Come Springtime, Thank Phytochromes

By Victoria Clare

Posted May 7, 2021

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D: Oh look, Yaël, some flowers outside are budding. Looks like spring is coming early this year.

Y: Thanks, phytochromes.

D: Phytochromes?

Y: Well, Don, they're the molecules we have to thank for those flowers budding. Phytochromes in plants detect light and temperature, which control how quickly plants grow.

D: How does that work, exactly?

Y: I'll give you a little background: phytochrome molecules can be active or inactive, and when they're active, they make a plant grow more slowly. Plants actually grow more slowly during the day than they do at night because sunlight activates the molecule.

D: So how does temperature come into play?

Y: When night falls, phytochromes switch to their inactive state. But the amount of time it takes the phytochromes to make the switch, and therefore how long the plant ends up spending growing quickly or growing slowly, depends on the temperature. When it's winter and phytochromes detect cold temperatures, that switch takes longer, which means plants spend more time growing slowly.

D: It's like if I'm trying to stop staring out the window daydreaming and start getting my work done, I'll be spending more time daydreaming and less time working if I take a long time convincing myself I need to get working.

Y: Something like that. Anyway, when the temperatures get higher in spring and summer, the switch from active to inactive happens a lot more quickly, which means the phytochromes spend more time in their inactive states, and plants grow quickly.

D: That's a lot of behind‑the‑scenes work for those pink and white blossoms everywhere. Speaking of which, do you think we should get back to work?

Phytochromes are molecules in flowers with a very important role. (Ashok Boghani/flickr)

When you look outside and see flowers budding, thank phytochromes. Phytochromes are the molecules in plants that detect light and temperature, which control how quickly plants grow. Here's how it works:

Phytochrome molecules can be active or inactive, and when they're active, they make a plant grow more slowly. Plants actually grow more slowly during the day than they do at night because sunlight activates the molecule.

When night falls, phytochromes switch to their inactive state. But the amount of time it takes the phytochromes to make the switch, and therefore how long the plant ends up spending growing quickly or growing slowly, depends on the temperature. When it's winter and phytochromes detect cold temperatures, that switch takes longer, which means plants spend more time growing slowly.

It's kind of like if you're trying to stop staring out the window daydreaming and start getting work done, you'd be spending more time daydreaming and less time working if you take a long time convincing yourself to get working.

When the temperatures get higher in spring and summer, the switch from active to inactive happens a lot more quickly, which means the phytochromes spend more time in their inactive states, and plants grow quickly.

That's a lot of behind‑the‑scenes work for those pink and white blossoms everywhere, phytochromes definitely deserve some thanks.

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