Phototropism

Almost all plants are capable of carrying out the process of photosynthesis , and this process is key to their survival as it allows them to manufacture sugar molecules that serve as fuel and construction materials . But plants can respond to light in other ways as well. These responses not related to photosynthesis allow plants to adapt to their environment and to be able to improve their growth.

What is phototropism

Phototropism consists of a response to light in plants, which involves growth to or from a light source . This response that the plant has allows the green parts of the plant to come closer to a source of light energy, which can then be used for photosynthesis .

In the year 1880, Charles Darwin and his son Francis published an article in which they explained the inclination of the grass towards the light. Specifically, they examined this response in very young plants that had just sprouted whose leaves and shoots were still covered by a pod called a coleoptile .

The process is considered as a hormonal reaction of the plants that is used to stimulate their growth . We can say then that phototropism is the movement that a plant makes in order to find a source of light , in other words, it consists of the change of location or orientation of the plant to receive the sun’s rays . It can also be considered as a chemical signal ; since when some types of hormones are released in the plant system, the cells of the part that receives sunlight grow faster.

Types of phototropism

There are two important types of phototropism which are the following:

• Positive phototropism : is the strategy of plants to capture as much light sun as they can through their leaves . When the seedlings grow by the force of gravity, they immediately receive a clue to guide their path and in this way they are able to bend in the direction of the light source. This movement is carried out by means of auxin, which is a phytohormone which is regulated by the amount of sun and is also responsible for flexing the plants in search of light.
• Negative phototropism : it is the tendency that some types of plants have to move away from sunlight. An example of this are the roots , which grow contrary to the direction of the sun, but take advantage of the moisture and nutrients in the soil.

Auxins

Auxins are potent hormone of growth that occurs naturally by plants. It is located in the shoots and the tips of the roots and promotes cell division, the stem and the growth of the roots. They can also drastically affect the orientation of the plant by promoting cell division to the side of the plant in response to sunlight and gravity .

Auxins have four very important effects on plant growth:

• Stimulation of shoot elongation : they positively influence cell elongation, which increases the length of the plant.
• Controlling Seedling Orientation : When a new sprout grows in the ground or towards the light, it depends on where the auxins are located and how they influence the cells within the plant. Auxins will move downward due to gravity and laterally, away from light.
• Stimulating the branching of the root .
• Promoting fruit development : Auxins in the flower promote the maturation of the ovary wall and promote the steps in the full development of the fruit.

Experiment

An experiment that can be carried out in a simple way is using, for example , sunflower or corn seeds . You will need a cardboard box in which the plant will be placed. The box should be drilled about 2 inches apart and then closed with the plant in it. As the plant grows, you can see how it looks for the opening that we have made previously

Examples of phototropism

Some examples of phototropism are as follows:

• The ficus make their roots migrate out looking for water sources so that when they come under streets or pavement, cement and pipes break their way to make it to achieve what they need. This is an example of positive phototropism .
• A clear example that we easily observe of positive phototropism are sunflowers that have a great ability to face the sun. Thus they can have constant access to the sun’s rays.
• Some water plants can grow in the opposite direction of the sun’s rays. In the same way, the roots of terrestrial plants seek to bury their roots in the earth.