Ants aquaplaning on a pitcher plant

Dec. 18, 2012 — An insect-trapping pitcher plant in Venezuela uses its downward pointing hairs to create a 'water slide' on which insects slip to their death, new research reveals. The research was published December 19, in the journal Proceedings of the Royal Society B.

Hairs on plants, called trichomes, are typically used to repel water. However, the Cambridge researchers observed that the hairs on the inside of Heliamphora nutans pitcher plants were highly wettable, prompting them to test whether this phenomenon is related to the trapping of insects.

They found that wetting strongly enhanced the slipperiness of the trap and increased the capture rate for ants almost three-fold -- from 29 per cent when dry to 88 per cent when wet. Upon further examination, they found that the wetting affected the insects' adhesive pads while the directional arrangement of the hairs was effective against the claws.

Dr Ulrike Bauer, lead author of the paper from the University of Cambridge, said: "When the hairs of the plant are wet, the ants' adhesive pads essentially aquaplane on the surface, making the insects lose grip and slip into the bowl of the pitcher. This is the first time that we have observed hairs being used by plants in this way, as they are typically used to make leaves water repellent."

They also found that the plant used a wicking method during dryer times to pull moisture from the bowl of the pitcher up to the hairy trapping surface, enabling them to capitalise on this aquaplaning effect even when there is no rain.

Dr Bauer added: "This very neat adaptation might help the plants to maximise their nutrient acquisition."

The Heliamphora nutans pitcher plant lives on the spectacular table mountains of the Guyana Highlands in Southern Venezuela, between altitudes of 2000-2700m. The pitchers can grow up to 18 cm tall and 7 cm wide and trap mainly ants.

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The above story is reprinted from materials provided by University of Cambridge, via EurekAlert!, a service of AAAS.

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Journal Reference:

Ulrike Bauer et al. 'Insect aquaplaning' on a superhydrophilic hairy surface: how Heliamphora nutans Benth. pitcher plants capture prey. Proceedings of the Royal Society B, December 19, 2012

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Plant sniffs out danger to prepare defenses against pesky insect

Dec. 17, 2012 — A plant may start to prime its defenses as soon as it gets a whiff of a male fly searching for a mate, according to Penn State entomologists.

Once tall goldenrod plants smell a sex attractant emitted by true fruit fly males, they appear to prepare chemical defenses that make them less appealing to female flies that could damage the plants by depositing eggs on them, the researchers said.

"It's become increasingly clear in recent years that plants are responsive to odors," said Mark Mescher, assistant professor of entomology. "But previous examples of this are all plant-to-plant. For example, some plants have been shown to respond to the odor of insect-damaged neighbors by priming their own defenses. What's new about this is that it seems that plants may sometimes be able to smell the insects themselves."

A tall goldenrod plant's reaction to these odors also appears to make it less attractive to other insects that might feed on it, according to the researchers, who reported their findings in the current issue of Proceedings of the National Academy of Sciences.

In a field study, the researchers exposed some plants to the odor of the male fly and then counted the number of exposed and unexposed plants on which female flies laid eggs by noting the distinctive scarring that occurs when females puncture the stem to lay their eggs inside, Mescher said.

The researchers found that females were significantly less likely to lay eggs on plants exposed to the male emission and about four times more likely to lay eggs on plants in a control group that were not exposed to this odor cue.

Compared to the control group, other herbivores, such as beetles, also caused significantly less damage to of the tall goldenrod plants exposed to the fly emissions, both in the field and in laboratory experiments.

"It would seem that the plant senses the odor of the fly," Mescher said. "Then, it primes its defenses so that it can respond faster to the threat."

Over years of evolution, the true fruit fly has established a close relationship with tall goldenrod, according to Mescher, who worked with Anjel Helms, doctoral student in ecology; Consuelo De Moraes, professor of entomology; and John Tooker, assistant professor of entomology.

The male fly, which in the Northeast usually emerges in mid-May, perches on the upper leaves of the tall goldenrod plants and emits a chemical blend that may act as an attractant to the female flies, which emerge later, according to Tooker. Once a female mates with the male, it deposits its eggs in the stem of the plant.

Tooker said that the female flies lay their eggs only in tall goldenrod plants, so there is a close association between the two species.

A few weeks after the fly's eggs hatch a bulbous growth, called a gall, appears on the stem of the tall goldenrod plant. The gall does not kill the tall goldenrod, but Tooker said the galled plant does not produce as many seeds as ones without galls. Its seeds also tend to be smaller and less likely to germinate.

"It seems that plants that are able to anticipate an attach by the fly and defend themselves against this damage will be more successful, producing higher quality seeds for the next generation," Tooker said. "So there must be a strong advantage for plants that can perceive the fly odor."

The researchers are not sure how tall goldenrod plants are able to detect the odor of the fly.

"Our understanding of plant olfaction in general remains quite limited," said Mescher.

But, the researchers said they believe that other plants may use insect odors to detect danger and prepare defenses.

"I suspect that this may be happening in many plants," said Tooker. "But we don't yet know how widespread it is."

The National Science Foundation supported this work.

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A. M. Helms, C. M. De Moraes, J. F. Tooker, M. C. Mescher. Exposure of Solidago altissima plants to volatile emissions of an insect antagonist (Eurosta solidaginis) deters subsequent herbivory. Proceedings of the National Academy of Sciences, 2012; DOI: 10.1073/pnas.1218606110

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Ancient red dye powers new 'green' battery: Chemists use plant extract in eco-friendly, sustainable lithium-ion battery

Dec. 11, 2012 — Rose madder -- a natural plant dye once prized throughout the Old World to make fiery red textiles -- has found a second life as the basis for a new "green" battery.

Chemists from The City College of New York teamed with researchers from Rice University and the U.S. Army Research Laboratory to develop a non-toxic and sustainable lithium-ion battery powered by purpurin, a dye extracted from the roots of the madder plant (Rubia species).

More than 3,500 years ago, civilizations in Asia and the Middle East first boiled madder roots to color fabrics in vivid oranges, reds and pinks. In its latest technological incarnation, the climbing herb could lay the foundation for an eco-friendly alternative to traditional lithium-ion (Li-ion) batteries. These batteries charge everything from your mobile phone to electric vehicles, but carry with them risks to the environment during production, recycling and disposal.

"Purpurin," on the other hand, said team member and City College Professor of Chemistry George John, "comes from nature and it will go back to nature." The team reports their results in the journal Nature's online and open access publication, Scientific Reports, on December 11, 2012.

Most Li-ion batteries today rely on finite supplies of mined metal ores, such as cobalt. "Thirty percent of globally produced cobalt is fed into battery technology," noted Dr. Leela Reddy, lead author and a research scientist in Professor Pulickel Ajayan's lab in the Department of Mechanical Engineering and Materials Science at Rice University. The cobalt salt and lithium are combined at high temperatures to make a battery's cathode, the electrode through which the electric current flows.

Mining cobalt metal and transforming it, however, is expensive, Dr. Reddy explained. Fabricating and recycling standard Li-ion batteries demands high temperatures, guzzling costly energy, especially during recycling. "In 2010, almost 10 billion lithium-ion batteries had to be recycled," he said .

Production and recycling also pumps an estimated 72 kilograms of carbon dioxide -- a greenhouse gas -- into the atmosphere for every kilowatt-hour of energy in a Li-ion battery, he noted. These grim facts have fed a surging demand to develop green batteries, said Dr. Reddy.

Fortunately, biologically based color molecules, like purpurin and its relatives, seem pre-adapted to act as a battery's electrode. In the case of purpurin, the molecule's six-membered (aromatic) rings are festooned with carbonyl and hydroxyl groups adept at passing electrons back and forth, just as traditional electrodes do. "These aromatic systems are electron-rich molecules that easily coordinate with lithium," explained Professor John.

Moreover, growing madder or other biomass crops to make batteries would soak up carbon dioxide and eliminate the disposal problem -- without its toxic components, a lithium-ion battery could be thrown away.

Best of all, purpurin also turns out to be a no-fuss ingredient. "In the literature there are one or two other natural organic molecules in development for batteries, but the process to make them is much more tedious and complicated," noted Professor John.

Made and stored at room temperature, the purpurin electrode is made in just a few easy steps: dissolve the purpurin in an alcohol solvent and add lithium salt. When the salt's lithium ion binds with purpurin the solution turns from reddish yellow to pink. "The chemistry is quite simple," coauthor and City College postdoctoral researcher Dr. Subbiah Nagarajan explained.

The team estimates that a commercial green Li-ion battery may be only a few years away, counting the time needed to ramp up purpurin's efficiency or hunt down and synthesize similar molecules. "We can say it is definitely going to happen, and sometime soon, because in this case we are fully aware of the mechanism," said Professor John.

"When you can generate something new or unheard of, you think of chemistry in a different way," he added. "That a natural material or dye can be used for a battery, that is exciting, even for me."

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Arava Leela Mohana Reddy, Subbiah Nagarajan, Porramate Chumyim, Sanketh R. Gowda, Padmanava Pradhan, Swapnil R. Jadhav, Madan Dubey, George John, Pulickel M. Ajayan. Lithium storage mechanisms in purpurin based organic lithium ion battery electrodes. Scientific Reports, 2012; 2 DOI: 10.1038/srep00960

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What happens to plant growth when you remove gravity?

Dec. 7, 2012 — It is well known that plant growth patterns are influenced by a variety of stimuli, gravity being one amongst many. On Earth plant roots exhibit characteristic behaviours called 'waving' and 'skewing', which were thought to be gravity-dependent events. However, Arabidopsis plants grown on the International Space Station (ISS) have proved this theory wrong, according to a study published in BioMed Central's open access journal BMC Plant Biology: root 'waving' and 'skewing' occur in spaceflight plants independently of gravity.

In plant roots, 'waving' consists of a series of regular, undulating changes in the direction of root tips during growth. It is thought to be associated with perception and avoidance of obstacles, and is dependent on gravity sensing and responsiveness. 'Skewing' is the slanted progression of roots growing along a near-vertical surface. It is thought to be a deviation of the roots from the direction of gravity and also subject to similar mechanisms that affect waving. Even though the precise basis of these growth patterns is not well understood, gravity is considered to be a major player in these processes.

To test what happens to plant root growth when you remove gravity entirely, a research team from the University of Florida, Gainesville, USA, grew two types of Arabidopsis thaliana cultivars -- Wassilewskija (WS) and Columbia (Col-0) -- on the ISS. The plants were grown in specialized growth units that combined a plant habitat with a camera system which captured images every six hours. Imaging hardware delivered the telemetric data in real-time from the ISS, and comparable ground controls were grown at the Kennedy Space Centre.

The phenomenon of negative-phototropism in plant roots is well documented, but its role in orienting root growth is still being explored. The authors found that, in the absence of gravity, but in the presence of directional light, spaceflight roots remained strongly negatively phototropic and grew in the opposite direction of the shoot growth, as they do back on Earth. The path taken by the roots as they grew also retained the complex patterns of waving and skewing, characteristic of Earth-grown, gravity-influenced, roots. Furthermore, while in orbit, each cultivar retained its unique terrestrial skewing pattern.

However, the team observed that the degree of waving exhibited by the plants in space did not match what would be predicted for roots showing an equivalent amount of skewing back on Earth. In space, waving was far more subtle. This result reinforces the idea that waving and skewing represent two separate phenomena, and that gravity is not a mechanistic part of the basic waving and skewing processes.

Lead authors Anna-Lisa Paul and Robert Ferl commented "Although plants use gravity as an orientating tropism on the Earth's surface, it is clear that gravity is neither essential for root orientation, nor is it the only factor influencing the patterns of root growth. It seems that other features of the environment are also required to ensure that a root grows away from the seed, thereby enhancing its chances of finding sufficient water and nutrients to ensure its survival."

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Anna-Lisa Paul, Claire E. Amalfitano and Robert J. Ferl. Plant growth strategies are remodelled by spaceflight. BMC Plant Biology, (in press) 2012 [link]

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