How do plants know which way is up?

Ainissa Ramirez is a scientist, author and a self-proclaimed “Science Evangelist.” She is the creator of a podcast series called “Science Underground.” She joins Hari Sreenivasan to discuss one of her latest podcast episodes about how plants know which way is up.


Ainissa Ramirez is a scientist, author and a self-proclaimed science evangelist.

She is the creator of a podcast series called 'Science Underground.'

She joins me to discuss one of her latest podcast episodes about how plants know which way is up.

That is kind of a question I never really thought about, but, yes, why don't they grow roots going this way instead of that way?


So, it's dark.

You're a seed, and you're in the ground.

How do you know which way is up?

I mean, there's --

I got nothing.

That's right.

That's exactly it.

Well, it ends up that they have special cells that sort of look like this Mason jar.


The cells have something that's very heavy inside, and they're located at the tips of the roots, and wherever those rocks are, the roots know that that's where gravity is, and so they point in that direction.

This is inside, on a cellular level.

There are special cells.

They're called statocytes.

Statocytes, okay.

And inside are statoliths -- those are the rocks -- and so let's say the plant gets knocked over.

Your cat knocks over your plant.


Well, they're in a different position now, and so the plant knows that this is where gravity is.

This is where we should go, if I'm a root.

Now, the shoots have similar cells, too, and they go in the opposite direction.

They're like, 'Oh. If that's where gravity is, well, then, I will go in the opposite direction.'

180 degrees opposite.

That's right.

That's right.

And this is just over a couple hundred thousand million years of evolution.

Evolution, yeah.

They figured it out, and we actually have something similar in our ears.

This is how we know about... This is how we keep balance.

We have small rocks, calcium rocks, that are in our ears that tell us where to go.

And when we get dizzy, and when we get kind of out of sorts, it's that tiny...

That's right.



It's because one of these calcium cells has gotten dislodged or moved, and it's causing us to be a little dizzy.

It's a horrible feeling when you feel completely out of balance.

I mean, you could be holding on to this desk, and you still feel like you're falling or something else.

It's very unsettling, and it's so amazing that it's such a tiny, tiny object in our brains that, you know, is balancing...

Is giving us information.



Right. Yeah.

You could be completely stable, and that rock being dislodged will change your perspective.

We have also sent plants into space.

That's right.

That's right.

And so why didn't they go haywire then?

Well, this is what's interesting.

If we want to go out to Mars, we're going to have to make our own food.

We can't, you know, take-out won't go all the way out there.

I saw the Matt Damon movie.

We all know that's how it works.

That's right.

We got to science the hell out of this.

That's right.

So what we're going to have to do is, we're going to have to grow in space, and if we know that plants are, you know, they use gravity to determine which way to point their roots...


...and if we're in microgravity, what we have to do is think about how we can make sure that they feel that gravity.


The other thing that's important is that plants actually respond to light.

In fact, their shoots respond to light even more, so if you show a light, the shoot will know that this is the way I should go.

And will the other parts say, 'Well, I'm going the other way than the shoots?'

Well, it's not to the same extent, but the roots also know that if they see light, then they've gone in the wrong direction, so they'll go around.

So in zero gravity what happens?

So in zero gravity, they're still doing experiments to figure that out because this is key.

How are we going to create vegetation in space?

But they have grown things, but they're in microgravity.

Zero gravity, still to be determined.

So in the sci-fi movies, we always see this giant spinning greenhouses...

That's right.


Creating some semblance of gravity...

Yeah. That's right. try to pull the roots down.

The centrifugal force, just like if you're at the amusement park and you're in the teacup, and it's spinning you around.

That's creating a sense of gravity, so the plants will know, okay, if they're going in this direction, the rocks will actually be going in this direction because they're spinning.


That's how we're going to be able to grow food in space?

That's right.

Well, I'm glad we've sorted that out on this episode.

That's just... So is there something that we've learned from what plants do in space and even just what we've learned on the ground that helps us produce a more robust plant, one that can deal in, you know, kind of different types of soil or different light conditions and less light?

Mm-hmm, mm-hmm.

Well, scientists are working on this all the time because it ends up that when we grow corn, we want to grow it very densely so we can have a lot of it.

Now, if other corn stalks are being shaded, well, then, that one won't grow.


So we're trying to figure out how we can change the susceptibility and the sensitivity of plants so that they will continue to grow, even in a very dense situation, and people are working on that problem right now.

All right.

Ainissa Ramirez, thanks for joining us.

Thank you.