Feature: Life Sciences
The Fantastic World of Plants
Underneath the quiet majesty of the oak and the ubiquitous existence of grass, plants are anything but passive. As members of a loud, mobile species on an earth that clamors and crawls with creatures, we humans can sometimes forget that plants are every bit as active and interesting as ourselves.
Plant biologists do not forget. They study the way a plant defends itself from infection and damage, the astounding diversity of plants around the world, the mechanisms a plant uses to recognize pollen, the medicinal properties of plant compounds, the potential of plants as fuel, and the development of a plant from a tiny shoot to the glory of its maturity.
The basic, fundamental research in the College of Agriculture and Life Sciences highlights the many opportunities for students and researchers in plant biology
These stories are just a snapshot of the exciting, groundbreaking research that is occurring in plant biology. Plant breeding, agriculture, human health, and the ecosystem itself are all dependent on the discoveries of researchers like CALS plant scientists.
“The College of Agriculture and Life Sciences is extraordinarily well positioned to critically train, not only the next generation of basic plant scientists, but also a generation of young scientists who will study ways to apply basic science breakthroughs to real problems,” says William Crepet, professor and chair of the Department of Plant Biology.
A career in plant biology could mean being a professor and researcher, a health practitioner or nutritionist, an entrepreneur in biotechnology, an ethnobotanist, or an adventure guide.
Willow as Green Fuel
Plant biologists are helping to find solutions to our energy crisis. One of the scientists working on the next generation of green energy is Larry Smart ’87, associate professor in the Department of Horticultural Sciences at the New York State Agricultural Experiment Station in Geneva. There, he is breeding shrub willow, a bioenergy crop with many advantages.
“The product is wood chips,” Smart says, “which have broad appeal as fuel in woodfired plants or as pellets in home boilers and wood stoves. The wood chips are comparable in quality to other hardwoods.” When scientists figure out how to break down the tough cellulose in plants, willow also can be used to generate cellulosic ethanol.
“Once you plant willow, you can harvest it repeatedly,” Smart says. “It requires very little in terms of cultivation activity—you only have to prepare the field once, and you can successively harvest the crop for 25 years. It requires very little input of pesticides and herbicides. Overall it is very sustainable.”
Smart is breeding willow to increase yield. He selects for growth traits such as stem diameter, number of stems, and height, as well as pest and disease resistance.
Willow is a relatively new contender in the bioenergy market. There is very little willow acreage in the United States, and growers are reluctant to invest in a crop they haven’t heard much about. Fortunately, Smart points out, not many changes in infrastructure are needed to use willow as a source of fuel. Growers would only need a harvester fitted with a willow cutter head; coal power plants interested in co-firing might need a milling station, some minor modifications to the boiler, and space for a woodchip pile.
“Willow is appropriate as a feedstock for heat and power, for pelletizing, and some point in the future for cellulosic ethanol,” Smart says. As an ambitious target, he hopes to have one million acres of willow planted in 10 years. Currently, there are eight yield trial sites in New York and more than a dozen others across North America.
The solution to our energy needs will be a patchwork that builds on local strengths and needs. With Smart’s research, willow may be one of the energy options for New York, many parts of Canada, and the upper Midwest.
Plants as Warriors
“The plant can adapt to very moderate changes in temperature—sometimes responding to a change of only a couple of degrees,” she says, “but how the plant does that is unknown.”
Temperature can affect whether the plant will be able to mount an immune response to pathogens. Raise the temperature a few degrees warmer than average, and a plant may not be able to resist infection.
Plants fight pathogens with their innate immune systems by identifying features common among pathogens. But some pathogens have evolved compounds known as effectors that are disguises which suppress the plant’s defense response. To counter this, plants have resistance (R) genes that can recognize the effectors secreted by pathogens. The plant and the pathogen are in a constant race to see who has the best weapon and the sneakiest attack.
“These R genes are different between plant species,” says Hua. “Even among members of the same species, they are rapidly evolving.” This variability allows the plant to recognize different pathogens and respond appropriately.
The immune system in plants is not always turned on, otherwise the plant would be in a constant state of stress, trying to fight off infections that might not be present. Higher temperatures seem to push the switch to an “off” position, leaving a heat-stressed plant vulnerable to attack. Hua is working to understand which genes regulate the system.
“We have plants with mutations in the R gene that could alter the temperature sensitivity of the plant immune system. The R gene can be active at higher temperatures where it would normally become inactive. That is sufficient to confer heat-stable resistance,” she says.
As global warming occurs, if we understand the cues a plant uses to regulate its response to temperature, then we are in a better position to engineer heat-stable disease resistance in food crops and prevent famine.
Signals for Fertilization
Whether transported by bird, bee, wind, or some other vehicle, a pollen grain hopes to settle down on the surface of a stigma, where, if all goes well, it will send a small tube down the style and into the ovary of the plant where fertilization takes place. June Nasrallah, PhD ’77, the Barbara McClintock Professor of Plant Biology, studies the mechanisms that allow for the communication between the pollen and the stigma.
In the crucifer family, this communication is based on a specific interaction between two genes at the S-locus—a specific location in the plant genome. “You will find that in any species there are many different S-locus variants, as many as 100,” she says. “Whenever the stigma and the pollen express the same S-locus variant, fertilization is inhibited.”
How plants fertilize is important for natural variation. A mix of genes can result in offspring better adapted to their environment, be it the forest or the field. In nature, many plants strive to outcross rather than inbreed by distinguishing between other and self.
Nasrallah discovered the two genes at the S-locus. The first codes for a protein called a receptor kinase. This protein is expressed only in the surface cells of the stigma where it is ready to receive its ligand, a small peptide expressed in the pollen grain and coded by the second gene at the S-locus. A kinase-ligand system works like a lock and key: When the lock and key match, a signal is sent and fertilization cannot occur—the door is locked. Nasrallah hopes to learn how the stigma prevents the pollen grain from growing a tube.
“There are times when a plant might be in a jam—for example at the edge of the geographical range of the species,” Nasrallah says. “A plant at the edge will not have other members of the species to mate with. There is great pressure in this situation to find another way to set seed.” Self-fertilization then becomes indispensible. If through a mutation, one or both of the S-locus genes are lost, the lock never meets key and the plant is self-fertile.
Plant breeders and seed producers want to understand the mechanisms a plant uses to favor outcrossing. To combine traits like disease resistance and hardiness, plant breeders create hybrid seed. If the plant is a self-fertilizer, like the tomato, breeders must remove the pollen-laden anthers from each flower by hand, before sprinkling the plants with the appropriate, genetically distinct pollen. Using Nasrallah’s research, plant breeders could instead introduce S-locus genes, thus shutting down self-fertilization and guaranteeing hybrid vigor.
Life Begins with the Shoot
Plant stem cells hold secrets that could help us cure disease and understand cancer. Mike Scanlon, associate professor of plant biology, studies the shoot apical meristem, home to a population of the plant’s stem cells.
“Stem cells in plants are unique because, unlike animals, plants maintain populations of stem cells,” says Scanlon. “That is why plants continue to make organs—stems, flowers—throughout their life; whereas in an animal, the stem cells are mostly active very early in the embryo.”
The mechanisms that regulate the cells of the shoot apical meristem are complex, involving thousands of genes. Scanlon uses laser microdissection to tease apart the cells and look at genes expressed in tissue samples as minute as a single cell. Using genetics and molecular biological methods, Scanlon discovers what makes a stem cell a stem cell and how a cell determines whether it will ultimately be a leaf, a stem, or a flower.
“Everything above the ground in the plant comes from the shoot apical meristem, so these genes affect everything from grain yield to biomass,” he says.
During a plant’s development, genes are turned on and off, resulting in the production of different proteins and RNA that then produce other proteins and RNA. This effect is known as a signal cascade, and many cellular processes are controlled through such cascades. For example, one of Scanlon’s projects is focused on a small RNA pathway that regulates leaf growth in corn. A mutation in the pathway results in thin filaments instead of normal, wide leaves. In Arabidopsis thaliana (mouse-ear cress), a model plant for understanding molecular pathways, the same RNA pathway regulates flowering time.
Basic research like Scanlon’s helps plant breeders understand what traits to breed for, helps chemists identify plants with medicinal compounds, and helps researchers elucidate the pathways that are deregulated in the out-of-control growth of cancer cells.
“We’ve done a lot of work to understand what genes are required to sustain the meristem,” Scanlon says. “One of these genes controls the biosynthesis of vitamin B1. Blocking the ability to utilize vitamin B1 is one way to treat some forms of cancer, which tells us that there are common mechanisms to regulate stem cells and cancer, between plants and animals.”
To the aspiring plant biologist, Scanlon has some good advice. “Keep your eyes and your ears open,” he says. “There are opportunities to expand your research into areas you might not have envisioned. There is so much we don’t know and we don’t understand.”
The Biodiversity of Patagonia
Maybe it happened while visiting the largest colony of Magellanic penguins in the world, or as they hiked above the Andes tree line, or when they reached Tierra del Fuego, home of the southernmost forests in the world. When it happened, during a three-week trip to Patagonia, a group of students gained a richer perspective on the natural environment.
The trip took place this past January under the guidance of Kevin Nixon, professor of plant biology, with the help of Tom Whitlow, associate professor of horticulture, and through the generosity of Cornell benefactor Susan E. Lynch. The trip gave the students hands-on experience in biodiversity, ecology, and taxonomy—putting to good use the lessons learned in class the previous semester.
“Patagonia seems to have a certain appeal that transcends botany and seems mythical,” Nixon says. “People always think of the Galapagos as influencing Darwin, but a lot of his thought was shaped by what he saw passing through Patagonia.”
The students hiked sections of a transect from the Atlantic, across the dry Patagonian steppe in the rain shadow of the Andes, into the temperate rainforest in Chile, down the mountains to the Pacific, and ending in the southernmost city of Ushuaia, in Tierra del Fuego. They observed the changes in vegetation and learned how to survey and identify many species along the way. “We saw an incredible assemblage of plants,” says Nixon. “Even though humans have been in Patagonia for a long time, it is still one of the best preserved and least populated areas in the world.”
Nixon has deep knowledge about the plants of Patagonia. His research focuses on biodiversity and developing plant databases to catalog that richness. He says that there are still untold species of plants that we might need for medicine, building materials, fuels, and food. He also points out that changes in biodiversity are good indicators of how our planet may be heading under the sway of climate change.
“Understanding and cataloguing is the first step in maintaining nature. If you don’t know what is there, you can’t protect it,” Nixon says.
Finding Botanical Cures
Long before modern medicine, people turned to the plant world for cures. Many of these natural remedies have been forgotten, but science and medicine are discovering that the compounds synthesized by nature have potent and useful effects.
Eloy Rodriguez, the James A. Perkins Professor of Environmental Studies in the Department of Plant Biology and Institute of Environmental Toxicology, finds the intersection between botany, health, medicine, and chemistry fascinating.
Manuel Aregullin (left) and Eloy Rodriguez
“Taxol, for example, is a drug used to treat cancer, but for years it was used medicinally by Native Americans who extracted it from the bark of the Pacific Yew.” This compound is just one of many compounds that were discovered in plants and now used in medicine.
Rodriguez has found that students are increasingly interested in natural medicine. He is committed to the complex and integrative discipline of natural medicine, teaching a course called Plant Natural Remedies and Ethnohealth/Medicine. Rodriguez believes that for students interested in medicine, pharmacology, and nutrition, a solid training in plant biology is crucial. “Health initiatives involve billions and billions of dollars,” he explains, “all related mostly to the drug industry. And more and more, the alternative and natural drugs are commanding a share of that market.”
Another researcher interested in the medicinal value of plants is Manuel Aregullin, senior research associate in the Department of Plant Biology, and head of the Laboratory of Natural Products and Medicinal Chemistry.
“It is not surprising that plants have these chemicals,” Aregullin says. “They allow the plant to defend itself from potential pathogens, fungal infections, and herbivory.”
Currently, Aregullin is researching Botrychium virginianum. Commonly called the rattlesnake fern, it is a medicinal plant used by Native Americans to treat tuberculosis. Very little is known about the chemistry of the fern, even though it is widely distributed in North America. He also is investigating Euonymus alatus, the burning bush, a plant that contains an enzyme inhibitor that might fight cancer.
Aregullin’s course Strategies and Methods in Drug Discovery focuses on the scientific process that identifies chemicals in nature useful for developing new pharmaceuticals.
He is the principal investigator and director of the NIH–funded Minority Health and Health Disparities International Research Training Program, founded by Rodriguez. The program takes students to the Dominican Republic to learn about the ethnobotany and chemical ecology of the Caribbean.