Cauliflowers have a unique organ configuration with a plethora of spirals stacked throughout a wide range of scales. Until now, it has been unclear how such a fractal, self-similar organization originates from developmental pathways. According to a new study, cauliflowers are actually buds that are intended to become flowers but never do; the unique shape of the Romanesco cultivar is explained by the fact that its stems produce buds at an increasing rate.
The swirling green cones that make up the head of Romanesco cauliflower produce a fractal design, which repeats itself on multiple scales. Now, the genes that underlie this stunning structure have been identified, and the fractal pattern has been replicated in a common lab plant, Arabidopsis thaliana, researchers report in the Science.
Romanesco has spire-like flowers and is chartreuse in hue. Each one appears to be the same, albeit getting smaller and smaller. Romanesco develops a logarithmic spiral naturally and is an approximation (because it eventually ends) fractal, which is a geometric curve with a recurring pattern that gets smaller in scale as the shape gets smaller in scale. The form of each portion or floret (in this example) is the same as the form of the whole. If you’re wondering how many spirals are on one head of Romanesco, the answer is a Fibonacci number.
Romanesco is one of the most conspicuous fractal shapes that you can find in nature. The question is, why is that so? By altering three genes, the researchers grew a Romanesco-like head on A. thaliana. Two of those genetic tweaks hampered flower growth and triggered runaway shoot growth.
Christophe Godin
“Romanesco is one of the most visible fractal designs in nature,” says Christophe Godin, a computer scientist at France’s ENS de Lyon and member of the National Institute for Research in Digital Science and Technology. “However, the question is, why is this the case?” Scientists have been unable to find a solution for a long time.
“Cauliflowers exhibit a high degree of self-similarity, with seven or more clones of the same bud.” This is especially noticeable on the Romanesco cauliflower, which is one of the first images that comes up when you search ‘plant fractals’ online. The Romanesco is notable for its very well-defined, pyramidal buds that accumulate along endless spirals.”
Godin and his colleagues knew an Arabidopsis variant could produce small cauliflower-like structures. So the team manipulated the genes of A. thaliana in both computer simulations and growing experiments in the lab. Working with the extensively studied plant helped the researchers simplify their experiments and distill the essential fractal-spawning mechanism.
The researchers created a Romanesco-like head on A. thaliana by modifying three genes. Two of the genetic changes impeded flower growth and caused runaway shoot growth. According to plant biologist François Parcy of the CNRS in Paris, instead of a flower, the plant grows a shoot, and on that shoot, it grows another shoot, and so on. “It’s a domino effect.”
The researchers then changed another gene, increasing the growth area at the end of each shoot and allowing swirling conical fractals to form. “You don’t have to tweak the genetics all that much to have this morphology to appear,” Parcy explains. He adds the team’s next step will be to “manipulate these genes in cauliflower.”
Romanesco, also known as broccoflower or Roman cauliflower, is a chartreuse-colored, one-of-a-kind vegetable renowned for its aesthetic and mild flavor. It is sometimes mistaken for a cross between broccoli and cauliflower, but it is botanically distinct (although related). The compact flowering head encircled by leaves resembles its cruciferous cousins, but the stalks form spirals instead of like a little tree. These near-perfect fractals, which form the overall spiral of a romanesco head, making it an appealing market choice. The appealing vegetable is more expensive than broccoli and cauliflower, but it is prepared similarly, with only a rinse and chop necessary.
The findings reveal that a brief entry of buds into a flowering stage drastically changes their functioning and permits them to grow without leaves and replicate practically indefinitely, unlike regular stems. The unique shape of the Romanesco cauliflower is explained by the fact that its stems develop buds at an increasing rate, whilst other cauliflowers produce buds at a steady rate.
This acceleration gives each floret a pyramidal look, emphasizing the structure’s fractal nature. The study focuses on how the selection of mutations in plants during the domestication process has transformed their morphology, sometimes dramatically, into the fruits and vegetables we see on store shelves.
