Whether the source of the burst is enzymatic or otherwise, the difference in burst magnitude could also be partly explained by differences in habitat. Oceanic H2O2 levels are primarily controlled by photochemical formation from the interaction of light with DOC and atmospheric deposition (Scully et al. 1996, Hanson et al. 2001, Gerringa et al. 2004), and therefore baseline H2O2 levels vary geographically. The baseline concentration of H2O2 in surface seawater near Palmer Station, Antarctica, is very low; between 12 and 21 nM (Resing et al. buy PS-341 1993). In comparison, 100–300 nM H2O2 was reported in the Gulf of Mexico (Zika et al. 1985), 100–140 nM in

the Mediterranean (Johnson et al. 1989), 50–100 nM from the Caribbean (Moore et al. 1993), and 160–200 nM off the coast of California (Clark et al. 2010). If sympatric organisms have adapted to higher baseline ROS levels, any defensive production of ROS may

have to be larger in order to be effective. RNS may be a component of the oxidative burst, and protein nitration occurs when RNS react with tyrosine residues to form nitrotyrosine (Radi 2004). We detected no nitrotyrosine in protein extracts from oxidant-producing species flash frozen 30 s after wounding. However, it is possible that RNS such as ONOO− are a component of immediate oxidant release and simply cause too little protein nitration to identify Akt inhibitor by our detection methods. For example, S. latissima incubated with 1 μM ONOO− for either 30 s or 5 min at 13°C contained no detectible MCE protein nitration while nitrotyrosine residues were easily detected from S. latissima incubated for either 30 s or 5 min with 1 mM ONOO− using the same extraction and analysis methods as for the Antarctic macroalgae. This indicates that there may be a threshold of ONOO− under which cells can cope without allowing protein nitration substantial enough to detect using

our methods. A striking difference between the oxidant release of Antarctic macroalgae upon wounding and oxidant release from other macroalgae upon wounding, mechanical stress, and pathogen elicitation is the substantially smaller role of H2O2 (Table 1). H2O2 was involved in the immediate wound response of one of five Antarctic species where its presence was assayed: the brown alga D. anceps. However, it did not account for total oxidant production, while H2O2 accounted for >95% of all oxidant release where tested in macroalgae elicited by any means in previous reports (Collén and Pedersén 1994, Bouarab et al. 1999, Küpper et al. 2001, Ross et al. 2005). Consequently, we know the oxidant release of D. anceps is complex, involving at least one other oxidant in addition to H2O2. In the remaining species that released oxidants immediately after wounding (A. mirabilis, P. decipiens, and T. antarcticus), H2O2 was not a detectable component of the oxidant release nor do we know the identity or number of oxidants released.