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domingo, 7 de agosto de 2016

NSF: Sunflowers move from east to west, and back, by the clock .- Dando vuelta al reloj los girasoles se mueven de este a oeste....

http://www.nsf.gov/news/news_summ.jsp?cntn_id=139271&WT.mc_id=USNSF_51&WT.mc_ev=click

Plant biologists discover how sunflowers use internal circadian timing to follow the sun

When they're mature, sunflowers stop tracking the sun and instead face solely eastward.
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August 4, 2016

It's summertime, and the fields of Yolo County, Calif., are filled with rows of sunflowers, dutifully facing the rising sun.

At the nearby University of California, Davis, plant biologists have now discovered how sunflowers use their internal circadian "clocks," acting on growth hormones, to follow the sun during the day as they grow.

"It's the first example of a plant's clock modulating growth in a natural environment, and having real repercussions for the plant," said Stacey Harmer, a plant biologist at UC Davis and senior author of a paper reporting the discovery published this week in the journal Science.

Harmer is a molecular biologist who studies circadian clocks, usually in the plant Arabidopsis, which is smaller than a sunflower. Previously, Harmer had discovered links between "clock" genes and the plant hormone auxin, which regulates growth.

Harmer and her collaborator Benjamin Blackman of UC Berkeley needed the next example, and they found it in the sunflower.

The research was funded by the National Science Foundation's Plant Genome Research Program.

"Just like people, plants rely on the daily rhythms of day and night to function," said the program's director, Anne Sylvester. "Sunflowers, like solar panel arrays, follow the sun from east to west. These researchers tapped into information in the sunflower genome to understand how and why sunflowers track the sun."

Swinging east then west

Growing sunflowers begin the day with their heads facing east, swing west through the day, and turn back to the east at night.

"The plant anticipates the timing and the direction of dawn, and to me that looks like a reason to have a connection between the clock and the growth pathway," Harmer said.

This sunflower behavior had been described by scientists as far back as 1898, but no one had thought to associate it with circadian rhythms.

Plant biologist Hagop Atamian, also of UC-Davis, along with Harmer and Blackman carried out a series of experiments with sunflowers in the field, in pots outdoors, and in indoor growth chambers.

By staking plants so they couldn't move, or turning potted plants around daily so they were facing the wrong way, the scientists showed that they could disrupt the sunflowers' ability to track the sun. The plants also showed a decrease in leaf area and biomass compared with control plants.

When the sunflowers were moved into an indoor growth chamber with immobile overhead light, they continued to swing back and forth for a few days. That's the kind of behavior you would expect from mechanism driven by an internal clock, Harmer said.

Finally, the indoor plants did start tracking "the sun" again when the apparent source of lighting was moved across the growth chamber by turning adjacent lights on and off during the day.

The plants could reliably track the movement and return at night when the artificial day was close to a 24-hour cycle, but not when it was closer to 30 hours.

Growth mechanisms

How do the plants move their stems during the day? Atamian put ink dots on the stems and filmed them with a video camera. On a time-lapse video, he could measure the changing distance between the dots.

When plants were tracking the sun, the east side of the stem grew more rapidly than the west side, he found. At night, the west side grew faster as the stem swung the other way. The team identified a number of genes that were expressed at higher levels on the sunward side of the plant during the day, or on the other side at night.

Harmer said that there appear to be two growth mechanisms at work in the sunflower stem. The first sets a basic rate of growth for the plant, based on available light. The second, controlled by the circadian clock and influenced by the direction of light, causes the stem to grow more on one side than another, and therefore sway east to west during the day.

As the sunflower matures and the flower opens up, overall growth slows and the plant stops moving during the day and settles down facing east. This seems to be because the circadian clock ensures that the plant reacts more strongly to light early in the morning than in the afternoon or evening, so it gradually stops moving westward during the day.

Why face the sun?

Why do mature sunflowers face east?

The researchers grew sunflowers in pots in the field, and rotated some of them to the west. By measuring the flowers with an infrared camera, they found that the east-facing sunflowers heated up more quickly in the morning -- and also attracted five times as many pollinating insects. Heating up west-facing flowers with a portable heater brought more pollinators back to the flowers.

"Bees," said Harmer, "like warm flowers."

Additional co-authors of the paper are Nicky Creux of UC Davis, and Evan Brown and Austin Garner of the University of Virginia.

-NSF-

Media Contacts Cheryl Dybas, NSF, (703) 292-7734,
cdybas@nsf.gov
Andy Fell, UC Davis, (530) 752-4533,
ahfell@ucdavis.edu

Related WebsitesNSF Grant: Investigating the Mechanistic Basis and Adaptive Significance of the Coordination of Plant Growth by External and Internal Cues:
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1238040&HistoricalAwards=false
Ten things to know about the flowers of fall: Sunflowers: https://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=132980

The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering. In fiscal year (FY) 2016, its budget is $7.5 billion. NSF funds reach all 50 states through grants to nearly 2,000 colleges, universities and other institutions. Each year, NSF receives more than 48,000 competitive proposals for funding and makes about 12,000 new funding awards. NSF also awards about $626 million in professional and service contracts yearly.

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Honeybees visit a mature sunflower. Here, the bees are collecting nectar rather than pollen.
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A sunflower just before maturation. Soon the yellow ray petals will unfold.
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Sunflower being visited by a native bee, the "ultra green sweat bee."
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This mature sunflower was imaged using forward-looking infrared (FLIR) imaging; bees are white.
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Young sunflowers are good solar-trackers, following the sun by day and re-orienting at night.
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The National Science Foundation (NSF)
Guillermo Gonzalo Sánchez Achutegui
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domingo, 19 de octubre de 2014

nsf.gov - National Science Foundation - Ten things to know about the flowers of fall: Sunflowers.- Diez cosas que debe saber sobre las flores en Otoño: Girasoles

Hola amigos: A VUELO DE UN QUINDE EL BLOG., la Fundación Nacional de Ciencia de los Estados Unidos se hacen una serie de interrogantes sobre la floración del girasol..como..." Como campos de otoño se convierten brillante con color, ¿qué podemos aprender de filas en carretera de los girasoles - y las semillas de girasol ampliamente utilizado para alimentar a las aves en un clima más frío?....

Por ejemplo, con qué frecuencia y bajo qué condiciones la evolución toman el mismo camino? Cuando las poblaciones independientes evolucionan las mismas características, son los cambios genéticos subyacentes similares o diferentes?...

Para asomarse al mundo de la especiación - cómo uno ramas especie en otra - la Fundación Nacional de Ciencia de los Estados (NSF) hablaron con George Gilchrist, un de los directores del programa en la División de Biología Ambiental de la agencia y con Ken Whitney, un biólogo de plantas en la Universidad de Nuevo México quien estudia poblaciones de girasoles experimentales en Texas.......

Con el financiamiento de la NSF, Whitney y botánico Loren Rieseberg de Indiana University Bloomington y la Universidad de Columbia Británica están aprendiendo si girasoles son convergentes o divergentes en sus rasgos.........

sunflowers in a farm field next to houses

Flowers of fall: Sunflowers cover roadside farm fields in autumn.
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October 14, 2014

As fall fields turn bright with color, what might we learn from roadside rows of sunflowers--and the sunflower seeds widely used to feed birds in colder weather?

Scientists are finding that answers to biological and environmental questions large and small may be hidden in the petals of common sunflowers.

For example, how frequently and under what conditions does evolution take the same path? When independent populations evolve the same characteristics, are the underlying genetic changes similar or different?

To peer into the world of speciation--how one species branches into another--the National Science Foundation (NSF) spoke with George Gilchrist, a program director in the agency's Division of Environmental Biology and with Ken Whitney, a plant biologist at the University of New Mexico who studies populations of experimental sunflowers in Texas.

With funding from NSF, Whitney and botanist Loren Rieseberg of Indiana University Bloomington and the University of British Columbia are learning whether sunflowers are converging or diverging in their traits.

1) Why do scientists study sunflowers?

Whitney (KW): Sunflowers represent a "recent" success story. In the past three million years, this group has diverged (or branched into new species) in some 50 species in North America. Sunflowers live in a variety of habitats, from forests to deserts to salt marshes.

Sunflowers also contain examples of many important processes, including the evolution of both annual and perennial lifestyles, hybridization (mating between species) and the phenomena of polyploidy (the doubling of chromosome sets in a lineage). All this combines in an "evolutionary cauldron."

2) Where did sunflowers originate?

(KW): The genus Helianthus, true sunflowers, is native to North America. The common sunflower, H. annuus, and its seeds are one of only three crops that were domesticated north of Mexico. The second, sumpweed, was a favorite of Native Americans, but is no longer in use; the third, Jerusalem artichoke, is actually the root of another sunflower species, H. tuberosus.

3) What are the major commercial uses of sunflowers?

(KW): Oilseed sunflower varieties are used to produce oil used in cooking. A separate set of varieties, called confectionary varieties, has been developed to produce the large seeds we eat directly--such as those that are roasted and salted.

4) How do sunflowers link North America and Russia?

(KW): Although the crop sunflower originated in North America, it had to travel to Europe to achieve its current form. Much of the breeding for large seed size and high oil content was done in Russia in the 1800s, a legacy that is still with us in the sunflower variety called "Russian Mammoth." Many of us grow this plant in home gardens.

Sunflower varieties from Russia made it back to the U.S. in the late 1880s, but it was not until the 1930s and 1940s that crop sunflowers were grown on a large commercial scale in the United States.

5) What's the difference between wild sunflowers and those that are domesticated and grown as crops?

(KW): Both wild and crop sunflowers are the same species, H. annuus. Wild sunflowers have many flowering heads on each plant, and have small seeds. A major event in the domestication of the sunflower was the creation of a "monocephalic" plant with a single large flowering head and large seeds.

6) How much diversity is there in wild sunflowers?

(KW): The 50 or so species of wild sunflowers are both ecologically and genetically diverse. The U.S. Department of Agriculture maintains seed stocks of most wild sunflower species, in part because they contain genetic material that can be used to improve cultivated sunflower varieties. For example, a pest-resistant species might provide genes that could decrease pest damage in cultivated sunflowers.

7) What ecological factors drive sunflowers' diversity?

(KW): Sunflowers live in a wide range of habitats, and are widespread across the North American continent. That geographic range means that sunflowers have adapted to very different environmental conditions during the course of their radiation.

8) Are there medical treatments derived from sunflower products?

(KW): Sunflower products, especially the oil from the seeds, have long been used in folk medicine, but I'm not aware of any uses in modern medicine.

9) Do wild sunflowers hybridize? What role has hybridization played in speciation?

(KW): Sunflowers are notorious for hybridizing: mating across species boundaries and exchanging genetic material between species. Sometimes this genetic exchange leads to improved performance, for example in the Texas sunflower our team has been studying.

We have evidence that when wild H. annuus captured genes from another species, H. debilis, it was able to expand its range southward and become a new subspecies, H. annuus texanus. In other sunflowers, hybridization may lead to entirely new species. The sunflowers H. annuus and H. petiolaris have hybridized repeatedly and have produced three new sunflower species that live on the desert floor, on sand dunes, and in salt marshes.

Gilchrist (GG): This research has been critical to understanding how hybridization can lead to rapid speciation. While many hybrids are sterile, some genetic changes create hybrids with extra sets of chromosomes that are fully fertile, but reproductively isolated from their parents.

These new hybrid sunflowers often are uniquely adapted to new habitats that neither of the parent species occupies. Speciation by hybridization is very common in plants and may play a major role in plant diversification.

10) Do insects and pathogens attack sunflowers?

(KW): Sunflowers are indeed attacked by insects, especially grasshoppers, caterpillars, aphids and their relatives, as well as by fungal and bacterial pathogens.

A sunflower's life, scientists say, is no bed of roses.

--	Cheryl Dybas, NSF (703) 292-7734 cdybas@nsf.gov

Related WebsitesNSF Grant: Repeatability and genetic architecture of adaptive introgression: a long-term experimental evolution study in sunflowers:

http://www.nsf.gov/awardsearch/showAward?AWD_ID=1257965&HistoricalAwards=false