The Last Word On Nothing

I wrote this post in 2019, and am still gobsmacked by flower hormones.

Last November, my mother gave me several crumpled paper bags full of flower bulbs for my birthday. Daffodils, hyacinths, snowdrops, paperwhites — the bulbs promised frilly, fragrant bounty and I couldn’t wait to plant them.

Then life got hectic. The bags sat in a corner for a week, then a month. By the time I opened the bags again, in early January, some of the bulbs were dusted with mildew. I’d lost the instructions for when to plant the different types of bulbs, and what bulb belonged to which type of flower. As I brushed the mold away, I contemplated how little I knew, not just about these flowers, but about flowers in general.

Understanding flowers is not trivial. Darwin referred to the awesome expansion of flowering plants during the late Cretaceous period as “the abominable mystery.” The ability to manipulate flowering has always been key to crop domestication, allowing humans to expand the range of rice, wheat, corn and other staples. Despite this, scientists only recently discovered how flowering works on a molecular level. 

The story is surprisingly brutal, and begins with chrysanthemums. In the early 1930s, Russian plant physiologist Mikhail Chailakhyan was trying to figure out how plants sense light and dark, and decide when to flower. He shone light on different parts of chrysanthemum plants — the stem, the leaves — and found it was the leaves that sensed light. When leaves detect a certain daylength, the plant bursts into bloom, he discovered. 

By then, scientists knew about hormones, signaling chemicals that travel through the bloodstream in animals. Hormones are molecules of transformation, controlling everything from the sprouting of hair to the thickening and thinning of the uterine lining.  Chailakhyan proposed the existence of a hormone in plants that travels from leaf to stem and triggers flowering. He dubbed the hormone “florigen,” or “blossom-former.”

Chailakhyan performed experiment after experiment to prove that florigen exists.  He transferred sap from the leaves of a flowering tobacco plant into the Chenopodium rubrum, or goosefoot plant, and showed that it induced the sprouting of tiny purple blossoms. A similar infusion in potato plants triggered the formation of tubers, he and his colleagues showed.