Tom Kimmerer: Tree Biology

Seed parasites control development in Douglas-fir seeds

Thu, 30 Jun 2005 02:34:41 GMT

A seed is a wonderful place to live if you are a small insect. Protected by the seed coat and the fruit or cone, nourished by storage compounds like starch and fats, a developing insect has everything it needs. Many insects oviposit (plant eggs) directly into developing embryos. If an insect makes the wrong choice and oviposits into an unfertilized ovule, the developing insect may be out of luck. In conifers, unfertilized ovules become empty seeds, and the tree puts no resources into empty seeds.

Patrick von Aderkas of the University of Victoria and his colleagues found that some insects can avoid making the wrong choice by making the plant feed a larva even if the ovule was not fertilized. A tiny chalcid wasp, Megastigmus spermotrophus (Hymenoptera: Torymidae), deposits eggs in Douglas-fir ovules before they are fertilized. As the wasp larva develops, resources are directed to the seed just as if it had been fertilized. Instead of depending on the tree to supply resources to a fertilized see, Megastigmus manipulates seed development to its own advantages.

von Aderkas P et al 2005 Seed parasitism redirects ovule development in Douglas fir. Proc. Royal Society B Early Online Publishing

The unique toxicity of buckeye

Wed, 29 Jun 2005 03:48:58 GMT

While camping along a creek in central Kentucky last week, I was reminded of the unusual chemistry of buckeyes. The creek had long ago been dammed to make a quiet pool for swimming, and buckeyes were scattered along the shore, their branches with young fruits overhanging the water. Long ago, Native Americans would dam quiet creeks like this one and use buckeyes to catch fish. After damming the creek, they would collect and crush the buckeye fruits and float them on the surface of the creek. Fish, stunned by the poisonous buckeye, would float to the surface. Despite the toxicity of the seeds, Native Americans used them as a food source. As with many nuts, the toxic compounds were leached out in water before pounding the seeds into meal to make flour.

Buckeyes are uniquely toxic among temperate trees. Most trees in temperate zones are defended by phenolic compounds such as tannins. Their toxicity is generally low. A few trees, such as yellow-poplar, Liriodendron tulipifera, contain alkaloids and are a bit more toxic. Buckeyes are in an entirely different realm of toxicity. Most parts of a buckeye are lethal to livestock and other mammals, including humans. Even the flower nectar is toxic to honeybees. I have seen piles of dead bees beneath buckeye trees in the spring. I don't know what the native pollinators of buckeyes might be. Honeybees are not native to North America.

The toxins in buckeye include the coumarin glycoside aesculin, one or more saponins including aescin and one or more alkaloids. Aesculin has potent pharmacological properties, causing severe gastrointestinal and nervous system symptoms. [Note: this paragraph was edited to correct an error in the description of aesculin].

Buckeyes are elegant trees common along creeks, coves and lower slopes in Kentucky. They are easy to spot with their broad, palmately compound leaves, showy fragrant flowers and large fruits. Buckeyes are the earliest understory trees to leaf out in the spring. There are two eastern buckeyes whose ranges overlap in Kentucky: Ohio buckeye, Aesculus glabra, and yellow buckeye, Aesculus flava. In central Kentucky, both species are found along the Kentucky River and its tributaries, and hybrid trees are common.

Why is one particular genus so uniquely toxic? It's impossible to say. In the tropics, where pressure from herbivores is greater than in temperate forests, trees have a great diversity of toxic substances. In temperate forests, this kind of lethal chemistry is rare. Off the top of my head, I can't think of another North American tree genus with such toxicity to a wide variety of animals as we find in buckeyes.

Update: Aesculin is the glycoside of 6,7-dihydroxycoumarin (also known as aescin or escin). Aescin is a product of commerce, used in the pharmaceutical industry for a variety of drugs, and obtained commercially from flowering ash, Fraxinus ornis. It appears that the toxicity of buckey is related to the combination of this potent drug along with saponins and alkaloids.

Update: Coincidentally, Wayne Hughes at Niches has a nice photo essay up about bottlebrush buckeye, Aesculus parviflora, posted on the same day.

Developing fruit of hybrid buckeye, Aesculus sp.

Leaf of yellow buckeye. Leaves do not contain aesculin but do contain other toxins including saponins.

Tangled Bank

Wed, 15 Jun 2005 16:49:10 GMT

The latest Tangled Bank is up at Geomblog. Tangled Bank is a blog carnival for science writers. The current offering has lots of great articles and is worth a visit.

Beardstongue

Mon, 13 Jun 2005 14:25:44 GMT

Wayne Hughes, at Niches, continues his interesting series on the development of complex flowers with beardstongue, whose inflorescence is technically described as a thyrse.

Ancient date palm of Judea germinated after 2000 years

Sun, 12 Jun 2005 03:19:44 GMT

The date palms of Judea are praised in the Bible and the Koran for their beauty, shade, food and medicinal qualities. Now we may get a chance to taste the famed fruit. A date seed found during archeological excavations of Masada, where Jewish Zealots killed themselves rather than fall to the Romans, has germinated and appears likely to survive.

Radiocarbon dating confirms the archeological evidence: the seed is about 2,000 years old. This is the oldest seed ever germinated. Lotus seeds of about 1200 years' age have been germinated in China, but none as old as this.

The seed was obtained by Dr. Sarah Sallon, a physician and scholar of medicinal plants of the Middle East. It was germinated by Dr. Elaine Soloway of the Arava Institute for Environmental Studies.

At the time of the fall of Masada, when Israel ceased to exist for 1900 years, vast plantations of date palms were found throughout the region. Dates were an important food and medicine. The biblical land of "milk and honey" refers to date honey. The Koran describes the date as a symbol of goodness, and the date palm is associated with heaven. By the time of the Crusades, all the date palms had been destroyed. Modern Israel, for which dates are important symbolically and economically, grows date trees imported from California and originating elsewhere in the Middle East. So, the growth of this seedling could potentially resurrect a highly important plant, both economically and culturally.

There is an important unknown, that will not be revealed for at least 20 years: is the tree a male or female? Dates are dioecious, bearing male flowers on one tree and female on another. If this tree is a male, it will only be a historical curiosity. If it is a female, there should be adequate pollen from males of other date palms to allow the tree to bear fruit.

If all goes well, we could once again taste the fruits of the land of milk and honey, thanks to the Zealots of Masada and the curiosity of a group of scientists.

Role of mycorrhizal fungi in nitrogen nutrition

Fri, 10 Jun 2005 17:52:28 GMT

Mycorrhizae, the intimate mixture of plant roots and fungal tissue, benefit the host plant in many ways, including increased phosphorus and water availability. The role of mycorrhizae in nitrogen nutrition has been a subject of debate. Now, USDA scientists report in Nature (article not yet posted) that arbuscular mycorrhizal fungi take up inorganic nitrogen from soil, store it as the amino arginine and then transfer it to the host plant. It now appears that mycorrhizae benefit the host plant by increasing nitrogen availability.

If this is borne out by further studies, and extended to the ectomycorrhizae, the other major mycorrhizal type, it has important lessons for plant management. Crop producers may find that they can boost productivity by reducing nitrogen fertilization. It is known that nitrogen fertilizer reduces the frequency of mycorrhizae and favors formation of non-mycorrhizal roots. By promoting the development of mycorrhizae, productivity could be boosted without added nitrogen. Since nitrogen is one of the most expensive, and most polluting, of agrichemicals, a reduction in its use could have many benefits.

This research also shows that fungi play a more important role in the world's nitrogen cycle than previously realized. This should prompt additional research into revising the nitrogen budgets of farms and forests to reflect the role of fungi.

Arbuscular mycorrhiza of corn. The bright green object is the mycorrhiza (the combination of root and fungus). The round objects are spores and the filaments are fungal hyphae. Photo courtesy of USDA ARS.

Putting the smell back in flowers

Fri, 10 Jun 2005 16:37:01 GMT

Horticulturists have selected and bred fantastic ornamental plants with showy, often dramatic flowers. Along the way to today's modern flowers, something has been lost. In the last 50 years, as breeders have selected for better or new colors, larger flowers, longer stems and longer shelf life, they seem to have inadvertently selected against smell. Many modern flowers lack odor or have minor smells compared to their wild ancestors or older cultivars. Now breeders are beginning to pay more attention to smell and to select modern cultivars for odor as well as appearance. Nursery catalogs are beginning to list smell along with color and other descriptors. The desire for strong fragrance is also behind the resurgence in traditional and heirloom varieties.

Plants seeking fungus for mutual relationship

Fri, 10 Jun 2005 12:30:14 GMT

Mycorrhizae, the mixture of plant tissue and fungal tissue to form roots, are critical to the success of plants on land. Mycorrhizae increase the soil volume occupied by a plant and enable plants to obtain nitrogen and phosphorous that otherwise would not be available. Mycorrhizal fungi also helps plant roots resist invasion by disease-causing fungi and increase water uptake. Trees are utterly dependent on the mycorrhizal habit and cannot survive without their fungal partners. The earliest fossil roots are mycorrhizae, and today nearly all wild plants and many domesticated plants mycorrhizal.

How do plants persuade a fungus to colonize their roots? Plant scientists have long known that many mycorrhizal fungi can be cultured in the lab only in the presence of extracts of their host plant roots. What is the essential ingredient that attracts fungi and allows them to grow in intimate contact with plant cells?

In a painstaking series of experiments reported in today's Nature, Kohki Akiyama, Ken-ichi Matsuzaki and Hideo Hayashi of Osaka Prefecture University and the Japan Science and Technology Agency have answered that question, at least for one plant species. Lotus root extracts promote branching of hyphae in germinating Gigaspora margarita fungi. This branching is characteristic of the formation of one type of mycorrhiza, the vesicular-arbuscular (VAM or AM) mycorrhiza. By carefully fractionating chemical groups in Lotus roots , Akiyama and colleagues identified the stimulating compounds as a type of sesquiterpenes known as a strigalactone.

Interestingly, these same compounds had previously been identified as germination promoters for seeds of Orobanche, Striga and other hemiparasitic plants. These plants couple to host plants via the fungal partner of the mycorrhizal relationship.

This is an important finding. It will allow scientists to focus on the factors that stimulate or inhibit formation of mycorrhizae, and possibly to select plants with improved promotion growth due to better mycorrhizal relations.

This has been a remarkable year in plant biology so far, with major strides in many areas, such as the discovery of the way auxin works. Identification of the stimulating factor in mycorrhizal formation is very important. Both of these discoveries open up new avenues for research in areas of plant science that were stagnated by a lack of new routes to explore.

Big Bucky blooming live on your computer

Tue, 07 Jun 2005 01:31:57 GMT

Our earlier post on gigantic corpse lilies blooming in San Francisco and Wisconsin led to the following comment from Darrell Schulte at UW-Madison. Click on the link to see the Big Bucky corpse lily in bloom. Watch for a while - only when you see people in the scene will you appreciate how huge the flower is, and you can listen to people talking about the stink. Thanks, Darrell!

FOR IMMEDIATE RELEASE 6/6/05 CONTACT: Brian Rust (608) 263-9484, rust@doit.wisc.edu TITAN TV: LIVE SMELLY PLANT NOW ON A DESKTOP NEAR YOU! MADISON - The University of Wisconsin-Madison's giant stinky flower is now just a click away. As of Monday (June 6), live views of the titan arum known as Big Bucky are available on the Internet. The large flower is expected to transition into malodorous bloom sometime this week, and it may draw large crowds seeking to experience the rare plant. But for those unable to make the trek to the UW-Madison campus and the Birge Hall greenhouse where the plant resides, a live video broadcast can be accessed from the Internet at: http://webstreamer2.doit.wisc.edu/titan_arum/ The play-by-play broadcast, which features the striking plant from three camera angles, including a bird's-eye view, will continue until the blooming event is over. Additional information about the plant, as well as news and viewing hours and opportunities, can be found on the Web at http://www.news.wisc.edu/titanarum2005/. Special features, such as interviews with the plant's caretakers, are planned. Produced by the UW-Madison Division of Information Technology, the titan arum webcast is streaming at two different rates to accommodate the range of broadband users, and downloadable clips and "highlights" and interviews for dial-up users. In 2001, a cruder Web cam protocol was used and generated an enormous volume of interest worldwide. The current broadcast is a live video stream, as opposed to the photo sequences used by Web cams. The titan arum is native to the equatorial rain forests of Indonesia. It is a relatively rare plant and is known for its capacity to generate an overpowering smell of carrion when it blooms. The smell attracts pollinators such as flies, beetles and bees. In captivity, there have been only an estimated 65 blooms since 1889, when the first cultured titan arum blossomed at the Royal Botanical Gardens in Kew, England. ### - Terry Devitt, (608) 262-8282, trdevitt@wisc.edu

A lucid explanation of inflorescences

Mon, 06 Jun 2005 15:04:38 GMT

An inflorescence is a cluster of flowers on one stem. Botanists have a lot of names for different kinds of inflorescences, like spike, corymb, raceme. These names are hard to keep straight, but they are important for plant identification and understanding reproduction. Dr. Wayne Hughes, at Niches, has the most lucid, simple explanation I have seen of how different inflorescences form. By following the expression of each floral meristem, Wayne focuses on the important distinctions among inflorescence types. Thanks, Wayne for another great article.

Sorting out Citrus

Mon, 06 Jun 2005 14:22:54 GMT

The USDA has one of the world's largest collections of Citrus at its National Clonal Germplasm Repository for Citrus and Dates in Riverside, California. The collection is an important ex situ repository for preserving Citrus genotypes (meaning a site outside the natural range of the genus). Citrus originates in Southeast Asia, China and India. Many Citrus populations are threatened by industrial and housing development, so an ex situ germplasm collection is especially important. An interesting article in the ARS Agricultural Research magazine describes the Citrus conservation work of Robert Krueger and his colleagues at Riverside. One problem with the ARS germplasm collection is that recordkeeping was often spotty. Of the 900 accessions in the collection, many were of unknown or poorly documented origin. Using molecular techniques, Krueger found that most of the genetic diversity in the collection was in about 50 trees. This is not surprising because most commercial Citrus is of hybrid origin, so a small number of plants can encompass much of the genetic diversity. This combination of a traditional germplasm collection and molecular analysis to sort out the collection is very powerful in helping conserve the genetic diversity of this important genus. The article is well worth reading.

Fruits of lemon, Citrus limon, in a commercial orchard in Ventura County, California

Wollemi pine going to Japan

Fri, 03 Jun 2005 02:40:14 GMT

Wollemi pine, Wollemia nobilis, an extremely rare Australian species will be planted in Japan in an effort to broaden its range as a hedge against extinction. The tree, known only from the fossil record until 1994, when David Noble discovered living stands in a remote national park near Sydney, will go on sale in Japan next spring. About 500,000 seedlings will be sold to Japanese gardeners. Proceeds from the sale will go to conservation of the native stands in Australia.

Pines are revered in Japan as symbols of long life. Australian conservationists expect Wollemi pine to be extremely popular in Japan.

Wollemi pine should become available as an ornamental tree in other parts of the world, including North America, in 2006. Availability at first will be limited. Wollemi pine is probably hardy to USDA Zone 7 and above, so it is suitable for cultivation in the southern US.

See earlier story.

Changing plant classification

Wed, 01 Jun 2005 13:42:53 GMT

At Niches, Wayne has a nice lucid explanation in simple terms of why botanical nomenclature, the arcane set of rules for naming plants, is changing. Names change either because of changes in the rules of nomenclature or because of reassignment of plants to different taxa. The latter is especially common now because of all the new information provided by DNA and RNA analysis. Far from being a stable naming system, modern plant taxonomy is fraught with changes and perils.

One minor quibble with this excellent little essay. Wayne says that soybean has the Genus name Glycine and the species name max. I think it is more accurate to say that the Genus is Glycine and the species name is Glycine max. The specific epithet is max. Sorry, Wayne, but I wouldn't let my students get away with that!

Tangled Bank #29

Wed, 01 Jun 2005 09:50:54 GMT

Thanks to Chris at Organic Matter, there is a new Tangled Bank (#29) featuring a blog version of a natural history museum. Chris has put together a whopping collection of 40 articles on science, natural history, and anthropology. My article on maple rustling is there. There is also a stunning photo and essay about Kadsura interior flowers from UBC Botanical Garden. Great job, Chris!

A tree mystery: Death of a hemlock

Tue, 31 May 2005 18:45:01 GMT

A hemlock tree, planted in a yard 14 years ago, died suddenly. The homeowner left town with the tree apparently healthy and returned two weeks later to find the tree had lost all its needles. On inspection, all the above-ground parts of the tree were dead. We excavated the tree with an Air Knife to see if there were below-ground signs or symptoms that might indicate the cause of death. We found extensive injury to the cambium, phloem and xylem below the ground level of the tree.

Stem of a dead hemlock showing extensive injury.

What caused all this damage? Read more for the solution.

Corpse flower blooms in San Francisco

Tue, 31 May 2005 16:58:26 GMT

A huge, stinky flower is blooming again in San Francisco's Conservatory of Flowers. The flower, which can be as much as 10 ft. tall when it opens, is the second largest flower in the world, and smells of a combination of rotting meat and sweaty socks. The corpse flower, also known as the titan arum, Amorphophallus titanum, is from Sumatra also home to the world's largest flower Rafflesia, Rafflesia arnoldii (spectacular pictures are here). Once thought to be closely related, recent DNA analysis places Rafflesia in its own family and order, while the corpse flower is in the Arum family, Araceae. The common name, corpse flower, is a direct translation of the Indonesian name, bunga bangkai.

Large stinky flowers are adapted to attract pollinators, just like sweeter flowers. However, in this case, the pollinators are probably flies and beetles that are attracted to rotting meat or vegetation (the pollination guild of corpse flower has not received much scholarly attention). A brief article on pollination in Amorphophallus is on the Aroid Society web site. The smelly compounds have low volatility, and these plants have the remarkable ability to generate a substantial amount of heat during flowering. This heat serves to increase evaporation of the smelly compounds. The way that flowers heat themselves to release odors was extensively studied in voodoo lily by the Indonesian-born botanist Bastiaan J.D. Meuse. Bastiaan discovered that salicylic acid, an important regulatory compount in plants, triggers the heating of arum flowers. Bastiaan passed away in 1999 after a prolific and distinguished career.

Update: "Big Bucky", a corpse flower at the University of Wisconsin, is getting ready to flower for the first time since 1991.

Maple rustlers at work

Tue, 31 May 2005 15:12:02 GMT

In the Pacific Northwest, bigleaf maple is a highly valued wood for musical instruments and furniture, especially if it is figured. Figured wood includes bird's eye, ripple and other patterns which make the wood exceptionally beautiful. More often than not, trees with figured wood are gnarled, decayed or have other defects that lessen their value as sawlogs, but dramatically raise their value in the specialty wood market. Figure in trees is often the result of very subtle growth abnormalities. The shifting of cambial cell divisions by small angles between years of growth results in ripple patterns. Bird's eye is the result of the growth and division of trace buds beneath the bark. Burls, which usually contain highly figured wood, may result from virus or fungal infections. The physiologic and genetic factors that cause figures wood are not known. A gallery of great photos of figured wood is at Jim Mattson's lab at Simon Fraser University. Jim and his colleagues are investigating the genetic causes of wood figure, in hopes of being able to propagate trees with a high probability of producing figured wood.

The price paid for this high-value wood is high enough that timber rustlers are a major problem. The Seattle Post-Intelligencer tells us that maple theft is rampant in towns and rural areas around Seattle. Since woodoworkers will often pay hundreds of dollars for a single board of figured wood sufficient to make a guitar, thieves have substantial motivation for their deeds. A single pick-up truck load of good figured wood can fetch $5,000, not bad for a day's work. Or a night's work, since the trees are sometimes taken while a homeowner sleeps.

A new Washington state law will require that transport of figured or specialty wood be accompanied by a permit. The permit must be signed by the land owner where the wood was harvested. Until the new law takes effect in July, law enforcement authorities have to prove that the wood was stolen.

The real problem here is that wood is a commodity, whose origin is unknown to the end user. Once a log is sawn, the identity of the wood product is lost. All over the world, illegal logging ranging from huge forests in Borneo to individual trees in Washington brings a flood of illicitly obtained wood to the market. As long as there is no systematic effort to track the origin of the wood, many of the wood products we buy will come from illegal operations. Third-party certification programs, such as Smartwood, provide a trusted chain-of-custody system that allows the origin of wood to be tracked. Woodworkers and consumers have a moral obligation to avoid the use of illicit wood, but this message does not seem to have penetrated the wood market sufficiently. Considerably more consumer education is required before guitars like the Gibson Les Paul Smartwood guitar becomes the norm in the marketplace.

Conflicts over cypress in Louisiana

Mon, 30 May 2005 12:13:22 GMT

National Public Radio has a well-balanced two-part story on conflicts among conservationists, landowners, loggers and the Corps of Engineers over logging of baldcypress, Taxodium distichum. Like its close relative coast redwood, baldcypress regrows rapidly after logging and is a good candidate for sustainable forest management. However, since the last round of logging in Louisiana abot a hundred years ago, the hydrology of Louisiana has been radically altered. Today, the cypress swamps do not have a seasonaly dry period. Mature cypress does fine in standing water, but seeds require exposed soil to germinate. Logging now may result in conversion of the swamps into marshes, which lack trees. The conflict is not over whether the cypress should be logged - they are on private property and most conservationists support the landowners needs to log their property. However, they argue that logging should be delayed by ten years or more to allow time for an ambitious project to restore the original hydrology of the region.

How auxin works in plants

Mon, 30 May 2005 00:58:28 GMT

In a previous article, I described important new research by Mark Estelle and his colleagues showing how auxin works. Here is a useful diagram by Nicolle Rager Fuller, courtesy of the National Science Foundation, showing the new understanding of auxin's action.

Auxin works in a cell by binding specifically to a protein called TIR1. The combination of TIR1 and auxin, along with a couple of other proteins, destroys a repressor protein that stops growth genes from being expressed. Once these growth genes are activated, they are expressed and produce proteins that control plant growth. Growth genes could include those that promote cell elongation and division, or differentiation. This new understanding of how auxin works does not tell us everything about how auxin promotes root formation, branch suppression and all its other roles. It gives scientists new ways to do experiments to reveal these details.

One of the great mysteries of plant biology has been solved

Wed, 25 May 2005 23:31:59 GMT

Auxin is a plant hormone with multiple and confusing roles in plants. Mark Estelle, Nihal Dharmasiri and Sunethra Dharmasiri at Indiana University have figured out how auxin works. This is a monumental achievement and will help unravel many other mysteries of plant development. [Press releases from Indiana University and the National Science Foundation. Paper to be published in Nature] [UPDATE: The paper is in Nature now. Abstract is available here.]

Auxin is produced in shoot tips and moves downward, never up, in the plant body. Its roles range from inhibiting lateral branch growth to promoting root formation, from measuring gravity to helping fruits develop. I recall finding the roles of auxin, which had to be memorized in undergraduate plant physiology, endlessly confusing and conflicting. The reason for the confusion was clear: we knew the end effects of auxin but not how it did its work.

Estelle and his colleagues found that auxin attaches to a protein called TIR1. The auxin-TIR1 combination switches on growth by removing another protein that stops growth genes from being expressed. Once the growth genes are expressed, they make proteins that are used by the plant to produce new cells.

There is still, of course, much to be learned. One of the great things about a major discovery like this is that it opens up huge opportunities for scientists to probe the details of plant growth. It is safe to predict that, if the Estelle labs results are confirmed by other researchers, there will be a flood of new discoveries to come.

And finally, students of plant physiology will have a rational explanation for some of the mysteries that have bedeviled them.

The research is being published in Nature. It is supported by the National Science Foundation, National Institutes of Health and the US Department of Agriculture.

Update: There are actually two papers in today's Nature regarding auxin attaching to TIR1 protein. The second paper, by Stefan Kapinski, University of York, and Ottoline Leyser, Umea Institute of Plant Biology, appears to come to the same conclusions as the work of Estelle and his colleagues.

Programmed cell death in plants

Wed, 25 May 2005 17:40:21 GMT

When plants are wounded or infected by viruses, bacteria or fungi, they respond by walling off the infected or injured cells. This response is an important part of the plant immune system. In trees, this is known as "compartmentalization", but more generally is called "Programmed Cell Death" (PCD), or the "hypersensitive reaction." PCD is a critical immune response in plants. Understanding how PCD works will help plant breeders to improve the ability of plants to defend themselves against pests and pathogens.

How do plants kill off some cells without killing others? The margins of killed areas are usually very discrete, with some cells dead and cells immediately adjacent appearing perfectly normal. You can see this in almost any plant leaf that has been injured, infected or infested - the margin between dead and living cells is usually a sharp line.

Savithramma Dinesh-Kumar and his colleagues at Yale University have found that plant cells produce both "pro-survival" and "pro-death" signals. Without the pro-survival signals, the pro-death signal can move out of the infected area and cause further cell death. Dinesh-Kumar and his colleagues were able to silence the pro-survival gene, stopping the gene from expressing itself. When tobacco leaves with the pro-survival gene silenced were infected with a virus, the zone of death spread throughout the plant.

The presence of both pro-survival and pro-death signals in plant cells illustrates the complexity and sophistication of the plant immune system. The experiments were also complex and sophisticated. Dinesh-Kumar first had to develop the techniques for silencing individual genes involved in PCD before he could separate the pro-survival and pro-death signals. The research, published in Cell, was funded by the National Science Foundation.

An illustration of PCD in a leaf. The brown cells have been killed by the pro-death signal. Green cells outside the kill zone are protected by the pro-survival signal. The virus (purple) elicits the response, but cell death is an immune response of the plant. Illustration by Nicole Rager Fuller courtesy of the National Science Foundation

American chestnuts on Ohio surface mines

Tue, 10 May 2005 14:39:12 GMT

Ohio has begun planting American chestnut on surface mines in the eastern part of the state. The project is part of the American Chestnut Foundation's effort to restore chestnut to its former glory, uses blight-resistant hybrids of American and Chinese Chestnut. The breeding project, expected to take at least 100 years, mates American chesnuts with Chinese chestnuts and selects resistant progeny. These will then be backcrossed through consecutive generations to select for trees with nearly pure American chestnut characters and genes, but with the blight resistance of Chinese chestnut. The project is led by Brian McCarthy, a forest biologist at Ohio University.

American chestnut was once the dominant species in mid-slope Appalachian forests. They accounted for up to 70% of the stocking (basal area of all the trees) in these forests. Chestnuts produce starchy nuts rich in protein and fat and were an important food resource for wildlife, and for people and their livestock. The tree was wiped out by an epidemic of chestnut blight, caused by the fungus Endothia parasitica. The blight killed billions of trees in only a few years as it swept down the Applachians. My friend Junior Marshall recalls that one year at Robinson Forest the fall colors of the chestnut were magnificent and the following year (1939), they were all dead.

Surface mines may seem an odd place to plant chestnuts. However, they appear to do well in some mine sites. I have found American chestnut on mine spoils in eastern Kentucky.

Ancient tree planted at Kew

Tue, 10 May 2005 14:17:43 GMT

Wollemi pine (Wollemia nobilis), one of the most ancient and rare trees in the world, has a new home at the Royal Botanical Garden, Kew. Sir David Attenborough planted the tree at Kew, and Kenneth Branagh planted one the same day at Wakehurst Place, Kew's garden in Sussex. These planting are the first of this extremely rare and newly discovered tree. Other botanical gardens are in line to plant Wollemi pine, and the species will be commercially available within the next year.

Wollemi pine was known only from the fossil record. An ancient lineage in the Araucariaceae, Wollemi pine dominated much of the southern world in the Cretaceous. Fossils resembling parts of Wollemi pine are known from Cretaceous sediments in Australia, and possibly are found in New Zealand, South America and India. During the Cretaceous, these regions were part of a single southern continent, Gondwanaland. Wollemi pine may have been a dominant species in southern forests from the Cretaceous to at least the Tertiary, a span of 143 million years. The oldest known fossil (the type specimen) of Wollemia dates from 90 Mya. The discovery of living specimens means that the genus, if not the species, has been around for at least 145 million years and possibly as long as 200 million years.

In 1994, David Noble, a National Parks and Wildlife Officer in New South Wales, Australia, found Wollemi pines in a deep gorge in Wollemi National Park in the Blue Mountains only 200 km from Sydney. Since then, two other small stands have been located in the same area. The exact location is a closely guarded secret to protect the trees from collectors. The botanical description of the genus and species were publihed in 1995 (Jones, WG, Hill, KD & Allen, JM 1995. Wollemia nobilis, a new living Australian genus and species in the Araucariaceae. Telopea 6:173-176).

Horticultural interest in the tree is extremely high. The Royal Botanical Gardens, Sydney (RBGS), has established a Wollemi Pine site to provide information about the availability of plants for commerce, as well as general information about the tree. RBGS also has an informational site with detailed information about this fascinating plant.

A sneaky flower

Thu, 05 May 2005 14:14:11 GMT

Wayne, over at Niches, has a beautiful photo essay about the sneaky behavior of pipevine, Aristolochia macrophylla. Definitely worth reading.

Phenology: Springwatch in Britain

Fri, 29 Apr 2005 18:42:03 GMT

The Springwatch project in Britain, sponsored by the Woodland Trust and the BBC, is a large-scale effort to record the timing of spring events in nature. The project has been enormously successful, with over 114,000 observations turned in to date. Initial results suggest that many events normally associated with spring have been occurring throughout the mild British winters of recent years. What is most important is that this kind of large-scale citizen participation in phenology records, if kept up over a long time, will provide scientists with enormously useful information on the impacts of climate change on the natural world.

This is also a great educational tool, one that could easily be implemented in the US. It not only serves an important role in climate change research, but it is an educational tool as well. Any community process that enhances the ability of the citizenry to observe nature is a benefit.