All at once by the clock
What we see as the flower of a sunflower consist actually out of hundreds of tiny flowers. These develop one by one, from the outside in, forming a spiral. Till the moment of opening, that they do in groups, ring by ring, the outside ring first. But how the plant coordinates this was up to now a mystery. Now American and South African researchers have discovered that this coordination is done by the circadian clock.
To study the coordination of flower opening the researchers looked at how the flowers developed in different daylengths. Doing this they noticed a synchronisation of the flowers independent on the daylength they were growing in. Each flower ring had synchronised the development of its ovary, its stamen, style, and stigma.
To investigate if the circadian clock is involved in this synchronisation, the researchers studied the plants grown under different light/dark regimes. The researchers still observed a synchronised development when the plants were growing in constant darkness. But when they started the night earlier, then they noticed a delay of 24 hours in flower development, but it was still synchronised. Only when the placed the plants in constant light, then the synchronisation was broken, and the flowers developed only depending on age. All suggesting that the circadian clock is playing a role in it.
Synchronising flower opening attracted more pollinators
The researchers studied subsequently the influence of this synchronisation on the pollination of the flowers. They grew plants in different conditions and when they opened the flowers then they placed the plants outside early in the morning. Plants grown under the same conditions as outside attracted lots of pollinators early in the morning. But this was not the case for plants grown under continuous light, or for plants that opened their flowers later due to a jetlag.
Sunflowers attract more pollinators through synchronising their flower opening. Coordinating this by the circadian clock enables the plant to time the flower opening in such a way that it occurs daily at the same time. In this way pollinators know at which time of day to visit the flower.
Literature
Carine M Marshall, Veronica L Thompson, Nicky M Creux, and Stacey L Harmer (2023) The circadian clock controls temporal and spatial patterns of floral development in sunflower. eLife 12:e80984. https://doi.org/10.7554/eLife.80984
Plant en Zo 