Photoprotection

Photoprotection refers to the physiological and biochemical strategies that organisms use to limit damage from light, especially ultraviolet radiation and excess photosynthetically active radiation. In photosynthetic organisms such as plants, algae, and cyanobacteria, photoprotection aims to prevent photoinhibition, oxidative stress, and tissue damage while maintaining photosynthetic efficiency.

In plants and algae, the most studied component is non-photochemical quenching, a mechanism that dissipates excess absorbed light as heat in the light-harvesting complexes. The xanthophyll cycle plays a central role, converting violaxanthin to antheraxanthin and zeaxanthin under high light to facilitate energy dissipation. Antioxidant systems, including ascorbate, glutathione, and enzymes such as superoxide dismutase, catalase, and peroxidases, detoxify reactive oxygen species. Plants also repair photodamaged components, notably the D1 protein of photosystem II. Protective pigments such as flavonoids and anthocyanins absorb UV and scavenge reactive species, and leaf structural features and acclimation responses reduce light absorption or improve dissipation.

In animals, photoprotection relies largely on shielding and repair. Melanin production in the skin absorbs ultraviolet radiation, reducing DNA damage. DNA repair pathways, particularly nucleotide excision repair, remove UV-induced lesions. Antioxidant defenses help counteract photooxidative stress, and prophylactic measures such as sunscreen and protective clothing limit exposure.

The study of photoprotection informs agriculture, ecology, and medicine by explaining how organisms cope with changing light environments and how to enhance crop resilience or human protection against light-induced damage.