Format: ORAL

Miren I. Arzac, Jon Miranda-Apodaca, Laura Gonzlez-Coso, Usue Prez-Lpez, Antonio Hernndez, Beatriz Fernndez-Marn, Jos I. Garca Plazaola

Department of Plant Biology and Ecology, University of the Basque Country (UPV/EHU), Leioa, Spain

Alpine plants are exposed to very contrasting conditions of irradiance and UV radiation imposed by a day/night regime during the summer period. To maintain their photosynthetic efficiency under these conditions, alpine plants need to dissipate the excess energy and scavenge the reactive oxygen species (ROS) formed, via different photoprotective mechanisms. At chloroplast level, some carotenoids such as those involved in the xanthophyll cycle directly participate in the dissipation of excess energy. Some of them (such as zeaxanthin) are additionally strong antioxidants that act together with other antioxidant molecules (e.g. lutein, -carotene and -tocopherol).These lipophilic antioxidants are associated with plastoglobules, lipoprotein structures attached to thylakoid membranes that respond to stress conditions by changing their size and number. While daily modulation of some protective mechanisms such as the xanthophyll cycle are rather well known, daily oscillations in other molecules (tocopherols) and structures (plastoglobules) are virtually unexplored. In the present study, we aim at unravelling how the leaves of alpine plants are able to thrive under such strong diurnal oscillations, and in particular, what the role of those lipophilic antioxidants and their holding structures (plastoglobules) is on such responses. For this purpose, we studied five alpine species during a day/night cycle (Ranunculus glacialis, Saxifraga oppositifolia, Veronica alpina, Geum reptans and Doronicum grandiflorum) naturally growing in a talus field at 2630 m a.s.l. near Col du Galibier (French Alps). Combining physiological, biochemical and ultrastructural analyses our results show daily changes in plastoglobule size and number. The analysed antioxidants also presented oscillations, mainly the xanthophyll cycle. However, the changes were species-dependent, indicating possible different strategies among alpine plants living under similar conditions.We conclude that thylakoid membranes and their components present the ability to adapt according to daily changes of high irradiance in different species of alpine plants.