Evidence from warm past confirms recent IPCC estimates of climate sensitivity

 

New evidence showing the level of atmospheric CO2 millions of years ago supports recent climate change predications from the Intergovernmental Panel on Climate Change (IPCC). A multinational research team, led by scientists at the University of Southampton, has analysed new records showing the CO2 content of the Earth's atmosphere between 2.3 to 3.3 million years ago, over the Pliocene. During the Pliocene, the Earth was around 2ºC warmer than it is today and atmospheric CO2 levels were around 350-400 parts per million (ppm), similar to the levels reached in recent years. By studying the relationship between CO2 levels and climate change during a warmer period in Earth's history, the scientists have been able to estimate how the climate will respond to increasing levels of carbon dioxide, a parameter known as 'climate sensitivity'. The findings, which have been published in Nature, also show how climate sensitivity can vary over the long term. "Today the Earth is still adjusting to the recent rapid rise of CO2 caused by human activities, whereas the longer-term Pliocene records document the full response of CO2-related warming," says Southampton's Dr Gavin Foster, co-author of the study. "Our estimates of climate sensitivity lie well within the range of 1.5 to 4.5ºC increase per CO2 doubling summarised in the latest IPCC report. This suggests that the research community has a sound understanding of what the climate will be like as we move toward a Pliocene-like warmer future caused by human greenhouse gas emissions." Lead author of the study, Dr Miguel Martínez-Botí, also from Southampton said: "Our new records also reveal an important change at around 2.8 million years ago, when levels rapidly dropped to values of about 280 ppm, similar to those seen before the industrial revolution. This caused a dramatic global cooling that initiated the ice-age cycles that have dominated Earth's climate ever since." The research team also assessed whether climate sensitivity was different in warmer times, like the Pliocene, than in colder times, like the glacial cycles of the last 800,000 years. Professor Eelco Rohling of The Australian National University in Canberra says: "We find that climate change in response to CO2 change in the warmer period was around half that of the colder period. We determine that this difference is driven by the growth and retreat of large continental ice sheets that are present in the cold ice-age climates; these ice sheets reflect a lot of sunlight and their growth consequently amplifies the impact of CO2 changes." Professor Richard Pancost from the University of Bristol Cabot Institute, added: "When we account for the influence of the ice sheets, we confirm that the Earth's climate changed with a similar sensitivity to overall forcing during both warmer and colder climates." Story Source: The above story is based on materials provided by University of Southampton. Note: Materials may be edited for content and length. Journal Reference: M. A. Martínez-Botí, G. L. Foster, T. B. Chalk, E. J. Rohling, P. F. Sexton, D. J. Lunt, R. D. Pancost, M. P. S. Badger, D. N. Schmidt. Plio-Pleistocene climate sensitivity evaluated using high-resolution CO2 records. Nature, 2015; 518 (7537): 49 DOI: 10.1038/nature14145

Scientists reprogram plants for drought tolerance

 

Crops and other plants are constantly faced with adverse environmental conditions, such as rising temperatures (2014 was the warmest year on record) and lessening fresh water supplies, which lower yield and cost farmers billions of dollars annually. Drought is a major environmental stress factor affecting plant growth and development. When plants encounter drought, they naturally produce abscisic acid (ABA), a stress hormone that inhibits plant growth and reduces water consumption. Specifically, the hormone turns on a receptor (special protein) in plants when it binds to the receptor like a hand fitting into a glove, resulting in beneficial changes -- such as the closing of guard cells on leaves, called stomata, to reduce water loss -- that help the plants survive. While it is true that crops could be sprayed with ABA to assist their survival during drought, ABA is costly to make, rapidly inactivated inside plant cells and light-sensitive, and has therefore failed to find much direct use in agriculture. Several research groups are working to develop synthetic ABA mimics to modulate drought tolerance, but once discovered these mimics are expected to face lengthy and costly development processes. The agrochemical mandipropamid, however, is already widely used in agricultural production to control late blight of fruit and vegetable crops. Could drought-threatened crops be engineered to respond to mandipropamid as if it were ABA, and thus enhance their survival during drought? Yes, according to a team of scientists, led by Sean Cutler at the University of California, Riverside. The researchers worked with Arabidopsis, a model plant used widely in plant biology labs, and the tomato plant. In the lab, they used synthetic biological methods to develop a new version of these plants' abscisic acid receptors, engineered to be activated by mandipropamid instead of ABA. The researchers showed that when the reprogrammed plants were sprayed with mandipropamid, the plants effectively survived drought conditions by turning on the abscisic acid pathway, which closed the stomata on their leaves to prevent water loss. The finding illustrates the power of synthetic biological approaches for manipulating crops and opens new doors for crop improvement that could benefit a growing world population. "We successfully repurposed an agrochemical for a new application by genetically engineering a plant receptor -- something that has not been done before," said Cutler, an associate professor of botany and plant sciences. "We anticipate that this strategy of reprogramming plant responses using synthetic biology will allow other agrochemicals to control other useful traits -- such as disease resistance or growth rates, for example." Study results appear online Feb. 4 in Nature. Cutler explained that discovering a new chemical and then having it evaluated and approved for use is an extremely involved and expensive process that can take years. "We have, in effect, circumvented this hurdle using synthetic biology -- in essence, we took something that already works in the real world and reprogrammed the plant so that the chemical could control water use," he said. Protein engineering is a method that enables the systematic construction of many protein variants; it also tests them for new properties. Cutler and his co-workers used protein engineering to create modified plant receptors into which mandipropamid could fit and potently cause receptor activation. The engineered receptor was introduced into Arabidopsis and tomato plants, which then responded to mandipropamid as if they were being treated by ABA. In the absence of mandipropamid, these plants showed minimal difference from plants that did not possess the engineered protein.

7 Things You Didn't Know About Coffee

 

Coffee is one of the world's favorite beverages and the second most valuable legally traded commodity in the world, second only to oil.  Experts estimate that 2.25 billion cups of coffee are consumed each day worldwide.  But, how much do you know about your favorite brew?  Keep reading to learn 7 buzz-worthy facts about your good old cup of joe. Tara Moore/Taxi/Getty Images The US People Drink More Coffee Than Anyone Else In the World About 83% of the adult people in the USA drink coffee, averaging three cups of coffee per person per day.  That's 587 million cups of joe every single day.  It's no wonder that the world's two largest coffee chains --- Starbucks and Dunkin' Donuts --- are both based in the United States.  Starbucks has over 13,000 stand alone coffee shops in the United States, meaning that you can never get more than 130 miles away from a Frappucino. Hotel Finca Rosa Blanca. Akila McConnell, licensed to About.com   The Coffee Bean Isn't a Bean The coffee bean isn't a bean.  What we call the coffee bean is actually the seed of the coffee cherry, or the fruit of the coffee tree.  The coffee cherry is ripe when it turns bright red.  Then, it is picked, rinsed, and the pulp is removed from the seed/bean.  Most coffee berries have two coffee beans/seeds within but certain berries will only have one bean/seed, which are called peaberries.  Peaberries have a stronger flavor and are prized as premium coffee blends. Hop over to this slideshow to read about the entire process of how your coffee moves from seed to cup. More » 1850: A servant serves coffee to a group of Yemeni coffee merchants who have set up camp in the desert on their way to Mocha. Hulton Archive/Getty Images   The Word Coffee Owes Its Origin to Many Languages The word “coffee” has roots in several languages. In Yemen, which is where the coffee plant was discovered and one of the earliest cultivators of coffee, the bean was called qahwah, which was a truncated form of qawhat al-bun, meaning "wine of the bean."  The Muslim trade routes brought coffee to the Middle East where the Turks called the liquid kahveh.  The Dutch called the brew koffie and brought the liquid to England along their trade routes with Asia and Africa, which finally became coffee in English. More » Good quality coffee versus bad quality coffee. Akila McConnell, licensed to About.com Ice Water Will Tell You if Your Coffee Was Roasted Well If you're standing in the grocery store bewildered by the array of coffee --- ranging from $1 per pound to $12 per pound --- I've got one simple trick that will help you determine if the coffee you're purchasing is high quality roasted coffee.  Just put one tablespoonful of ground coffee on top of a glass of ice water.  If your coffee stays on top of the water and does not leach into the water after a few minutes, it's been roasted properly.  If it leaches, then it's either over-roasted or under-roasted. Keep reading this post to learn more about why this trick works.   1674, A 'women's petition' against the debilitating effects of drinking coffee, the stimulating hot beverage containing caffeine. Hulton Archive/Getty Images  17th Century Women Wanted to Ban Coffee In the 17th century, coffee became popular in England and continental Europe.  Many believed that coffee had intoxicating properties like alcohol, which led some clergy to ban it in their towns.  And, a (pretty hilarious) anonymous women's petition in 1675 proposed the ban of coffee because of the "grand inconvenience" when coffee "enfeebled" and "eunuch'd" their husbands. Jump over to this post to read more about the history of coffee. More » Latte art. Carlina Teteris/Moment You Can Get Barista Trained and Learn How to Make Latte Art At Espresso Academy in Florence, Italy, you can spend days perfecting the art of making coffee.  Learn how to become a barista in a two day course or take an advanced class on latte art.  If you can't make it over to Europe, Intelligentsia Coffee Shop offers public tasting and education classes at each of their retail locations in Los Angeles, New York, and Chicago.  For example, you can take a 3 hour Barista training class for $200 or a tour of their roasting works for $50. Jump over to this post to learn more about seven great coffee tours and experiences across the world. More » Coffee and coffee beans. Anthony Dawson/Moment   Coffee Might Just Be Good For Your Health Coffee might just be a superfood because its antioxidant properties combined with caffeine has been shown to: reduce mortality from heart disease reduce the risk of diabetes, dementia, colon cancer, cirrhosis, gallstones, and Parkinson's disease provide headache relief and asthma relief So, you can feel good about picking up your cup of coffee tomorrow morning.  But, don't drink too much!  Overconsumption of coffee can increase your death rates. More »   Source : www.about.com

How will ocean acidification impact marine life?

 

Coral reefs are one of the key calcifying species threatened by ocean acidification. Many marine organisms--such as coral, clams, mussels, sea urchins, barnacles, and certain microscopic plankton--rely on equilibrated chemical conditions and pH levels in the ocean to build their calcium-based shells and other structures. A new analysis published in the journal Environmental Science and Technology provides a holistic analysis of how species will be affected worldwide under different climate scenarios. "Calcifying species are indispensable for ecosystems worldwide: they provide nursery habitats for fish, food for marine predators, and natural defenses for storms and erosion. These species are also particularly vulnerable to ocean acidification triggered by increased fossil fuel emissions," says IIASA researcher Ligia Azevedo, who led the study. Just as carbonated soda water is more acidic than flat tap water, higher levels of carbon dioxide (CO2) in the ocean cause the water to become more acidic. And high acidity makes it more difficult for calcifying species to make their calcium structures such as shells, reefs, and exoskeletons. "Previous studies have shown that marine species were being negatively affected by decreasing ocean pH levels. But until now most studies looked at individual species. This study is one of the first to analyze the impact on the whole community of calcifying species, while also looking at both pH levels and CO2 partial pressure," says Azevedo. The study examines the impact of increased ocean acidity on species growth, reproduction, and survival. It used two climate change scenarios from the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5): In the low emissions scenario, ocean pH is projected to decrease from 8.1 to 7.95, while in the high emissions scenario, median ocean pH is expected to decrease to 7.80. (Lower pH indicates higher acidity). The analysis finds that under the high emissions scenario, between 21-32% of calcifying species would be significantly affected, based on a threshold of 10% of a species population being affected. In the low emissions scenario, only 7-12% of species would be affected. Azevedo notes that while the study is an important new milestone for ocean acidification research, it does not show what level of impact which species population can handle, that is, how much acidification is too much. "It's hard to say what the level of impact would mean for different organisms -- a 10% rate could be no problem for some species, but for other more sensitive species it could mean one step closer to local extinction," explains Azevedo. The study also emphasizes that much uncertainty remains about the level of acidification that would lead to major impacts on calcifying species -- in part because of varying experimental results. The researchers say that the analysis is an important step forward to provide policymakers a better understanding of the big picture of climate impacts on the ocean. Azevedo says, "The main benefit of this study is to provide a new research framework that policymakers could use for climate policy planning, life cycle impact assessment, and environmental risk assessment." Story Source: The above story is based on materials provided by International Institute for Applied Systems Analysis. Note: Materials may be edited for content and length. Journal Reference: Ligia B. Azevedo, An M. De Schryver, A. Jan Hendriks, Mark A. J. Huijbregts. Calcifying Species Sensitivity Distributions for Ocean Acidification. Environmental Science & Technology, 2015; 49 (3): 1495 DOI: 10.1021/es505485m

A novel shuttle for fatty acids

 

Oils from plant seeds provide the basis for many aspects of modern life that are taken for granted, being used to make cooking oil, soap, fuel, cosmetics, medicines, flooring, and many other everyday products. Whether derived from olives, oil palm, rapeseed, soybeans, peanuts or sunflowers, the major energy-rich constituents of these oils are lipids containing fatty acids made in the plants' chloroplasts. While most of this process by which plants make fatty acids is well-known, the mechanism by which these important molecules get out of the chloroplast was unclear. But now biologists at the Ludwig Maximilians University in Munich have discovered a previously unknown transport system for fatty acids in plant cells. LMU biologist Dr. Katrin Philippar and members of her research group have shown in a paper publishing today in the open access journal PLOS Biology that a novel chloroplast membrane protein plays a central role in the process of transporting fatty acids from where they are generated in chloroplasts out into the cell cytoplasm before they become incorporated into lipid molecules. The work may open new routes to improve the production of biofuels. Fatty acids are the major constituents of lipids. In plants, fatty acids are synthesized exclusively in the chloroplasts, and must be exported into the cell cytoplasm -- the aqueous interior of the cell in which the chloroplasts are suspended -- before they can be incorporated into lipid molecules. "However, the mechanism for how fatty acids are transported across the membranes of the chloroplast was thus so far unclear," says LMU biologist Dr. Katrin Philippar. She and members of her research group have shown in the paper publishing in PLOS Biology that a member of a previously uncharacterized protein family plays a central role in this process. The researchers identified an integral membrane protein in the inner chloroplast envelope of the model plant Arabidopsis thaliana. They subsequently named the protein FAX1 (for 'fatty acid export 1') on the basis of studies on Arabidopsis strains that had either lost the capacity to produce FAX1 or synthesized FAX1 proteins in excess amounts. These investigations revealed that FAX1 is essential for the synthesis of the fatty acid- and lipid-rich layers that coat pollen grains and form the general waxy layer on the plant surface. In addition, in plants that are unable to express FAX1, the lipid content outside chloroplasts is decreased. In lines that overproduced FAX1, on the other hand, the researchers observed the opposite effect. In particular, levels of so-called triacylglycerol lipids (TAGs) were found to be significantly higher in leaves and flowers of these strains than in wild-type plants. "Furthermore, we were able to show that, when introduced into yeast cells, FAX1 can transport fatty acids. On the basis of all these findings, we conclude that FAX1 in Arabidopsis mediates export of fatty acids across the inner envelope membrane of the chloroplast. Thus, our work elucidates a novel and previously entirely unknown mechanism of fatty acid transport," Philippar explains. "FAX1 also has an influence -- probably indirect -- on carbohydrate metabolism in the cell because lipids and carbohydrates serve as the primary sources of metabolic energy in plants," she adds. The significance of FAX1 function for the synthesis of TAGs is of special interest, because TAG-rich plant oils provide the basis for the production of biofuels. "Our experiments indicate that overexpression of FAX1 increases the overall level of TAGs in Arabidopsis. So further investigation of the members of this protein family may lead to new strategies for the manufacture of biofuels," Philippar concludes. Interestingly, proteins found in vertebrate mitochondria, whose biological role has remained unknown as well, are related to the FAX family. Further study of the FAX proteins therefore promises to throw new light on the function of these enigmatic gene products as well. Story Source: The above story is based on materials provided by PLOS. Note: Materials may be edited for content and length. Journal Reference: Nannan Li, Irene Luise Gügel, Patrick Giavalisco, Viktoria Zeisler, Lukas Schreiber, Jürgen Soll, Katrin Philippar. FAX1, a Novel Membrane Protein Mediating Plastid Fatty Acid Export. PLOS Biology, 2015; 13 (2): e1002053 DOI: 10.1371/journal.pbio.1002053

Splash down: High-speed images capture patterns by which raindrops spread pathogens among plants

 

While historical weather records suggest that rainfall may scatter rust and other pathogens throughout a plant population, the mechanism by which this occurs has not been explored, until now. In a paper published in the Journal of the Royal Society Interface, a team from MIT and the University of Liege, in Belgium, presents high-speed images of raindrops splashing down on a variety of leaves coated with contaminated fluid. As seen in high resolution, these raindrops can act as a dispersing agent, in some instances catapulting contaminated droplets far from their leaf source. The researchers observed characteristic patterns of dispersal, and found that the range of dispersal depends on a plant's mechanical properties -- particularly its compliance, or flexibility. Lydia Bourouiba, the Esther and Harold E. Edgerton Career Development Assistant Professor of Civil and Environmental Engineering at MIT, says understanding the relationship between a plant's mechanical properties and the spread of disease may help farmers plant more disease-resistant fields. "We can start thinking of how to smartly reinvent polyculture, where you have alternating species of plants with complementary mechanical properties at various stages of their growth," says Bourouiba, who is a senior author of the paper. "Polyculture is an old concept if you look at native cultures, but this is one way to scientifically show that by alternating plants in one field, you can mechanically and naturally reduce the range of transmission of a pathogen during rainfall." Tracking the fluid dynamics of outbreak In their paper, Bourouiba and Tristan Gilet, of the University of Liege, first addressed a widely held assumption: that pathogens coat leaves in a thin film. The team ran experiments with dozens of types of common foliage, including ivy, bamboo, peppermint, and banana leaves. They conducted hundreds of experiments for each type of foliage, using 30 examples of real plant foliage and 12 artificially engineered materials. In initial trials, the researchers simulated rainfall by running water through a container pricked with tiny holes. The container was suspended several meters in the air, high enough for drops to reach terminal velocity -- the speed of an actual raindrop ­upon impact. The researchers captured the sequence of events as raindrops hit each leaf, using high-speed videography at 1,000 frames per second. From these images, Bourouiba and Gilet noted that as water fell, leaves were unable to support a thin film, instead forming drops on their surface. The team concluded that pathogens, in turn, must rest as droplets -- not film -- on a leaf's surface. "That can initially seem like a small difference, but when you look at the fluid dynamics of the fragmentation and resulting range of contamination around an infected leaf, it actually changes a lot of the dynamics in terms of the mechanism by which [pathogens] are emitted," Bourouiba says. To observe such dynamic differences, the team first simulated rainfall over a flat surface coated with a thin film. When a droplet hit this surface, it launched a crown-like spray of the filmy substance, though most of the spray stayed within the general vicinity. In contrast, the team found that raindrops that splashed onto leaves covered with droplets, rather than a film, launched these drops far and wide. From crescent moons to catapults To examine the effect of raindrops on surface drops in more detail, the researchers performed a separate round of experiments, in which they dotted leaves with dyed water -- a stand-in for pathogens. They then created a setup to mimic one single drop of rain, using lasers to delicately calibrate where on the leaf a drop would fall. From these experiments, Bourouiba and Gilet observed two main patterns of dispersal: a crescent-moon configuration, in which a raindrop flattens upon impact, sliding underneath the dyed droplet and launching it up in an arc, similar to the shape of a crescent moon; and inertial detachment, where a raindrop never actually touches a dyed droplet, but instead pushes the leaf down, causing the dyed droplet to slide downwards, then catapult out -- a consequence of the inertia of the leaf as it bounces back up. After capturing hundreds of raindrop impacts on a range of leaf types, Bourouiba and Gilet realized that whether a droplet assumes a crescent-moon or inertial detachment configuration depends mainly on one property: a leaf's compliance, or flexibility. They found that in general, the floppier a leaf, the less effective it was at launching a wide arc, or crescent-moon of fluid. However, at a certain flexibility, the crescent-moon pattern morphed into one of inertial detachment, in which fluid, in the form of larger drops than what the crescent moon can produce, was flung further from the leaf. From their observations, the researchers developed a theoretical model that quantitatively captures the relationship between a leaf's flexibility, the fragmentation of the fluid, and its resulting pattern of raindrop-induced dispersal. The model, Bourouiba says, may eventually help farmers design fields of alternating crops. While the practice of polyculture has traditionally relied on reducing the spread of disease by alternating plants with varying resistance to pathogens, Bourouiba says the intrinsic mechanical properties -- not biological immunology -- of plants could themselves help contain the spread of disease. "If this were done optimally, ideally you could completely cut the spread to just one neighboring plant, and it would die there," Bourouiba says. "One plant could play the role of a shield, and get contaminated, but its mechanical properties would not be sufficient to project the pathogen to the next plant. So you could start reducing the efficacy of spread in one species, while still using agricultural space effectively." Don Aylor, an emeritus scientist of plant pathology and ecology at the Connecticut Agricultural Experiment Station in New Haven, Conn., says Bourouiba's results may be particularly useful in tamping down disease in small plant populations. "This could help set separation distances for crops of small plants, such as strawberries, that are usually planted in close proximity," says Aylor, who did not contribute to the study. "The farmer would also have to consider the effect of splashing on plastic mulch often used in such crops. In summary, this is a nice study and introduces some findings that are certainly worth following up on."

Inhospitable climate fosters gold ore formation

 

February 4, 2015 ETH Zürich The Witwatersrand Basin in South Africa holds the world’s largest gold deposits across a 200-km long swathe. Individual ore deposits are spread out in thin layers over areas up to 10 by 10 km and contain more gold than any other gold deposit in the world. Some 40% of the precious metal that has been found up to the present day comes from this area, and hundreds of tons of gold deposits still lie beneath the earth. The manner in which these giant deposits formed is still debated among geologists. Geologists are now trying to reconcile the contradictions of two previously published theories. Hard and dangerous labor: The mines provide no place to stand. The Witwatersrand Basin in South Africa holds the world's largest gold deposits across a 200-km long swathe. Individual ore deposits are spread out in thin layers over areas up to 10 by 10 km and contain more gold than any other gold deposit in the world. Some 40% of the precious metal that has been found up to the present day comes from this area, and hundreds of tons of gold deposits still lie beneath the earth. The manner in which these giant deposits formed is still debated among geologists. Christoph Heinrich, Professor of Mineral Resources at ETH and the University of Zurich, recently published a new explanation in the journal Nature Geoscience, trying to reconcile the contradictions of two previously published theories. The prevailing 'placer gold' theory states that the gold at Witwatersrand was transported and concentrated through mechanical means as metallic particles in river sediment. Such a process has led to the gold-rich river gravels that gave rise to the Californian gold rush. Here, nuggets of placer gold have accumulated locally in river gravels in the foothills of the Sierra Nevada, where primary gold-quarz veins provide a nearby source of the nuggets. But no sufficiently large source exists in the immediate sub-surface of the Witwatersrand Basin. This is one of the main arguments of proponents of the 'hydrothermal hypothesis', according to which gold, chemically dissolved in hot fluid, passed into the sediment layers half a billion years after their deposition. For this theory to work, a 10 km thick blanket of later sediments would be required in order to create the required pressure and temperature. However, the hydrothermal theory is contradicted by geological evidence that the gold concentration must have taken place during the formation of host sediments on the Earth's surface. Rainwater rich in hydrogen sulphide Heinrich believes the concentration of gold took place at the Earth's surface, indeed by flowing river water, but in chemically dissolved form. With such a process, the gold could be easily 'collected' from a much larger catchment area of weathered, slightly gold-bearing rocks. The resource geologist examined the possibility of this middle way, by calculating the chemical solubility of the precious metal in surface water under the prevailing atmospheric and climatic conditions. Experimental data shows that the chemical transport of gold was indeed possible in the early stages of Earth evolution. The prerequisite was that the rainwater had to be at least occasionally very rich in hydrogen sulphide. Hydrogen sulphide binds itself in the weathered soil with widely distributed traces of gold to form aqueous gold sulphide complexes, which significantly increases the solubility of the gold. However, hydrogen sulphide in the atmosphere and sulphurous gold complexes in river water are stable only in the absence of free oxygen. "Quite inhospitable environmental conditions must have dominated, which was possible only three billion years ago during the Archean eon," says Heinrich. "It required an oxygen-free atmosphere that was temporarily very rich in hydrogen sulphide -- the smell of rotten eggs." In today's atmosphere, oxygen oxidises all hydrogen sulphide, thus destroying gold's sulphur complex in a short time, which is why gold is practically insoluble in today's river water. Volcanoes and bacteria as important factors In order to increase the sulphur concentration of rainwater sufficiently in the Archean eon, basaltic volcanism of gigantic proportions was required at the same time. Indeed, in other regions of South Africa there is evidence of giant basaltic eruptions overlapping with the period of the gold concentration. A third factor required for the formation of gold deposits at Witwatersrand is a suitable location for concentrated precipitation of the gold. The richest deposits of gold ore in the basin are found in carbon-rich layers, often just millimetres to centimeters thick, but which stretch for many kilometres. These thin layers contain such high gold concentrations that mining tunnels scarcely a metre high some three kilometres below the Earth's surface are still worthwhile. The carbon probably stems from the growth of bacteria on the bottom of shallow lakes and it's here that the dissolved gold precipitated chemically, according to Heinrich's interpretation. The nature of these life forms is not well known. "It's possible that these primitive organisms actively adsorbed the gold," Heinrich speculates. "But a simple chemical reduction of sulphur-complexed gold in water to elementary metal on an organic material is sufficient for a chemical 'gilding' of the bottom of the shallow lakes." The gold deposits in the Witwatersrand, which are unique worldwide, could have thus been formed only during a certain period of the Earth's history: after the development of the first continental life forms in shallow lakes at least 3 billion years ago, but before the first emergence of free oxygen in the Earth's atmosphere approximately 2.5 billion years ago. Story Source: The above story is based on materials provided by ETH Zürich. The original article was written by Peter Rüegg. Note: Materials may be edited for content and length. Journal Reference: Christoph A. Heinrich. Witwatersrand gold deposits formed by volcanic rain, anoxic rivers and Archaean life. Nature Geoscience, 2015; DOI: 10.1038/ngeo2344

Ingenious fine-tuning of plant photosynthesis

 

Malgorzata Pietrzykowska has investigated the specific roles of the two most abundant membrane proteins on Earth, Lhcb1 and 2. Both of them are responsible for light harvesting which is the basis of photosynthesis, the process which sustains life on Earth by providing the oxygen we breathe and the food we eat. Light is collected by pigments called chlorophylls, which absorb mainly blue and red light, whilst green light is reflected, giving plants their characteristic colour. The majority of chlorophylls are associated with the Lhc (light harvesting chlorophyll) protein superfamily, which in flowering plants consists of 13 members. "You have surely noticed that the amount of light during the day is continuously changing. Unlike animals, plants cannot move towards or away from sunlight, therefore they have evolved mechanisms which allow them to cope with the rapid changes in light quality and intensity," says Malgorzata Pietrzykowska. One such process, called state transition, allows plants to redistribute the excess energy from photosystem II (PSII) to photosystem I (PSI), or vice versa. State transitions are regulated by phosphorylation/dephosphorylation of Lhcb1 and Lhcb2. In the model plant species Arabidopsis thaliana Lhcb1 is encoded by as many as five genes, while Lhcb2 is encoded by three, and the proteins are 98% similar at amino acid sequence level. "When I started my PhD, I was amazed by the seemingly huge redundancy of these two proteins. Why do plants need so many copies of almost identical proteins?" asks Malgorzata Pietrzykowska. Malgorzata Pietrzykowska shows that Lhcb1 is important for regulating the amount of light harvesting and for providing quenching sites when too much light is absorbed. More importantly, the abundance of Lhcb1 modulates the size and provides flexibility to the photosynthetic membranes. The role of Lhcb2 on the other hand is mainly in, and limited to, state transitions. When photosystem II is receiving too much energy, Lhcb2 phosphorylation allows detachment of LHCII trimers (consisting of both Lhcb1 and Lhcb2) from PSII, therefore less energy is transferred to PSII. At the same time these trimers attach to photosystem I forming LHCII-PSI complexes, whose formation balances allows energy flow to PSI. In summary, Malgorzata Pietrzykowska shows that despite their similarity, the functions of Lhcb1 and Lhcb2 are different but complimentary in fine-tuning photosynthetic light absorption. This thesis can be found online at: http://umu.diva-portal.org/smash/record.jsf?aq2=%5B%5B%5D%5D&c=2&af=%5B%5D&searchType=SIMPLE&query=Malgorzata+Pietrzykowska&language=sv&pid=diva2%3A779204&aq=%5B%5B%5D%5D&jfwid=-7764&sf=all&aqe=%5B%5D&sortOrder=author_sort_asc&onlyFullText=false&noOfRows=50&dswid=-6624 Story Source: The above story is based on materials provided by Umeå universitet. Note: Materials may be edited for content and length.