Reversibility of cold- and light-stress tolerance and accompanying changes of metabolite and antioxidant levels in the two high mountain plant species Soldanella alpina and Ranunculus glacialis.

Two high mountain plants Soldanella alpina (L.) and Ranunculus glacialis (L.) were transferred from their natural environment to two different growth conditions (22 degrees C and 6 degrees C) at low elevation in order to investigate the possibility of de-acclimation to light and cold and the importance of antioxidants and metabolite levels. The results were compared with the lowland crop plant Pisum sativum (L.) as a control. Leaves of R. glacialis grown for 3 weeks at 22 degrees C were more sensitive to light-stress (defined as damage to photosynthesis, reduction of catalase activity (EC 1.11.1.6) and bleaching of chlorophyll) than leaves collected in high mountains or grown at 6 degrees C. Light-stress tolerance of S. alpina leaves was not markedly changed. Therefore, acclimation is reversible in R. glacialis leaves, but constitutive or long-lasting in S. alpina leaves. The different growth conditions induced significant changes in non-photochemical fluorescence quenching (qN) and the contents of antioxidants and xanthophyll cycle pigments. These changes did not correlate with light-stress tolerance, questioning their role for light- and cold-acclimation of both alpine species. However, ascorbate contents remained very high in leaves of S. alpina under all growth conditions (12-19% of total soluble carbon). In cold-acclimated leaves of R. glacialis, malate represented one of the most abundant compounds of total soluble carbon (22%). Malate contents declined significantly in de-acclimated leaves, suggesting a possible involvement of malate, or malate metabolism, in light-stress tolerance. Leaves of the lowland plant P. sativum were more sensitive to light-stress than the alpine species, and contained only low amounts of malate and ascorbate.