Why are sunflowers towards the sun?

There is a substance called 3-Indoleaceticacid  in the plant body, similar to growth hormone in the human body, which is responsible for conveying information to cells and directing the growth and development of plants. Under the influence of light, 3-Indoleaceticacid will be transported from the stem end of sunflowers to the light side to the backlight side, resulting in concentration differences. As a result, the growth on the backlight side will be faster, while on the light side it will be slower, and the sunflower’s flower disc will turn towards the direction of the sun. The transportation of 3-Indoleaceticacid requires the assistance of transporters on the cell membrane – transport proteins, among which a very important member is the efflux protein PIN responsible for transporting auxin from inside the cell to outside the cell. How do these “porters” work?

As the first discovered plant hormone, auxin is involved in almost every process of plant growth and development regulation, such as embryonic development, tissue differentiation, phototropism, and gravitropism. A notable feature of auxin is its directional intercellular transmission, known as polar transport, in which PIN family proteins play a crucial role. Specific members of the PIN family exhibit asymmetric distribution on the cytoplasmic membrane, and their distribution positions determine the direction of auxin transport. Analyzing the three-dimensional structure of PIN protein is of great help for people to understand the “transport” process of auxin, which is an urgent scientific problem in the field of auxin research. It also helps people design small molecule inhibitors for PIN protein and find more effective and safer agricultural herbicides or plant growth regulators.