Impact of soluble sugar concentrations on the acquisition of freezing tolerance in accessions of Arabidopsis thaliana with contrasting cold adaptation -: evidence for a role of raffinose in cold acclimation

In the present study the cold acclimation potential of two accessions of Arabidopsis thaliana was investigated. Significant variation was found for basic tolerance as well as the capacity to acclimate to freezing temperatures. During cold acclimation, levels of soluble sugars increased in both genotypes, but raffinose accumulation discriminated the more tolerant accession Col-0 from C24. Concentrations of other compatible solutes such as proline and glutamine were also higher in cold-acclimated Col-0 than C24 plants. Changes of invertase activity during cold exposure corresponded to changes in sucrose and fructose, but not glucose concentrations and were consistent with an initial chilling response and a later decline in hexose metabolization. When vacuolar invertase was suppressed by siRNA expression, reduced sucrolytic activity resulted in elevated leaf sucrose concentration, whereas the fructose content was strongly reduced. This led to elevated freezing tolerance in the cold-tolerant genotype Col-0, but not in C24. The most pronounced metabolic changes in invertase-inhibited Col-0 plants occurred for proline and glutamine concentrations, indicating indirect metabolic effects of altered sugar concentrations.