Carbohydrates in white spruce and lodgepole pine seedlings during winter : outdoors, in freezer-storage and in thawing
Creators: name: Lévesque, Françoise
Publisher: name: University of British Columbia
Year: 2009

description: Studies were conducted to examine factors associated with total non-structural carbohydrate (TNC) depletion during winter, either outdoors, in freezer-storage or in thawing. To see if TNC depletion was mainly due to respiration, two experiments were conducted. In Experiment 1, respiratory C02 evolution of white spruce (Picea glauca (Moench) Voss.) was monitored in -2°C storage for 4 months and in +2°C and +7°C thawing regimes for 6 weeks. In Experiment 2, white spruce and lodgepole pine (Pinus contorta Dougl.) respiration was monitored in -2°C storage for 2 months. In the following 6 weeks of +2°C and +7°C thawing regimes, only spruce respiration frost hardiness in storage. Starch synthesis occurred in -2°C storage although no clear environmental signals could have triggered this activity. Soluble sugars were analyzed by HPLC to explore sugar dynamics in relation to frost hardiness and growth resumption. Spruce and pine seedlings from outdoors, the 4 months freezer-storage treatment and the +2°C thawing regime were analyzed. Contents of individual sugars were plotted against frost hardiness to identify any relationship to dehardening. The results suggested that shoot raffinose content is well correlated with hardiness of spruce and pine. More species and conditions need to be tested to establish the strength of this relationship. To explore the possibility of root to shoot CH2O transport via phloem, white spruce seedlings were girdled at the collar zone. Intact and girdled seedlings were freezer-stored for 4 months and transferred to a +2°C thawing regime for 4 weeks. Thereafter, the temperature in thawing was increased to +7°C for 2 additional weeks. Shoot and root TNC content were compared for intact and girdled seedlings. The results showed that significant phloem transport was not likely in -2°C storage or when seedlings were exposed to +2°C for 4 weeks. However, once transferred to +7°C, there was a disproportionate accumulation of free sugars in roots of girdled seedlings, suggesting that normal root to shoot phloem transport was blocked. monitoring was considered in Experiment 2. TNC was measured every month beginning in December in white spruce and lodgepole pine for seedlings overwintered outdoors for 3 months, for seedlings left outdoors 2 months and then lifted in February for freezer-storage, and for seedlings freezer-stored for 4 months. TNC was also measured twice during the two thawing regimes for seedlings cold-stored for 2 and 4 months. Respiration rates and TNC depletion were compared. Frost hardiness was monitored for spruce and pine at months 0, 2 and 4 during freezer-storage and every two weeks during thawing. For seedlings kept outdoors, frost hardiness was monitored at months 0, 2 and 3. Respiration increased following a disturbance (e.g. lifting for storage) but stabilized at a lower steady-state rate thereafter. Measured TNC depletion matched respiration rate in the 4 months freezer-storage but not in any other cases. The Q10 calculated between -2°C and +2°C was found to be extreme for steady-state respiration rates, indicating a disproportionate increase in activity when seedlings are transferred from freezer-storage to thawing. Frost hardiness was released relatively slowly following 4 months of freezer-storage. Dehardening was faster for seedlings kept outdoors. Seedlings placed in freezer-storage in February were able to regain