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Science Square (Issue 92)
May 1, 2013

Caffeine as a repellent defense chemical

Wright GA et al. Caffeine in Floral Nectar Enhances a Pollinator's Memory of Reward. Science, 2013; 339 (6124): 1202

Caffeine is thought to be a repellent defense chemical in the plant kingdom but a recent study showed for the first time that there are low doses of caffeine in the nectar of various plants (including citrus fruits) and this has very important consequences on bee behavior, pollination and overall ecological balance. After discovering a trace amount of caffeine in many types of nectars, scientists decided to test the effect of caffeine on bees, which are primary feeders of nectars. They first trained bees to respond to a sugar reward when they would smell a certain floral scent. During the experiments, half of the bees received caffeine and the other half did not. After a few days, reward responses of bees against the same set of scents were tested again to evaluate whether they could remember the exact floral scents over time. The results were very clear; bees who had caffeine responded to the floral scents three times greater, suggesting that caffeine dramatically improved their olfactory memories. Interestingly, although caffeine tastes bitter to many insect types, the levels in the plant nectarines are too low to taste yet high enough to enhance their long-term memories. Remembering floral traits is actually a difficult task for bees, as they buzz from flower to flower every day. Caffeine definitely helps bees to remember where the flowers were, thereby improving their foraging skills. In turn, plants end up spreading their pollens more efficiently with a faithful pollinator. Since bees are the major pollinators for many crops and wild flowering species, declines in bee populations would bring serious problems to agriculture and ecosystems in general. Thus, understanding the mechanisms of how bees forage and mediate efficient pollinations would definitely help us to manage natural biodiversity and sustainable crop production.

1600 Years of Ice in Andes Melted in 25 Years

Thompson LG et al. Annually Resolved Ice Core Records of Tropical Climate Variability Over the Past ~1800 Years. Science, 2013; DOI: 10.1126

The human release of greenhouse gases, emitted mostly from the combustion of fossil fuels in cars, factories and power plants, is a major cause for global warming. Global warming has much more dramatic consequences on places with high latitudes (like tropics) and high altitudes. Quelccaya ice cap, the world’s largest tropical ice sheet, seems to be one of the most affected places on earth by the global climate change. Quelccaya is located on a volcanic plain that is 18,000 feet above sea level in the Peruvian Andes. Team of glaciologists has been drilling deep into this rapidly melting ice cap, collecting ice samples and analyzing the chemical tracers to reconstruct past climatic variations in the area. Scientists typically estimate the history of ice sheets by carbon dating the plants that had been frozen by the glacier but later exposed as the ice cap melts over time. Several years ago, the same group of researchers found that the plant population that had been exposed after melting was 4,700 years old. In this recent study, 1000 feet of additional melting has revealed plants that are 6,300 years old. A simple yet terrifying interpretation of these results is that ice that accumulated over approximately 1,600 years melted back in no more than 25 years. Scientists predict that the rate of ice melting in the area appears to be faster than any time in the geological record since the end of the last ice age. In addition to potentially terminal problems in the climate and ecosystem of Andes, recent melting also raises important concerns about water supplies for Andean communities. Although melting might increase current water supplies in the short run, it might bolster population growth in urban areas of Andes and create much acute problems in the area in the long run.

Bioengineering Transplantable Kidneys

Song JJ et al. Regeneration and Experimental Orthotopic Transplantation of a Bioengineered Kidney. Nature Medicine, 2013; DOI: 10.1038

Kidney failure is a common medical problem in many parts of the world and there is no available cure. The only possible treatments for kidney failures are dialysis and organ transplantation. Both of these solutions are costly, not permanent and medically problematic. Towards creating personalized replacement kidneys, researchers from Massachusetts General Hospital in Boston made a great advancement by making a functioning rat kidney in their laboratory. Researchers used a technique called “decellularization” that had previously been used to generate working hearts, lungs and livers. Researchers first stripped out the functional cells of a rat kidney using a detergent solution, which would leave a white cellular matrix called “collagen scaffold” that gives the organ its original three-dimensional structure. This step is absolutely essential for successful organ regeneration as intricate architecture of the kidney can be preserved only with such technique. Then, they introduced fresh kidney and blood vessel cells isolated from newborn rats onto this scaffold. After 12 days of incubation, seeded cells grew perfectly to cover the collagen scaffold. Next, these regenerated kidneys were implanted into a live rat, where they efficiently filtered the rat blood and produced urine, without any signs of bleeding or clotting. Although this new technology needs a lot of improvement and refinement, it will ultimately lead to the development of functional bioengineered kidneys from patients’ own cells for immediate transplantation.