FIGURE LEGENDS
FIGURE 1. Effect of long-term stress acclimation on partitioning of PSII (a) and PSI (b) in UWO 241 and SAG 49.72 grown under control and long term stress conditions. ΦNO, non-regulated energy dissipation; ΦNPQ, non-photochemical energy quenching; ΦPSII, PSII quantum yield; ΦPSI, PSI quantum yield; ΦND, donor side limitation; ΦNA, acceptor side limitation. C, Control; HL, High Light; LT, Low Temperature; HS, High Salt. Values are means with standard deviations (n=3). All parameters were measured at growth irradiance (see Table 1).
FIGURE 2. Capacity for nonphotochemical quenching in UWO 241 (UWO) and SAG 49.72 (SAG) grown under control and high stress conditions. C, Control; HL, high light; LT, low temperature; HS, high salt. Letters - a, statistical significance between control vs. stress within one algal species; b, statistical significance between UWO 241 vs. SAG 49.72 when grown under same treatment (n=3; p<0.05).
FIGURE 3. 77K Chl a fluorescence emission spectra of the mesophile SAG 49.72 (a) and the psychrophile UWO 241 (b) and acclimated to control and long-term stress treatments. C, Control; HL, high light; LT, low temperature; HS, high salt.
FIGURE 4. Photosystem I (P700) oxidation/reduction of the mesophile SAG 49.72 and the psychrophile UWO 241 grown under control and long-term stress conditions. a. Oxidation state of P700. b. Re-reduction kinetics of P700+. P700oxidation/reduction was monitored in the presence of far red light. Letters - a, statistical significance between control vs. stress within one algal species; b, statistical significance between UWO 241 vs. SAG 49.72 when grown under same treatment (n=3; p<0.05). C, Control; HL, high light; LT, low temperature; HS, high salt; ND, not detectable.
FIGURE 5. Photosystem I oxidation/reduction kinetics in UWO 241 grown under control and long-term stress conditions. P700 oxidation/reduction was monitored in the presence of red actinic light following DCMU pretreatment. (a) Oxidation state of P700. (b) Re-reduction kinetics of P700+. Letters statistical significance between control vs. stress (n=3; p<0.05). C, Control; HL, high light; LT, low temperature; HS, high salt. (c) P700+ re-reduction kinetics.
FIGURE 6 . NPQ and CEF exhibit a linear relationship. C. raudensis SAG 49.72 and C. sp. UWO241 grown under control and long-term stress conditions. NPQ axis represents maximum NPQ values determined from light response curves. CEF represents P700 re-reduction rates. Dashed and solid lines show linear regression for all data points or individual organisms, respectively (n=3 or 7-9 for NPQ and CEF, respectively).
FIGURE 7. Activity of AsA-GSH pathway enzymes, ascorbate peroxidase (APX, a) and glutathione reductase (GR, b) the mesophile SAG 49.72 and the psychrophile UWO 241 grown under control and long-term stress conditions. Letters - a, statistical significance between control vs. stress within one algal species; b, statistical significance between UWO 241 vs. SAG 49.72 when grown under same treatment (n=3; p<0.05). C, Control; HL= high light; LT, low temperature; HS, high salt.
FIGURE 8. Photoinhibition and recovery in the mesophile SAG 49.72 and the psychrophile UWO 241. Cultures grown under control conditions exposed to either high light (HL, 300 μmol m­-2s-1) or low temperature LT, (2oC) short-term stress for 60 min then returned to control conditions for 120 min to recover. (a) Percent photoinhibition was determined by loss of photochemical ability (FV/FM) relative to time zero. (b) Photochemical quenching, qL. C. nonphotochemical quenching, ɸNPQ (n=3).
FIGURE 9. Production of reactive oxygen species in UWO 241 (P) vs. SAG 49.72 (M) during short-term incubation in low temperature (5oC) or high light (300 μmol m-2s-1) stress. Algal samples were incubated for 1 hour in the presence of NBT dye to detect superoxide. Data is normalized to time 0. Letters - a, statistical significance between control vs. stress within one algal species; b, statistical significance between UWO 241 vs. SAG 49.72 when grown under same treatment (n=3; p<0.05).
Table 1. Growth conditions for UWO 241 and SAG 49.72 used in this study.