Leaf glazing by peroxyacetyl nitrate

Peroxyacetyl nitrate (PAN) is a potent phytotoxic agent and a major component of photochemical smog. It is an atmospheric pollutant, not a biological pathogen, that induces a specific physiological disorder in plants known as "leaf glazing," where the undersides of leaves develop a glossy, metallic, or oil-like sheen.

This injury significantly affects various plant species, including sensitive greenhouse crops such as Poinsettia, as well as lettuce, spinach, and beans. The damage occurs when PAN molecules enter the plant's leaf tissues through the stomata, subsequently oxidizing cellular lipids and proteins, leading to cell death.

Typical symptoms include the aforementioned glazing on the abaxial leaf surface, followed by the development of bronzing, silvering, or necrotic lesions. As the damage progresses, affected tissues lose their turgor, turn brittle, and eventually result in leaf abscission, which drastically reduces both the yield and the ornamental quality of the plant.

The development of this disorder is heavily dependent on environmental conditions, specifically high solar radiation coupled with the presence of precursor pollutants like nitrogen oxides and volatile organic compounds. Calm, sunny days promote the accumulation of smog, creating high-risk scenarios for vegetation grown in industrial or urbanized regions.

Management and prevention focus primarily on environmental control. For high-value greenhouse crops, installing activated charcoal filters in ventilation systems effectively scrubs PAN from the air. Additionally, selecting resistant cultivars and avoiding planting in areas with poor air circulation or high traffic density are crucial strategies for minimizing the impact of atmospheric stress on crops.