Uncertainty persists regarding the mechanism by which sunflowers orient themselves towards light.
Sunflowers, known for their vibrant yellow petals and strong stalks, may appear to be a basic summer pleasure. However, scientists have found that these plants possess a mysterious quality – they do not follow traditional methods to follow the sun’s movement in the sky.
Throughout the day, sunflowers exhibit heliotropism by tracking the movement of the sun above them. This is achieved by the elongation of cells on the east side of the stem, causing their heads to gradually tilt towards the west.
During the night, the cells of the stems stretch on the opposite side, causing the heads to turn and face east.
According to researchers, the mechanisms responsible for solar tracking are a surprising enigma.
According to Professor Stacey Harmer from the University of California, Davis, many of our findings were unexpected.
Plants tend to grow towards sources of light due to the activation of phototropins, which are blue light receptors, on the illuminated side of their stems. This activation results in concentrated levels of auxins, a type of hormone, on the opposite “dark” side.
These auxins stimulate an elongation of cells, resulting in the stem bending towards the light.
Recent studies indicate that this process clarifies the reason why sunflowers curve towards synthetic light when indoors, but it does not seem to justify how sunflowers naturally follow the movement of the sun.
In the journal Plos Biology, Harmer and colleagues revealed their analysis of the activated genes in sunflower stems grown indoors and exposed to artificial blue light from a specific direction.
The findings indicate that the genes associated with phototropins were primarily activated on the illuminated side of the stem, while those related to auxins and cell growth were activated on the shaded side. This suggests that sunflowers grown indoors respond to blue light through traditional mechanisms.
However, the team discovered a discrepancy when examining the stems of outdoor sunflowers. Both the east and west sides of the stem, which are exposed to direct sunlight and shade respectively, displayed a similar activation of genes.
The scientists subsequently experimented with obstructing either blue and ultraviolet light or red and far-red light separately. They discovered that neither of these attempts had an impact on heliotropism in the plants outdoors, implying that there are likely multiple pathways for light signaling operating simultaneously.
The team discovered that when sunflowers grown indoors were placed outdoors, they immediately began following the sun’s movement.
On their initial day outside, there was a variation in the genes activated in their stems compared to when they were inside or on following days outside. This indicates the presence of a mechanism for adjustment.
According to Harmer, the research indicates that results obtained in controlled settings may not accurately represent real-world situations.
She stated that our findings indicate that the processes of solar tracking and phototropism are more complex than initially thought in natural settings.