Tag: transport

Clays transport more water into the Earth’s interior than we thought

Clays transport more water into the Earth’s interior than we thought

Nobody knows how much water is contained in the Earth’s interior. It’s 6400 kilometres from the surface to the centre, but the deepest point we can get to is mere 12 kilometres, so most estimations are based on assumptions and extrapolations about the composition of our planet’s mantle and core. A study by a research team led by Yongjae Lee from Yonsei University (South Korea), conducted at PETRA III as well as at Pohang (South Korea) and the Advanced Photons Source at Argonne National Laboratory (USA), now shows that minerals might carry more water into the Earth’s deep mantle than previously assumed.

Water affects many properties of Earth’s interior: heat, deformation, volcanic and seismic activity and more. These in turn have a direct influence on life on Earth. Knowing more precisely how water distribution across the Earth began and how it has changed over the Earth’s 4.6 billion-year history might give us clues as to how it will evolve in the future.

Experiments performed at DESY’s synchrotron facility PETRA III, PLS-II at Pohang, South Korea and the Advanced Photons Source at Argonne National Laboratory, USA demonstrated that sediment minerals from Earth’s continents called clays can significantly influence the water household of the Earth’s interior. This study was conducted as part of an effort to understand how the subduction process that sends tectonic plates down to the mantle affects the global transport and distribution of water through changes in the water content contained in minerals composing the subducting plate.

The team of scientists led by Yongjae Lee from Yonsei University (South Korea) used a heated diamond anvil cell, an experimental device that can expose material to extremely high pressures and temperatures, for experiments to simulate the path clay minerals would take in a cold subduction zone, where one tectonic plate disappears into the mantle underneath another tectonic plate. They then studied the breakdown of those clays in detail. The study published in Nature Communications concludes that clays in subducting sediments are responsible for delivering up to 22% of the total water transported into the lower mantle, which is a significant amount and helps constrain the question of how much water could be in the Earth’s deep interior in total.

When continental rocks weather and break down they eventually transform into clay minerals. “Clays are layered sheet silicates that are easily transported to the ocean via rivers and make up the top most part of the oceanic plate. When these sediments are transported via tectonic movement to the edges of the continents and dive down into the Earth’s interior via the subduction process, they are exposed to elevated pressures and temperatures,” explains Yoonah Bang, lead author and former student at Yonsei University. One of the major minerals contributing to the clays in the sediments is the alumina-carrying silicate mineral called pyrophyllite (Al2Si4O10(OH)2), “Using a pressure cell consisting of resistively heated diamond anvils, we are able to simulate pressures of up to some 230,000 atmospheres and temperatures of 900 degrees Celsius to mimic the subduction path pyrophyllite will take when it dives down to the lower mantle” says Bang.

In cold subduction zones like those located in the west Pacific, pyrophyllite transforms to the minerals gibbsite (Al(OH)3) and diaspore (AlO(OH)) at a depth of some 135 kilometres. During this process, the minerals take up water from the surrounding hydrated slab and carry it down to a depth of 185 kilometres. From here sequential transformations take place to other water-bearing minerals that eventually drag the same amount of water initially contained in pyrophyllite to a depth of 700 kilometres in the lower mantle. “This shows how important it is to clearly understand the role of clay minerals during the subduction process,” explains Y. Lee, who led this work. “Our research implies that clay minerals such as pyrophyllite would have transported about 2~3% of global ocean water down to the lower mantle over 2.5 billion years.”

“The findings contribute to the overall understanding of the hydration of the Earth through its history”, says Hanns-Peter Liermann, leader of the ‘Extreme Conditions Beamline’ P02.2 at PETRA III, where part of the research was performed.

Read more on DESY website

Image: An illustration depicting that water contained in clay minerals is transported to the lower mantle through breakdown reactions along the subducting plate

Credit: Authors/Original Publication

Deciphering the sugar transport in plants

Deciphering the sugar transport in plants

Synchrotron studies to understand sucrose highway

In most plant species, sucrose is the main form of assimilated carbon produced during photosynthesis. Sucrose is essential for plant growth, as it provides a source of carbon to produce new molecules, but also energy for the plant cells. Sucrose has also an associated role as a signalling molecule, by regulating the growth of new organs, accumulation of storage proteins, and flowering in plants. Long-distance sucrose distribution from the green source tissues, generally leaves, to energy-demanding sink tissues (flowers, fruits, new organ in formation) is mediated by a specific and highly modified vascular tissue called phloem. The transport of sucrose in the phloem is an active transport, as sucrose is loaded in the conductive tissue by specific proteins from the SUC/SUT family. The SUC1 transporter from A. thaliana is located on the membrane of cells and use the proto-motive force to drive the loading of sucrose. Despite their key role in plants, the working mechanism of these SUCs transporters is not yet well understood.

A team of researchers from the Aarhus University recently published a new study in Nature Plants to understand the precise mechanism of action of the SUC1 transporter. They used X-ray diffraction data collected at I04 and I24 beamlines at Diamond to determine the 3D structure of this transmembrane protein. They wanted to understand how SUCs protein recognise sucrose, and how transport is proton coupled. As sugar transport is a key feature in plants, understanding how proteins can fine-tune the sugar concentration in conductive tissue is fundamental. Lead author of this study, Dr Bjørn Panyella Pedersen explained:

Active sucrose transport and loading into the phloem determines the turgor pressure. This pressure creates the vascular flow of nutrients (sucrose and all other components of the sap), and determines which parts of the plant will grow in response to environmental signals. Ultimately, we hope our research will help to augment control of growth and morphology in plants.

For their study, the team used a well-known plant model, Arabidopsis thaliana. This plant is widely used as model because it has a sequenced and annotated genome, and huge collections of mutant lines exists, allowing characterisation of plants where a specific gene is not expressed. Furthermore, this plant has a fast life cycle and produces numerous seeds.

In this study, the researchers present the structure of SUC1, and key elements to explain both the recognition of sucrose by the transporter, and the active transport by proton coupling. They produced SUC1 transporters and performed in-vivo assays to determine if the protein was functioning, and then proceed to solving the structure at the microfocus beamline I24. Dr Bjørn Panyella Pedersen says:

We have used Diamond’s beamlines I24 and I04 for our research since 2014, both in person and by remote data collection. We have always been very happy with the support and quality of the beamlines at Diamond. Brexit and the Corona years have made our access to the facility more challenging at times but with the help from the support staff we have been able to maintain our work at Diamond.

Read more on the Diamond website

Image: The 2.7 Å electron density map of SUC1 (2mFo-DFc map contoured at 1σ). Density corresponding to the N and C domain are coloured cyan and orange, respectively. EHR and IHR domains are coloured pale yellow.