Heterogeneity of photosynthetic light acclimation within single leaves of Fagus sylvatica

Abstract Key message Rolled sun leaves of Fagus sylvatica L. showed strong heterogeneous light acclimation of the photosynthetic apparatus across the leaf lamina as reflected in blue light excited chlorophyll fluorescence. Abstract Many grasses, but also dicotyledonous species have rolled leaves, which is interpreted as a resistance mechanism against drought. Rolled leaves intercept less light, which causes a reduced heat load but may also induce an acclimation of the photosynthetic apparatus to reduced irradiance. We have investigated the light acclimation of different parts of permanently rolled leaves of beech ( Fagus sylvatica L.) using various methods based on chlorophyll fluorescence as well as by HPLC analysis of photosynthetic pigments. Chlorophyll fluorescence emission excited by blue light showed a strong heterogeneity across the leaf lamina, with the highest emission in the upward bent sides of the leaf and minimal emission in the center and tip of the lamina. Heterogeneity was absent in flat shade leaves and the flat sun leaves of another beech tree and also in all types of leaves when red light was used for fluorescence excitation. Since blue-induced fluorescence intensity was negatively correlated with the pool size of the violaxanthin cycle, it is concluded that the heterogeneity in blue light-excited fluorescence was caused by the variation of these carotenoid pigments across the leaves. Also light saturated electron transport rate and sensitivity to photoinhibition indicated shade acclimation of the upward bent leaf sides. It is concluded that leaf rolling in beech leaves may also have a photoprotective function.