Cold acclimation has a differential effect on leaf vascular bundle structure and carbon export rates in natural Arabidopsis accessions originating from southern and northern Europe
Acclimation to low but non-freezing temperature represents an ecologically important process for Arabidopsis thaliana but also for many other plant species from temperate regions. Cold acclimation comprises and affects numerous molecular and physiological processes and the maintenance of sugar supply of sink tissue by photosynthetically active source tissue is preliminary for plant survival. Here, we analysed the correlation of changes in vascular bundle structure at the leaf petiole and sucrose exudation rates before and after cold acclimation. We compared six natural Arabidopsis accessions originating from southern and northern Europe. Photosynthetic capacities, i.e. maximum and effective quantum yield of photosystem II, revealed a significant effect of condition but not of genotype. Only for northern accessions we observed a highly significant negative correlation between leaf sucrose exudation rates, xylem and petiole cross section areas. Further, only for northern accessions we observed a significant increase of vascular bundle and leaf petiole cross section area during cold acclimation. In contrast, variance of cross section areas of cold acclimated southern accessions was strongly reduced compared to control plants while mean areas remained similar under both conditions. In summary, our findings suggest that natural Arabidopsis accessions from northern Europe significantly adjust sink strength and leaf vascular bundle structure to stabilize plant growth and photosynthesis for survival under low and freezing temperature.