Early signaling components in ultraviolet-B responses: distinct roles for different reactive oxygen species and nitric oxide

The nature and origin of the reactive oxygen species (ROS) involved in the early part of Ultraviolet-B (UV-B)-induced signaling pathways were investigated in Arabidopsis thaliana using a range of enzyme inhibitors and free radical scavengers. The increase in PR-1 transcript and decrease in Lheb transcript in response to UV-B exposure was shown to be mediated through pathways involving hydrogen peroxide (H2O2) derived from superoxide (O (2) over circle (-)). In contrast, the up-regulation of PDF1.2 transcript was mediated through a pathway involving O (2) over circle (-) directly. The origins of the ROS were also shown to be distinct and to involve NADPH oxidase and peroxidase(s). The up-regulation of Chs by UV-B was not affected by ROS scavengers, but was reduced by inhibitors of nitric oxide synthase (NOS) or NO scavengers, Together these results suggest that UV-B exposure leads to the generation of ROS, from multiple sources, and NO, through increased NOS activity, giving rise to parallel signaling pathways mediating responses of specific genes to UV-B radiation. (C) 2001 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.