Although UV-B is a minor component of sunlight, it has a disproportion
ately damaging effect on higher plants. Ultraviolet-sensitive targets
include DNA, proteins and membranes, and these must be protected for n
ormal growth and development. DNA repair and secondary metabolite accu
mulation during exposure to UV-B have been characterized in considerab
le detail, but little is known about the recovery of photosynthesis, i
nduction of free-radical scavenging and morphogenic changes. A future
challenge is to elucidate how UV-B-exposed plants balance damage, repa
ir, acclimation and adaptation responses in a photobiologically dynami
c environment.