Cold- and light-induced changes of metabolite and antioxidant levels in two high mountain plant species Soldanella alpina and Ranunculus glacialis and a lowland species Pisum sativum

Leaves of the two cold-acclimated alpine plant species Ranunculus glacialis and Soldanella alpina and, for comparison, of the non-acclimated lowland species Pisum sativum were illuminated with high light intensity at low temperature. The light- and cold-induced changes of antioxidants and of the major carbon and phosphate metabolites were analysed to examine which metabolic pathways might be limiting in non-acclimated pea leaves and whether alpine plants are able to circumvent such limitation. During illumination at low temperature pea leaves accumulated high quantities of sucrose, glucose-6-phosphate, fructose-6-phosphate, mannose-6-phosphate and phosphoglycerate (PGA) whereas ATP/ADP-ratios decreased. Although the PGA content also increased in leaves of R. glacialis the other metabolites did not accumulate and ATP/ADP-ratios remained fairly constant in either alpine species. These data indicate a inorganic phosphate (Pi)-limitation in the chloroplasts of pea leaves but not in the alpine species. However, the total phosphate pool and the percentage of free Pi were highest in pea and did not change during illumination in cold. In contrast, free Pi contents declined markedly in R. glacialis leaves, suggesting that Pi is available for metabolism in this species. In S. alpina leaves contents of ascorbate and glutathione doubled in light and cold, while the contents of sugars did not increase. Obviously, S. alpina leaves can use assimilated carbon for ascorbate synthesis, rather than for the synthesis of sugars. A high capacity for ascorbate synthesis might prevent the accumulation of mannose-6-phosphate and Pi-limitation.