Corals hosting different genotypes Selleck Ulixertinib of Symbiodinium may have varying thermal bleaching thresholds, but changes in the symbiont’s antioxidant system that may accompany these differences have received less attention. This study shows that constitutive activity and up-regulation of different parts of the antioxidant network under thermal stress differs between four Symbiodinium types in culture and that thermal susceptibility

can be linked to glutathione redox homeostasis. In Symbiodinium B1, C1 and E, declining maximum quantum yield of PSII (Fv/Fm) and death at 33°C were generally associated with elevated superoxide dismutase (SOD) activity and a more oxidized glutathione pool. Symbiodinium F1 exhibited no decline in Fv/Fm or growth, but showed proportionally larger increases in ascorbate peroxidase (APX) activity and glutathione content (GSx), while maintaining GSx in a reduced state. Depressed growth in Symbiodinium B1 at a sublethal temperature

of 29°C was associated with transiently increased APX activity and glutathione pool size, and an overall increase in glutathione reductase (GR) activity. The collapse of GR activity at 33°C, together with increased SOD, APX and glutathione S-transferase activity, contributed to a strong oxidation of the glutathione pool with subsequent death. Integrating responses of multiple components of the antioxidant network highlights the importance of antioxidant plasticity in explaining type-specific temperature responses in Symbiodinium. “
“Macrocystis pyrifera is selleck compound a widely distributed, highly productive, seaweed. It is known to use bicarbonate (HCO3−) from seawater in photosynthesis and the main mechanism of utilization is attributed to the external catalyzed dehydration of HCO3− by the surface-bound enzyme carbonic anhydrase (CAext). Here, we examined other putative HCO3− uptake mechanisms in

M. pyrifera under pHT 9.00 (HCO3−: CO2 = 940:1) and pHT 7.65 (HCO3−: CO2 = 51:1). Rates of photosynthesis, Ribonuclease T1 and internal CA (CAint) and CAext activity were measured following the application of AZ which inhibits CAext, and DIDS which inhibits a different HCO3− uptake system, via an anion exchange (AE) protein. We found that the main mechanism of HCO3− uptake by M. pyrifera is via an AE protein, regardless of the HCO3−: CO2 ratio, with CAext making little contribution. Inhibiting the AE protein led to a 55%–65% decrease in photosynthetic rates. Inhibiting both the AE protein and CAext at pHT 9.00 led to 80%–100% inhibition of photosynthesis, whereas at pHT 7.65, passive CO2 diffusion supported 33% of photosynthesis. CAint was active at pHT 7.65 and 9.00, and activity was always higher than CAext, because of its role in dehydrating HCO3− to supply CO2 to RuBisCO. Interestingly, the main mechanism of HCO3− uptake in M.