Flavonoid-related ROS scavenging in sun and shade linden leaves

Petra Majer visited Prof. Monika Schreiner in Germany (15 days in February 2011)

The difference between leaves grown on the sunny and on the shaded parts of the same tree in morphology and chemical composition is a widely known phenomenon. High solar radiation - visible and UV-B light - can be damaging to plant cells by promoting the accumulation of highly reactive oxygen species (ROS), like singlet oxygen, causing oxidative stress. Acclimation to high light is based on two main protective mechanisms that help preventing damage: direct energy dissipation from the photosystems and scavenging of ROS by the antioxidant system. 

Our research aim was to connect antioxidant content, specific ROS scavenging ability and acclimation potential of leaves grown under different light conditions. Therefore we collected leaves from the sunny and shaded side of a linden (Tilia platyphyllos L.) tree and characterized them in terms of photosynthesis (photochemical yield and energy dissipation) and antioxidant capacity (singlet oxygen scavenging ability). We found that sun leaves were not more effective in energy dissipation but had significantly (5-fold) higher singlet oxygen scavenging ability then shade leaves.

We needed a characterization of the leaf metabolites which are potential singlet oxygen scavengers. As flavonoids are important as antioxidants and have singlet oxygen scavenging ability, we chose to analyze these compounds in our samples finding collaboration within this COST Action with Prof. Monika Schreiner and coworkers from the Leibniz-Institute of Vegetable and Ornamental Crops, as experts on this field. We found that sun leaves contained significantly higher amounts of all the three flavonoid aglycones present in large-leaved linden leaves: quercetin, kaempferol and myricetin. The difference in quercetin content was the most significant.

In the frame of this cooperation we could show that leaves grown under higher solar radiation with higher amounts of UV-B has elevated concentrations of flavonoids and these compounds are important in the high light acclimation of these leaves through their singlet oxygen scavenging ability. These results will help the understanding of the acclimation of leaves to solar light. A joint publication on the acquired results is in preparation and the results of the work will also form a part of my PhD thesis. I am grateful for the possibility of visiting this institute and we hope that this work served as a starting point of long-term collaboration between the two groups.