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 vers us plants grown in a growth chamber under UV-filtered cool white fluor escent bulbs have been determined using three criteria: (1) level of e ndogenous DNA damage as sites for the UV endonuclease from Micrococcus luteus, (2) susceptibility to pyrimidine dimer induction by a UV chal lenge exposure and (3) ability to repair UV-induced damage. We find th at outdoor-grown plants contain approximately equal frequencies of end ogenous DNA damages, are less susceptible to dimer induction by a chal lenge exposure of broad-spectrum UV and photorepair dimers more rapidl y than plants grown in an environmental chamber under cool white fluor escent lamps plus a Biter that removes most UV radiation. These data s uggest that plants grown in a natural environment would be less sensit ive to UVB-induced damage than would be predicted on the basis of stud ies on plants grown under minimum UV.