Researchers report that they have found the first flower variety with bi-directional color change

An enlarged image clearly showing the alternating orange and pink colors of the petals. Credit: ©2022 H. Tsukaya CC-BY

We all love flowers, and perhaps one of the most appealing things about flowers is the wide variety of shapes, sizes, and of course, colors that they come in. But did you know that some flowers can change color? While not unique to flowers, this trait has been observed in hundreds of different species for at least several decades.

Color-changing flowers are thought to do this because they signal pollinating insects that the flower is ready to provide nectar or pollen, which rewards them. This is considered an “honest” signal.

But the opposite can also be seen; Some plants display a “dishonest” signal, with some of their buds displaying their standard color while others display their signal color. This behavior is thought to increase the overall visibility of the plant at a distance to potential pollinators.

Regardless of the strategy used by the plant in question, all of the examples of color-changing flowers that were found were unidirectional: once the color changed, it doesn’t change back. So imagine the surprise that Professor Hirokazu Tsukaya of the University of Tokyo must have felt when he saw a flower of the Causonis japonica plant change color and then change color again and again.

“Although I studied this plant in detail after discovering that there were at least two varieties in 2000, the bi-directional, color-changing flowers were a totally unexpected finding,” Tsukaya said.

“My colleague Professor Nobumitsu Kawakubo from Gifu University is an expert in long-term time-lapse video recording of pollinating flowers. He and his student were originally trying to research pollination behavior between the different species of Causonis japonica and expected to see the familiar change from its standard orange color to bright pink. But they couldn’t believe it when they watched the time-lapse video and saw that not only did it go back to orange, but that change oscillated between the two states. They informed me of this finding; this forced us to find out why. So we started a collaboration.”

The unique bi-directional color-changing petals have only now been observed because the plant in nature is a chaotic bundle of buds, leaves and flowers that grows quite quickly. So it wasn’t really possible to track individual flowers over time. But thanks to carefully controlled time-lapse video recordings, individual blossoms can now be tracked and lead to observations like this one. Credit: ©2022 H. Tsukaya CC-BY

Thanks to carefully recorded time-lapse videos from the field and detailed observations in the lab, Tsukaya was able to connect which physiological changes in the flowers were occurring simultaneously with their color changes.

“The initial orange state coincides with the male stage of the flower’s maturation when it secretes nectar,” Tsukaya said.

“As the stamen – the male part – ages and sheds, the flowers turn pink. Just a few hours later, the pistil – the female part – begins to ripen, secrete nectar and the flower turns orange again. Once this stage is over, the flower has faded to pink. The main chemical responsible for the color change is the orange-yellow carotenoid; its cycle of accumulation and depletion is also the fastest known to date. That fact was another surprise for us.”

The chemical name carotenoid sounds a bit like the word “carrot”. This is no coincidence, since the same chemical gives the typical carrot its orange color. It’s a good source of vitamin A, and given that the color-changing flowers show the fastest accumulation of carotenoids ever seen, it’s no surprise that the researchers believe their discovery has future application in the development of carotenoid-rich vegetables that ripen faster or contain more yield of beneficial vitamins.

“Our next steps will be to figure out what drives the behaviors we observe,” Tsukaya said.

“A big question we have is: At what level are the phases of the cycles regulated? Is it caused by proteins caught in a feedback cycle, or is something happening at the genetic level? We will investigate this further and hope to find an explanation soon. It is strange to think that farmers in Japan several hundred years ago hated Causonis japonica because of its vigorous nature. But one novelist, Kyoka Izumi, wrote so positively about them that I wonder if it has helped sustain some interest in their preservation. Whatever the reason, I’m glad they’re here now to share their secrets with us. I’m excited to see what we’ll discover next.”

The study appears in the journal Scientific Reports.

More information:
Oscillating flower color changes of Causonis japonica (Thunb.) Raf. (Vitaceae) related to sexual phase changes, Scientific Reports (2022). DOI: 10.1038/s41598-022-24252-z

Provided by the University of Tokyo

Citation: Researchers report finding the first bidirectional color-changing flower variety (2022, December 1st), retrieved December 1st, 2022 from .html

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