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

Changes in metabolism that accompany cold acclimation and deacclimation, su ch as increasing levels of raffinose family oligosacharides (RFO) during co ld 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 co llected at 1560, 2250, and 2900 m elevation near Fort Collins, Colo. Buds f rom all sites tolerated at least -85 degreesC in December, and buds from 29 00 m, the highest elevation, hardened most quickly in fall and retained the ir hardiness the longest in late winter and early spring. Exposure to liqui d nitrogen caused bud break in normally endodormant (15 November collection date) buds. RFO levels were highly correlated to low temperature during ac climation and to lowest survival temperatures. Endogenous raffinose and sta chyose increased as temperatures dropped in early winter and diminished as temperatures rose in spring. Arrhenius plots showed that raffinose accumula tion was strongly low-temperature dependent during acclimation. Its loss, w hile also temperature dependant in spring, was not as pronounced as during fall acclimation. Buds from all three sites survived cryopreservation at -1 96 degreesC when first prefrozen at 5 degreesC/h and stored >4 h at -20 deg reesC or colder. Differential scanning calorimetry data suggest that an aqu eous component froze separately from tissues that underwent a glass transit ion in buds that survived cryopreservation. This study documents a complete dormant season hardiness profile of aspen linking hardiness with changes i n endogenous soluble sugars.