sábado, 30 de agosto de 2014
Saving the banana | Science News for Students
These Cavendish bananas probably look familiar because they are the kind found in grocery stores across North America and Europe. But Cavendish bananas are just one of hundreds of varieties eaten around the world.
Among the biggest worries is a nasty soil-borne fungus known as Tropical Race 4, or TR4. It causes “Panama disease,” which makes plants wilt and die.
But now TR4 threatens not only the Cavendish, but also many other varieties of bananas. The stalk on the end of a banana plant has a big structure at the end that is the male flower. Female flowers ring the stalk. Each of those female flowers develops into a single banana. The bananas are called “fingers;” the rows of bananas are “hands.”
Bananas don’t grow on trees. Reaching a height of nearly 3.5 meters (11.5 feet), banana plants lack woody trunks.
Banana plants grow fast.
One way that farmers grow new plants from these types is by removing suckers from mature plants and transplanting them.
Large plantations, however, typically start new plants from tissue culture. That means they take cells from a plant, put them in a nutrient broth and allow those cell clumps to develop into new plants. These clones are being planted over and over throughout the world.
Because each plant now has the exact same set of genes, if one plant is susceptible to a disease, all its clones will be too.
Not all bananas are seedless, though. Some bananas contain dozens of pea-sized seeds.
Last year, banana growers in Mozambique noticed some unhealthy plants. Fearing the worst, farmers had their plants tested. As a bunch of bananas ripen on one stem, a sucker (on the left of the plant’s main stalk) begins to grow from the base of the plant. When the taller plant is finished fruiting, the sucker will grow to take its place.
This fungus — and the Panama disease it causes — is one of the world’s biggest threats to bananas. The name of the disease reflects the country where it was first discovered attacking Gros Michel bananas.
The 2013 Mozambique blight was the first time Panama disease had showed up in Africa, notes Altus Viljoen.
Even careful control measures can’t completely protect plants from the fungus. That’s because TR4 is patient. Once a new banana plant begins to grow next to it, the fungus can attack once more.
Panama disease is not the only threat to bananas. Bacteria infect banana plants, causing them to wilt. Tiny worm-like nematodes can burrow into the roots, making the plants fall over. Unable to photosynthesize in the damaged areas, infected plants produce fewer and smaller fruit.
Now Viljoen, Swennen and other scientists are racing against time to stop the further spread of TR4 — which threatens more than half of the world’s edible bananas.
One approach to stopping the fungus: finding plants that are resistant to it. Such disease-resistant plants wouldn’t become infected. In the meantime, banana growers must slow TR4’s spread.
The center plant displays yellowing leaves, one of the telltale symptoms of Panama disease.
He’s a plant pathologist at Wageningen University and Research Centre in the Netherlands. The new test would allow farmers to test suspicious plants, soil and water for those snippets of TR4’s DNA, even out in their banana fields.
If those measures are successful, farmers could stop the disease in its tracks, guarding healthy nearby plants.
Detection of the fungus is essential. Still, the ultimate goal is the development of disease-resistant plants.
Swennen, the banana breeder, oversees a massive collection of banana plants. These bananas come from across the globe. So far, more than 90,000 plants have been given to farmers in more than 100 countries.
Bananas aren’t always big and yellow. Some of the world’s 1,400 banana varieties, 400 of which are edible, are small and reddish.
Most bananas at ITC are tropical.
Breeding new varieties from one parent that is tasty and another that is disease-resistant (a technique called cross-breeding) might one day create dessert bananas immune to TR4.
Swennen works with teams in Uganda, Tanzania and Nigeria to cross-breed African bananas. They climb ladders to get to the tops of banana plants. From those fruits, the workers must collect seeds and then grow those seeds into new plants.
Another complication: Those seeds can’t simply be planted in soil. Only 30 percent of the released embryos will develop into plants.
Despite such challenges, IITA and Uganda's National Agricultural Research Organization have succeeded in breeding disease-resistant plants. So far, they have 27 varieties of East African cooking bananas that are resistant to both the Black Sigatoka fungus and the worm-like nematodes that have long been problems for banana growers. Some varieties of bananas are filled with pea-sized seeds.
When small farmers in Asia and Africa plant the new varieties, they will be able to grow enough bananas to sustain their families.
Fibers from the banana plant’s stem go into making clothing and ropes.
In some ways, small farmers in Asia and Africa have less to worry about than do those at big plantations, Swennen says. That’s because each small farmer plants a variety of crops.
On this western side of the Atlantic, plantations specialize in Cavendish bananas. Small farmers in Africa and Asia may grow several different varieties of bananas. They also grow many kinds of crops, such as maize, cassava, okra and melon, under and around their banana plants.
So Dale adds to existing varieties the genes that make a plant resistant to TR4. His method may keep the best features of our dessert banana (flavor, texture and its ability to be shipped long distances) while adding disease resistance.
Dale starts by taking genes from wild bananas. These bananas are full of big, hard seeds, so they aren’t good for eating. But the wild plants are resistant to both strains of Panama disease — TR4 and Race 1.
So he is inserting resistance genes into both types of plants.
To do so, Dale uses a common soil bacterium that naturally inserts pieces of DNA into plants. He takes a single cell from a Cavendish or Gros Michel banana plant. Then he uses the bacterium to insert the genes that would make the plant resist infection by TR4 or Race 1.
Often a clone, particularly among plants, has been created using the cell of an existing organism.
cooking banana Bananas eaten while still green. Grown in the East African highlands, cooking bananas are steamed or boiled into a porridge.
The cross-bred plants will exhibit features of both parent plants.
In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.
monoculture Large areas planted with a single type of crop.
resistance (as in disease resistance) The ability of plants to fight off disease.
Tissue culture is commonly used to create genetically identical plants.
TR4 is the deadliest strain, currently threatening nearly 85 percent of the world’s bananas.
jueves, 21 de agosto de 2014
Miles de especies viven en un lago subterráneo al que la luz y el aire no han llegado en millones de años
Bajo los hielos de la Antártida hay vida en abundancia .
Lo acaba de demostrar una expedición norteamericana, llamada Wissard (Whillans Ice Stream Subglacial Access Research Drilling), formada por investigadores de varias universidades y que esta semana ha publicado en Nature sus primeras conclusiones.
Bajo una capa de hielo de más de 800 metros de grosor, los científicos han encontrado todo un ecosistema viviendo en un lago subterráneo al que la luz y el aire no han llegado en millones de años.
Las formas de vida descubiertas son microorganismos unicelulares que para subsistir convierten amoniaco y metano en energía.
La mayor parte de estos organismos pertenecen al dominio de las Arqueas, en el que se encuentran los seres vivos más antiguos del planeta.
martes, 27 de mayo de 2014
Las hormigas son capaces de complejas estrategias de resolución de problemas que podrían aplicarse ampliamente como técnicas de optimización.
Una hormiga individual busca alimento caminando de forma caótica, mientras que la búsqueda colectiva de comida se hace de forma ordenada, según revela un estudio matemático que se publica en 'Proceedings of the National Academy of Sciences'.
La dopamina convierte a las hormigas en súper-hormigas para luchar por el trono
Entender este paso del caos a una autoorganización sorprendentemente eficaz podría ayudar a analizar fenómenos similiares como la forma en la que los seres humanos navegan por Internet.
"Las hormigas tienen un nido por lo que necesitan algo así como una estrategia para llevar a casa la comida que encuentran", argumenta el autor principal Lixiang Li, afiliado al Centro de Seguridad de la Información y el Laboratorio Estatal de Redes y Tecnología de Conmutación de la Universidad de Beijing, en China, y el Instituto Potsdam para la Investigación del Impacto Climático, en Alemania.
viernes, 16 de mayo de 2014
Cada brazo es autónomo y contiene una sustancia química que desactiva las ventosas
cuando éstas se encuentran con otra de sus extremidades.
Investigadores en Israel resolvieron el misterio de cómo los pulpos logran que no se les enreden los tentáculos.
Las ocho extremidades de este molusco cefalópodo están cubiertas por cientos de ventosas que se pegan a casi cualquier cosa, con una excepción importante: su propia piel.
Descubrieron que cada extremidad es autónoma y contiene una sustancia química que desactiva las ventosas cuando éstas se encuentran con otra de las extremidades del mismo pulpo.
Los tentáculos vuelven a crecer si el pulpo los pierde.
jueves, 19 de septiembre de 2013
Posted by Christopher James-NYU on September 18, 2013
HIV, the virus that causes AIDS, has an alternate way to replicate, researchers have discovered.
"Although this is not the virus' main method for replicating, having this option available can help HIV survive," says David N. Levy, an associate professor of science and craniofacial biology at the New York University College of Dentistry.
"These new findings suggest one mechanism by which HIV may be surviving in the face of antiviral drugs, and suggests new avenues for research into eliminating infection," adds Levy, who led the research published in the Journal of Virology.
For decades, scientists have been confident that HIV-1, the virus that causes AIDS, must insert its genetic material into a cell's DNA in order to reproduce. This process, called "integration," makes the virus a permanent part of the cell.
Some of these infected cells can remain as long as the person is alive, and this is one reason why HIV+ individuals must remain on anti-HIV drugs for life.
HIV-1 can sometimes skip this integration step entirely, the researchers discovered.
The integration step is highly inefficient and actually fails up to 99 percent of the time, leaving most viruses stranded outside of the safe harbor of cell's DNA. The assumption was that these stranded, or "unintegrated", viruses were unable to reproduce, but Levy's team has found that if the conditions are right, they can generate new viruses that infect new cells.
The unintegrated viruses can survive for many weeks in cells, allowing HIV to "hide out" in a dormant state. The ability of HIV-1 to go dormant helps it avoid elimination by antiviral drugs and immune responses.
"There is intense interest by researchers in the idea that new drugs might be developed to help to completely eliminate the virus from infected individuals," says Levy. "We think that the new replication mechanism we have found could provide a target for drugs designed to eliminate infection."
The National Institutes of Health supported the work.
Source: New York University
Researchers from the Center for Infection and Immunity at Columbia University's Mailman School of Public Health in the US, have estimated that there may be at least 32,000 viruses circulating in mammals which are awaiting discovery.
miércoles, 11 de septiembre de 2013
UNIVERSITY PARK, Pa. -- Some symbiotic bacteria living inside Colorado potato beetles can trick plants into reacting to a microbial attack rather than that of a chewing herbivore, according to a team of Penn State researchers who found that the beetles with bacteria were healthier and grew better.
"For the last couple of decades, my lab has focused on induced defenses in plants," said Gary W. Felton, professor and head of entomology. "We had some clues that oral secretions of beetles suppressed defenses, but no one had followed up on that research."
Seung Ho Chung, graduate student in entomology working with Felton, decided to investigate how plants identified chewers and how herbivores subverted the plants defenses.
"I thought we could identify what was turning the anti-herbivore reaction off," said Felton. "But it was a lot more difficult because we had not considered microbes."
According to Felton, the beetles do not have salivary glands and so they regurgitate oral secretions onto the leaves to begin digestion. These secretions contain gut bacteria.
Plant defenses against chewing insects follow a jasmonite-mediated pathway that induces protease inhibitors and polyphenol oxidase, which suppress digestion and growth. Plant defenses against pathogens follow a salicylic acid mediated pathway. When the antimicrobial response turns on, it interferes with the response to chewing, allowing the beetles to develop more normally.
Chung and Felton used tomato plants to identify exactly what was turning off the response to chewing. They note, however, that the Colorado potato beetle also attacks eggplant and potato plants. They report the results of their work in the current online edition of the Proceedings of the National Academy of Sciences.
The researchers allowed beetle larva to feast on antibiotic-treated leaves and natural leaves and found that on the antibiotic-treated leaves, the beetles suffered from the plant's anti-herbivore defense, but on the natural leaves the larva gained more weight and thrived.
Chung and Felton then investigated expression of genes in the anti-herbivore pathway and the production of enzymes. They found that the presence of bacteria decreases the anti-herbivore response.
The researchers also isolated and grew the bacteria from the Colorado potato beetle guts. They found 22 different types of bacteria, but only three types suppressed the anti-herbivore response. During a variety of other experiments, they found that in all cases presence of the bacteria that could suppress the anti-herbivore response led to healthier beetles.
The researchers are now beginning to see if these bacteria are present in Colorado potato beetles all over the U.S. and also in Europe.
Also working on this project were Cristina Rosa, research associate in entomology; Erin D. Scully, graduate student in the intercollege program in genetics; Michelle Peiffer, research assistant in entomology; John F. Tooker, assistant professor of entomology; Kelli Hoover, professor of entomology and Dawn S. Luthe, professor of plant science.
The U.S. Department of Agriculture and the National Science Foundation supported this work.