Temperature-related shifts in soluble carbohydrate content during dormancy and cold acclimation in Populus tremuloides

Changes in metabolism that accompany cold acclimation and deacclimation, such as increasing levels of raffinose family oligosacharides (RFO) during cold acclimation demonstrated in several woody species, are of interest in a search for genetic control of environmental adaptation by cold-hardy woody plants. This study examined the relationship of temperature to endodormancy and cold hardiness in trembling aspen (Populus tremuloides Michx.) buds collected at 1560, 2250, and 2900 m elevation near Fort Collins, Colo. Buds from all sites tolerated at least –85°C in December, and buds from 2900 m, the highest elevation, hardened most quickly in fall and retained their hardiness the longest in late winter and early spring. Exposure to liquid nitrogen caused bud break in normally endodormant (15 November collection date) buds. RFO levels were highly correlated to low temperature during acclimation and to lowest survival temperatures. Endogenous raffinose and stachyose increased as temperatures dropped in early winter and diminished as temperatures rose in spring. Arrhenius plots showed that raffinose accumulation was strongly low-temperature dependent during acclimation. Its loss, while also temperature dependant in spring, was not as pronounced as during fall acclimation. Buds from all three sites survived cryopreservation at –196°C when first prefrozen at 5°C/h and stored >4 h at –20°C or colder. Differential scanning calorimetry data suggest that an aqueous component froze separately from tissues that underwent a glass transition in buds that survived cryopreservation. This study documents a complete dormant season hardiness profile of aspen linking hardiness with changes in endogenous soluble sugars.