Biology, Everywhere

Electron Micrograph of Pollen

Biology is everywhere.

I needed to drop off some Arabidopsis plants with Robyn Roth, an electron microscopist in the Department of Cell Biology and Physiology at the Washington University Medical School. She is helping us peer inside pollen that is chilled instantly in liquid helium--just four degrees above absolute zero--so that the living cell is frozen in time. That way, we can see how pollen is structured before it has a chance to touch water and reanimate.


Walking through the lab, brimming with tanks of liquid nitrogen, potent solvents and specialized tools for dissecting fixed samples, I noticed the phone on the wall. Sitting innocuously in the middle of this equipment that allows us to peer inside (once) living cells was a simple pattern, a right-handed helix from the coiled phone cord.

DNA. The famous, infamous, structure of the repository of life's information. The 1962 Nobel Prize. The perfectly obvious, in hindsight, mechanism for both replicating itself and for translating the information from the four bases, A, T, C, G, into the building blocks of proteins, three letters at a time. The right-handed double helix is all of these things.

And today, it's how the phone cord coiled on itself. I pointed this out to Robyn and then we both went on with our days, where our work pushes just a little bit further into understanding all of what this simple and beautiful structure can create in every living thing around us.

Pollen in the Windy City

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.