Imbibition refers to the movement of water molecules absorbed by any living or dead material of plant by joint action of capillary and electrostatic force. Imbibition is a passive process without conversion of metabolic products or energy utilized.
Features of Imbibition
Seed germination completely depends on radicle formation and imbibition of seeds by water; Cellulose, hemicellulose, pecten and other proteinaceous hydrophilic substance of the dry seed swells when subjected to water. Significant adaptation of plant to produce dry seed is to protect from the harsh condition germination where it causes death to their progeny.
Apart from seed germination; imbibition plays a small role in transfer of water and nutrition in plants; by its ability to move the water over a very small distance. Transport over large distance is dependable on the species of plants and are explored less.
Imbibition along with other passive forces also contributes to water transport in root hairs. The phenomenon is easily understood; as a dead tree trunk in water swells voluminously is the exact mechanism of uptake of water by imbibition. The volume of the imbibant (i.e.) cellulose or hemicellulose, pecten increases the whole volume of the plant or the trunk does not increase because of the rearrangement and reorientation of the water molecules attachment to the imbibant makes water to obtain less volume.
Main difference between a diffusion and imbibition is that it involves a solid as an absorbing substance (i.e.) the solid substance is the imbibant ; developing higher pressure after absorption. Imbibition is more specific to Hydrophilic colloids to absorb or transport water; is irreversibly dependent on matric pressure which was once termed as imbibition pressure. The pressure is similar to osmotic pressure which is really high to even break a rock and removes the external hard seed coat facilitating germination of seed. Imbibition takes place in both living and dead parts of plant.
History of Imbibition
Imbibition is a regular process of water uptake in plants especially in trunk is derived from Latin word – imbibere which means to drink in. In Ancient times during pyramid construction in Egypt; Egyptians used to break stones using the technique of imbibition. The small trunk pieces are inserted in rock cervices and trunks are soaked with water. The trunks expand absorbing the water produces high pressure induces a force up to 1000 kPa to break open a rock.
Similarly, the imbibition is used to break skull sutures to operate surgery in brain in ancient days by “Witch Doctors”. Witch Doctors opens the skull by prior treatment of skull by soaked seeds which on germination opens the seed coat produces force to open the skull allowing to perform the surgery. Imbibition examples are well present in our day today life; where the wooden doors, windows or other wooden articles exposed to sun rain absorb water and swells; which disables the ability of wood to function properly.
Imbibition in Water Transport
Passive forces constitute movement of water from the soil to roots hairs of plants and constitutes short distance transport of water. Water from soil due to the difference in concentration gradient move from higher concentration to lower concentration.
Short distance transport is easily achieved by either of the physical forces or in combination. Later, the transpiration pull created use to the evaporation and active transport in intracellular protein structures also constitutes transport of materials and water throughout the length of the plant.
Imbibition in Seed Germination
Water becomes essential for a seed to germinate at favorable environmental condition. Seeds undergo dehydration and rehydration process for germination. Once the seed is matured the water content of the seeds are given out by dehydration where the storage and genetic material are intact enough to survive for few days. On favorable condition with water the seed imbibes water and swells because of absorption of water. This causes a pressure to build up which breaks the seed coat for the seed to germinate. Following imbibition, a heat is generated; which is essential to drive the metabolic activities for seed development; caused by the liberation of heat because of water absorption.
The developmental changes in seeds are:
• Releasing hydrolytic enzymes to digest and mobilize the reserves
• Cell division and cell enlargement is started again
• Respiratory pathways start
• Development proceeds to produce new plant.
Process of Imbibition depends on the chemical and electrostatic forces and the colloidal substance available to take up water. These are the 2 main contains for imbibition to occur:
Water potential is necessary between the imbibant and the water. Generally, imbibition takes place when the potential difference between the substance is high like in plants; the cellulose and pecten are colloid which absorbs water and transfer the water content from the lower potential region to higher potential region. Water potential on a colloid must be lower for a water to be absorbed.
Affinity between imbibant and liquid is essential. Colloids such as cellulose, pecten have higher affinity to water than to ether
Factor Affecting Imbibition
Imbibition depends on both internal environment of plants and external factors of the environment.
Temperature: Imbibition increase with an increase in temperature. Higher temperature increases the rate of imbibition by the movement produced by the kinetic energy of the colloids or the imbibing molecules. This the main external environmental factor influencing imbibition. At lower temperature; the surface becomes stiffer for absorption and enter a dormant stage or die due to unfavorable conditions.
Osmotic Potential: Osmotic potential between the imbibant and the medium must be steeper for imbibition to occur consistently and effectively. Increase in solute concentration in water leads to less absorption of water which does not support the movement of water or the germination.
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- Experimental Investigation on the Imbibition Capacity and Its Influencing Factors in Hydrate Sediments. ACS Omega . 2020 Jun 9;5(24):14564-14574.
- Studies on the molecular mechanisms of seed germination. Proteomics . 2015 May;15(10):1671-9.