Scientists are amazed by the capacity of sunflowers to follow the sun across the sky and to rotate 180 degrees in the nighttime in order to greet the sun as it rises from the east.
A team of biologists from UC Berkeley and UC Davis has the answer to this question. Thus, it seems that the eastern side of the stem gets longer than the western part, which makes the sunflowers track the sun during the day. At night, the western side gets longer, making the flower go towards the east.
Follow the Sun
The mature flower does not have the same behavior, as the clock genes stop the differential growth. The plant faces east, in order to gain as much heat from the sun as possible. The orientation towards East makes the plant be more appreciated by pollinating bees.
The process is most likely an evolutionary adaptation, as being the first example of a plant changing its growth in its environment.
The plants have an internal clock that regulates the daily cycle of hormones, just like animals do. The biologists explain that the clock genes are connected to auxin, a plant hormone that influences the growth.
The scientists tried another experiment, and staked the sunflowers so they could not move and moved them every day so that they were facing in opposite direction than usual. Consequently, the plant’s ability to follow the sun was impaired. Moreover, the plants had less biomass and fewer leafs than the ones that were able to move.
The Unique Sunflowers
There are other plans that can orientate their leaves to capture the sun rays better, but none can act like the sunflowers. The interesting behavior had been described by scientists as early as 1898, but the connection to the circadian rhythm was only discovered now.
Some studies tried to understand the orientation in the 60s, but they were unable to identify the internal element that caused it.
The explanation was in the genes. The rate of growth is based on the available light and the direction of the light. The second is controlled by the circadian clock and results in growing on one side more and orientate towards the east and then move to the west.
The researchers plan to explore the differential growth and to understand how the adaptive function of the circadian clock is applied to other species and is expressed in other features throughout the living world.
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