Photomorphological and photochemical effects of UV-B radiation of Brassica napus (L.) and Arabidopsis thaliana (L.) heynh: Morphological, cellular and structural biological changes

Reductions in plant growth and morphology are some of the most widely reported effects of solar UV-B on plants. A key goal of this thesis was to investigate the nature of the UV-B photoreceptor(s) that trigger these changes. Cotyledon curling in B. napus and Arabidopsis was found to be a UV-B specific response. Mediation of this morphological change by a signal-transduction pathway was investigated. The morphology of UV-B-irradiated phytochrome and cryptochrome photoreceptor mutants of Arabidopsis was found to be similar to wild-type plants, indicating that these photoreceptors do not mediate the changes. A photosynthesis mutant of Arabidopsis with an apparent lesion in the photosystem I reaction center was isolated, and found to also undergo cotyledon curling in the presence of UV-B. Hence, UV-B effects on photosynthesis are not the basis of cotyledon curling. To examine the absorbance characteristics of the photoreceptor. The first action spectrum for morphological changes triggered by UV-B in light-grown Brassica napus (L.), upward cotyledon curling, is reported. In the course of the study dry weight accumulation and carotenoid concentration were found to be physiological parameters most highly sensitive to UV-B. Photosynthetic efficiency was found to change 24 h after a brief exposure to UV-B indicating that other processes may be regulated by the UV-B photoreceptor(s). Some of these represent acclimation, while others represent stress. Characterization of UV-B-induced changes in epidermal cells from cotyledons of B. napus was carried out since this is a likely site of UV-B photoreception. Investigation of their protein composition and secondary metabolism is reported. The profiles of soluble proteins changed after a brief exposure to UV-B. The concentration of sinapoylmalate and sinapoylglucose were shown to accumulate in response to UV-B. The photocross-linking of plant proteins by UV-B, as well as an analysis of the basis of such photochemical events is reported.