Efficient Heat Dissipation and Cyclic Electron Flow Confer Daily Air Exposure Tolerance in the Intertidal Seagrass Halophila beccarii Asch

Abstract

Seagrasses inhabiting the intertidal zone experience periodically repeated cycles of air exposure and rehydration. However, little is known about the photoprotective mechanisms in photosystem (PS)II and PSI, as well as changes in carbon utilization upon air exposure. The photoprotective processes upon air exposure in Halophila beccarii Asch., an endangered seagrass species, were examined using the Dual-PAM-100 and non-invasive micro-test technology. The results showed that air exposure enhanced non-photochemical quenching (NPQ) in both PSII and PSI, with a maximum increase in NPQ and Y(ND) (which represents the fraction of overall P700 that is oxidized in a given state) of 23 and 57%, respectively, resulting in intensive thermal energy dissipation of excess optical energy. Moreover, cyclic electron transport driven by PSI (CEF) was upregulated, reflected by a 50 and 22% increase in CEF and maximum electron transport rate in PSI to compensate for the abolished linear electron transport with significant decreases in pmfLEF (the proton motive force [pmf]) attributable solely to proton translocation by linear electron flow [LEF]). Additionally, H+ fluxes in mesophyll cells decreased steadily with increased air exposure time, exhibiting a maximum decrease of six-fold, indicating air exposure modified carbon utilization by decreasing the proton pump influxes. These findings indicate that efficient heat dissipation and CEF confer daily air exposure tolerance to the intertidal seagrass H. beccarii and provide new insights into the photoprotective mechanisms of intertidal seagrasses. This study also helps explain the extensive distribution of H. beccarii in intertidal zones.

Channeling of Carbon Flux Towards Carotenogenesis in Botryococcus braunii: A Media Engineering Perspective

“…Conversely, the quantum yield of PSII photochemistry Y(II) is higher in cultures supplemented with carbon than in the control condition. As a result, we demonstrate that the carbon flux helps the cells to undergo regulated changes efficiently as compared with the control condition; moreover, due to the lack of carbon, control cells might undergo photoinhibition, suggesting that a greater number of PSII reaction centers are closed in the control condition ( Fang et al, 2020 ; Lu et al, 2020 ). Carbon supplementation further helped in the increase in the Y(I), suggesting that the photosynthetic efficiency was stable and balanced as compared with that in the control condition.…”

“…The photosynthetic parameters were estimated as described previously ( Kareya et al, 2020 ). For PSI: Y(I) = (Pm′–P)/Pm, Y(NA) = (Pm–Pm′)/Pm, Y(ND) = P/Pm as described by Klughammer and Schreiber (1994) ; Baker (2008) , and Fang et al (2020) . The P700 + signals (P) could range from a minimum (P700 entirely reduced) to a maximum level (P700 fully oxidized), where P denotes P700 + signals, Pm is P700 fully oxidized, and Pm′ is P700 fully reduced.…”

Exogenous Arachidonic Acid Affects Fucoxanthin Biosynthesis and Photoprotection in Phaeodactylum tricornutum

“…Chlorophyll fluorescence of the algae cells (7.5 mg/mL Chl concentration) were recorded using the MAXI version of the IMAGING-PAM M-Series chlorophyll fluorescence system (Heinz-Walz, Effeltrich, Germany) after darkness adaptation for 20 min. The parameters F v /F m (the maximal quantum yield of PSII), and Y(II) (the effective quantum yield of PSII) were calculated as the following Equations (1) and (2) [ 44 ]: F v / F m = ( F m − F 0 )/ F m Y(II) = ( F m ’ − F t )/ F m ’ …”

“…The algal strains were qualified to the same Chl concentration (7.5 mg/mL) and adapted in the dark for 20 min before measurement. The parameters were calculated according to the Equations from (3) to (5) [ 44 ]: Y(I) = ( P m ’ − P )/ P m NPQ = ( F m − F m ’ )/ F m ’ Y(NO) = F / F m where P m represents the maximal P700 change, and P m ’ represents the maximum P700 + signal under AL without far-red (FR) light.…”

Valorization of carbon dioxide (CO2) to enhance production of biomass, biofuels, and biorenewables (B3) in Chlorella saccharophilaUTEX247: a circular bioeconomy perspective

“…For calculation of photosynthetic paramenters such as Photosystem I (PSI): Y(I) = (Pmʹ–P)/Pm, Y(NA) = (Pm–Pmʹ)/Pm, Y(ND) = P/Pm. The P700+ signals (P) could range from a minimum (P700 entirely reduced) to a maximum level (P700 fully oxidized), where P denotes P700+ signals, Pm is P700 fully oxidized, and Pmʹ is P700 fully reduced; Y(I) quantum yield of photochemical energy conversion, Y(ND) quantum yield of non‐photochemical energy dissipation due to donor side limitation, Y(NA) quantum yield of non‐photochemical energy dissipation due to acceptor side limitation 30–33 …”