Plants and Photosynthesis: Translocation

Translocation in plants refers to the movement of food molecules (solutes) from the leaves to other parts of the plant, such as stems and roots.
The process happens in the plant’s phloem tissue, which consists of sieve tubes and companion cells.
The ‘source’ of the solutes is often the leaves where photosynthesis has taken place, converting light energy, carbon dioxide and water into food for the plant.
The ‘sink’ is the location within the plant the solutes are moved to. This can be areas of the plant that need to grow, like new leaves or flowers, or where they need to be stored, like the roots or fruits.
Translocation is an energy-requiring process. The energy mostly comes from ATP (adenosine triphosphate).
Energy is used to actively transport solutes into the phloem, causing the solute concentration to increase.
This change in concentration induces water to move from the xylem into the phloem by osmosis, increasing the pressure within the phloem and driving the flow of solutes to the sink.
At the sink, solutes are unloaded and used or stored, reducing the concentration in the phloem. This results in water moving back into the xylem, reducing the pressure and maintaining the flow of solutes from source to sink.
It’s worth remembering that translocation isn’t limited to transporting solutes downwards - it can move materials upwards, to side shoots or to storage organs.
Translocation is essential for the normal growth and development of plants since it facilitates the distribution of crucial organic compounds produced during photosynthesis.
In horticulture and crop production, understanding translocation helps in the successful application of plant growth regulators and herbicides.