Environmental pH and a Glu364 to Gln mutation in the chlorophyll-binding CP47 protein affect redox-active TyrD and charge recombination in Photosystem II

In Photosystem II, loop E of the chlorophyll-binding CP47 protein is located near a redox-active tyrosine, Y-D, forming a symmetrical analog to loop E in CP43, which provides a ligand to the oxygen-evolving complex (OEC). A Glu364 to Gln substitution in CP47, near Y-D, does not affect growth in the cyanobacterium Synechocystis sp. PCC 6803; however, deletion of the extrinsic protein PsbV in this mutant leads to a strain displaying a pH-sensitive phenotype. Using thermoluminescence, chlorophyll fluorescence, and flash-induced oxygen evolution analyses, we demonstrate that Glu364 influences the stability of Y-D and the redox state of the OEC, and highlight the effects of external pH on photosynthetic electron transfer in intact cyanobacterial cells

Ocean acidification and seaweed reproduction: increased CO₂ ameliorates the negative effect of lowered pH on meiospore germination in the giant kelp 'Macrocystis pyrifera' (Laminariales, Phaeophyceae)

The worldwide effects of ocean acidification (OA) on marine species are a growing concern. In temperate coastal seas, seaweeds are dominant primary producers that create complex habitats and supply energy to higher trophic levels. Studies on OA and macroalgae have focused on calcifying species and adult stages, but critically, they have over-looked the microscopic stages of the reproductive life cycle, which, for other anthropogenic stressors, e.g., UV-B radiation, are the most susceptible life-history phase. Also, environmental cues and stressors can cause changes in the sex ratio, which has implications for the mating system and recruitment success. Here, we report the effects of pH (7.59 - 8.50) on meiospore germination and sex determination for the giant kelp, 'Macrocystis pyrifera' (Laminariales), in the presence and absence of additional dissolved inorganic carbon (DIC). Lowered pH (7.59 - 7.60, using HCl-only) caused a significant reduction in germination, whereas added DIC had the opposite effect, indicating that increased CO₂ at lower pH ameliorates physiological stress. This finding also highlights the importance of appropriate manipulation of seawater carbonate chemistry when testing the effects of OA on photosynthetic organisms. The proportion of male to female gametophytes did not vary significantly between treatments, suggesting that pH was not a primary environmental modulator of sex. Relative to the baseline (pH 8.19), gametophytes were 32% larger under moderate OA (pH 7.86) and 10% larger under extreme OA (pH 7.61). We suggest that metabolically active cells can compensate for the acidification of seawater. This homeostatic function minimizes the negative effects of lower pH (high H + ions) on cellular activity. The 6 - 9% reduction in germination success under extreme OA suggests that meiospores of 'M. pyrifera' may be resistant to future OA

Seawater carbonate chemistry and giant kelp Macrocystis pyrifera reproduction processes during experiments, 2011

The worldwide effects of ocean acidification (OA) on marine species are a growing concern. In temperate coastal seas, seaweeds are dominant primary producers that create complex habitats and supply energy to higher trophic levels. Studies on OA and macroalgae have focused on calcifying species and adult stages but, critically, they have overlooked the microscopic stages of the reproductive life cycle, which, for other anthropogenic stress e.g. UV-B radiation, are the most susceptible life-history phase. Also, environmental cues and stressors can cause changes in the sex ratio which has implications for the mating system and recruitment success. Here, we report the effects of pH (7.59-8.50) on meiospore germination and sex determination for the giant kelp, Macrocystis pyrifera (Laminariales), in the presence and absence of additional dissolved inorganic carbon (DIC). Lowered pH (7.59-7.60, using HCl-only) caused a significant reduction in germination, while added DIC had the opposite effect, indicating that increased CO2 at lower pH ameliorates physiological stress. This finding also highlights the importance of appropriate manipulation of seawater carbonate chemistry when testing the effects of ocean acidification on photosynthetic organisms. The proportion of male to female gametophytes did not vary significantly between treatments suggesting that pH was not a primary environmental modulator of sex. Relative to the baseline (pH 8.19), gametophytes were 32% larger under moderate OA (pH 7.86) compared to their size (10% increase) under extreme OA (pH 7.61). This study suggests that metabolically-active cells can compensate for the acidification of seawater. This homeostatic function minimises the negative effects of lower pH (high H+ ions) on cellular activity. The 6-9% reduction in germination success under extreme OA suggests that meiospores of M.pyrifera may be resistant to future ocean acidification

Diffusion boundary layers ameliorate the negative effects of ocean acidification on the temperate coralline macroalga Arthrocardia corymbosa.

Anthropogenically-modulated reductions in pH, termed ocean acidification, could pose a major threat to the physiological performance, stocks, and biodiversity of calcifiers and may devalue their ecosystem services. Recent debate has focussed on the need to develop approaches to arrest the potential negative impacts of ocean acidification on ecosystems dominated by calcareous organisms. In this study, we demonstrate the role of a discrete (i.e. diffusion) boundary layer (DBL), formed at the surface of some calcifying species under slow flows, in buffering them from the corrosive effects of low pH seawater. The coralline macroalga Arthrocardia corymbosa was grown in a multifactorial experiment with two mean pH levels (8.05 'ambient' and 7.65 a worst case 'ocean acidification' scenario projected for 2100), each with two levels of seawater flow (fast and slow, i.e. DBL thin or thick). Coralline algae grown under slow flows with thick DBLs (i.e., unstirred with regular replenishment of seawater to their surface) maintained net growth and calcification at pH 7.65 whereas those in higher flows with thin DBLs had net dissolution. Growth under ambient seawater pH (8.05) was not significantly different in thin and thick DBL treatments. No other measured diagnostic (recruit sizes and numbers, photosynthetic metrics, %C, %N, %MgCO3) responded to the effects of reduced seawater pH. Thus, flow conditions that promote the formation of thick DBLs, may enhance the subsistence of calcifiers by creating localised hydrodynamic conditions where metabolic activity ameliorates the negative impacts of ocean acidification

Diagnostics of the health of the coralline alga <i>Arthrocardia corymbosa</i>.

<p>Physiological and reproductive metrics used as diagnostics of the health of the coralline alga <i>Arthrocardia corymbosa</i> grown under four combinations of DBL (diffusion boundary layer) thickness and pH. (a) photosynthetic competence (F_V:F_M), (b) chlorophyll <i>a</i> content, (c) elemental stoichiometry (C:N molar ratio) and (d) reproductive output (number and size of recruits). The bars and points represent the mean ± standard error of 6 individual replicates.</p

Carbonate saturation state (Ω_C) of seawater at the surface of the coralline alga <i>Arthrocardia corymbosa</i>.

<p>Computed values of the carbonate saturation state (Ω_C) of seawater at the surface of the coralline alga <i>Arthrocardia corymbosa</i>, in the light and dark, under four combinations of pH and DBL (diffusion boundary layer) thickness (see Supplementary Information). The Ω_C initial value is that of new seawater that has been introduced into the culture chamber. ‘Ω_C day’ is the calculated Ω_C at the seaweed surface after 4.4 h incubation in the light, and Ω_C night is that after 4.4 h in the dark. The bars represent the mean ± standard error of 6 individual replicates, and in some the error bars are too small to be seen.</p

Photograph of the geniculate coralline alga <i>Arthrocardia corymbosa</i> taken at the collection site.

<p>Photograph of the geniculate coralline alga <i>Arthrocardia corymbosa</i> taken at the collection site.</p

Modification of seawater pH at the surface of the coralline algae.

<p>Conceptual scheme of the interplay between seawater carbonate chemistry (i.e. pH), organismal modification of the local chemical environment during a day/night cycle and flow regime illustrating the potential feedbacks between these inter-related processes. Slow flow denotes the slow flow conditions used in our study.</p

Wilhelmina Stålberg och de fyrkantiga äggens gåta : nationsbyggande via historien i skönlitterär prosa kring mitten av 1800-talet - en betraktelse ur genusperspektiv

Background Oesophageal adenocarcinoma is the sixth most common cause of cancer death worldwide and Barrett’s oesophagus is the biggest risk factor. We aimed to evaluate the efficacy of high-dose esomeprazole proton-pump inhibitor (PPI) and aspirin for improving outcomes in patients with Barrett’s oesophagus. Methods The Aspirin and Esomeprazole Chemoprevention in Barrett’s metaplasia Trial had a 2 × 2 factorial design and was done at 84 centres in the UK and one in Canada. Patients with Barrett’s oesophagus of 1 cm or more were randomised 1:1:1:1 using a computer-generated schedule held in a central trials unit to receive high-dose (40 mg twice-daily) or low-dose (20 mg once-daily) PPI, with or without aspirin (300 mg per day in the UK, 325 mg per day in Canada) for at least 8 years, in an unblinded manner. Reporting pathologists were masked to treatment allocation. The primary composite endpoint was time to all-cause mortality, oesophageal adenocarcinoma, or high-grade dysplasia, which was analysed with accelerated failure time modelling adjusted for minimisation factors (age, Barrett’s oesophagus length, intestinal metaplasia) in all patients in the intention-to-treat population. This trial is registered with EudraCT, number 2004-003836-77. Findings Between March 10, 2005, and March 1, 2009, 2557 patients were recruited. 705 patients were assigned to low-dose PPI and no aspirin, 704 to high-dose PPI and no aspirin, 571 to low-dose PPI and aspirin, and 577 to highdose PPI and aspirin. Median follow-up and treatment duration was 8·9 years (IQR 8·2–9·8), and we collected 20 095 follow-up years and 99·9% of planned data. 313 primary events occurred. High-dose PPI (139 events in 1270 patients) was superior to low-dose PPI (174 events in 1265 patients; time ratio [TR] 1·27, 95% CI 1·01–1·58, p=0·038). Aspirin (127 events in 1138 patients) was not significantly better than no aspirin (154 events in 1142 patients; TR 1·24, 0·98–1·57, p=0·068). If patients using non-steroidal anti-inflammatory drugs were censored at the time of first use, aspirin was significantly better than no aspirin (TR 1·29, 1·01–1·66, p=0·043; n=2236). Combining highdose PPI with aspirin had the strongest effect compared with low-dose PPI without aspirin (TR 1·59, 1·14–2·23, p=0·0068). The numbers needed to treat were 34 for PPI and 43 for aspirin. Only 28 (1%) participants reported study-treatment-related serious adverse events. Interpretation High-dose PPI and aspirin chemoprevention therapy, especially in combination, significantly and safely improved outcomes in patients with Barrett’s oesophagus.</p