Sammendrag
Cold response and freezing tolerance of perennial crops such as the cultivated strawberry (Fragaria ananassa Duch.) is of major interest for Norwegian breeders and farmers due to the harsh climatic conditions in Norway. The successful production of the cultivated strawberry relies on the plants ability to acclimate to cold, survive winter and re-grow in spring. Physiological, biochemical and molecular changes occur in plant systems upon cold stress. To understand the stress responses occurring in plants several projects have been carried out resulting in characterisation of many genes and the identification of functional roles of proteins in stress responses. Here both Fragaria ananassa and the woodland strawberry (Fragaria vesca) have been utilized to assess short- and long-term effects of cold treatment on metabolic regulation and metabolite patterns in Fragaria sp. The following two experimental sections were set up to cover different aspects of plant cold acclimation processes: Ten different genotypes of Fragaria vesca and one cultivar of Fragaria nubicola were subjected to chilling temperatures under controlled temperature conditions. To examine the cold hardiness of Fragaria ananassa, cultivars Polka and Honeoye were grown in a field outside under natural environmental conditions. GC-MS-based metabolic profiling was applied. Different genotypes of Fragaria vesca showed an up-regulation of the citric acid cycle, the accumulation of sugars and an increase in amino acids. Some genotypes seemed better adapted to cold exposure than others. The two cultivars of Fragaria ananassa also displayed increases in citric acid cycle activity and the accumulation of sugar. The cultivar Honeoye seemed to adapt better to low temperatures than the cultivar Polka. Accumulation of sugar seems to be an adaptation to low temperature which is present in both wild and cultivated strawberries. However, variation between genotypes and cultivars in sugar accumulation and level of amino acid production suggests the presence of adaptive variation in cold stress responses. Results from this study suggest some pathways for metabolic regulation of cold stress tolerance, but further studies are needed to test whether this is caused by regulatory variation or genetic differences. This is needed in order to be able to for example genetically modify cold tolerance of cultivated strawberried in the future.
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