Long-Term Temperature Acclimation of Photosynthesis in Steady-State Cultures of the Polar Diatom <Emphasis Type="Italic">Fragilariopsis cylindrus</Emphasis> |
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Authors: | Email author" target="_blank">Thomas?MockEmail author Nikolai?Hoch |
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Institution: | (1) Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany;(2) Present address: School of Oceanography, University of Washington, Box 357940, Seattle, Washington, USA |
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Abstract: | Cultures of the obligate psychrophilic diatom Fragilariopsis cylindrus (Grunow) were grown for 4 months under steady-state conditions at −1 °C and +7 °C (50 μmol photons m−2 s−1) prior to measurements in order to investigate long-term acclimation of photosynthesis to both temperatures. No differences in maximum intrinsic quantum yield of PS II (FV/FM) and relative electron transport rates could be detected at either temperature after 4 months of acclimation. Measurements of photosynthesis (relative electron transport rates) vs. irradiance (P vs. E curves) revealed similar values for relative light utilization efficiency (α = 0.57 at −1 °C, α = 0.60 at +7 °C) but higher values for irradiance levels at which photosynthesis saturates (EK) at −1 °C and, therefore, higher maximum photosynthesis (PMAX = 54 (relative units) at −1 °C, PMAX = 49 at +7 °C). Nonphotochemical quenching (NPQ) measurements at 385 μmol photons m−2 s−1 indicated higher (37%) NPQ for diatoms grown at −1 °C compared to +7 °C, which was possibly related to a 2-fold increase in the concentration of the pigment diatoxanthin and a 9-fold up-regulation of a gene encoding a fucoxanthin chlorophyll a,c-binding protein. Expression of the D1 protein encoding gene psbA was ca. 1.5-fold up-regulated at −1 °C, whereas expression levels of other genes from Photosystem II (psbC, psbU, psbO), as well as rbcL, the gene encoding the Rubisco large subunit were similar at both temperatures. However, a 2-fold up-regulation of a plastid glyceraldehyde-P dehydrogenase at −1 °C indicated enhanced Calvin cycle activity. This study revealed for the first time that a polar diatom could efficiently acclimate photosynthesis over a wide range of polar temperatures given enough time. Acclimation of photosynthesis at −1 °C was probably regulated similarly to high light acclimation. |
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Keywords: | acclimation diatom electron transport Fragilariopsis cylindrus low temperature macroarray polar PSII |
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