Plant Symposia

Freezing tolerance is a key factor limiting the geographical distribution of plant species and agricultural yield. Plants from temperate regions increase their freezing tolerance in response to low, non-freezing temperatures in a process termed cold acclimation. Natural variability in the freezing tolerance of Arabidopsis thaliana was phenotyped by electrolyte leakage analysis in 54 accessions from throughout the Northern hemisphere under non-acclimated and acclimated conditions. Additionally, analysis of secondary metabolites was performed using liquid chromatographymass spectrometry (LC-MS). This revealed a massive accumulation of flavonols and anthocyanins during cold acclimation. The patterns of these compounds differed significantly between accessions. Further, the expression of genes encoding transcription factors and enzymes involved in flavonoid biosynthesis was investigated by qRT-PCR. Comprehensive correlation analysis allowed the identification of genes and metabolites that are closely connected in their respect ive pathways. Comprehensive studies of k.o. mutants and over-expressors of different steps in the flavonol and anthocyanin biosynthesis pathway indicated a functional role of specific groups of these molecules in plant freezing tolerance. In addition to many metabolites, COR proteins are massively induced during cold acclimation. We investigated the role of chloroplast-localized COR15A and COR15B in RNA interference knock-down and in over-expression lines, which showed that COR15 proteins are necessary for Arabidopsis to achieve full cold acclimation. Enzyme activity measurements indicated that different chloroplast enzymes differ in their in-vivo freeze-thaw stability. However, while cold acclimation increased the freezing stability of some enzymes, the absence or presence of COR15 proteins had no influence on enzyme activity after freezing, ruling out a role of COR15 proteins in enzyme stabilization in vivo. Rather, our data support a role of COR15 proteins in stabilizing cellular membranes. P-2