Jonathan Drori: Every pollen grain has a story

38,179 views ・ 2010-04-08

TED


Please double-click on the English subtitles below to play the video.

00:15
Thank you. I have two missions here today.
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00:18
The first is to tell you something about pollen, I hope,
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00:22
and to convince you that it's more than just something that gets up your nose.
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00:25
And, secondly, to convince you
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that every home really ought to have a scanning electron microscope.
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00:30
(Laughter)
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00:32
Pollen is a flower's way of making more flowers.
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00:36
It carries male sex cells
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from one flower to another.
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This gives us genetic diversity,
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or at least it gives the plants genetic diversity.
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00:44
And it's really rather better not to mate with yourself.
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00:48
That's probably true of humans as well, mostly.
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00:52
Pollen is produced by the anthers of flowers.
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00:54
Each anther can carry up to 100,000 grains of pollen,
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so, it's quite prolific stuff.
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01:01
And it isn't just bright flowers
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that have pollen; it's also trees and grasses.
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01:07
And remember that all our cereal crops are grasses as well.
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01:12
Here is a scanning electron micrograph of a grain of pollen.
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01:16
The little hole in the middle, we'll come to a bit later,
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01:19
but that's for the pollen tube
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01:21
to come out later on. A very tiny tube.
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01:23
So, that's 20 micrometers across,
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01:25
that pollen grain there.
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01:27
That's about a 50th of a millimeter.
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01:29
But not all pollen is quite so simple looking.
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01:32
This is Morina. This is a plant --
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01:35
which I've always thought to be rather tedious --
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named after Morin,
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01:39
who was an enterprising French gardener,
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01:41
who issued the first seed catalog
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in 1621.
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01:45
But anyway, take a look at its pollen.
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01:49
This is amazing, I think.
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01:51
That little hole in the middle there is for the pollen tube,
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01:53
and when the pollen finds its special female spot
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01:56
in another Morina flower,
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just on the right species, what happens?
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02:01
Like I said, pollen carries the male sex cells.
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02:04
If you actually didn't realize that plants have sex,
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02:07
they have rampant, promiscuous
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02:09
and really quite interesting and curious sex. Really.
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02:11
(Laughter) A lot.
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02:15
My story is actually not about plant propagation,
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02:18
but about pollen itself.
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02:20
"So, what are pollen's properties?" I hear you ask.
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02:23
First of all, pollen is tiny. Yes we know that.
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02:25
It's also very biologically active,
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02:27
as anyone with hay fever will understand.
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02:29
Now, pollen from plants, which are wind-dispersed --
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like trees and grasses and so on --
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tend to cause the most hay fever.
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02:37
And the reason for that is they've got to chuck out
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masses and masses of pollen to have any chance
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of the pollen reaching another plant of the same species.
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Here are some examples --
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they're very smooth if you look at them --
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of tree pollen that is meant to be carried by the wind.
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02:53
Again -- this time, sycamore -- wind-dispersed.
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02:55
So, trees: very boring flowers,
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not really trying to attract insects.
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03:01
Cool pollen, though.
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03:03
This one I particularly like.
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03:05
This is the Monterey Pine, which has little air sacks
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03:08
to make the pollen carry even further.
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03:10
Remember, that thing is just about 30 micrometers across.
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03:14
Now, it's much more efficient if you can get insects to do your bidding.
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03:17
This is a bee's leg
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with the pollen glommed onto it from a mallow plant.
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03:24
And this is the outrageous and beautiful
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03:26
flower of the mangrove palm.
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03:28
Very showy, to attract lots of insects to do its bidding.
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03:31
The pollen has little barbs on it,
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03:33
if we look.
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03:35
Now, those little barbs
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obviously stick to the insects well,
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but there is something else that we can tell from this photograph,
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and that is that you might be able to see a fracture line
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across what would be the equator of this, if it was the Earth.
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That tells me that it's actually been fossilized, this pollen.
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03:50
And I'm rather proud to say
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that this was found just near London, and that 55 million years ago
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London was full of mangroves.
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03:58
Isn't that cool?
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04:00
(Laughter)
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04:03
Okay, so this is another species evolved to be dispersed by insects.
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04:06
You can tell that from the little barbs on there.
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04:09
All these pictures were taken with a scanning electron microscope,
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04:12
actually in the lab at Kew Laboratories.
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04:14
No coincidence that these were taken
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04:16
by Rob Kesseler, who is an artist,
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04:18
and I think it's someone with a design and artistic eye
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04:21
like him that has managed to bring out the best in pollen.
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04:25
(Laughter)
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04:27
Now, all this diversity
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means that you can look at a pollen grain
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and tell what species it came from,
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04:34
and that's actually quite handy if you
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maybe have a sample and you want to see where it came from.
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04:39
So, different species of plants
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04:41
grow in different places,
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and some pollen carries further than others.
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So, if you have a pollen sample,
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then in principle, you should be able to tell
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where that sample came from.
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04:54
And this is where it gets interesting for forensics.
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04:59
Pollen is tiny. It gets on to things, and it sticks to them.
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05:03
So, not only does each type of pollen look different,
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05:05
but each habitat has a different combination of plants.
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05:09
A different pollen signature, if you like,
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or a different pollen fingerprint.
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05:16
By looking at the proportions and combinations
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05:18
of different kinds of pollen in a sample,
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you can tell very precisely where it came from.
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05:24
This is some pollen embedded in a cotton shirt,
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similar to the one that I'm wearing now.
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05:30
Now, much of the pollen will still be there
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after repeated washings.
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05:34
Where has it been?
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05:37
Four very different habitats might look similar,
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but they've got very different pollen signatures.
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05:42
Actually this one is particularly easy, these pictures were all taken
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in different countries.
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But pollen forensics can be very subtle.
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05:48
It's being used now to track
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where counterfeit drugs have been made,
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where banknotes have come from,
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to look at the provenance of antiques
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and see that they really did come from the place
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the seller said they did.
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06:02
And murder suspects have been tracked
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using their clothing,
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certainly in the U.K., to within an area
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that's small enough that you can send in tracker dogs
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to find the murder victim.
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So, you can tell from a piece of clothing
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to within about a kilometer or so,
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where that piece of clothing has been recently
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and then send in dogs.
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And finally, in a rather grizzly way,
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the Bosnia war crimes;
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some of the people brought to trial were brought to trial
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because of the evidence from pollen,
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which showed that bodies had been buried,
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exhumed and then reburied somewhere else.
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06:41
I hope I've opened your eyes,
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if you'll excuse the visual pun, (Laughter)
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to some of pollen's secrets.
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06:47
This is a horse chestnut.
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06:49
There is an invisible beauty all around us,
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each grain with a story to tell ...
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each of us, in fact, with a story to tell
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from the pollen fingerprint that's upon us.
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06:58
Thank you to the colleagues at Kew,
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and thank you to palynologists everywhere.
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07:02
(Applause)
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