Clues to how plants evolved to cope with cold

Dec. 22, 2013 — Researchers have found new clues to how plants evolved to withstand wintry weather. In a study to appear in the December 22 issue of the journal Nature, the team constructed an evolutionary tree of more than 32,000 species of flowering plants -- the largest time-scaled evolutionary tree to date. By combining their tree with freezing exposure records and leaf and stem data for thousands of species, the researchers were able to reconstruct how plants evolved to cope with cold as they spread across the globe. The results suggest that many plants acquired characteristics that helped them thrive in colder climates -- such as dying back to the roots in winter -- long before they first encountered freezing.

Fossil evidence and reconstructions of past climatic conditions suggest that early flowering plants lived in warm tropical environments, explained co-author Jeremy Beaulieu at the National Institute for Mathematical & Biological Synthesis (NIMBioS) at the University of Tennessee.

As plants spread to higher latitudes and elevations, they evolved in ways that helped them deal with cold conditions. Plants that live in the tundra, such as Arctic cinquefoil and three-toothed saxifrage, can withstand winter temperatures below minus 15 degrees Celsius.

Unlike animals, most plants can't move to escape the cold or generate heat to keep them warm. It's not so much the cold but the ice that poses problems for plants. For instance, freezing and thawing cause air bubbles to form in the plant's internal water transport system.

"Think about the air bubbles you see suspended in the ice cubes," said co-author Amy Zanne of the George Washington University. "If enough of these air bubbles come together as water thaws they can block the flow of water from the roots to the leaves and kill the plant."

The researchers identified three traits that help plants get around these problems.

Some plants, such as hickories and oaks, avoid freezing damage by dropping their leaves before the winter chill sets in -- effectively shutting off the flow of water between roots and leaves -- and growing new leaves and water transport cells when warmer weather returns.

Other plants, such as birches and poplars, also protect themselves by having narrower water transport cells, which makes the parts of the plant that deliver water less susceptible to blockage during freezing and thawing.

Still others die back to the ground in winter and re-sprout from their roots, or start growing as new plants from seeds when conditions are right.

To compile the plant trait data for their study, the researchers spent hundreds of hours scouring and merging multiple large plant databases containing tens of thousands of species, largely with the support of the National Evolutionary Synthesis Center in North Carolina and Macquarie University in Australia.

When they mapped their collected leaf and stem data onto their evolutionary tree for flowering plants, they found that many plants were well equipped for icy climates even before cold conditions hit.

Plants that die back to the ground in winter, for example, acquired the ability to die and come back when conditions improve long before they first experienced freezing. Similarly, species with narrow water transport cells acquired a finer circulatory system well before they confronted cold climates.

"This suggests that some other environmental pressure -- possibly drought -- caused these plants to evolve this way, and it happened to work really well for freezing tolerance too," said Zanne.

The only exceptions were plants that shed and replace their leaves seasonally -- these plant groups didn't gain the ability to drop their leaves during winter until after they encountered freezing, Beaulieu added.

As a next step, the researchers plan to use their evolutionary tree to find out how plants evolved to withstand other environmental stresses in addition to freezing, such as drought and heat.

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Some plants may not adapt quickly to future climate change

Dec. 22, 2013 — Using the largest dated evolutionary tree of flowering plants ever assembled, a new study suggests how plants developed traits to withstand low temperatures, with implications that human-induced climate change may pose a bigger threat than initially thought to plants and global agriculture.

The study appearing Sunday (Dec. 22) in the journal Nature and co-authored by University of Florida scientists shows many angiosperms, or flowering plants, evolved mechanisms to cope with freezing temperatures as they radiated into nearly every climate during pre-historic times. Researchers found the plants likely acquired many of these adaptive traits prior to their movement into colder regions. The study also suggests some modern angiosperms, including most flowering plants, trees and agricultural crops, may not have the traits needed to rapidly respond to human-induced climate change, said study co-author Pam Soltis, a distinguished professor and curator of molecular systematics and evolutionary genetics at the Florida Museum on the UF campus.

"Only some plants were able to make the adjustments to survive in cold climates," said Soltis, who also is a member of the UF Genetics Institute. "In fact, some had traits used for other purposes that they co-opted for cold tolerance. The results have implications for plant response to climate change -- some plant lineages, including many crops, will not have the underlying genetic attributes that will allow for rapid responses to climate change."

Early flowering plants are thought to have been woody -- meaning they maintain a prominent stem above ground across years and changing weather conditions, such as a maple tree -- and restricted to warm, wet, tropical environments. But they have since put down roots in colder climates, dominating large swaths of the globe where freezing occurs. How they managed this expansion has long vexed researchers searching for plants' equivalent to the winter parka.

"Until now, we haven't had a compelling narrative about how leaf and stem traits have evolved to tolerate cold temperatures," said lead author Amy Zanne, assistant professor of biology in George Washington University's Columbian College of Arts and Sciences who earned her doctorate at UF. "Our research gives us this insight, showing us the 'whens,' 'hows' and 'whys' behind plant species' trait evolution and movements around the globe."

Zanne continued: "Freezing is a challenge for plants. Their living tissues can be damaged. It's like a plant's equivalent to frostbite. Their water-conducting pipes can also be blocked by air bubbles as water freezes and thaws. So over time, if plants moved into colder climates, they've had to figure out how to get around these problems."

Identifying evolutionary adaptations to these problems and likely paths to them required the team to build two sets of data. Researchers first created a database of 49,064 species, recording whether each maintains a stem aboveground over time, loses or keeps its leaves, has been exposed to freezing, and the width of its water-carrying pathways. Researchers combined the information with a dated evolutionary tree of 32,223 plant species and modeled the evolution of species' traits and climate over time, which identified the order of evolutionary events.

"We can determine the relative order of events without a dated tree, but the dated tree allows us to say exactly when something happened, so that we can correlate the events with geological events, like big changes in Earth's temperature," Soltis said.

Using this "timetree," researchers identified three repeated evolutionary shifts they believe flowering plants made to fight the cold. Plants either dropped their leaves seasonally, shutting down the pathways that would normally carry water between roots and leaves; developed thinner water-conducting pathways, allowing them to keep their leaves while reducing the risk of air bubbles developing during freezing and thawing; or avoided the cold seasons altogether as herbs, losing aboveground stems and leaves and retreating as seeds, or storing organs underground, such as tulips or potatoes.

"Angiosperms were not successful until they got the adaptation to drop their leaves," said study co-author Doug Soltis, a Florida Museum distinguished professor with appointments in UF's biology department and the UF Genetics Institute. "Sometimes the trait evolves for some other purpose, and then the organism is able to adapt and use it for something new."

Researchers found that woody plants most often became herbs or developed thinner pathways before moving into freezing climates, while plants that dropped their leaves usually did so after moving into freezing climates. But the changes did not occur rapidly, Pam Soltis said.

"Some of these changes were probably not as simple as we once thought," she said. "Adjusting to big shifts in their environments is probably not easy for plants to do."

The researchers plan to use the findings to explore other aspects of plants' evolutionary history, including examining how they respond to environmental changes other than freezing temperatures.

"The onset of freezing temperatures did not affect the entire world, but only certain habitats became colder," Pam Soltis said. "Certain lineages could not move into the cold, but were able to persist unaffected by the cold in warmer areas. With climate change that is human-induced, all habitats will be affected over a short period of time, and plants and other organisms will have to adapt quickly if they are to survive."

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Get touchy feely with plants: Gently rubbing them with your fingers can make them less susceptible to disease

Sep. 12, 2013 — Forget talking to plants to help them grow, gently rubbing them with your fingers can make them less susceptible to disease, a paper in the open access journal BMC Plant Biology reveals.

Gently rubbing the leaves of thale cress plants (Arabidsopsis thaliana) between thumb and forefinger activates an innate defense mechanism, Floriane L'Haridon and colleagues report. Within minutes, biochemical changes occur, causing the plant to become more resistant to Botrytis cinerea, the fungus that causes grey mould.

Rubbing the leaves is a form of mechanical stress. Plants frequently have to deal with mechanical stress, be it caused by rain, wind, animals or even other plants. Trees growing on windy shorelines, for example, sometimes respond by developing shorter, thicker trunks.

But plants also respond to more delicate forms of mechanical stress, such as touch. Some responses are obvious -- the snapping shut of a Venus fly trap, the folding leaflets of a touched touch-me-not plant (Mimosa pudica) -- whilst some are more discrete. Plants also launch an arsenal of 'invisible' responses to mechanical stress, including changes at the molecular and biochemical level.

Rubbing the thale cress leaves triggered a host of internal changes. Genes related to mechanical stress were activated. Levels of reactive oxygen species increased. And the protective outer layer of the leaf became more permeable, presumably to aid the escape of various biologically active molecules that were detected and which are thought to contribute to the observed immune response. This data could also suggest that the mechanical stress is perceived by mechano-sensors that subsequently initiate resistance.

Similar effects occur when plants are physically wounded. Team members previously showed how physically wounding thale cress increases levels of reactive oxygen species, also triggering a strong, transient immunity to the grey mould fungus. Here they show basically the same thing, but in response to an extremely gentle form of wounding -- mechanical stimulation by touch -- that unlike wounding, leaves cells intact.

Wounding and rubbing exemplify how plants can react to a situation that in principle could cause them to become more vulnerable. Instead, they react to touch by deploying a carefully-orchestrated defence response, an evolutionary skill that that presumably boosts survival.

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Plants in space: A novel method for fixing plant tissue samples maximizes time, resources, and data

Sep. 11, 2013 — At work on the International Space Station, researchers studying plant and cell growth in space encountered a challenge. Imaging revealed interesting spaceflight-associated root morphologies. They needed to fix the tissues for further study back on Earth, but conventional fixation methods require separate fixatives depending on whether the sample is intended for molecular or morphological study. If the scientists wanted to study how spaceflight affected patterns of gene expression central to morphological patterns of cell growth, they needed a fixation method that would allow them to study both perspectives.

Most scientists at work in the laboratory rely on protocols that have been developed without the need for restrictions on the amount of space, time, or reagents they use. For scientists conducting experiments in spaceflight, time and resources are strictly regulated and limited, and researchers must know in advance which protocols will maximize the usefulness of the data they collect.

University of Florida professors Anna-Lisa Paul and Robert Ferl and colleagues are collaborating with the National Aeronautics and Space Administration (NASA) to understand plant growth and development in spaceflight. Along with lead author and graduate student Eric Schultz, they have developed a single fixation protocol for use in space that allows plant material to be used for multiple experimental applications. Their new protocol for sample preparation was tested on Arabidopsis tissues harvested on the International Space Station and is described in the August issue of Applications in Plant Sciences.

Because of limitations in astronaut crew time and orbital resources, previous spaceflight fixation protocols were designated as either molecular or morphological, due to the separate fixatives required for each application. Tissues for morphologic study were fixed in 3% glutaraldehyde (or a similar solution), and tissues for molecular study were fixed in the tissue storage reagent RNAlater. RNAlater has not commonly been used as a morphologic fixative, as it can produce unclear images with high background staining.

The new method developed by Schultz et al. puts RNAlater-fixed samples through a desalination process to return them to a fresh-like state, and then uses low-temperature scanning electron microscopy (cryo-SEM) to preserve tissues for imaging. Because few laboratories have access to the necessary equipment for cryo-SEM, the authors tested and developed a protocol that emulates cryo-SEM using standard SEM equipment and, importantly, that results in minimal tissue damage.

Although it was developed to address specific constraints for spaceflight experiments, Paul notes that their new method is broadly applicable. "There are a lot of situations where biologists want to collect samples in extreme situations. In our case -- a space vehicle orbiting the Earth."

The new protocol maximizes the amount of data obtained from a single sample and allows for the concomitant examination of both molecular and morphological features. Using a single fixation protocol, direct comparisons between changes in morphology and altered gene expression can be made. Such an analysis not only makes full use of samples and replicates but also enables a robust analysis of the relationship between heredity and development. "Putting two tools together, it is powerful to look at the morphology in conjunction with the genes that are being expressed," says Paul.

The new protocol boasts low costs and high accessibility, and has wide application to any situation where recovery of biological resources is limited. Notably, this includes researchers collecting and preserving samples in the field, where space for materials is at a premium. "In places where sampling is limited, difficult, or expensive, the use of preservatives allows for more routes to analysis," notes Ferl.

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Danger at Home Lurks in Pills, Plants, Chemicals and More

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FRIDAY, June 8 (HealthDay News) -- If you have children or pets, you've probably looked around your house to see what potential hazards you need to lock up or move, like the cleaning products under the sink. But it's easy to overlook something a child might find appealing.

That windshield washer fluid in the garage might look like a big jug of blue fruit drink to a child. Medication that's red and round can look a lot like a candy to a youngster.

No home can be 100 percent safe, but you can take steps to protect your family from the most serious threats in your home.

"You have to anticipate what kids might do," said Rose Ann Soloway, a clinical toxicologist with the National Capital Poison Center in Washington, D.C. "They're smart and fast, and they like to imitate us."

"I compare children getting into medicines and poisons to a young child rolling over for the first time and falling off a bed or couch," Soloway said. "How often do you hear parents say, 'I didn't know he could do that' when a child rolls over for the first time? While it's not possible to be with a child 24 hours a day, it's important that the things that can really hurt them have as many barriers as possible. Keep anything dangerous locked up and out of reach. Children rely on us to provide a safe environment."

So what are the biggest problems that could be lurking in your home?

"The most dangerous are probably medications," said Dr. Jennifer Lowry, a medical toxicologist at Children's Mercy Hospitals and Clinics in Kansas City. "Parents don't always put them away. Grandparents don't always remember that they could be an issue. Their medications may be in pill boxes that are easy to open. And, older adults are on more medications that can be toxic to children."

Soloway said that the medications of greatest concern when taken by those who don't need them are blood pressure and heart medications, as well as narcotic medications to relieve pain. It's also not always children who are an issue with medications. Poison control centers get lots of calls from older adults who've mixed up their medications.

But even pills people might think are safe can be an issue if the dose is large enough.

"Everything can be a poison depending on the dose," said Lowry. People might not be concerned about leaving vitamins accessible, but iron can be extremely toxic, she noted.

Soloway said that personal care products also prompt a lot of calls to poison control centers. "The ones we worry about are those with alcohol in them," she said. "Children can get alcohol poisoning from mouthwash. Children see adults putting it in their mouths, so why wouldn't they? But, they don't get the swish-and-spit part."

Then there are pesticides, which can be dangerous if they're swallowed, breathed in or gotten on the skin. "It's so important to understand that these products are intended to kill an organism," Soloway noted.

Products called hydrocarbons, such as gasoline, kerosene, lighter fluid and lamp oil, are also a concern. Though they generally pass through the digestive system without causing too much damage, they can get into the lungs, causing a serious condition called aspiration pneumonia, if a child swallows one of the products and then vomits it up.

Immediate harm can come from products that can cause chemical burns on contact, including drain openers, toilet bowl cleaners and dishwasher detergent.

But preventing poisonings at home really boils down to common sense, Lowry said. Store cleaning products and other chemicals in their original containers and store them on a high shelf. The same goes for medications -- or, even better, keep them in a locked box. Replace childproof caps tightly after you use a medication.

If you have to use a pesticide or a cleaning product, use them in well-ventilated areas and follow the label instructions. "If a warning is there, pay attention to it," advised Soloway. She also recommended using just the amount of product that you need.

People who have plants in their homes need to know exactly what they are, as some can be irritating and others safe, Lowry said. And without knowing the kind of plant, it's difficult for poison control to help.

She also suggested getting down on your hands and knees and crawling around your house to get the same view your child might have. "That's when you'll see grandma's heart medicine that fell under the couch," Lowry said.

If the worst happens and you or a child has come into contact with a poisonous substance or ingested it, the first thing to do is to call 1-800-222-1222. That's a nationwide number that will link you to a poison control center, which has experts who can judge whether the situation can be handled at home or whether an ER visit is needed.

More information

The U.S. Centers for Disease Control and Prevention has more tips on preventing poisoning.

For more on the risks of poisonings at home, read a companion article on one woman's story.

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