Have you ever wondered why do plants, kept indoors or under shade, lean towards the area where they get exposed to the sunlight? Charles Darwin was the first scientist who discovered the reason behind plants leaning towards sunlight. This tendency of plants of leaning towards sunlight is known as “Phototropism” wherein “photo” means “light” and “tropism” means “turn.” This is what plants exactly do – they turn towards the light.
The reason behind this movement is the fact that sunlight is essential for making food. The green substance or Chlorophyll in the leaves makes food for the plants with the help of water from the soil and carbon dioxide from the air. This process of food making (photosynthesis) is possible only in the presence of sunlight. The leaves therefore tend to bend towards the sunlight.
Now the question arises what substance in the plant makes it bend towards the sunlight? A plant growth hormone called “Auxin” is responsible for this kind of movement. Auxin has the tendency to move away from the sunlight and help plant’s dark side grow faster than the side perched under light.
When plant receives light equally, the hormone remains spread out in the plant, but when a portion of the plant comes under shade then this hormone breaks down and begins to concentrate in the shady side. This shady side of the plant then begins to grow faster towards the sunlight. This process wherein the development of the plant is controlled by the light is called as photomorphogenesis. Sunflower plant is a visible example of positive phototropism.
The plants also have the ability to sense the light like us with the help of macromolecules known as “photoreceptors.”
