Epsilon Open Archive

Abstract

Since trees are sessile they have evolved elaborate mechanisms that anticipate oncoming winter and allow the trees to withstand extreme changes in their environment. Trees need to stop growth and initiate cold hardiness well before cold temperatures become damaging, consequently the timings of growth cessation and dormancy are important adaptive traits for their ability to survive in harsh winter conditions. If the trees fail to anticipate the onset of winter they will suffer severe damage, whereas early growth cessation will reduce the growing season and their productivity, thereby causing loss of fitness. Thus, the optimal timing of growth cessation is the point at which these risks are balanced. Hence, plants from different latitudes have different critical daylengths, and cease growth at different times. In the work this thesis is based upon, my colleagues and I examined changes in the transcription of genes involved in various processes that are co-induced by shorter than critical daylengths, e.g. cold hardiness and the production of storage proteins. In addition, we showed that differences in growth cessation timing in trees also depends on other factors acting downstream of daylength sensing. Abscisic acid (ABA) is a plant hormone that is known to play an important role in seed dormancy and also has proposed involvement in bud dormancy. It is known that ABA levels increase after growth cessation, concurrently with the establishment of dormancy, suggesting that it may play a role in dormancy induction. To further investigate this possibility we constructed trees with reduced sensitivity to ABA. These trees were unable to enter dormancy. In summary, this thesis describes molecular-level investigations of growth cessation and the transition to dormancy, in which microarrays, real-time polymerase chain reaction assays and transgenic hybrid aspen were used. Through better understanding of how trees perceive light signals and subsequent events, in the future it may be possible to engineer trees with altered activity-dormancy transition traits to improve their productivity.