Effects of Ultraviolet Radiation on Plants and Their Protective Mechanisms

Excessive use of halogenated compounds has led to ozone layer depletion, increasing ultraviolet (UV) radiation reaching the Earth's surface. UV radiation significantly impacts plant growth and performance. The observed rise in malondialdehyde (MDA) and other aldehydes indicates increased free radical production under UV radiation, overwhelming the plant's defense capacity and causing damage to biological membranes. While UV-A rays elevate malonaldehyde levels in leaves, the damage to cell membranes is less severe than UV-B and UV-C. Plants respond by developing resistance mechanisms to cope with this stress. Defensive compounds such as ascorbic acid (vitamin C), dehydroascorbic acid, proline, and antioxidant enzymes (e.g., catalase, peroxidase, glutathione reductase, and ascorbate peroxidase) play a crucial role in reducing UV-induced damage. Reactive oxygen species (ROS), the UVR8 protein, and photoreceptors such as phytochrome and cryptochrome are integral components of the UV signaling pathway. The text also discusses how UV light can impede photosynthesis and growth processes, while also highlighting the beneficial effects of UV that promote the production of various pigments, including flavonoids and carotenoids, and enhance the stress tolerance of plants. Understanding these defense mechanisms is essential for sustainable plant health and ecosystem resilience.