ALFALFA SEEDLINGS GROWN OUTDOORS ARE MORE RESISTANT TO UV‐INDUCED DNA DAMAGE THAN PLANTS GROWN IN A UV‐FREE ENVIRONMENTAL CHAMBER

Abstract The relative UV sensitivities of alfalfa seedlings grown outdoors versus plants grown in a growth chamber under UV‐filtered cool white fluorescent bulbs have been determined using three criteria: (1) level of endogenous DNA damage as sites for the UV endonuclease from Micrococcus luteus. (2) susceptibility to pyrimidine dimer induction by a UV challenge exposure and (3) ability to repair UV‐induced damage. We find that outdoor‐grown plants contain approximately equal frequencies of endogenous DNA damages, are less susceptible to dimer induction by a challenge exposure of broad‐spectrum UV and photorepair dimers more rapidly than plants grown in an environmental chamber under cool white fluorescent lamps plus a filter that removes most UV radiation. These data suggest that plants grown in a natural environment would be less sensitive to UVB‐induced damage than would be predicted on the basis of studies on plants grown under minimum UV.