Introductory Crop Physiology (1+1)

Imbibition

Certain substances, if placed in a particular liquid absorb it and swell up.
For example, when some pieces of grass or dry wood or dry seeds are placed in water they absorb the water quickly and swell up considerably so that their volume is increased. These substances are called as imbibants and the phenomenon as imbibition is also called as hydration.
Certain force of attraction is existing between imbibants and the involved substance.
In plants, the hydrophilic colloids viz., protein and carbohydrates such as starch, cellulose and pectic substances have strong attraction towards water.
Imbibition plays a very important role in the life of plants. The first step in the absorption of water by the roots of higher plants is the imbibition of water by the cell walls of the root hairs. Dry seeds require water by imbibition for germination.
As a result of imbibition, a pressure is developed which is called as imbibition pressure or matric potential (ψm). It is analogous to the osmotic potential of a solution. With reference to pure water, the values of ψm are always negative.
The water potential of an imbibant is equal to its matric potential plus any turgor or other pressure (pressure potential) which may be imposed upon the imbibant.
ψw =ψm + ψP
If the imbibant is unconfined to turgor or any such pressure, the equation will be ψw : ψm
There are three major physical changes will takes place during hydration. They are,

• Change in volume.
• Change in temperature.
• Change in pressure.