PDF《UV-B radiation》

Furness et al. 2005a;

Hectors et al. 2007;

Yang et al. 2008;

Wargent et al. 2009a,b;

Klem et al. 2012;

Robson &

Aphalo 2012). However, the role of UVR8 in these UV-B-mediated morphological changes remains poorly understood. The analysis of published plant UV responses, and particu- larly UV-B-induced morphological changes,is complex due to variations in genotype and experimental conditions (Xu &

Sullivan 2010). For example, different Arabidopsis thaliana ecotypes display quantitatively different morphological responses when exposed to UV-B (Biswas &

Jansen 2012), whereas in Silene nocti?ora vegetative and ?owering stems display a different doseCresponse when exposed to UV-B (Qaderi et al. 2008). In Arabidopsis, low UV doses induce rather different effects on plant morphology than higher doses (Fig. 1) (Brodführer 1955). In nature, UV-B levels ?uctuate depending on temporal, seasonal and meteorological factors, and these ?uctuations often correspond with particular Correspondence: O. Urban. e-mail: [email protected] Plant, Cell and Environment (2015) 38, 856C866 doi: 10.1111/pce.12374 bs_bs_banner ?

2014 John Wiley &

Sons Ltd

856 plant developmental phases and the position of leaves in the canopy. In contrast, many UV studies are based on the exposure of plants to a constant, chronic level of UV-B under controlled indoor conditions. Notwithstanding the uncertain environmental relevance of many published plant UV studies, there now seems to be a consensus that UV-B-induced stress is a rare event (Ballaré et al. 2011).Thus, over the last decade, plant UV-B research has experienced a major paradigm shift, with the focus moving from stress caused by high UV-B doses and stress-induced signalling to UV-B-speci?c regulatory events triggered by very low UV-B doses and mediated through a dedicated UV-B photoreceptor (Jenkins 2009;

Jansen &

Bornman 2012). Indeed, realistic experimental manipulations of solar UV-B have demonstrated that damaging UV-B-associated stress is the exception rather than the norm in most natural environments (Searles et al. 2001;

Li et al. 2010). This paradigm shift necessitates a re-appraisal of commonly reported UV-B-mediated mor- phological responses, while creating an opportunity to explore the links between established changes in plant mor- phology and our new understanding of signalling and molecular-level responses.Here,we will review the concept of the UV-B-induced phenotype at the cell and plant level, explore underlying regulatory mechanisms,possible functions as well as consequences for plant growth and plantCplant interactions. UV-B RESPONSES AT THE MOLECULAR LEVEL Major progress has been made in elucidating the mole- cular pathways underlying many UV-B responses (Rizzini et al. 2011;

Tilbrook et al. 2013). The UV-B photoreceptor UVR8 mediates acclimation responses to chronic UV-B doses (exposure to moderate doses over several days) (Kliebenstein et al. 2002), whereas acute (sudden and short- term) exposure to high UV-B induces more generic mitogen- activated protein kinases (MAPK) (Besteiro et al. 2011) and/or signalling cascades activated by reactive oxygen species (ROS) (Hideg et al. 2013).At present, it is not known whether UV-B-mediated morphological changes at cell, organ and organismal level are underpinned by UV-B- speci?c low dose signalling, by generic stress-mediated path- ways, or are associated with the complex metabolic changes that occur during acclimation. Here we will review the evi- dence that links speci?c molecular and cellular processes to UV-B-mediated morphological changes. Regulation of plant morphology via the UVR8 pathway The UV-B-speci?c photoreceptor, UVR8, is a co-regulator of UV protection, controlling the expression of genes involved in ?avonoid biosynthesis, DNA repair and anti- oxidative defence (Brown et al. 2005;