PDF《UV-B radiation》

Review Re-interpreting plant morphological responses to UV-B radiation T.

Matthew Robson1 , Karel Klem2 , Otmar Urban2 &

Marcel A. K. Jansen3

1 Department of Biosciences, University of Helsinki, Helsinki 00014, Finland,

2 Global Change Research Centre AS CR, Brno CZ 60300, Czech Republic and

3 School of Biological, Earth and Environmental Science, University College Cork, Distillery Fields, Cork, Ireland ABSTRACT There is a need to reappraise the effects of UV-B radiation on plant morphology in light of improved mechanistic under- standing of UV-B effects, particularly elucidation of the UV RESISTANCE LOCUS

8 (UVR8) photoreceptor. We review responses at cell and organismal levels, and explore their underlying regulatory mechanisms, function in UV pro- tection and consequences for plant ?tness. UV-induced mor- phological changes include thicker leaves, shorter petioles, shorter stems, increased axillary branching and altered root:shoot ratios. At the cellular level, UV-B morphogenesis comprises changes in cell division, elongation and/or differ- entiation. However, notwithstanding substantial new knowl- edge of molecular, cellular and organismal UV-B responses, there remains a clear gap in our understanding of the inter- actions between these organizational levels, and how they control plant architecture. Furthermore, despite a broad con- sensus that UV-B induces relatively compact architecture, we note substantial diversity in reported phenotypes. This may relate to UV-induced morphological changes being under- pinned by different mechanisms at high and low UV-B doses. It remains unproven whether UV-induced morphological changes have a protective function involving shading and decreased leaf penetration of UV-B, counterbalancing trade-offs such as decreased photosynthetic light capture and plant-competitive abilities. Future research will need to dis- entangle seemingly contradictory interactions occurring at the threshold UV dose where regulation and stress-induced morphogenesis overlap. Key-words: auxin homeostasis;

canopy structure and light interception;

chronic/acute stress;

?avonoid accumula- tion;

plantCplant interactions;

stress-induced morphogenic responses (SIMR);

ultraviolet radiation;

UVR8 photorecep- tor;

whole-plant phenotype. INTRODUCTION Plants use solar radiation, not just as a source of energy, but also as a source of information about the environment.Well- documented examples of information harvesting include the capability to sense and respond to the timing, duration, wave- length, dose and direction of light, and this underlies processes such as photoperiodicity, phototropisms and photomorphogenesis (Kendrick &

Kronenberg 1994). The term photomorphogenesis is often used to describe light- regulated plant development, that is, the induction by light of signalling cascades that trigger a broad range of responses at the molecular, cellular and organismal level. Here, we will use the term photomorphogenesis in a stricter sense to explore the morphological responses of plants grown under different UV-B conditions. UV-B wavelengths (280C315 nm) are biologically active, with low doses inducing changes in gene expression, physiol- ogy, metabolite accumulation and morphology (Heijde &

Ulm 2012;

Schreiner et al. 2012). A speci?c UV-B photore- ceptor, UV RESISTANCE LOCUS

8 (UVR8), has been identi?ed (Rizzini et al. 2011). UVR8-mediated processes include antioxidant defence and accumulation of phenolic pigments (Jenkins 2009;

Hideg et al. 2013). UVR8 is also involved in the regulation of plant morphology under UV-B radiation. UV-induced architectural changes include, among others, thicker leaves, shorter petioles, leaf curling and altera- tions in leaf shape and width, decreases in stem elongation, increased axillary branching or tillering, and altered root:shoot ratio and structure of the in?orescence (Jansen 2002;