Increase in Rubisco activity and gene expression due to elevated temperature partially counteracts ultraviolet radiation–induced photoinhibition in the marine diatom Thalassiosira weissflogii

Abstract

We performed outdoor experiments to evaluate the effect of temperature on photoinhibition properties in the cosmopolitan diatom Thalassiosira weissflogii. Cultures were exposed to solar radiation with or without ultraviolet radiation (UVR, 280-400 nm), UV-A (320-400 nm), and UV-B (280-320 nm) at both 20uC and 25uC. Four possible cellular mechanisms involved in UVR stress were simultaneously addressed: carbon incorporation, chlorophyll a fluorescence of photosystem II, xanthophyll cycle activity, and ribulose-1,5-biphosphate carboxylase : oxygenase (Rubisco) activity and gene expression. Experiments consisted of daily cycles (i.e., the daylight period) and short-term incubations (i.e., 1 h centered on local noon). Samples incubated at 25uC had significantly less UVR-induced inhibition of carbon fixation and effective photochemical quantum yield compared to those incubated at 20uC. At 25uC Rubisco activity and gene expression were significantly higher than at 20uC. The higher Rubisco activity and gene expression were correlated with less dissipation of excess energy, evaluated via non-photochemical quenching, and the de-epoxidation state of the xanthophyll pigments, as more photons could be processed. An increase in temperature due to climate change would partially counteract the negative effects of UVR by increasing the response of metabolic pathways, such as those involved in Rubisco. This, in turn, may have important consequences for the ecosystem, as higher production (due to more Rubisco activity) could be expected under a scenario of global warming.

Mixotrophic trade‐off under warming and UVR in a marine and a freshwater alga

“…6) according to our hypothesis and the studies of Wilken et al (2012) and Chan et al (2018). For Isochrysis galbana, warming also stimulated specific-PP, apparently mediated by increasing metabolic pathways (i.e., RuBisCO;Helbling et al 2011). The results also showed a notable mismatch between Ф PSII and PP, as reported by Behrenfeld et al (1998) and Gilbert et al (2000).…”

“…For Isochrysis galbana , warming also stimulated specific‐PP, apparently mediated by increasing metabolic pathways (i.e., RuBisCO; Helbling et al. ). The results also showed a notable mismatch between Ф PSII and PP, as reported by Behrenfeld et al.…”

Ocean acidification mediates photosynthetic response to UV radiation and temperature increase in the diatom <i>Phaeodactylum tricornutum</i>

“…On the other hand, high levels of UV can lead to degradation of periplasmic carbonic anhydrase (CAe) (Wu and Gao, 2009), as well as Rubisco and D1 protein (Bischof et al, 2002;Bouchard et al, 2005), and increased temperature could have stimulated the repair of the damaged molecules. The beneficial effects of increased temperature on photosynthesis under UV stress have been previously documented (Sobrino and Neale, 2007;Gao et al, 2008;Halac et al, 2010;Helbling et al, 2011), showing lower UV-induced inhibition or damages at higher temperatures. Differential sensitivities to UV have been reported in marine picoplankters when grown under elevated CO 2 concentrations, with Nannochloropsis gaditana having lower sensitivity while Nannochloris atomus showed neutral response (Sobrino et al, 2005).…”

Temperature-dependent growth and photophysiology of prokaryotic and eukaryotic oceanic picophytoplankton

“…This has also been found in larger phytoplankton species, such as the diatoms Chaetoceros gracilis, Thalassiosira pseudonana, and T. weissflogii (So b rino & Neale 2007, Halac et al 2010, Helbling et al 2011. Reduced levels of photoinhibition may be associated with enhanced enzymatic conversions of the xanthophyll pigment cycle (Demmig-Adams & Adams 1992), enhanced D1 repair (Bouchard et al 2006) and the potential enhancement of Rubisco activity (Helbling et al 2011). Further study is neccessary to confirm whether these processes are also involved in temperature acclimation in P. marinus, Prochlorococcus sp., Ostreococcus sp.…”

“…(WH7803) (Fu et al 2007). In eukaryotic nanophytoplankton, other chan ges in the light-harvesting complex involved in low temperature acclimation are a reduction in photo system II (PSII) reaction center size and abundance (Davison 1991, Wilson & Huner 2000 and an in crease in photoprotective pigments relative to light-harvesting pigments (Wilson & Huner 2000, Helbling et al 2011. As temperature increases, the constraints on photosynthesis gradually decrease with increased chl a synthesis and enhanced light capture (Fal kowski & Raven 1997, Stramski et al 2002.…”