I have never experienced a frost with a plant before, but I would assume that once the frost melted off the next morning, you would have a good shot at some bud rot and possibly develop mildew issues. More importantly, if plant fibers that contain H2O actually freeze, I would have to imagine that cellular breakdown would happen as the H2O freezes and expands within the plants cell walls. Maybe one of the weed docs can come in and give a little better explanation here.