CO2 emissions arising from the burning of fossil fuels have altered seawater chemistry far more rapidly than the Earth has previously experienced, and the rate and extent of this change are expected to affect shallow water marine organisms. The increased CO2 diffuses from the atmos- phere into ocean surface waters, resulting in increased partial pressure of CO2, and reduced (CO3 2- ) and pH. The CO2-driven ocean acidification leads to a decrease in calcium carbonate (CaCO3) satu- ration state in the ocean surface waters and has potential impacts on calcifiers. The present study focuses on the effects of ocean acidification on early developmental and reproductive stages of calci- fiers, both of which are believed to be the most vulnerable stages to environmental change within a life cycle. Laboratory experiments revealed that ocean acidification has negative impacts on the fer- tilization, cleavage, larva, settlement and reproductive stages of several marine calcifiers, including echinoderm, bivalve, coral and crustacean species. There appear to be significant ontogenetic impacts and species-specific differences in tolerance to the high CO2 levels. The conclusion is that future changes in ocean acidity will potentially impact the population size and dynamics, as well as the community structure of calcifiers, and will therefore have negative impacts on marine eco- systems. Further studies are needed to evaluate the potential impacts on non-calcifiers, as well as the synergistic impacts of ocean acidification and climate change. Studies should also focus on the adaptive capability of marine organisms, which will be crucial to the ability to forecast how marine organisms and ecosystems will respond to the world's oceans as they warm and acidify.

/pdf/effects-of-co2-driven-ocean-acidification-on-the-early-3y8n4y7gxd.pdf

Effects of CO2-driven ocean acidification on the early developmental stages of invertebrates

Proton channels exist in a wide variety of membrane proteins where they transport protons rapidly and efficiently. Usually the proton pathway is formed mainly by water molecules present in the protein, but its function is regulated by titratable groups on critical amino acid residues in the pathway. All proton channels conduct protons by a hydrogen-bonded chain mechanism in which the proton hops from one water or titratable group to the next. Voltage-gated proton channels represent a specific subset of proton channels that have voltage- and time-dependent gating like other ion channels. However, they differ from most ion channels in their extraordinarily high selectivity, tiny conductance, strong temperature and deuterium isotope effects on conductance and gating kinetics, and insensitivity to block by steric occlusion. Gating of H+ channels is regulated tightly by pH and voltage, ensuring that they open only when the electrochemical gradient is outward. Thus they function to extrude acid from cells. H+ch...

https://www.physiology.org/doi/pdf/10.1152/physrev.00028.2002

Voltage-Gated Proton Channels and Other Proton Transfer Pathways

https://www.ldeo.columbia.edu/~polissar/OrgGeochem/popp-et-al-1998-effect-of.pdf

Effect of Phytoplankton Cell Geometry on Carbon Isotopic Fractionation

There is strong evidence that aquaporins are central components in plant water relations. Plant species possess more aquaporin genes than species from other kingdoms. According to sequence similarities, four major groups have been identified, which can be further divided into subgroups that may correspond to localization and transport selectivity. They may be involved in compatible solute distribution, gas-transfer (CO2, NH3) as well as in micronutrient uptake (boric acid). Recent advances in determining the structure of some aquaporins gives further details on the mechanism of selectivity. Gating behaviour of aquaporins is poorly understood but evidence is mounting that phosphorylation, pH, pCa and osmotic gradients can affect water channel activity. Aquaporins are enriched in zones of fast cell division and expansion, or in areas where water flow or solute flux density would be expected to be high. This includes biotrophic interfaces between plants and parasites, between plants and symbiotic bacteria or fungi, and between germinating pollen and stigma. On a cellular level aquaporin clusters have been identified in some membranes. There is also a possibility that aquaporins in the endoplasmic reticulum may function in symplasmic transport if water can flow from cell to cell via the desmotubules in plasmodesmata. Functional characterization of aquaporins in the native membrane has raised doubt about the conclusiveness of expression patterns alone and need to be conducted in parallel. The challenge will be to elucidate gating on a molecular level and cellular level and to tie those findings into plant water relations on a macroscopic scale where various flow pathways need to be considered.

Plant aquaporins: multifunctional water and solute channels with expanding roles.

Summary
A number of lines of evidence (Mr, number of -OH groups, measured fluxes at inner mitochondrial membranes) suggest the intrinsic PSi(OH)4 of about 10-10 m s-1 in the plant cell plasmalemma. While relatively low, such a PSi(OH)4 could maintain the intracellular concentration of Si(OH)4 equal to that in the medium for a phytoplankton cell of 5 μm radius growing with a generation time of 24 h. Such passive entry could not account for SiO, precipitation such as is required for scale (Chrysophyceae) or wall (Bacillariophyceae) production in terms of either the generation of a super-saturated solution or the quantity of SiO2 required; active transport occurs at the plasmalemma (and possibly at an internal membrane) of such cells. The energy required for silicification, even in a diatom with an Si/C ratio of 0.25, is only some 2% of the total energy (as NADPH and ATP) needed for growth; the energy cost of leakage of Si(OH)4 due to the intrinsic permeability of lipid bilayers to Si(OH)4 is never more than 10% of the cost of silicification.

In vascular land plants the entry of Si from the soil into the xylem can involve a flux ratio (mol Si/m3 water) that is less than (e.g. Leguminoseae) equal to (e.g. many Gramineae) or greater than (e.g. Oryza, Equisetum) the concentration (mol m-3) in the bathing solution. Even the low influx of the Leguminoseae cannot be accounted for by the ‘lipid solution’ value of PS(OH)4, but requires entry coupled (phenomenologically) to water influx with a reflexion coefficient of about 0.9. The situation in most Gramineae is described by such a coupling with a reflexion coefficient near O, while the accumulation of Si (relative to water) in Oryza and Equisetum involves an apparent reflexion coefficient which is negative, i.e. an active transport system stoichiometrically related to water flux. Even in Leguminoseae with a transpiration-stream concentration of Si(OH)4 of only 20 mmol m-3 (cf. the soil solution at 200 mmol m-3), the fact that only I % of the water in the xylem is retained in the plant means that Si(OH)4 at transpirational termini approaches saturation; super-saturation, and precipitation of SiO, occurs in Gramineae and Equisetum. SiO2 precipitation occurs mainly near transpirational termini but can also occur in the xylem vessels and endodermis of roots, for example. Si(OH)2 mobility in the phloem seems to be very restricted.

The energy costs of SiO2 relative to organic compounds as structural and defensive materials are in the ratio of 1:10-1:20 (on the basis of weight of material). The relative rarity of SiO2 as a structural material is discussed in the context of the evolution of Si(OH)4-transport mechanisms.

J. Gutknecht

Papers

Diffusion of carbon dioxide through lipid bilayer membranes: Effects of carbonic anhydrase, bicarbonate, and unstirred layers