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

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 Biter 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.