Saturday, July 10, 2010

AGRICULTURE'S NEXT REVOLUTION -- PERENNIAL GRAIN -- WITHIN SIGHT

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Earth-friendly perennial grain crops, which grow with less fertilizer, herbicide, fuel, and erosion than grains planted annually, could be available in two decades, according to researchers writing in the current issue of the journal Science.

Perennial grains would be one of the largest innovations in the 10,000 year history of agriculture, and could arrive even sooner with the right breeding programs, said John Reganold, Washington State University (WSU) Regents professor of soil science and lead author of the paper with Jerry Glover, a WSU-trained soil scientist now at the Land Institute in Salina, Kansas.

"It really depends on the breakthroughs," said Reganold. "The more people involved in this, the more it cuts down the time."

Published in Science's influential policy forum, the paper is a call to action as half the world's growing population lives off marginal land at risk of being degraded by annual grain production. Perennial grains, say the paper's authors, expand farmers' ability to sustain the ecological underpinnings of their crops.

"People talk about food security," said Reganold. "That's only half the issue. We need to talk about both food and ecosystem security."

Perennial grains, say the authors, have longer growing seasons than annual crops and deeper roots that let the plants take greater advantage of precipitation. Their larger roots, which can reach ten to 12 feet down, reduce erosion, build soil and sequester carbon from the atmosphere. They require fewer passes of farm equipment and less herbicide, key features in less developed regions.

By contrast, annual grains can lose five times as much water as perennial crops and 35 times as much nitrate, a valuable plant nutrient that can migrate from fields to pollute drinking water and create "dead zones" in surface waters.

"Developing perennial versions of our major grain crops would address many of the environmental limitations of annuals while helping to feed an increasingly hungry planet," said Reganold.

Perennial grain research is underway in Argentina, Australia, China, India, Sweden and the United States. Washington State University has more than a decade of work on perennial wheat led by Stephen Jones, director WSU's Mount Vernon Research Center. Jones is also a contributor to the Science paper, which has more than two dozen authors, mostly plant breeders and geneticists.

The authors say research into perennial grains can be accelerated by putting more personnel, land and technology into breeding programs. They call for a commitment similar to that underway for biologically based alternative fuels.

(Photo: WSU)

Washington State University

DO BOSONS EVER MASQUERADE AS FERMIONS?

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Of all the assumptions underlying quantum mechanics and the theory that describes how particles interact at the most elementary level, perhaps the most basic is that particles are either bosons or fermions. Bosons, such as the particles of light called photons, play by one set of rules; fermions, including electrons, play by another.

Seven years ago, University of California, Berkeley, physicists asked a fundamental and potentially disturbing question: Do bosons sometimes play by fermion rules? Specifically, do photons act like bosons all the time, or could they sometimes act like fermions?

Based on the results of their experiment to test this possibility, published June 25 in the journal Physical Review Letters, the answer is a solid "no."

The theories of physics – including the most comprehensive theory of elementary particles, Quantum Field Theory, which explains nature's electromagnetic, weak and strong nuclear forces (but not gravity) – rest on fundamental assumptions, said Dmitry Budker, UC Berkeley professor of physics. These assumptions are based on how the real world works, and often produce amazingly precise predictions. But some physicists would like to see them more rigorously tested.

"Tests of (these assumptions) are very important," said Budker. "Our experiment is distinguished from most other experimental searches for new physics in that others can usually be incorporated into the existing framework of the standard model of particles and forces. What we are testing are some of the fundamental assumptions on which the whole standard model is based."

Among these assumptions is the boson/fermion dichotomy, which is mandated by the Spin-Statistics Theorem of quantum field theory. Bosons, which are governed by Bose-Einstein statistics, are particles with an intrinsic spin of 0, 1, 2 or another integer, and include photons, W and Z bosons, and gluons. The fermions, governed by Fermi-Dirac statistics, are all particles with odd-half-integer spins – ½, 3/2, 5/2, etc. – and include the electron, neutrinos, muons and all the quarks, the fundamental particles that make up protons and neutrons.

Bosons can pile on top of one another without limit, all occupying the same quantum state. At low temperatures, this causes such strange phenomena as superconductivity, superfluidity and Bose-Einstein condensation. It also allows photons of the same frequency to form coherent laser beams. Fermions, on the other hand, avoid one another. Electrons around a nucleus stack into shells instead of collapsing into a condensed cloud, giving rise to atoms with a great range of chemical properties.

"We have this all-important symmetry law in physics, one of the cornerstones of our theoretical understanding, and a lot depends on it," said Budker, who is also a faculty scientist at Lawrence Berkeley National Laboratory (LBNL). "But we don't have a simple explanation; we have a complex mathematical proof. This really bothered a lot of physicists, including the late Nobel laureate Richard Feynman."

"It's a shame that no simple explanation exists," said Budker, because it ties together basic assumptions of modern physics. "Among these assumptions are Lorentz invariance, the core tenet of special relativity, and invariance under the CPT (charge-parity-time) transformation, the idea that nature looks the same when time is reversed, space is reflected as in a mirror, and particles are changed into antiparticles. Lorentz invariance results from the entanglement of space and time, such that length and time change in reference frames moving at constant velocity so as to keep the speed of light constant.

"Another one of the assumptions of the spin-statistics theorem is microcausality," said UC Berkeley post-doctoral fellow Damon English. "A violation wouldn't exactly be the same type of paradox as travelling back in time to kill your great-grandfather, but more along the lines of receiving a flash of light before it was emitted."

In their experiment, Budker, English and colleague Valeriy Yashchuk, a staff scientist at LBNL's Advanced Light Source, were able to reduce the existing limit that photons act like fermions by more than a factor of a thousand.

"If just one pair of photons out of 10 billion had taken the bait and behaved like fermions, we would have seen it," English said. "Photons are bosons, at least within our experimental sensitivity."

In 1999, Budker, and David DeMille, now a professor of physics at Yale University, completed a similar preliminary experiment, conducted partially at Amherst College and partially at UC Berkeley, establishing that photons act as bosons, not fermions. The new experiment improves the precision of the Amherst/UC Berkeley experiment by a factor of about 3,000.

The experiment bombarded barium atoms with photons in two identical laser beams and looked for evidence that the barium had absorbed two photons of the same energy at once, thereby kicking an electron into a higher energy state. The particular two-photon transition the scientists focused on was forbidden only by the Bose-Einstein statistics of photons. If photons were fermions, the transition would "go like gang-busters," said English.

The experiment detected no such "fermionic" photons, establishing the distinctness of bosons and fermions, and validating the assumptions underlying Bose-Einstein statistics and Quantum Field Theory.

"Spacetime, causality, and Lorentz invariance are safe,…for now," English said.

Using the same tabletop experiment, they also observed for the first time that the spin of the nucleus can alter the atomic environment to allow the otherwise bose-statistics forbidden transition. The most common isotopes of barium, barium-138 and barium-136, have zero nuclear spin, so the electron levels are undisturbed and the two-photon absorption is impossible. Two other isotopes, barium-135 and -137, have a nuclear spin of 3/2, which creates a hyperfine splitting of the electron energy levels and enables still very weak, but detectable, two-photon absorption.

"We will keep looking, because experimental tests at ever increasing sensitivity are motivated by the fundamental importance of quantum statistics," said Budker. "The spin-statistics connection is one of the most basic assumptions in our understanding of the fundamental laws of nature."

(Photo: Damon English/UC Berkeley)

University of California, Berkeley

MITOCHONDRIAL GENOME ANALYSIS REVISES VIEW OF THE INITIAL PEOPLING OF NORTH AMERICA

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The initial peopling of North America from Asia occurred approximately 15,000-18,000 years ago, however estimations of the genetic diversity of the first settlers have remained inaccurate. In a report published online in Genome Research (www.genome.org), researchers have found that the diversity of the first Americans has been significantly underestimated, underscoring the importance of comprehensive sampling for accurate analysis of human migrations.

Substantial evidence suggests that humans first crossed into North America from Asia over a land bridge called Beringia, connecting eastern Siberia and Alaska. Genetic studies have shed light on the initial lineages that entered North America, distinguishing the earliest Native American groups from those that arrived later. However, a clear picture of the number of initial migratory events and routes has been elusive due to incomplete analysis.

In this work, an international group of researchers coordinated by Antonio Torroni of the University of Pavia in Italy performed a detailed mitochondrial genome analysis of a poorly characterized lineage known as C1d. Mitochondrial DNA (mtDNA) is passed down through the maternal lineage, and mtDNA sequence markers are extremely useful tools for mapping ancestry. Similar to other haplogroups that were among the first to arrive in North America, C1d is distributed throughout the continent, suggesting that it may have been also present in the initial founding populations. However, C1d has not been well represented in previous genetic analyses, and the estimated age of approximately 7,000 years, much younger than the other founding haplogroups, was likely inaccurate.

To resolve these inconsistent lines of evidence, the group sequenced and analyzed 63 C1d mtDNA genomes from throughout the Americas. This high-resolution study not only confirmed that C1d was one of the founding lineages in North America 15,000 to 18,000 years ago, but revealed another critical insight. "These first female American founders carried not one but two different C1d genomes," said Ugo Perego of the Sorenson Molecular Genealogy Foundation and primary author of the study, "thus further increasing the number of recognized maternal lineages from Beringia."

These findings raise the number of founding maternal lineages in North America to fifteen. Furthermore, this work emphasizes the critical need for comprehensive analysis of relevant populations to gather a complete picture of migratory events.

Alessandro Achilli of the University of Perugia, a coauthor of the report, suggests that the number of distinct mitochondrial genomes that passed from Asian into North America is probably much higher. "These yet undiscovered maternal lineages will be identified within the next three to four years," Achilli noted, "when the methodological approach that we used in our study will be systematically applied."

Cold Spring Harbor Laboratory

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