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.
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 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.
In one of the final stages of cyanobacterial Photosystem II (PS II) assembly, binding of up to four extrinsic proteins to PS II stabilizes the oxygen-evolving complex (OEC). Growth of cyanobacterial ...mutants deficient in certain combinations of these thylakoid-lumen-associated polypeptides is sensitive to changes in environmental pH, despite the physical separation of the membrane-embedded PS II complex from the external environment. In this perspective we discuss the effect of environmental pH on OEC function and photoautotrophic growth in cyanobacteria with reference to pH-sensitive PS II mutants lacking extrinsic proteins. We consider the possibilities that, compared to pH 10.0, pH 7.5 increases susceptibility to PS II-generated reactive oxygen species (ROS) causing photoinhibition and reducing PS II assembly in some mutants, and that perturbations to channels in the lumenal regions of PS II might alter the accessibility of water to the active site as well as egress of oxygen and protons to the thylakoid lumen. Reduced levels of PS II in these mutants, and reduced OEC activity arising from the disruption of substrate/product channels, could reduce the trans-thylakoid pH gradient (ΔpH), leading to the impairment of photosynthesis. Growth of some PS II mutants at pH 7.5 can be rescued by elevating CO2 levels, suggesting that the pH-sensitive phenotype might primarily be an indirect result of back-pressure in the electron transport chain that results in heightened production of ROS by the impaired photosystem.
In Photosystem
II
, loop E of the chlorophyll‐binding
CP
47 protein is located near a redox‐active tyrosine,
Y
D
, forming a symmetrical analog to loop E in
CP
43, which provides a ligand to the ...oxygen‐evolving complex (
OEC
). A Glu364 to Gln substitution in
CP
47, 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.
Abstract
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 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,
M
acrocystis pyrifera
(
L
aminariales), 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
CO
2
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
.
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.
Barrett's esophagus is an increasingly common disease that is strongly associated with reflux of stomach acid and usually a hiatus hernia, and it strongly predisposes to esophageal adenocarcinoma ...(EAC), a tumor with a very poor prognosis. We report the first genome-wide association study on Barrett's esophagus, comprising 1,852 UK cases and 5,172 UK controls in the discovery stage and 5,986 cases and 12,825 controls in the replication stage. Variants at two loci were associated with disease risk: chromosome 6p21, rs9257809 (Pcombined=4.09×10(-9); odds ratio (OR)=1.21, 95% confidence interval (CI)=1.13-1.28), within the major histocompatibility complex locus, and chromosome 16q24, rs9936833 (Pcombined=2.74×10(-10); OR=1.14, 95% CI=1.10-1.19), for which the closest protein-coding gene is FOXF1, which is implicated in esophageal development and structure. We found evidence that many common variants of small effect contribute to genetic susceptibility to Barrett's esophagus and that SNP alleles predisposing to obesity also increase risk for Barrett's esophagus.
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