The view from outside the lab |
I went to Chicago to figure out how pollen senses the world
around it.
My colleagues and I want to understand how plants sense and
respond to mechanical force. One might think that we have this figured out for
all kinds of creatures, but really we don’t. We kind of have no idea how animal
nerves sense touch. We think we have
a good idea of how hearing works, but we could end up being quite wrong.
In plants, we know even less. Plants are really sensitive to
gravity, touch, and all kinds of forces, we just don’t have a good idea of how
they really perceive them and change their behavior appropriately. One way to
do this is to use an ion channel that opens and closes based on pressure: a
mechanosensitive ion channel.
That’s how hearing works, converting air pressure into
electricity through an ion channel. A pressure wave—sound—in air enters the ear
and bends a molecular lever so that an ion channel opens. Instantly, charged
particles can flow through the channel, millions of them every second, and zzzp this makes a little electrical
pulse that our brains can decode into sound. That is a mechanosensitive ion
channel at work, and there is one in pollen and we do not know why.
My plants packed into my car for the trip |
(We always think of electrical impulses as the workings of
nerves. The cool thing is, even without nerves, these signals can be
interpreted by cells and used to change behavior. Ions also play a big role in
controlling how water flows, and we think that is what might be happening in my
pollen.)
My pollen has a protein that looks like a mechanosensitive
ion channel, but we don’t really know if it functions like that. So, I went to
Chicago to find out.
Dr. Paul Malchow has equipment we don’t, namely an electrode
that is extremely sensitive and can distinguish between different ions. By
using a putty that only lets individual ions through—hydrogen, calcium, chloride,
or the like—the voltage that the electrode measures near a cell can be linked
directly to the concentration of ions there. The tool I brought along was a
mutant plant, one that’s missing our potential ion channel. So, if I can see a
difference in the flow of ions near pollen grains with and without this
channel, we’d have good evidence that this channel is functional and can
control how ions flow around pollen.
An electrode measuring ions near pollen |
Does that tell us how pollen senses the world around it? No,
not exactly. It’s just a small piece of the puzzle that we rearrange and try to
piece together every week. If the channel does work like we expect, then we can
try to figure out what forces it responds to in pollen, why ion flow is so
important. If it is a dud, then we have to think harder about why pollen has
this imposter ion channel at all, and what exactly it’s doing, and whether that
has anything to do with mechanical force. We just don’t know. I don’t even have
the answer from the electrode data yet, that alone can be hard to interpret.
That may sound unsatisfying. It can certainly be
frustrating. But it’s never boring, because every week my mentor and I
reconsider everything we think we know about our pollen, about the evolution of
these channels, about what pollen needs to respond to in order to be
successful. It’s a little arcane, but it’s just a tiny piece of the puzzle for
figuring out how plants respond so elegantly to the world they inhabit,
twisting and turning to find nutrients and light, avoiding herbivores and
pests. Playing a part in painting this picture of how plants are themselves
really is satisfying.
So I went to Chicago, largely ignoring this beautiful city
to huddle in a cold laboratory watching videos of pollen being prodded with
electrodes. Happily.
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