They're not glowing on their own. They're tagged with a fluorescent protein that shows the flower doing a very strange thing — a thing that humans take for granted. Here's how flowers get rid of their own organs.

What if, at a certain point in your life, you could just shed an ungainly limb, a superfluous kidney, or a pesky uterus? It's impossible for us, but plants shed whole organs all the time. Every time we watch a bunch of roses listlessly drop petals on our kitchen table, or one stalk of a houseplant turn yellow and wither up, we're watching a plant drop an organ. Mostly we think that it's going to be a bummer to clean up. What we should be thinking is, how do they do that amazing thing?


We know that orderly organ removal — called abscission — involves the HAESA gene springing into action. That's what we're seeing in the picture above, the fluorescent green marker protein indicates that the HAESA gene is being expressed as those flowers drop petals.

If there is too much of a certain protein, AGL15, being expressed in the plant, the HAESA gene is suppressed, and the plant doesn't shed. How does a plant stop expressing the AGL15 protein? A group of proteins called MAP kinases can "phosphorylate" the protein - turn the protein off. What signals the MAP kinases to do their work? The HAESA gene does.

This sounds like a terrible idea. The HAESA gene is suppressed by the AGL15 protein, which can be turned off only by the MAP kinases, which are controlled by the HAESA gene . . . which as we said before, is suppressed. And sometimes it does work that way. When AGL15 is overexpressed by a plant, the plant simply doesn't drop its petals. (Which is great for florists. There are plenty of specially-bred plants designed to do just that.)


Most of the time, though, it works the other way. When abscission begins, the HAESA sends out a little signal to the MAP kinases, which suppress AGL15, which allows the HAESA gene to express itself more. The whole thing becomes a feedback loop which allows the gene responsible for getting rid of petals to increase its effectiveness exponentially as soon as it gets just a little signal out to the rest of the world.

[Source: Floral Organ Abscission is Regulated by a Positive Feedback Loop.]