In temperate regions the deep-rooted perennial sow-thistle Sonchus arvensis L. is a common agricultural weed due to its effective reproductive system and is regarded a threat to the growth of crops, particularly in organic farming. To manage harsh environmental conditions during the season, plant life history traits have evolved, known as dormancy. Previous studies have proposed that both dehydrins (DHN) and PIN-FORMED (PIN) proteins are important parts of this adaptation by preventing structural damage, maintaining essential enzyme activity during cold and affecting basipetal polar auxin transport, respectively. The aim of this study was therefore to investigate the expression pattern of dehydrins and PIN proteins in root buds of S. arvensis going through a seasonal dormancy cycle and see how they correlated to known dormancy phases in S. arvensis. In this study, phenology, root morphology and protein patterns, as well as of PIN2, PIN3 and DHNs accumulation pattern as detected with immunoblotting, all indicated that clear changes occur between the early and later stages of the buds. High levels of PIN3 in rootbuds from plant collected in August decreased later in season, which support the hypothesis of its involvement in auxin transport and thereby regulating paradormancy of adventitious buds. In October, another dramatic change in protein pattern that took place when buds entered dormancy and prepared for chilling temperature. Results from this study show that DHNs level increased in October. This support the hypothesis that DHNs are involved in the adaptation protecting the buds from winter conditions.