Translocation

Translocation

Definition and Overview

• Translocation refers to the transport of soluble organic compounds within a plant.
• This process occurs in the plant’s phloem tissue.
• These compounds are often referred to as assimilates or photosynthates.
• The main substance moved in this way is sucrose, a type of sugar.

Process

• Translocation begins in the source, typically the green parts of the plant where photosynthesis occurs.
• Sucrose is actively loaded into the phloem tissue, using energy.
• This creates a high concentration of solutes, leading to a decrease in water potential.
• Water follows by osmosis from the nearby xylem vessels, creating a positive hydrostatic pressure.
• This pressure difference facilitates the mass flow of assimilates towards the sink (area of low pressure such as roots or fruits).

Role of Companion Cells

• Companion cells play an essential role in translocation.
• They contain numerous mitochondria, providing energy for the active transport.
• These cells help to load sucrose into the sieve tubes of the phloem.

Evidence for Translocation

• Ringing experiments provide evidence for translocation.
• Certain chemical inhibitors can block the process.
• Radioactive tracers can be used to track the movement of sugars.

Importance of Translocation

• Translocation supplies sugars to non-photosynthetic parts of the plant, supporting their growth and development.
• It also helps in the distribution of other organic substances, such as amino acids and hormones.
• Sucrose transported can be used in cellular respiration or stored as starch.

Multi-Directional Flow

• Unlike xylem, phloem can transport substances in multiple directions, either up or down the stem.
• This allows a plant to respond flexibly to its nutrient needs at different times of the year.