzyme superoxide dismutase (SOD) contains either Mn or Fe in diatoms. Autoradiograms of 54Mn-labelled proteins show an increase in Mn content of SOD when diatoms are Fe-deficient, suggesting that Mn replaces Fe. This replacement could explain how diatoms increase SOD activities by 30% in response to low-Fe induced oxidative stress. Published field data suggests that Fe-limited plankton are enriched in Mn, supporting a role for Mn substitution in the ecology of the Fe-limited sea.