Dormancy, cold hardiness and height growth were examined in four poplar clones exposed to four temperature conditions (13.5ºC/8.5ºC, 18.5ºC/3.5ºC, 18.5ºC/13.5ºC and 23.5ºC/8.5ºC day/night temperatures) under short photoperiod. The selected clones were WP-69 (Okanese)- early acclimation, Walker and Katepwa - intermediate acclimation, and Prairie Sky- late acclimation. Changes in physical water properties and mobility within the vascular tissue region, vascular transition region into the axillary bud and the upper axillary bud were assessed during endodormancy development using Magnetic Resonance Microimaging (MRMI). <p>In summary:<br>a) There were distinct differences between poplar clones during dormancy induction in response to temperature. For example, Katepwa, Walker and WP-69 clones became endodormant but Prairie Sky did not enter endodormancy. Endodormancy development and cold acclimation in WP-69 were less affected by temperature than Katepwa and Walker suggesting that genotypic variation exists in response to temperature change.<p>b) Growth cessation, not endodormancy, was a prerequisite for cold acclimation since cold hardiness increased in Prairie Sky in the absence of endodormancy. However, increases in endodormancy coincided with increase in cold hardiness in other clones.<p>c) Low night temperatures (18.5ºC/3.5ºC) delayed endodormancy development and cold acclimation in all clones compared to the warm night temperature treatment (18.5ºC /13.5ºC). Night temperature was negatively correlated with time to growth cessation, and cold hardiness and positively correlated with dormancy development. Changes in night temperature may affect time to growth cessation, subsequently altering timing of cold acclimation and endodormancy development since growth cessation appeared to be a prerequisite for both processes. <p>d) ADC (Apparent Diffusion Coefficient), an indicator of water mobility within living tissues, was negatively correlated with endodormancy induction. Specifically, the transition region of vascular tissue between the stem and the lower axillary bud showed the highest correlation with endodormancy development. By contrast, decreases in T1 relaxation times, an indicator of biophysical water properties, were inconsistent with changes in endodormancy levels in axillary buds. Thus, ADC appears to correspond more closely with endodormancy development than changes in T1 relaxation times. <p>It is apparent that temperature impacts dormancy development in hybrid poplar. Underlying changes in water appear to correspond with changes in endodormancy. Under future warming scenarios, genotypes such as WP 69 (Okanese) that are less sensitive to temperature and maintain a consistent, endodormancy induction pattern, may be better fit to changing climates.

Dormancy, cold hardiness and height growth were examined in four poplar clones exposed to four temperature conditions (13.5ºC/8.5ºC, 18.5ºC/3.5ºC, 18.5ºC/13.5ºC and 23.5ºC/8.5ºC day/night temperatures) under short photoperiod. The selected clones were WP-69 (Okanese)- early acclimation, Walker and Katepwa - intermediate acclimation, and Prairie Sky- late acclimation. Changes in physical water properties and mobility within the vascular tissue region, vascular transition region into the axillary bud and the upper axillary bud were assessed during endodormancy development using Magnetic Resonance Microimaging (MRMI). <p>In summary:<br>a) There were distinct differences between poplar clones during dormancy induction in response to temperature. For example, Katepwa, Walker and WP-69 clones became endodormant but Prairie Sky did not enter endodormancy. Endodormancy development and cold acclimation in WP-69 were less affected by temperature than Katepwa and Walker suggesting that genotypic variation exists in response to temperature change.<p>b) Growth cessation, not endodormancy, was a prerequisite for cold acclimation since cold hardiness increased in Prairie Sky in the absence of endodormancy. However, increases in endodormancy coincided with increase in cold hardiness in other clones.<p>c) Low night temperatures (18.5ºC/3.5ºC) delayed endodormancy development and cold acclimation in all clones compared to the warm night temperature treatment (18.5ºC /13.5ºC). Night temperature was negatively correlated with time to growth cessation, and cold hardiness and positively correlated with dormancy development. Changes in night temperature may affect time to growth cessation, subsequently altering timing of cold acclimation and endodormancy development since growth cessation appeared to be a prerequisite for both processes. <p>d) ADC (Apparent Diffusion Coefficient), an indicator of water mobility within living tissues, was negatively correlated with endodormancy induction. Specifically, the transition region of vascular tissue between the stem and the lower axillary bud showed the highest correlation with endodormancy development. By contrast, decreases in T1 relaxation times, an indicator of biophysical water properties, were inconsistent with changes in endodormancy levels in axillary buds. Thus, ADC appears to correspond more closely with endodormancy development than changes in T1 relaxation times. <p>It is apparent that temperature impacts dormancy development in hybrid poplar. Underlying changes in water appear to correspond with changes in endodormancy. Under future warming scenarios, genotypes such as WP 69 (Okanese) that are less sensitive to temperature and maintain a consistent, endodormancy induction pattern, may be better fit to changing climates.

Norway spruce (Picea abies L. Karst) is a conifer belonging to the group gymnosperms and is an ecologically and economically important species in several parts of Europe. It is crucial for trees like Norway spruce to adapt timing of events such as bud set and growth cessation to the local environment in order to maximize the growth period while avoiding frost damage. This thesis aims at widening the knowledge about genetic control of annual growth rhythm in Norway spruce and particularly the control of bud set. Using spruce transformants ectopically expressing PaFT/TFL1-LIKE 2 (PaFTL2) the prior hypothesis that PaFTL2 induces bud set is confirmed. This is further supported by spatial and temporal expression patterns in seedlings and adult trees. It is further shown that gymnosperms possess at least two FLOWERING LOCUS T/TERMINAL FLOWER 1 (FT/TFL1)-like genes with TFL1-like function, suggesting the ancestor of FT and TFL1 to be more TFL1-like. PaFTL1 appears to have complementary expression patterns to that of PaFTL2 both spatially and temporally indicating they may act together to control growth in Norway spruce. Since bud set is controlled by photoperiod and circadian clock genes are implicated in this process, putative clock homologs were studied to gain insight into the circadian clock in gymnosperms. Several clock homologs were identified and their expression showed a diurnal pattern but the expression was rapidly damped in constant conditions. Transgenic Arabidopsis expressing putative core clock genes from spruce indicate that at least three genes, PaCCA1, PaGI and PaZTL, appear to have a conserved function between angiosperms and gymnosperms. Taken together these results suggest that gymnosperms have a similar core clock structure as angiosperms even though fundamental differences might exist since the cycling of the clock genes were rapidly damped in free-running conditions. The studies presented in this thesis support substantial conservation of pathway components controlling photoperiodic responses in angiosperms and gymnosperms and identify PaFTL2 as a component of growth rhythm control. However, important changes in these processes are also evident. The results provide a solid basis for future research on molecular mechanisms controlling an adaptive trait in an important non-model organism.