Regulation by Two Xanthophyll Cycles in Higher Plants Non-Photochemical Fluorescence Quenching and Energy Dissipation
- Autoría:
- Esteban R. & García Plazaola J.I.
- Año:
- 2014
- Libro:
- Plants, Algae and Cyanobacteria
- Página de inicio - Página de fin:
- 277 - 295
- Descripción:
-
Summary
The lutein epoxide (Lx) cycle (Lx-L cycle), initially described in tomato fruits, remained unexplored during the following 25 years until it was re-discovered in the stems of the parasitic plant Cuscuta reflexa. Since then, 15 years of continuous research have revealed that the Lx-L cycle is present in a wide diversity of species, allowing us to make significant progress in our understanding of this carotenoid cycle. However, due to its absence in some traditional model plant species, much of its functional significance remains to be clarified. We have therefore provided an overview of the current knowledge of this cycle as well as an ecological perspective of the possible benefits derived from the possession of two xanthophyll cycles (all plants possess a xanthophyll cycle involving violaxanthin, antheraxanthin, and zeaxanthin, i.e., the VAZ cycle, whereas only some species possess the Lx-L cycle). In the Lx-L cycle, Lx is de-epoxidized upon illumination, by the action of violaxanthin de-epoxidase (VDE), and transformed into lutein (L). Correlative evidence supports a role for this newly formed L (ΔL) in the regulation of thermal energy dissipation as assessed from the non-photochemical quenching of chlorophyll fluorescence (NPQ). The reversibility of this reaction in darkness differentiates two modes of operation, one "completed" in which the initial Lx pool is restored and one "truncated" in which ΔL remains for a longer period. The first, described in sun and shade leaves of a few unrelated species, apparently provides fine-tuning for the adjustment of photoprotective energy dissipation complementary to that exerted by the VAZ cycle. On the other hand, the "truncated" cycle is widespread amongst woody plants, but is restricted to shaded environments where it may act as a rapid switch for the photosynthetic apparatus from a photosynthetically highly efficient state to a photoprotected one. The latter may be necessary for chloroplast acclimation after transition to high light, such as that which occurs following gap formation in forests or budbreak and subsequent leaf greening in trees.