How sunflowers chase the sun using multiple signalling pathways

Amazing stuff!

"This phenomenon, called heliotropism, is one of many ways that light can control the movement of plants. But researchers still don’t fully understand how cells control these light-triggered behaviors at the molecular level. In a recent study ... plant biologists ... used gene expression profiling in sunflowers to get a closer look at the molecules at play during different light tracking behaviors. ..."

From the abstract:

"Sunflowers are famous for their ability to track the sun throughout the day and then reorient at night to face east the following morning. This occurs by differential growth patterns, with the east sides of stems growing more during the day and the west sides of stems growing more at night. This process, termed heliotropism, is generally believed to be a specialized form of phototropism; however, the underlying mechanism is unknown. To better understand heliotropism, we compared gene expression patterns in plants undergoing phototropism in a controlled environment and in plants initiating and maintaining heliotropic growth in the field. We found the expected transcriptome signatures of phototropin-mediated phototropism in sunflower stems bending towards monochromatic blue light. Surprisingly, the expression patterns of these phototropism-regulated genes are quite different in heliotropic plants. Most genes rapidly induced during phototropism display only minor differences in expression across solar tracking stems. However, some genes that are both rapidly induced during phototropism and are implicated in growth responses to foliar shade are rapidly induced on the west sides of stems at the onset of heliotropism, suggesting a possible role for red light photoreceptors in solar tracking. To test the involvement of different photoreceptor signaling pathways in heliotropism, we modulated the light environment of plants initiating solar tracking. We found that depletion of either red and far-red light or blue light did not hinder the initiation or maintenance of heliotropism in the field. Together, our results suggest that the transcriptional regulation of heliotropism is distinct from phototropin-mediated phototropism and likely involves inputs from multiple light signaling pathways."

Chasing the Sun | The Scientist Magazine® Sunflowers may use a complex set of molecules to track the sun in the sky.

Multiple light signaling pathways control solar tracking in sunflowers (open access)

Fig 1. Phototropic and autostraightening response in sunflower stems.