Translator: Tanya Cushman Reviewer: Cristina Bufi-Pöcksteiner
Most of us probably don't think about this,
but, actually, a plant's life is pretty stressful.
Think about all the things they have to worry about:
finding enough nutrients in the soil,
water - you know drought is a major problem in the world for plants -
that's below ground.
Above ground, they have the problem of dealing with competitors,
finding enough light,
absorbing CO2,
and my favorite stress is insects and disease always looking for them.
So while they look pretty happy and pleasant,
actually they're out there working really hard
to deal with the stresses they face.
A point I want to make with all of you
is that while we think of plants mainly as the furniture -
they're just sitting there doing nothing -
in point of fact,
they have a wide range of behaviors to deal with the stresses they face,
and that makes perfect sense
because, after all, they are rooted in one spot;
where the seed germinates is where the plant grows.
So plants really don't have the option
of leaving a bad spot and looking for a better one.
As a consequence, plants are exquisitely attuned to their environment,
they have almost 700 different kinds of sensors to sense their environment,
and they have exquisitely attuned behaviors
for dealing with those stresses as they come along.
For example, below ground, roots go searching, actively,
for concentrations of nutrients in water.
You can tell from this photo that my house plant root,
searching across the carpet in the living room,
is telling me it has definitely been stressed
and I should water it more often.
(Laughter)
Plants often enter into collaborations in order to solve these problems.
Most of the filaments you see in this picture, the white ones,
are not plant roots.
Those are fungal hyphae, little strands of fungus,
that extend the reach of the roots dramatically.
One thing you might notice are three plants in the picture,
and if you look very carefully,
you'll notice that the white threads join the three plants.
So what's happening here is a collaboration,
first of all between the plant and the fungus,
and that's mediated or negotiated through conversation that's chemical
between the plant and the fungus.
The plants are actually interacting with each other,
able to send nutrients and signals back and forth
through the network of fungus.
So this is a case of collaboration and conversation going on below ground
in order to allow the plants to do their job.
Alright, I'm going to have to reboot this.
Here we go, okay.
Above ground, light is a major issue.
Anyone who recognizes this as a grapevine
is familiar with the fact that many plants go searching for light.
Something that we don't often think about
is that the amount of light isn't the only thing plants are interested in.
Most plants are equipped with photoreceptors
that can tell them what the color of the light is surrounding them.
If you think about for a minute, does that make sense?
Well, yes.
The meaning of being surrounded by green
is that you're surrounded by your competitors.
So sensing a green environment
causes plants to turn on genetic programs that change its growth pattern
and go looking for light and escape from their competitors.
You can also notice that the grapevine is taking advantage of sensitive touch sense
and is getting help in its climb to the light
by gripping the substrate beneath it with a tendril.
Plants are very touch responsive
and frequently grab almost anything to get where they want to go.
But my favorite stress is insects.
Insects are, of course, a problem for plants,
and you can see in this picture - a wild tobacco plant -
that they can be a pretty profound problem.
But they don't have to do this much damage to be important.
As little as 10% loss of leaf area to a plant
significantly reduces its reproductive output.
So even a little nibbling by insects has a significant impact on plant performance.
In addition to the insects, which are easy to picture,
there are thousands of diseases that plants have to deal with as well.
Now in this particular case,
plants have come up with a really diverse way
of dealing with these kinds of pests, if you will.
If you've taken advantage of, experienced or used any of these items,
(Laughter)
you've done so to acquire whatever the active ingredient is,
whether it's the flavor of a spice,
the activity of aspirin - which originally came from willow bark -
or the others,
all of those chemicals that you are exploiting there
originally were insecticides,
natural insecticides,
and some of them are disease preventives as well.
But if you ask the question
if nicotine and caffeine act on central nervous systems -
which is why some people enjoy them -
plants don't have central nervous systems:
why does a coffee plant make caffeine?
To protect it against its enemies.
Now, something we discovered several years ago
is that plants also do this trick actively:
every plant that's been studied
has been shown to increase the concentrations of these chemical compounds
whenever they are attacked, whether it's by disease or insects.
So, here too, the plant has a dynamic behavior;
it changes in response to the stress as it arrives.
Now along the way,
we discovered what turned out to be a really unique and fascinating response
by plants to their enemies.
As it turns out, plants - in fact, this is true of every studied plant,
but I'm going to illustrate it with corn -
when plants are attacked by insects,
they hurl a bouquet of molecules into the air.
I'm picturing here many of the molecules that emerge from a corn plant
when it's being attacked by an insect.
Every plant produces a different suite of these things,
and every plant has a different response to a different stress, in this way.
You and I are familiar with those molecules
because they all represent or are parts of familiar odors.
These are volatile organic compounds,
which means they float around in the air, and when they get to your nose,
you think "clove" or "leafy" or other senses.
Now, what's going on here?
First of all, could we tell if this is happening?
Well, the answer is no.
If we walked through a cornfield,
even if it had a huge infestation of insects,
there wouldn't be enough of these molecules reaching your nose
for you to really detect it.
Now, you do get a sense of this when you mow the lawn
because some of those molecules are the same.
But generally speaking, these molecules are produced in such low concentrations
that the only thing that can really sense them
is a dog's nose or insect's antennae.
Why are they doing this?
Well, what we discovered some years ago
is that if we took two plants and allowed one to be attacked by insects,
collected the air from around that plant,
and exposed an unattacked plant to that air,
the unattacked plant would turn on the defenses I've been describing
that it needs to protect itself against insects.
The same thing happens with respect to disease,
and so far, every stress that we've ever exposed a plant to
has produced a different fingerprint of emitted volatiles.
What that means is you can tell what the plant has experienced,
even down to the insect species that attacked it
by examining the volatile signature.
So, what we have so far are a series of conversations:
below ground, roots are connecting with fungus,
the fungus is connecting roots,
signals are moving back and forth between plants via the fungus;
and above ground, a different kind of conversation.
This one is involving volatile organic compounds
emitted by a plant experiencing a stress,
and when those reach a nearby plant,
it cues responses that are appropriate to that stress.
In a sense,
the plants next door are prepped, or prepared, for upcoming attacks.
Now, thinking again about corn,
this is not the only thing that helps protect plants against their enemies.
Somewhere in our cornfield,
there are some insects feeding on the corn plant,
a little caterpillar, for example.
And one of the features of nature that helps control the numbers of those
is a whole group of tiny little insects we call parasitoids
that seek out, sting and lay their eggs in and kill insects that are pests.
This is a very critical part of the natural control of pests.
So somewhere in the cornfield, there's a caterpillar, and somewhere,
looking for the caterpillar is a tiny little wasp like this one,
which may only be a millimeter or two long - tiny, tiny.
This is a needle in the haystack problem for it.
So how does it find the caterpillar?
Well, you remember that when the plant is attacked by insects,
it emits a signature set of volatiles.
What the plant's doing is saying, "Over here. Here's lunch. Right here."
And the plants are calling in bodyguards with the volatiles that they emit.
These wasps are attuned to and can even learn the specific volatiles
associated with the plant that has the appropriate pest on it.
So this works together with the plants conversing with each other
to help protect the plant,
both in nature and in agriculture.
This really matters.
The tobacco plant I showed you earlier is really suffering
because it has been genetically deprived of its ability to speak.
This plant has been genetically modified so that it cannot do this signaling trick.
And you can see the consequences.
It really matters to plants to be able to have this conversation
both with each other and with their friends.
Now, everything I've told you so far
is well-substantiated by rigorous experimental work;
however, almost all of the experimental work has been done like this,
in containers
in which we concentrate the air around the plant that's being damaged,
collect that concentrated air,
and then use an instrument like this -
this is a gas chromatograph mass spectrometer GCMS -
and we take the air collected or materials collected from around our plants
in the glass jar, if you will,
and squeeze it through a pipe,
a glass tube called a column.
Our undergraduate working on this project is holding the column that we commonly use
to separate the odors that are emitted by plants in the laboratory,
and the one she is holding is 30 meters, 100 feet, long.
Okay, it's all coiled up.
But it takes that long a tube to separate all of the individual molecules,
one from the next.
Once they have passed through that tube and they come out the end of it,
one at a time, each of a different type,
then the mass spectrometer helps us identify what each of those is.
This is the laboratory of Dr. Lynn, here on the University of Missouri campus,
and this requires a really terrific chemist
to do this kind of work.
Well, this isn't going outdoors anytime soon.
If you really wanted to verify what I've been saying
about molecules flying through the air and bringing in friendly insects,
you'd really like to know that that's going on
out in the cornfield or in the backyard, okay?
So we've been teaming up in collaboration with some engineers
to try to develop a version of this device to which we could feed a stream of air -
taken outdoors -
which would be so sensitive
that it would separate and analyze and tell us
about the presence and abundance of those individual odor molecules,
on the spot.
And here's what we've been able to turn that device into.
The chip on the right is the equivalent of the 100-foot tube.
Our engineer colleagues
have managed to shrink the column necessary for separating these molecules
down to an engraving on that chip that's that size.
The chip on the left is the device we use instead of the mass spectrometer
to identify the molecules.
Our collaborator and his students have developed this
so that air from the plant goes in one end of the gas chromatograph,
comes out the other end and crosses the other chip,
which has engraved pits on it,
each of which contains a polymer - chemical material -
with an affinity for the volatiles in the air.
Schematically, here's what it looks like:
the air comes across that chip from the gas chromatograph,
one kind of molecule at a time;
the polymer has an affinity for certain kinds of molecules in the mixture;
once those molecules find themselves in contact with the polymer, it swells,
and what that does is change the way the polymer interacts with the laser.
And we can use the difference
between the before and after characteristics of that polymer
to tell that a particular molecule is present
and even what its concentration is.
What could we do with this?
Well, once we have an effective nose,
that's about the size of a shoe box,
we could mount it on a tractor, for example.
A tractor moves through the fields, sniffing the plants,
and when it encounters a plant
that is emitting the specific signature chemicals of [being] attacked by a pest,
it stops and sprays it.
This is called "precision agriculture."
Economists tell us that this alternative to treating a pest infestation
saves enormous amounts of money and, of course, the environment as well.
Normally, if you are, for example, a soybean farmer,
and you're interested
in whether your soybean crop has a significant pest infestation,
you usually hire someone -
it's a popular summer job for high school students -
who goes up and down the rows looking for insects
and probably has some kind of calculation:
if they see more than so many insects in a ten-minute period, they report that.
Then what's done is the entire field is sprayed with pesticide.
That could be many, many acres for a couple of plants that are infested.
The negative impact it has is probably familiar to all of us,
among other things,
that's what contributes to the dead zone in the Gulf of Mexico.
So we're very hopeful that we can take this nose
and spot-treat pest infestations instead of the normal treatment.
Plants report almost everything they do this way.
Everything we've ever exposed a plant to
has produced a bouquet of volatiles specific to what that stress was.
Normal parts of plant life also produce volatiles - signature bouquets -
of specific types.
For example, the bouquet of a ripening fruit changes as it ripens.
Now, harvesting fruits at the perfect moment of ripeness
is a big issue for fruit producers.
Grape growers and wine makers tell me that if they could improve that process -
knowing when the bunch of grapes is ready to harvest for the perfect wine -
they'd be very, very interested in that.
Of course, we'd probably all be paying $50 a bottle of wine then, but ...
But this a problem for grape growers and other fruit producers.
That's true - well, in fact, this picture of a vineyard in Missouri
is taken of a person who is hand harvesting,
and the reason for that is that person needs to have an eye for ripeness
and goes from bunch to bunch, examining each one
and asking the question, is this one ready or not?
Because the sugar content influences the alcohol content of the wine
and all the other chemistry depends on ripeness,
she has to be an expert and pick the right grapes on the right day.
That process is becoming increasingly mechanized.
This is actually the same vineyard, Stone Hill Winery in Missouri.
Some grapes are harvested mechanically.
As you can imagine,
it's really difficult to stop and decide whether the grapes are ripe
with something like that.
So either a handheld device or a device like the one I showed on the tractor
would greatly enhance the ability of fruit producers, like these,
to accurately tell when to harvest their fruits.
And this would be the case for tomatoes in greenhouses,
all over the place.
Another place where that same problem occurs is in the grocery store.
I don't know about you,
but for me it's a nightmare trying to figure whether the mango is ready.
(Laughter)
And the reason for that is that the color of the mango
is not necessarily a terrific reporter of ripeness;
sometimes it is, sometimes it isn't.
If you think about it for a moment,
many people, and this is one of our collaborators, sniff the fruit.
You can tell if a melon is ripe in a couple of ways:
you can thump it, and you can sniff it.
Well, we're proposing is to sniff fruits in a grocery setting
so that they can be staged.
That means placed out into the store for purchase
at just the right time to maximize sales.
Almost everything that a plant does is measurable by virtue of the odors.
That continues as the plant matures
and even after the plant is essentially dead,
or at least the parts of it [that are] harvested.
So, the take-home message here
is plants are not just standing or sitting or growing idly by
when stresses come to them.
They are equipped with diverse behaviors
for ameliorating the difficult situations they find themselves in.
Some of those behaviors are physical,
but a great number of them - perhaps the majority -
are chemical and therefore difficult or impossible to see.
The technology we're trying to develop essentially visualizes this "speech"
where each molecule is a word,
and the entire collection of molecules means something to some other organism.
What we'd like to do is make that meaning available to us
and finally show that plants are really just very slow animals.
(Applause)