Morphological and physiological responses of Brassica napus to ultraviolet-B radiation : Photomodification of ribulose-1,5-bisphosphate carboxylase/oxygenase and potential acclimation processes

Summary As the stratospheric ozone layer is depleted, the biosphere will be exposed to higher levels of ultraviolet-B (UV-B) radiation (290–320 nm). Using laboratory light sources that simulate the spectral quality of sunlight, we are examining some of the mechanisms involved in plant responses to UV-B. It was found that exposure of ribulose-l,5-bisphosphate carboxylase/oxygenase (Rubisco) from Brassica napus to UV-B in vivo or in vitro resulted in production of a high molecular weight (HMW) variant of the large subunit. Coincident with formation of the HMW product in vitro was a loss in tryptophan fluorescence. To protect against damage, plants can acclimate to UV-B. To this end, we have studied cotyledon curling in B. napus ; a photomorphogenic response specific to UV-B. To characterize the photoreceptor for curling, inhibitors of photochemical signaling were employed. A quencher of flavin excitation, and inhibitors of Ca ++ and cyclic nucleotide signaling diminished curling. Biosynthesis of flavonoids and other UV-absorbing pigments also occurred in B. napus exposed to the levels of UV-B that caused curling. To determine which flavonoids and other UV-absorbing compounds were UV-B specific, HPLC analysis was carried out. Approximately 20 distinct UV-absorbing pigments were produced in response to UV-B radiation. Thus, using B. napus we were able to follow UV-B induced damage and acclimation.