Explain the association between drought stress and photosynthesis in plants
Drought stress refers to the condition in which plants experience water scarcity or lack of irrigation, leading to reduced water availability in the soil. This condition negatively affects various physiological processes in plants, including photosynthesis.
Photosynthesis is the process by which plants convert sunlight, carbon dioxide, and water into glucose (energy) and oxygen. It occurs in specialized cell organelles called chloroplasts, mainly in the leaves. However, water is an essential component of photosynthesis and plays vital roles in the process.
During drought stress, the lack of water can directly influence the structure and function of leaves, impacting photosynthesis. The primary association between drought stress and photosynthesis is as follows:
1. Stomatal closure: To minimize water loss through transpiration, plants respond to drought stress by closing their stomata. Stomata are small openings on the surface of leaves that allow gas exchange, including the entry of carbon dioxide for photosynthesis and the release of oxygen. When stomata close, the influx of carbon dioxide is significantly reduced, limiting the availability of the primary substrate needed for photosynthesis.
2. Decreased carbon fixation: With stomatal closure, the supply of carbon dioxide to the chloroplasts is restricted, leading to decreased carbon fixation during photosynthesis. Consequently, the rate of the first stage of photosynthesis, known as the light-dependent reactions, may be hampered. These reactions require energy from sunlight to convert light energy into chemical energy in the form of ATP and NADPH, which are essential for the next stage of photosynthesis.
3. Reduced water-dependent processes: Photosynthesis requires a continuous supply of water not only for the plants to maintain turgor pressure but also for several water-dependent processes, such as electron transport and the enzymatic activity within chloroplasts. The lack of water during drought stress can disrupt these processes, impairing the overall efficiency of photosynthesis.
4. Oxidative stress: Drought stress can also induce oxidative stress in plants. When plants experience water shortage, the imbalance between the demand for water in photosynthesis and the limited water supply can lead to the accumulation of reactive oxygen species (ROS). ROS are harmful molecules that can damage cell membranes, proteins, and DNA, ultimately affecting photosynthetic structures and enzymes.
Overall, the association between drought stress and photosynthesis in plants is that water scarcity negatively influences the availability of carbon dioxide, reduces carbon fixation, disturbs water-dependent processes, and induces oxidative stress. These effects result in a decreased photosynthetic rate and overall productivity of the plant.