Chlamydomonas raudensis (UWO 241), Chlorophyceae, exhibits the capacity for rapid D1 repair in response to chronic photoinhibition at low temperature¹

Abstract

Maximum photosynthetic capacity indicates that the Antarctic psychrophile Chlamydomonas raudensis H. Ettl UWO 241 is photosynthetically adapted to low temperature. Despite this finding, C. raudensis UWO 241 exhibited greater sensitivity to lowtemperature photoinhibition of PSII than the mesophile Chlamydomonas reinhardtii P. A. Dang. However, in contrast with results for C. reinhardtii, the quantum requirement to induce 50% photoinhibition of PSII in C. raudensis UWO 241 (50 lmol photons) was comparable at either 8°C or 29°C. To our knowledge, this is the first report of a photoautotroph whose susceptibility to photoinhibition is temperature independent. In contrast, the capacity of the psychrophile to recover from photoinhibition of PSII was sensitive to temperature and inhibited at 29°C. The maximum rate of recovery from photoinhibition of the psychrophile at 8°C was comparable to the maximum rate of recovery of the mesophile at 29°C. We provide evidence that photoinhibition in C. raudensis UWO 241 is chronic rather than dynamic. The photoinhibitioninduced decrease in the D1 content in C. raudensis recovered within 30 min at 8°C. Both the recovery of the D1 content as well as the initial fast phase of the recovery of F v ⁄ F m at 8°C were inhibited by lincomycin, a chloroplast protein synthesis inhibitor. We conclude that the susceptibility of C. raudensis UWO 241 to low-temperature photoinhibition reflects its adaptation to low growth irradiance, whereas the unusually rapid rate of recovery at low temperature exhibited by this psychrophile is due to a novel D1 repair cycle that is adapted to and is maximally operative at low temperature.

The Antarctic Psychrophile Chlamydomonas sp. UWO 241 Preferentially Phosphorylates a Photosystem I-Cytochrome b6/f Supercomplex

“…This is in agreement with previous studies that show that UWO 241 exhibits rapid rates of D1 repair and recovery from photoinhibition at low temperatures (Pocock et al, 2007). Consequently, it appears that STT8 is present and active in UWO 241.…”

“…This is consistent with the fact that temperature-response curves for light-saturated rates of CO 2 -saturated oxygen evolution indicate that UWO 241 photosynthesizes maximally at 8°C at rates that are comparable to rates of the mesophile, C. reinhardtii, grown and measured at 29°C (Pocock et al, 2007). Although UWO 241 exhibits a low quantum requirement for photoinhibition and the degradation of the PSII reaction center polypeptide D1 (PsbA), this is complemented by a rapid, light-dependent recovery of PSII photochemistry associated with the de novo biosynthesis of D1 at low temperature (Pocock et al, 2007). Thus, this psychrophile appears to be photosynthetically adapted to growth at low temperature (Pocock et al, 2007).…”

“…Although UWO 241 exhibits a low quantum requirement for photoinhibition and the degradation of the PSII reaction center polypeptide D1 (PsbA), this is complemented by a rapid, light-dependent recovery of PSII photochemistry associated with the de novo biosynthesis of D1 at low temperature (Pocock et al, 2007). Thus, this psychrophile appears to be photosynthetically adapted to growth at low temperature (Pocock et al, 2007).…”

“…While SAG 49.72 favors energy partitioning for photoprotection through the induction of the xanthophyll cycle, the psychrophilic strain, UWO 241, favors energy partitioning for photoprotection through constitutive quenching processes involved in energy dissipation, even though UWO 241 exhibits an active xanthophyll cycle (Pocock et al, 2007;Szyszka et al, 2007). Although the molecular basis of the constitutive quenching process for photoprotection has not been elucidated unequivocally, this may reflect the differences in the predisposition for energy dissipation through either the Q2 or the Q1 site in PSII-LHCII supercomplexes (Jahns and Holzwarth 2012;Derks et al, 2015) or, alternatively, it may indicate quenching through PSII reaction centers, as suggested previously Sane et al, 2012).…”

Photoadaptation to the polar night by phytoplankton in a permanently ice-covered Antarctic lake

“…Two decades of intensive laboratory studies on axenic isolates of this organism have revealed that the photochemical apparatus is finely adjusted to the extremely stable low light and low temperature environment from which it was isolated (Morgan‐Kiss et al ,, , ; Morgan‐Kiss and Dolhi ). Evolution of a highly efficient photochemical apparatus in this species has been as a consequence of a loss of multiple acclimatory responses to environmental variability (Morgan‐Kiss et al ,; Pocock et al ; Szyszka et al ). Experiments on acclimation to light quality showed that C. raudensis exhibits a novel requirement for blue light and reverts to a downregulated photochemical state under dark incubation or in the presence of red light (Morgan‐Kiss et al ).…”