Write a Short Notes on Imbibition in Plants

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Imbibition in plants is the process by which water is absorbed by the hydrophilic surface of a cell. Water absorbed will enter the cell through diffusion, causing it to swell. Imbibition occurs due to the existence of a water potential gradient between the surface of the adsorbent or the dry material and the imbibed liquid or water.

Imbibition is a physical process related to the properties of colloids.
It is not related to the viability of the seeds.
It occurs in live seeds and in seeds that have been killed by heat or other means.

Imbibition in Plants and Seed Germination

Imbibition is necessary for seed germination. Even though the cell wall retains water, swelling of the seeds is the first step of germination. Swelling of the seed mobilizes reserve food material, leading to the emergence of cotyledons.

The extent of imbibition is determined by

Composition of the seed
Permeability of the seed coat or fruit to water
Availability of water in liquid or gaseous form in the environment.

The imbibitional stages of seeds can be divided into three phases.

During Phase I, dry seeds uptake water rapidly and reorganize cell organelles, such as mitochondria for respiration. During this period, intact membranes are restored for the organelle function and activities of the cell.
Phase II is a lag phase when water content levels off. During this phase, transcription (synthesis of messenger RNA) and translation occur.
At Phase III, there is an increase in water content due to the radicle emergence and elongation by substantial water absorption. Therefore, Phase III is considered the postgerminative stage.

Imbibition Pressure

During imbibition in plants, molecules of solvent enter the substance, which is swelling, causing solvation of the colloid particles and, in addition, occupying the free capillary spaces and the intermicellar spaces of the colloid. The swelling of the colloid results in the production of considerable pressures, called imbibition pressure.

Imbibition pressure prevents the colloid from swelling. It is of great importance as it leads to the breaking of the seed coat during germination and also makes room in the soil for the developing seedling.

The magnitude of imbibition pressure indicates the water-retaining power of the seed. This helps during germination by determining the amount of water for rehydrating the seed tissues.

Imbibition and Water Potential

Dry seeds have a high water potential of up to -900 bars. This allows them to readily imbibe water. Imbibition causes a reduction in water potential and kinetic energy. The reduced kinetic energy or energy loss is through the release of heat energy.

Imbibition does not need a semipermeable membrane. It occurs due to the presence of water in the cell wall. Cellulose has a high matric potential that helps retain water even after dessication of seeds. Only mechanical drying under high temperature will cause a complete dessication of the cell wall.

Examples of Imbibition in Plants and Animal cells

Products from plant and animal cells also exhibit imbibition. Swelling of cork, sponge, wood, wooden doors and windows, etc., are examples of imbibition.
Swollen seeds that fall in rock crevices survive due to imbibition. Seeds imbibe water or moisture and swell. This swelling exerts pressure on the rock surfaces that prevents crushing. Thus, they can survive, grow roots, and develop into a new plant.

References

S. C Bhatla, M. A. Lal, Plant Physiology, Development and Metabolism,
https://doi.org/10.1007/978-981-13-2023-1_1
Nonogaki, M., & Nonogaki, H. (2016). Germination. In Encyclopedia of Applied Plant Sciences (pp. 509–512). https://doi.org/10.1016/b978-0-12-394807-6.00201-x
Mayer, A., & Poljakoff-Mayber, A. (1982). FACTORS AFFECTING GERMINATION. In Elsevier eBooks (pp. 22–49). https://doi.org/10.1016/b978-0-08-028853-6.50010-3

What is Imbibition in Plants?