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Science

The flower that changes color but then thinks about it

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Causonis japonica is the first to show a newly discovered characteristic. Its flowers can change color depending on the stage of the ripening cycle, and then return to the original color. While many flowers have been shown to change color depending on stage of maturation, Causonis japonica is the only known example of bidirectional color change .

 

Flowers that change color are thought to do so because they signal pollinating insects that the flower is ready to deliver nectar or pollen. This is considered an “honest” signal. But the opposite can also be observed: some plants show a “dishonest” signal, with some of their flowers showing their default color while others show their signal colour. This behavior is thought to increase overall visibility from afar. But whatever the strategy of the plant in question, all the examples of color-changing flowers found are one-way: once the color has changed, it doesn’t go back. Until Tokyo University professor Hirokazu Tsukaya saw a flower of the Causonis japonica plantchange color, and then change again, and again.

“Although I have studied this plant in detail, having discovered that there are at least two varieties as early as 2000, the bidirectional color-changing flowers were a completely unexpected discovery,” Tsukaya said.

“My colleague, Professor Nobumitsu Kawakubo of Gifu University, is an expert in time-lapse video recordings of pollinated flowers. He and his students initially set out to explore the pollination behaviors among different types of Causonis japonica and expected to see the plant’s flower change from its orange color to bright pink. But when they took a closer look at the time-lapse video recording, they realized that not only did the plant change back to orange, but that this change oscillated between the two states. They informed me of this discovery and this prompted us to find out why. So we started a collaboration”.

 

Thanks to time-lapse videos carefully captured in the field and detailed observations in the laboratory, Tsukaya was able to link the physiological changes taking place in flowers concurrently with their color changes.

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“The initial orange state coincides with the male stage of flower maturation, when it secretes nectar,” Tsukaya said. “When the stamen, the male reproductive organ of the flower, gets old and falls off, the flowers turn pink . A few hours later, the pistil – female part – begins to ripen , secretes nectar and the flower turns orange again . Once this stage is over, the flower turns pink again . The main chemical responsible for the color change is yellow-orange carotenoid , the same chemical that gives carrots their typical orange hue.

“A big question we ask ourselves is: at what level are the phases of the cycles regulated? Are they caused by proteins involved in a feedback loop, or is something occurring at the genetic level?” Tsukaya said.

 

“Our next steps will be to find out what governs the behaviors we have observed.”

  • Oscillating flower color changes of Causonis japonica (Thunb.) Raf. (Vitaceae) linked to sexual phase changes. (nature.com)
 

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