The photosynthetic performances of both the cryopreserved and non-cryopreserved B. psygmophilum and E. voratum culture isolates were measured using a PAM fluorometer (PHYTO-EDF; Heinz Walz GmbH, Germany) equipped with a fibreoptics probe. The gain of the culture isolates was determined before measurements began and set using a corresponding healthy culture for each of the culture isolates. In each experiment, sub-samples (1.4 mL) of each culture isolate were transferred into sterile two mL vials (Agilent Technologies, Beijing, China) wrapped with an aluminium foil (Emperor, New Zealand) and then incubated in the dark for 5 min to allow the full oxidation of photosystem II (PSII) reaction centers and electron transport chain. Five replicates (n = 5) of each culture isolate for both the cryopreserved and non-cryopreserved were used.
Rapid light curves (RLCs) were used to generate and extract detailed information on the saturation characteristics of PSII (Ralph & Gademann, 2005 (link); White, Anandraj & Trois, 2013 (link)). Fluorescence variables and PSII quantum yield (Fv/ Fm = (Fm − F0)/Fm) were measured where: F0 = initial fluorescence intensity, and Fm = maximal intensity under saturating light conditions, and Fv = Fm - F0(Long et al., 2018 (link)). The quantum yield of PSII was then calculated as Fv/ Fm (Strasser, Srivastava & Tsimilli-Michael, 2000 ). Relative ETR = Fv/ Fm × PAR ×0.5 × 0.84 where Fv/ Fm estimates the quantum yield of PSII, PAR = quantum flux density of incident photosynthetically active radiation (the actinic irradiance in μmol quanta m−2 s−1), 0.5 = a multiplication factor based on the assumption that 50% of the absorbed quanta are distributed to PSII, 0.84 = An assumption that an average of 84% of incident PAR is absorbed by the chlorophyll in the cell (Beer et al., 1998 (link); Schreiber, 2004 (link)). All PAM data and generation of RLCs were done using Phyto-Win software (v 1.45). The rapid light curves were generated by calculating maximum electron transport rate (ETRmax) through PSII for each level of actinic light as a function of irradiance (PAR). The measurements from the two different culture isolates were taken on days 12, 16, 20, 24, 28, 32 and 36 during their normal incubation period from late exponential to stationary growth phases. The photosystem II (PSII) maximum quantum yield and the maximum electron transport rate (ETRmax) of the cryopreserved and the control isolates were assessed and compared during the two main time points in their growth curve. First, during late exponential phase (day 12) when the Symbiodiniaceae isolates had the highest photosynthetic activity and second, during stationary phase (day 36) when they had low photosynthesis levels.
Rapid light curves (RLCs) were used to generate and extract detailed information on the saturation characteristics of PSII (Ralph & Gademann, 2005 (link); White, Anandraj & Trois, 2013 (link)). Fluorescence variables and PSII quantum yield (Fv/ Fm = (Fm − F0)/Fm) were measured where: F0 = initial fluorescence intensity, and Fm = maximal intensity under saturating light conditions, and Fv = Fm - F0(Long et al., 2018 (link)). The quantum yield of PSII was then calculated as Fv/ Fm (Strasser, Srivastava & Tsimilli-Michael, 2000 ). Relative ETR = Fv/ Fm × PAR ×0.5 × 0.84 where Fv/ Fm estimates the quantum yield of PSII, PAR = quantum flux density of incident photosynthetically active radiation (the actinic irradiance in μmol quanta m−2 s−1), 0.5 = a multiplication factor based on the assumption that 50% of the absorbed quanta are distributed to PSII, 0.84 = An assumption that an average of 84% of incident PAR is absorbed by the chlorophyll in the cell (Beer et al., 1998 (link); Schreiber, 2004 (link)). All PAM data and generation of RLCs were done using Phyto-Win software (v 1.45). The rapid light curves were generated by calculating maximum electron transport rate (ETRmax) through PSII for each level of actinic light as a function of irradiance (PAR). The measurements from the two different culture isolates were taken on days 12, 16, 20, 24, 28, 32 and 36 during their normal incubation period from late exponential to stationary growth phases. The photosystem II (PSII) maximum quantum yield and the maximum electron transport rate (ETRmax) of the cryopreserved and the control isolates were assessed and compared during the two main time points in their growth curve. First, during late exponential phase (day 12) when the Symbiodiniaceae isolates had the highest photosynthetic activity and second, during stationary phase (day 36) when they had low photosynthesis levels.
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