Translocation & Water Translocation of Cohesion Theory

1. Translocation:
What is Translocation?
Translocation is a biological mechanism involving the transfer of water and other
soluble nutrients from one part of the plant to another through the xylem and phloem,
which occurs in all plants.
Function of Translocation:
a) In higher plants, only the green parts can manufacture food and it must be
supplied to other non-green parts for consumption and also for storage.
b) Various plant hormones, proteins, and nucleic acids are also moved throughout
the plant via translocation.
c)During the germination of the seeds, the insoluble reserve food material of the
seed is converted into soluble from and is supplied to the growing regions of young
seedling till it has developed its own photosynthetic system i.e. leaves.
Water Translocation of Cohesion Theory:
This theory was given by Henry Dixon in 1914. This theory is quite convincing and
has been widely accepted. The cohesion theory is based on the force of cohesion
between water molecules. Forms a continuous water column from top to the root.
Water molecules remain joined to each other due to presence of H-bonds
between them. Although H-bond is very weak, but when they are present in
enormous numbers and develop a very strong mutual force of attraction or cohesive
force between water molecules. Therefore they remain form of a continuous water
column in the xylem.
The magnitude of this force is very high (about 350 atm or bars), therefore,
continuous water column in the xylem cannot be broken easily.
According to this theory, evaporation of water from the leaf to the atmosphere
and decrease the water potential of epidermal cell, which are direct contract with the
Atmosphere.
The water lost from epidermal cells is replaced by the water moving from the
adjacent cells along a water potential gradient. The water lost from leaf cells is
replaced by the water moving from the xylem elements in leaf veins
Due to this pattern of water movement, a Water tention is created in xylem
elements of the leaves.

2. This tention is transmitted downward to water in xylem elements of the roots through
the xylem of petiole and stem and the water is pulled upward in the form of
continuous unbroken water column and reach the transpiring surface up-to the top of
plants.
The water potential of root cells is lower than the water potential of soil, and
therefore, movement of water occurs from soil to the roots.