Sensitivity of photosynthetic processes to freezing temperature in extremophilic lichens evaluated by linear cooling and chlorophyll fluorescence
| Authors | |
|---|---|
| Year of publication | 2016 |
| Type | Article in Periodical |
| Magazine / Source | Cryobiology |
| MU Faculty or unit | |
| Citation | |
| Doi | http://dx.doi.org/10.1016/j.cryobiol.2016.10.002 |
| Field | Botany |
| Keywords | Usnea antarctica; Usnea aurantiaco-atra; Umbilicaria cylindrica; cryoresistance; Antarctica; James Ross Island; temperature stress |
| Description | Extremophilic lichens and their photosynthesizing photobionts from the cold regions of Earth are adapted to perform photosynthesis at subzero temperatures. To evaluate interspecific differences in the critical temperature for primary photochemical processes of photosynthesis, we exposed lichen thalli of Usnea antarctica, Usnea aurantiaco-atra, and Umbilicaria cylindrica to linear cooling from +20 to minus 50 °C at a constant rate of 2 °C/min. Simultaneously, two chlorophyll fluorescence parameters (FV/FM: potential yield of photosynthetic processes in photosystem II, YieldPSII: effective quantum yield of PS II) evaluating a gradual subzero temperature-induced decline in photosynthetic processes were measured by a modulated fluorometer. For the studied species, the response of FV/FM and YieldPSII to declining temperature showed an S-curve shape. The decline in FV/FM and YieldPSII at low temperatures started at minus 5 and +5 °C, respectively in the majority of cases. The decline was, however, species-specific. U. aurantiaco-atra showed a constant-rate decline of YieldPSII from the physiological temperature 20 °C. U. antarctica exhibited the first sign of FV/FM decline at minus 12 °C. The critical temperature related to full inhibition of the photosynthetic processes in PSII (FV/FM), was found at minus 20 °C. However, this occurred at minus 30 °C for U. cylindrica. In an individual sample, the critical temperature for FV/FM was typically lower than for YieldPSII. The method of linear cooling combined with simultaneous measurements of chlorophyll fluorescence parameters proved to be an efficient tool in the estimation of extremophilic species sensitivity/resistance to freezing. |
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