How do Tulips know when it’s Spring?

It’s spring here in the Netherlands, heralded first by crocus’s, then daffodils, and finally, the most Dutch flowers of all the tulips appear; and there is nothing quite as Dutch as a just below sea level landscape with windmills and Tulips. Naturally plants need to time their flowering with the presents of pollinators and with other members of their species. If your flower is to be attended to my a bee, it’s no use if the bees are shivering in their hive in the winter; and if your reproduction goal is not just to clone, a good time is not to be had alone. So how do the tulips know when to flower? The simplest answer is by sensing their environment. But that just leads us onto a second question:
how? This ‘how’ has fascinated botanist for centuries. Mikhail Chailakhyan, a Soviet scientist, was fascinated by how plants responded to different lengths of a day their response to the photoperiod. He began a series of experiments to discover what parts of a plant perceived light. When he exposed just some leaves of a plant to just the right amount of light for the species he was studying, he was able to induce the whole plant to flower. It was apparent, therefore, that light was sensed in the leaves, but a signal was somehow sent to the meristems to induce flowering. He followed this up with grafting experiments. Attaching a piece of a plant that would flower when the days become short to one that needed a long days of daylight to flower. When this new combined plant was exposed to short days, both sections of the plant could be induced to flower. With this experiment repeated across several different species, he concluded that there is a widespread signal for flowering, and in 1936 he coined the term florigen for this signalling molecule. Though this discovery didn’t make him popular in the Soviet Union, Trofim Lysenko, Starlin’s agricultural advisor, wasn’t happy. These results contradicted his own pseudoscientific theories, but while scientific rigor wasn’t on Lysenko’s side,
the Soviet secret police were. But unlike many of his colleagues who didn’t tow the Communist Party’s line on biological theory, Chailakhyan survived,
with a little help of fellow scientists. He couldn’t however find his elusive florogen. And so his hypothesis fell into disrepute,
and a rival hypothesis, proposing that flowering was induced by known hormones and metabolites, gained favor. In hindsight his lack of success isn’t really
surprising, the tools of his day were physiological and biochemical in nature, and to understand florigen, it would take the tools of modern molecular biology. In 2005, in the model plant Arabidopsis, a protein was discovered that appeared to be the elusive florigen. The gene, Flowering Locus T (referred to simply as FT) encodes a protein, produced in the leaves and transported, through the phloem, to the meristems, where it initiates flowering through a complex cascade of biochemical reactions. But FT doesn’t detect the plants environment directly. The expression of this gene is controlled
by a transcription factor – called Constans. This transcription factor is produced about 12 hours after dawn in a cycle regulated by the plants biological clock. However the Constans protein is only stable in light, so the protein can’t accumulate if night comes too soon. But if the daylight lasts long enough, Constans can activate the transcription of FT leading to flowering. But in tulip things are a little more complicated. In winter the tulip bulb is underground with no access to light, and the flower is actually already formed. Flower induction has to happen the season before. And there is not one, but several FT genes,
working to control flowering. During her PhD, my wife, took two of the tulip FT genes and put them in Arabidopsis, attached to a promoter that caused them to be overexpressed. In Arabidopsis, tulip FT 2 caused early flowering as you might expect from the way FT normally works but tulip FT 3 did the opposite and delayed flowering! But she wasn’t done, within the two proteins
two amino acids were identified as important, and so she swapped them, reversing the phenotypes, and narrowing down the causal part of these two proteins But, as is so often the case, more research is required to fully understand how these changes in their FT proteins allow all those dutch tulips know exactly when to flower. That research might just take a little while, though, as from seed to flower, a Tulip takes five to seven years.

26 thoughts on “How do Tulips know when it’s Spring?

  1. I tell ya, tulips would never survive in Minnesota, cause even we don’t know when spring starts. It just snows until it doesn’t. And then it snows some more.

  2. Fascinating research and results. The links in the description are very helpful. This is a Golden Age of botanical learning.

  3. There's evidence that seasonal temperature fluctuations have some bearing on things. Tulip bulbs chilled below 9C for several weeks will flower earlier (upon warming up again) than bulbs not chilled.

  4. Lysenko caused famine, I fucking hate that guy. There were a lot of problems with the Soviet Union but most of them weren't scientific. Having anti-gene crop scientists in power for a few decades was one of them.

    Addendum; I look forward to your exquisite content. I'm lucky to be aware of this channel, and I wish you growth.

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