How does abscisic acid protect plants against drought?
Abscisic acid (ABA) is a plant hormone that plays a crucial role in protecting plants against drought stress. Here are the mechanisms through which ABA helps plants cope with drought:
1. Stomatal Closure: When plants experience water scarcity, ABA helps in regulating the closure of stomata. Stomata are tiny openings on the surface of leaves that allow transpiration (loss of water vapor) and facilitate gas exchange. A high ABA level triggers the closure of stomata, reducing transpiration and preventing excessive loss of water from the leaves. This helps plants conserve water during drought conditions.
2. Root Growth Inhibition: ABA also inhibits the growth of roots. By doing so, it reduces water uptake and conserves the existing water in the soil for the survival and growth of the plant. This mechanism helps the plant maintain a balanced water status, even in the face of limited water availability.
3. Seed and Bud Dormancy: ABA induces and maintains seed dormancy, preventing premature germination in unfavorable environmental conditions such as drought. Additionally, it promotes bud dormancy, preventing early bud break and growth during dry periods. This allows plants to delay growth until more suitable conditions become available.
4. Cellular Protection: ABA helps protect plant cells from damage caused by drought stress. It can act as an antioxidant, scavenging harmful reactive oxygen species (ROS) that accumulate under drought conditions. By reducing oxidative stress and modulating various stress-related proteins, ABA helps maintain the integrity and function of plant cells.
Overall, ABA acts as a regulator that coordinates various physiological, developmental, and molecular responses in plants to cope with drought stress. By controlling stomatal closure, root growth inhibition, seed and bud dormancy, as well as providing cellular protection, ABA helps plants survive and adapt to drought conditions.
Abscisic acid (ABA) is a plant hormone that plays a crucial role in protecting plants against drought. Here are the key steps by which abscisic acid helps plants survive under water scarcity:
Step 1: Stomatal Closure:
When water availability is limited, the production of ABA increases in the leaf cells. ABA binds to specific receptors in the guard cells surrounding the stomata, which are the tiny pores on the leaf surface responsible for gas exchange. This binding triggers a series of biochemical events that result in the closure of the stomata, reducing water loss through transpiration.
Step 2: Regulation of Water Movement:
ABA also influences the movement of water within plant tissues. It promotes the accumulation of organic solutes called osmoprotectants, such as proline and sugars, in plant cells. These osmoprotectants help maintain the turgor pressure inside the cells, preventing water loss and dehydration.
Step 3: Inhibition of Growth:
During periods of drought stress, ABA inhibits plant growth through various mechanisms. It suppresses the elongation of new cells, reduces cell division, and redirects the plant's resources away from growth towards stress tolerance. By limiting growth, plants conserve energy and resources, focusing on survival under water-limited conditions.
Step 4: Seed Dormancy and Bud Dormancy:
ABA also plays a role in seed and bud dormancy. In dry conditions, ABA prevents premature germination of seeds or bud breakage, ensuring that the plant does not start growing during unfavorable conditions. This dormancy state helps plants conserve energy and increases their chances of survival until suitable conditions return.
Step 5: Inducing Stress-Responsive Genes:
ABA activates genes responsible for producing proteins known as stress-responsive proteins. These proteins play a vital role in protecting plant cells from damage caused by drought stress. They act as antioxidants, scavenging reactive oxygen species that accumulate during water scarcity and protect the plant's cellular components.
By implementing these steps, abscisic acid helps plants cope with drought stress and increases their chances of survival until water availability improves.