Translocation is the movement of sucrose around a plant. Leaves make glucose by photosynthesis, and much of it is changed into sucrose for transport. The sucrose dissolves in water to form a sugary sap, which is carried in the sieve tubes of the phloem.
The sucrose is moved from the leaves to every part of the plant that needs it. This includes the growing tips of the roots and shoots, where it is used for respiration and to make new cells. It also goes to fruits and to storage organs, such as potato tubers, where it is stored as starch.
Translocation can move sucrose both up and down the plant, which is different from the xylem where water only moves upwards. It is an active process that needs energy. The energy comes from respiration, and the companion cells with many mitochondria supply it to the sieve tubes.