UV-B component of sunlight causes measurable damage in field-grown maize (Zea mays L.): developmental and cellular heterogeneity of damage and repair

Ultraviolet radiation has diverse morphogenetic and damaging effects on plants. The end point of damage is reduced plant growth, but in the short term UV radiation damages specific cellular components. We measured cyclobutane pyrimidine dimers in maize DNA from plants grown in natural solar radiation. Green maize tissues had detectable DNA damage, roots had less damage, and anthers had much more damage than green leaves. This heterogeneity in damage levels may reflect differences in dose received or in damage repair. The architecture of green tissues had no measurable effects on DNA damage levels, as leaf sheath and leaf blade were equivalent. We observed a slight increase in damage levels in plants sampled at the end of the day, but there was no accumulation of damage over the growing season. We measured photoreactivation, and found substantial levels of this light-dependent repair in both the epidermis and inner cell layers of leaves, and in all organelles that contain DNA – the nucleus, chloroplasts and mitochondria. We conclude that maize has efficient mechanisms for photorepair of daily UV-induced DNA damage that prevent accumulation.