PDF《UV-B radiation》

Jenkins 2009;

Heijde &

Ulm 2012). The UVR8 protein interacts in a strictly UV-B-dependent manner with the ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC (COP1) (Favory et al. 2009), while accumulating in the nucleus where it controls gene expression. Further components of the UVR8-signalling cascade are ELONGATED HYPOCOTYL

5 (HY5) and REPRESSOR OF UV-B PHOTOMORPHOGENESIS

1 (RUP1) and RUP2 (Heijde &

Ulm 2012). Both cop1 and uvr8 mutants show no UV-B- induced photomorphogenic response (Favory et al. 2009). Thus, 4-day-old uvr8 seedlings raised under narrowband UV-B fail to show any UV-B-responsive hypocotyl shorten- ing, although wild-type plants might display as much as 50% inhibition of elongation (Favory et al. 2009). In contrast, transgenic UVR8 overexpressing Arabidopsis display par- ticularly strong inhibition of hypocotyl elongation under UV-B (Favory et al. 2009). These responses indicate the importance of UVR8 as a photoreceptor that controls 1.0 1.5 2.0 2.5

12 14

16 18

20 13

14 15

16 17

18 19 Branches Height (cm) Seed pods

0 25

50 75

100 % Solar UV radiation Figure 1. An example of a bell-shaped UV doseCresponse curve redrawn from Brodführer (1955). The number of Arabidopsis branches (top panel), height in cm (middle) and number of seedpods (lower) per individual. Data are means ±

1 SE of

20 individuals per UV treatment, and the ?tted line is a loess smoother. Plant morphological responses to UV-B

857 ?

2014 John Wiley &

Sons Ltd, Plant, Cell and Environment, 38, 856C866 seedling architecture (Kliebenstein et al. 2002). Yet, when uvr8 mutant plants are grown for longer periods under UV-B lamps under control conditions (Favory et al. 2009;

Wargent et al. 2009b) or under ambient sunlight outdoors (Morales et al. 2013), they are smaller than wild-type plants, a result which appears to be in direct contrast to the hypocotyl response. It has been argued that the strong growth reduction re?ects UV-B stress in the poorly UV-protected uvr8 mutant plants and consequent growth retardation. Thus, it is consid- ered that uvr8 mutant plants are insensitive to UV-B as an informational signal, but hypersensitive to UV-B stress (Favory et al. 2009). This hypothesis effectively reconciles UV-B stress with UVR8-mediated regulation in one model, with the outcome depending on the balance of the two ........