It’s been over three years since I first explored the field of do-it-yourself plant biotechnology in a blog post entitled DIY Plant Genetic Engineering?
Since then, interest and activity in DIY biotech has grown. For instance, please see a more recent blog post on the subject Bio-Hacking Plants?.
You can also read about this subject in Chapter 8 of my e-book Plant Trek.
And now, thanks to O’Reilly Media, there is even a quarterly newsletter on this interesting and timely subject.
As described on their website, BioCoder is the newsletter of a “biological revolution“.
“What revolution?”, you may ask.
Well, according to O’Reilly: “We’re at the start of a revolution that will transform our lives as radically as the computer revolution of the 70s. The biological revolution will touch every aspect of our lives: food and health, certainly, but also art, recreation, law, business, and much more.”
But I think few would argue that the prize for the “stinkiest” plants would have to go to the “Voodoo Lilies” and “Corpse Flowers”.
Indeed, if you wanted to create perfumes for zombies, you probably could not find better ingredients than extracts from “Voodoo Lilies” or “Corpse Flowers”.
This is because these flowers produce what has been described as “the signature scents of death and decay”. Their odors are most often compared to the putrid smells of decaying flesh or rotting meat.
My current favorite description of a Voodoo Lily smell is: “Dead mice. For a couple of days. In a plastic bag that you then open up and take a whiff.” (from livescience.com)
(Of course, zombie perfumes already exist – see here and here, for example. The American Chemical Society even has a YouTube video on “Eau de Death”. Interestingly, its ingredients include chemicals called putrescine and cadaverine, both of which are polyamines that may have hormone-like biological activity in plants – more on this later.)
A Voodoo Lily By Any Other Name Would Still Smell as Bad
Although several plant species sometimes wear the moniker “voodoo lily”, they all have at least two things in common – (1) their flowers smell like rotting flesh or feces (2) they are all members of the plant family Araceae.
Both an online and a scholarly search revealed that several plant species are often referred to as “Voodoo Lily” (though none is classified by botanists as a true lily):
Sauromatum guttatum & Sauromatum venosum appear to be the most common examples in the scientific literature. (And are you ready for the taxonomic synonyms of these species? Here they are: Arisaema venosum, Arum venosum, Arum sessiliflorum, Desmesia venosum, and Typhonium venosum)
For neither “Voodoo Lily” nor “Corpse Flower” was I able to identify the originators of these common names. (Dear Reader – Please feel to jump in with a comment if you happen to know.)
Why Do “Voodoo Lilies” and “Corpse Flowers” Smell So Bad?
If you think that the main reason these flowers produce fragrances reminiscent of rotting meat or feces is to attract some insect pollinators, such as flies and scavenger beetles, you’d be correct.
In a previous post entitled “Death and Pollination”, we saw how not only voodoo lilies but also other flowers, such as orchids, mimic the smell of carrion, which may attract a certain subset of potential pollinators. Such pollinators, especially flies, are also attracted to certain mushrooms, such as the Stinkhorn mushrooms (including the species Phallus impudicus), which also produces odors mimicking carrion or feces. (Since mushrooms are the sexual fruiting bodies of these fungi, the flies help disperse fungal spores.)
An interesting evolutionary question is: Do diverse plant species, as well as some fungal species, use the same or similar scents of carrion or feces to attract the same type of pollinators/spore dispersers, namely, flies? And could this be an example of convergent evolution ?
Some recent evidence seems to indicate that the answer is yes. For example: “We found that scents of both the fungus and angiosperms tended to contain compounds typical of carrion, such as oligosulphides, and of faeces, such as phenol, indole and p-cresol.” (From Ref. 1 below)
This was in general agreement with a previous study: “The odour released from the flower of the voodoo lily Sauromatum guttatum Araceae and the odour of the mushroom Phallus impudicus Phallaceae were analysed. The two species had the major constituents dimethyl disulphide and dimethyl trisulphide in common. Other major components of the S. guttatum excretion were β-caryophyllene, dimethyl sulphide, dimethyl tetrasulphide, indole and skatole. Linalool, trans-ocimene, and phenylacetaldehyde were released by P. impudicus.” (From: Ref. 2 below)
So, the biochemical answer to the question: “Why do “Voodoo Lilies” and “Corpse Flowers” smell like rotting meat?” is mainly because they produce sulfur-containing organic compounds, in particular dimethyl disulphide and dimethyl trisulphide, as mentioned above. But these flowers also produce other volatile organic compounds that add to their appeal to certain flies and beetles.
Though the precise nature of the chemicals responsible for the smell of “Voodoo Lilies” and “Corpse Flowers” is a complex subject, it has been nicely summarized as follows: “…there appear to be two major odour types among sapromyiophilous [pollinated by dung flies]Araceae: carrion smells (mainly oligosulphides) and dung-like odours (complex scent profiles with p-cresol, indole, 2-heptanone and others). Other aroids with distinct odours were generally dominated by one or two compounds, for example fish-scented species by trimethylamine and ‘cheesy’ pungent smelling species by isocaproic acid. (From Ref. 3 below)
By the way, another reason that some “Voodoo Lilies” and Corpse Flowers” smell so intensely bad is that part of the flower may actually heat up in order to promote the volatilization of these foul-smelling organic compounds. (This subject was explored a bit in a previous post.)
1. Johnson, S. D. and A. Jürgens (2010) “Convergent evolution of carrion and faecal scent mimicry in fly-pollinated angiosperm flowers and a stinkhorn fungus.” South African Journal of Botany, Vol. 76, pp. 796–807. (Abstract)
2. Borg-Karlson, A.-K., F. O. Englund, and C. R. Unelius (1994) “Dimethyl oligosulphides, major volatiles released from Sauromatum guttatum and Phallus impudicus.” Phytochemistry, Vol. 35, pp. 321–323. (Abstract)
3. Jürgens, A., S. Dötterl and U. Meve (2006) “The chemical nature of fetid floral odours in stapeliads (Apocynaceae-Asclepiadoideae-Ceropegieae).” New Phytologist, vol. 172, pp. 452-468. (Full Text PDF)
Since the daffodils are out in full force here in the upper left-hand corner of the U.S., I decided to revisit this post from 2013 and revise it a bit.
Hope you enjoy it (again?)….
Doesn’t the Scientific Study of Flower Development Ruin the Aesthetic Beauty of Flowers?
Here’s the best answer to that question that I know of, provided by Nobel Laureate (Physics, 1965) Prof. Richard Feynman:
OK, now back to flower development, in general, and daffodils, in particular.…
Where Does The Daffodil’s “Trumpet” Come From?
The answer to this question comes in a report published in 2013 online in The Plant Journal (please see Ref. 1 below). Although only a summary of this article is currently available online (unless you subscribe), I’ve read the full text (so that you don’t have to). Here’s my take on this story:
Maybe we should we should start by taking a closer look at the flower of the daffodil.
Starting from the outside working in, the six petals are actually “tepals”, which are a kind of developmental combination of sepals and petals.
Next up is the famous trumpet-shaped part of the daffodil flower called the corona (“crown”) that is the main subject of this blog post.
The central part of the daffodil flower consists of the six stamens that encircle the carpel (gynoecium). In the photo (right), you can barely see the anthers (produce pollen) of the stamens, and also you can only see the top of the carpel called the stigma (receives pollen).
When And How Is A Daffodil Flower Made?
You maybe surprised to find out that a miniature version of the daffodil flower actually develops not in the spring just before it blooms, but at the end of the previous growth season. Thus, a floral bud is fully formed, and over-winters, within the dormant bulb.
This means that plant scientists investigating daffodil flower formation (see Ref. 1 below) have to dissect out flower buds from the developing bulbs. Whew! (Thank goodness for grad students: nearly the ultimate in cheap labor. Ultimate = undergrads!)
Anyway, as a result of such efforts, Waters, et al.(Ref. 1 below) discovered that the daffodil corona forms relatively late in the flower-development program.
As described in a previous post, the flower-development program can be described like a play with several acts.
In the first act, the plant genetically shifts from a vegetative state to a flowering state.
In the second stage, which I call “arranging the chairs”, the spatial arrangement of the flower is determined.
In the third act, which I call “seating the guests”, the different flower parts (in this case, tepals, stamens and carpel) are seated in their appropriate “chairs”.
In daffodils (and perhaps other species within the Amaryllis plant family that have trumpet-shaped flowers) there apparently is a fourth act.
In this final act of daffodil flower development, new “chairs” are provided and arranged in a circle between the rings of the tepals and the stamens. The “late” guests are then seated.
The question was: to which of the four basic flower parts (sepals, petals, stamens, carpels) are these “late” guests related? Turns out they are genetically related to stamens.
But, of course, an obvious question is: How does the daffodil make something that looks like petals by starting with the genetic “blueprints” for stamens?
The honest answer is we simply don’t know at the present time. It should be mentioned, however, that some of the results of Ref. 1 show that there is a late burst of coronal growth in the spring, so a great deal of elaboration of the “stamen” program is happening to result in a petal-like structure. This and other evidence suggest that petal-like structures “…can be produced by different genetic pathways even within the same flower.” (from Ref 1 below)
Why The Trumpet-Shaped Flower?
Most explanations from botanists involve attracting pollinators. But who pollinates domesticated daffodils? Mostly likely, it’s people!
Most of the showy daffodils that we see in the spring in parks and around homes and businesses are a product of plant breeding, i.e., artificial selection, not natural selection. (You can read more about this here.)
That is, such daffodil flowers are a product of what has looked good to humans (daffodil breeders especially), not insects. Indeed, most of the domesticated daffodils that we see in the spring may not be especially attractive to bees, and thus the daffodils may not even be pollinated (unless the bees are desperate).
What about the origin and evolution of trumpet-shaped flowers (before humans got involved)?
No one can be absolutely certain of an answer, but the long narrow corona of the genus Narcissus may have evolved to accommodate pollination by bees over butterflies or moths, which can’t easily enter the tall narrow corona to access the pollen. (from Ref. 2 below)
If all of the above was a bit much, it might help to listen to a brief (4 min) audio clip about the daffodil’s mysterious trumpet courtesy of The Science Show on Australian Broadcasting Corporation’s RadioNational.
OK, if you’ve listened to this audio clip, then you’ve heard that the “trumpet” or “corona” of the daffodil flower is probably not an extension of the petals, as previously thought, but is a distinct organ – sharing genetic identity with stamens.
If you haven’t listened (and even if you have), you can read brief summaries of Ref. 1 below here and here.
1. Waters, M. T., A. M. M. Tiley, E. M. Kramer, A. W. Meerow, J. A. Langdale, and R. W. Scotland (2013) “The corona of the daffodil Narcissus bulbocodium shares stamen-like identity and is distinct from the orthodox floral whorls.” The Plant Journal, article first published online: 13 MAR 2013 (Abstract)
2. Graham, S. W. and S. C. H. Barrett (2004) “Phylogenetic reconstruction of the evolution of styler polymorphisms in Narcissus (Amaryllidaceae).” American Journal of Botany, Vol. 91, pp. 1007–1021. (PDF)
In the year 450 A.D., Attila the Hun was invading Europe, the last of the Roman empire was crumbling (including the abandonment of Londinium), the Aztec civilization in Mexico was just beginning, and a little moss plant (a bryophyte) was growing on Signy, a small subantarctic island.
Now fast-forward 1,564 years to the present day.
Small remnants of this moss plant, frozen in permafrost for over 1,500 years, are reportedly being regenerated in a laboratory at the University of Reading, in southern England, about 25 miles west of London.
In a recent report (see Ref. 1 below), researchers from the U.K. and New Zealand have broken the previous age record (about 400 years – see Ref. 2 below) for regeneration of intact, multicellular organisms from frozen environments. According to these scientists “…we show unprecedented millennial-scale survival and viability deep within an Antarctic moss bank preserved in permafrost.” (from: Ref. 1 below)
Here’s a brief (about 1 minute) YouTube video summarizing this report:
The mosses regenerated from core samples were carbon-dated to be at least 1,500 years old. But these aren’t even the oldest parts of the Signy Island frozen moss banks, which may be over 5,000 years old. Could mosses that were growing on Signy Island during the time of the construction of the Great Pyramid of Giza, about 2,600 B.C., be revived from frozen specimens? These researchers speculate that this may indeed be possible. (see Ref. 1 below)
But wait a minute? Haven’t 5,000-year-old seeds from ancient Egyptian tombs been germinated and revived?
But what’s apparently not a myth is the regeneration of 1,500-year-old frozen moss plants. And it also should be mentioned that the successful regeneration of whole, fertile plants from small pieces of 30,000-year-old frozen fruit tissue using plant tissue culture has been reported. (Please see Ref. 3 below.)
How can intact moss plants remain viable for over a thousand years in permafrost? And how can frozen plant cells apparently remain viable even after 30,000 years in permafrost?
Over fifty years ago, “David Keilin (Proc. Roy. Soc. Lond. B, 150, 1959, 149–191) coined the term “cryptobiosis” (hidden life) and defined it as “the state of an organism when it shows no visible signs of life and when its metabolic activity becomes hardly measurable, or comes reversibly to a standstill.”” and “Keilin noted that cryptobiosis resulted from such things as desiccation (anhydrobiosis), low temperature (cryobiosis), lack of oxygen (anoxybiosis) or combinations of these.” (from Ref. 4 below)
Though most of the reported research regarding cryptobiosis appears to have been conducted on tardigrades, the preservation of viable plant material in permafrost is likely due not only to cryobiosis but also to anoxybiosis and, especially, to desiccation.
Some mosses are well-known to be able tolerate drought and desiccation, and the cellular and molecular mechanisms responsible for this have been been studied (see Ref. 5, for example).
The desiccation tolerance of mosses likely involves both the accumulation of increased solutes (such as sucrose) and the production of protective proteins such as dehydrins in order to preserve cellular structures and also to aid in the recovery of the cells upon rehydration.
It wouldn’t be surprising if we find that the mosses revived after more than 1,500 years in permafrost relied on many of the same survival strategies that the desiccation-tolerant mosses use.
1. Roads, E., R. E. Longton and P. Convey (2014) “Millennial timescale regeneration in a moss from Antarctica.” Current Biology, Vol. 24, R222-R223, doi:10.1016/j.cub.2014.01.053. (Full Text)
2. La Farge, C., K. H. Williams, and J. H. England (2013) “Regeneration of Little Ice Age bryophytes emerging from a polar glacier with implications of totipotency in extreme environments.” Proc. Natl. Acad. Sci. (USA), Vol. 110, pp.9839–9844. (Full Text)
3.Yashina, S., et al. (2012) “Regeneration of whole fertile plants from 30,000-y-old fruit tissue buried in Siberian permafrost.” Proc. Natl. Acad. Sci. (USA), Vol. 109, pp. 4008–4013. (Full Text)
4. Clegg, J. S. (2001) “Cryptobiosis – a peculiar state of biological organization.” Comparative Biochemistry and Physiology, Part B, Vol. 128, pp. 613-624. (PDF).
5. Charron, A. J. and R. S. Quatrano (2009) “Between a Rock and a Dry Place: The Water-Stressed Moss.” Molecular Plant, Vol. 2, pp. 478-486. (Full Text)
Because plants are “rooted” to the place where they germinate, they don’t move. Indeed, it’s become almost a cliche to describe plants as displaying a “sessile life-style”, especially when contrasting them to animals.
But are all plants necessarily sessile organisms, never moving from the spot where they were “born”?
Well, if you’ve read the title of this post, then you already know the answer to this question is: No.
One of the most well-known plants that defies the “sessile life-style” rule is the so-called Walking Palm.
The key structural features of this plant that allows it to move are its “stilt roots”. These are adventitious support roots that grow down from lateral branches, branching in the soil.
By extending such stilt roots to one side or another, the palm tree moves laterally or “walks” through the forest. But why would it want to do so?
Some hypothesize that this “strategy” likely increases the “walking” palm’s ability to relatively rapidly (timeframe = a year, for example) exploit light gaps in the forest, compared to other trees.
Others think that this also allows the palm to right itself if knocked over by a fallen tree (see a diagram here illustrating this).
Below is a YouTube video that nicely describes the nature of the “walking” palm tree.
“Slithering” Toward the Sun
Question: What would you call a plant that germinates on the tropical forest floor, then grows upward toward the sun on the trunk and branches of a tree, and, when it reaches full sunlight, it causes the oldest portion of its shoot to die?
Whichever name you prefer, these plants start their life as ground-dwelling flowering plants. Like other vines, the plant then climbs the host. But the plant eventually loses its connection to the soil and becomes an epiphyte.
As pointed out by Mark W. Moffett (National Museum of Natural History, Smithsonian Institution) in a letter to The New Yorker: “One such nomad is the philodendron in your dentist’s waiting room. In a rain forest, some philodendrons remain a few yards in length and yet they meander through a tree’s canopy, acting like a snake searching for a place to bask. The plant grows small leaves and long thin stems to move quickly when in shade, changing over to the thick stems and large leaves when it reaches a patch of sunlight.” Moffett continues: “The results are fantastical: when a canopy-dwelling plant, such as an orchid, falls from a tree, it’s likely to perish in the understory shade. But the philodendron simply uncoils itself, crawls over to the nearest tree trunk, and climbs up again.”
Another important observation noted by Moffett: “Both walking trees and nomads change locations without muscles. Taking advantage of the “modular” strategy Pollan describes, they grow in the direction of motion while leaving their trailing parts to die.“
In this most interesting twist on “phototropism”, these nomadic “walking” and climbing plants are able to follow the sun by actually growing themselves, bodily, into the light.
Plants on Wheels
And now on a bit more whimsical note, I present for your consideration: “Plantas Nómadas” (English translation = “Nomadic Plants”).
Some of these VOCs we can smell, such as flower fragrances and pine scents. But many, such as the plant hormone ethylene, may either have no odor to us or be produced in such vanishingly small amounts that we cannot detect them. But some machines can…
Thanks to such machines (see Ref. 1 below, for example), plant scientists can routinely detect and analyze trace gases (down to 1 part per billion) released by plants under different conditions, not only in the lab, but also under natural conditions in the field. This has led to many new insights regarding plant-plant and plant-insect communication, as I’ve mentioned in previous posts, such as “Talking” Plants.
Collectively, plant VOCs may even have effects on the Earth’s atmosphere.
Two research reports regarding very different aspects of plant VOCs have recently caught my eye.
Some naturally-produced plant VOCs have been known for some time to act as a defense against insect herbivores (see here, for example). But a report in the 25 February, 2014, issue of Nature Communications (please see Ref. 2 below) adds a whole new dimension to plant-to-insect chemical signaling.
Briefly, a team of scientists have genetically-engineered tobacco plants to express an array of enzymes – using a combination of plant and insect genes – that collectively produce sex pheromones that attract moths. (One of the plant genes came from Euonymus alatus, a.k.a., “burning bush”.)
At this point, you may be asking “Why?”.
Answer: From Ref. 2 below – “Pheromones are environmentally friendly alternatives to traditional pesticides for the control of insect pests and indeed synthetic pheromones are produced in large amounts for this purpose. Current standard approaches to pheromone synthesis either require the use of hazardous chemicals or may result in the production of hazardous waste byproducts. We propose to overcome the problems inherent to synthetic pheromone production by designing and developing an innovative green chemistry alternative while minimizing hazards. Our strategy involves the use of a cost-effective plant factory expressing a suite of biosynthetic enzymes for production of moth pheromones.“
Published online 26 February, 2014, a report in Nature magazine (see Ref. 3 below) by German, Finnish and U.S. scientists “…elucidates the process by which gas wafting from coniferous trees creates particles that can reflect sunlight or promote cloud formation, both important climate feedbacks.” (From a summary of this research provided by the University of Washington.)
And here’s a bit more from Nature’s Editorial summary: “Forests emit large quantities of volatile organic compounds to the atmosphere. The condensable oxidation products of volatile organic compounds emitted by forests can form secondary organic aerosols or SOAs that can affect the Earth’s radiation balance by scattering solar radiation and by acting as cloud condensation nuclei. But our understanding of the link between biogenic volatile organic compounds and their conversion to aerosol particles remains limited. This study reveals that a direct reaction pathway can lead from volatile organic compounds to low-volatility vapours that can then condense onto aerosol surfaces producing secondary organic aerosol and can significantly enhance the formation and growth of aerosol particles over forested regions.”
Plants…they’re a gas!
1. Harren, F. J. M. and S. M. Cristescu (2013) “Online, real-time detection of volatile emissions from plant tissue.”, AoB PLANTS, Vol. 5 : plt003, doi: 10.1093/aobpla/plt003. (Full Text)
This new website – Global Forest Watch – not only allows users to precisely monitor forests but also will allow them to upload information, pictures, and videos from forests around the world.
Here’s a brief description from the website:
“Global Forest Watch (GFW) is a dynamic online forest monitoring and alert system that empowers people everywhere to better manage forests. For the first time, Global Forest Watch unites satellite technology, open data, and crowdsourcing to guarantee access to timely and reliable information about forests. GFW is free and follows an open data approach in putting decision-relevant information in the hands of governments, companies, NGOs, and the public.“
And here’s a brief YouTube video about Global Forest Watch:
A couple of weeks ago I was perusing the online edition of Wired magazine and spotted the following headline: “The Internet of Vegetables: How Cyborg Plants Can Monitor Our World”.
With a title like this, how could I not click on the headline and read the article? (Please see link #1 in the Online Resources below). What I read left me slightly amazed, mildly amused, and totally surprised.
I was slightly amazed because of the nature of the proposed research project described in this article. I was mildly amused because this project is somewhat reminiscent of investigations that took place over 40 years ago. And I was totally surprised because I had just read an obituary about Grover Cleveland “Cleve” Backster, Jr., who died last year (6/24/2013) at the age of 89.
Allow me to explain….
Do You Remember The Plant Polygraph Man?
Have you heard about the experiments during the 1970s in which plants were connected to “lie detectors” (a.k.a., polygraphs)? The polygraphs were used to attempt to measure changes in electrical activity within the plants, especially in response to various stimuli. This was the guy.
Cleve Backster performing one of his experiments – From: The New York Times (see Online Resources #2 below)
Cleve Backster “…was an interrogation specialist for the Central Investigation Agency (CIA), best known for his experiments with plants using a polygraph instrument in the 1960s which led to his theory of “primary perception” where he claimed that plants “feel pain” and have extrasensory perception (ESP), which was widely reported in the media but was rejected by the scientific community.” (from Wikipedia)
Backster was a proponent of “primary perception” for over 40 years. He became famous, (or infamous, depending on your point of view) chiefly thanks to the book The Secret Life of Plants. Ah, but we’ve been down this road before…here, here, and here… so, I won’t travel it again in this post. (By the way, an excellent, albeit skeptical, review of Backster’s work can be found here.)
Many people tried to reproduce Cleve Backster’s experiments, most without success, including TV’s Mythbusters.
But what does Cleve Backster’s plant polygraph experiments have to do with connecting plants to the internet?
The reason I was surprised and amused when reading the Wired article soon after reading Backster’s obituary was that, coincidentally, both have to do with electrical activity in plants.
PLants Employed As SEnsing Devices (PLEASED)
It’s been known for long time that it’s possible to detect electrical signals in plants, often in response to external stimuli. (Please see Ref. 1 below, for example.) But the physiological significance of such electrical signals has often been questioned.
The article in Wired magazine online described a current research project aimed at using computers to precisely characterize electrical signals in the plants, especially with regard to specific environmental stimuli. Moreover, if and when these electrical signals are so categorized, these investigators speculate that the plants can then be developed as a whole-organism sensing device, and even be inter-connected via the internet. (Please see Online Resources #3 below for link to their website.)
Perhaps a brief YouTube video, courtesy of this research group, may serve as a good introduction:
The major difference between these researchers and Cleve Backster is that the PLEASED project doesn’t involve the paranormal, namely, “primary perception”. This doesn’t mean, however, that this project isn’t fairly far out on the fringes of plant science and of feasibility.
For example, it seems like it would be a major challenge not only to assign a specific electrical signal to a specific plant bioresponse, but also to tease out a signal from amongst all the electrical “noise” inherent in a complex multicellular plant. And it seems totally impractical to use living plants – subject to the vagaries of wind and weather and disease and insects and light and darkness – as reliable biosensors.
Despite all this, my hat’s off to them and their collaborators for acquiring funding for this high-risk project. I wish them luck.
In closing, I should mention that this is certainly not the first time that it’s been suggested that plants be used as environmental biosensors. (Please see Ref. 2 below, for example.) More on plant biosensors to come….
In a previous post we saw some of the ways that cold-adapted plants are able to tolerate sub-freezing temperatures, or not.
But how do trees and other plants survive extreme cold, that is, temperatures well below zero degrees C.
“Different tree species differ in the depth of low temperatures each can survive. For example, live oak (Quercus virginiana) can survive down to about 20o F (-7oC); magnolia (Magnolia grandiflora) down to 5oF (-15oC); sweetgum (Liquidambar styraciflua) down to -15oF (-26oC); American elm (Ulmus americana) down to -40oF (-40oC); and, black willow (Salix nigra) down to -100oF (-73oC).” (from Ref. 1 below)
Exactly how trees survive extreme cold is complex, and much about the cellular mechanisms of extreme cold tolerance in trees is unknown. Also, much depends on how long the cold lasts and how cold it actually gets.
Basically, however, the chief problem faced by trees exposed to extreme cold is to try to keep living cells from freezing. They can do this in a number of ways, such as accumulating or producing solutes (sugars, e.g.) in order to decrease the freezing point of water and producing proteins that inhibit ice crystal formation. This allows deep supercooling of cells, to many degrees below the freezing point, without ice formation.
But at temperatures of -40o F and lower, these strategies may no longer work. Such temperatures typically cause ice crystal formation, intracellular freezing and cell death. In tree species that can tolerate temperatures below -40o F under natural conditions, living cells must be able to withstand gradual dehydration as the water freezes. How they do so is not well understood, though it likely involves the biosynthesis of specialized proteins and lipids that help protect cellular structures in conditions of extreme dehydration. (see Ref 2 below) It’s not surprising that some desert plants may use similar protective substances under extreme drought conditions.
In recent news, a group of researchers has “…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.” (from: Study offers clues to how plants evolved to cope with cold.)
Zanne, et al. (see Ref. 3 below) identified three traits that help plants cope with the freezing and thawing that causes air bubbles to form in the plant’s internal water transport system.
1. Some trees avoid freezing damage by dropping their leaves before the winter. This effectively stops the flow of water between roots and leaves. When warmer weather returns, they grow new leaves and water transport (xylem) cells.
2. Other trees also protect themselves by having narrower xylem cells, which makes the parts of the plant that deliver water less susceptible to blockage during freezing and thawing.
3. Many plants avoid winter temperatures by dying back to the ground in winter and re-sprouting from their roots in the spring, by producing seeds that can survive the winter and then, later on, the seeds germinate under warmer conditions, or by doing both.
Here’s a YouTube video that nicely illustrates the above:
1. Coder, K. D. (2011) “Trees and cold temperatures”. Publication WSFNR11-12 from The Daniel B. Warnell School of Forestry and Natural Resources, University of Georgia, Athens, Georgia, United States. (PDF)
2. Gusta, L. V. and M. Wisniewskib (2013) “Understanding plant cold hardiness: an opinion.” Physiologia Plantarum, Vol. 147, pp. 4-14. (PDF)
Several of the “tastier” plant news items for December 2013 relate to topics that were previously ruminated on here within the past year.
So, why not finish off our 2013 “banquet” of plant news with a trip back to the howplantswork.com “buffet table” to re-sample some of this year’s posts.
An impediment for many plant systematists, field ecologists, and evolutionary biologists is determining the correct identification of a plant sample in a rapid, repeatable, and reliable fashion. To help solve this problem, one of the newest tools currently available to these scientists is a technique called DNA barcoding. For example, last month it was reported that researchers used this technique to identify genetic fingerprints of endangered conifers: Barcodes for trees.
Genetically-modified organisms (GMO), in general, and genetically-engineered plants, in particular, were in the news all throughout 2013, including December. For example, that Chinese officials blocked the importation of GMO corn from the USA was reported in: Why are the Chinese scared of American corn? The topic of GMO plants appeared several times during 2013 in this blog, including GMO? OMG! and Transgenic Plants – Reality Check. Also, back in July, I offered an ebook on this subject called “Plant Trek”.
Are plants “intelligent” organisms? What, indeed, do they “know”? For example, do they feel “pain”? And can they “learn” and “remember”? These are some of the interesting questions raised by Michael Pollan last month, in the New Yorker. The topic of plant “intelligence” has come up in this blog on several occasions, most recently last September in a post entitled Smarty Plants – On Plant “Intelligence”, the “Vegetal Life” and Philosophical Botany. There’s a lot of skepticism, especially among plant scientists, in interpreting plants’ responses to their environments as some sort of “intelligence”, analogous to animals. Perhaps the best answer to the question of plant “intelligence” is provided by Prof. Tobias Baskin in a letter to the New Yorker in response to Pollan’s article.
I expect we’ll hear more on these and many other fascinating subjects about plants in 2014. With a bit of luck, we’ll be here to tell you about them.
German Lessons in Seattle German Language Classes and Tutoring for School, Business, Travel, and Fun Fair Prices! Quality Teaching! German with Eugen Private and Group Lessons in High-German and Swiss-German with Eugen Groff, Wedgwood, NE Seattle Click on photo for more information