Drought Resistance Mechanism in plants

What do you know about drought resistance mechanism in plants? Before going to know it we should know what is drought resistance?

What is drought resistance?

The ability of a crop species or variety to grow and yield satisfactorily in areas subjected to periodic water deficits is termed drought resistance.

Types of drought resistance

• Drought escape: The ability of a plant to complete the life cycle before serious soil and plant water deficits develop.
• Drought tolerance with high tissue water potential: The ability of the plant to endure periods of drought while maintaining a high plant water stress. This is also referred to as drought avoidance (Levitt, 1972).
• Drought tolerance with low tissue water potential: The ability of the plant to endure periods without significant rainfall and endure low tissue water potential.

Drought Resistance Mechanism in plants

Table – Mechanisms of drought resistance (after Jones et al. 1981)

1. Drought escape

• Rapid phenological development
• Developmental plasticity

2. Drought tolerance with low tissue water potential

(a) Maintenance of turgor

• Solute accumulation
• Increase in elasticity

(b) Desiccation tolerance

• Protoplasmic resistance

3. Drought tolerance with high tissue water potential

(a) Maintenance of water uptake

• Increased rooting
• Increased hydraulic conductance

(b) Reduction of water loss

• Reduction in epidermal conductance
• Reduction in absorbed radiation
• Reduction in the evaporative surface.

1. Drought Escape

Two features of desert ephemerals that are important in drought resistance are-

• Rapid phonological development.
• Developmental plasticity.

Rapid phonological development

Producing flowers with a minimum of vegetative structure enables them to produce seeds on a limited water supply.

Developmental plasticity

This feature enables the plants to produce an abundance of vegetative growth, flowers, and seeds in seasons of abundant rain, enabling the desert ephemerals to escape drought and survive long periods without rain.

In crop plants, the most significant advance in breeding for a water-limited environment is achieved by shortening the life cycle, thereby allowing the crops to escape drought. Therefore, there is a strong, consistent negative correlation between grain yield and days to first ear emergence, and 40-90% variation in wheat yield under drought conditions was accounted for by earliness. 

In wheat, it was observed that drought resistance is more excellent in early lines than late ones, even at the same intensity of drought. However, yield is often positively correlated with a maturity date indeterminate annual crops such as maize, sorghum, and sunflower under adequate water supply.

An essential aspect of developmental plasticity is the ability of plants to transfer assimilates accumulated before seed-filling to the grain during the seed filling stage. It was also suggested that when the water supply is adequate, only a tiny proportion of dry grain weight comes from the store of prior assimilate in the stems and roots. Still, when stress occurs in the seed filling stage, an increased proportion of the prior assimilate is transferred to the seed.

Plants frequently have an indeterminate habit of achieving developmental plasticity. This is an important survival mechanism in that it enables the large amounts of seed produced in wet years to carry the species through prolonged drought periods.

The selection of rapid phonological development is the most rewarding approach in breeding for thought resistance in crops. In cereals, drought resistance varieties of wheat and barley flowered early than the others. However, earliness is often negatively correlated with yield in the year of adequate rainfall.

2. Drought Tolerance at High Tissue Water Potential

The ability of the plant to endure periods of drought by maintaining high tissue water potential. This mechanism is also called drought avoidance.

To maintain a high water status during a high evaporative demand / or increasing soil water deficit, the plant has two options. It must either reduce the water loss or maintain its supply of water.

Reducing Water Loss

• Increased pubescence and
• Increased leaf waxiness

Maintenance of water uptake

• Deeper root system.
• Hydraulic conductance of plants (increasing either the diameter of xylem vessels or their numbers).

3. Drought Tolerance at a low tissue water potential

The plant can endure periods of drought and endure low tissue water potentials.