The specific features of the fatty acid (FA) composition and activity of acyl-lipid desaturases in bud glycolipids were studied in silver birch (Betula pendula Roth) growing at the same latitude – 62° N but at different longitudes – 34° and 130° E – in Karelia and Yakutia, respectively. Studies showed that the changes happening in the winter-spring season in glycolipids within the chloroplast membranes of primordia developing inside buds were quite similar in both regions. To wit, the share of unsaturated FAs, which prevail over saturates FAs, grew from January through May. At the same time, the unsaturation index and the double bond index also increased. During the endogenous dormancy period in
Karelia (January-March), unsaturated FAs were dominated by dienoic acids, and after a temperature rise (in April-May) by trienoic FAs. The pattern in Yakutia was the same, but the rise in the share of trienoic FAs took place only by the onset of the growing season (in May), which is obviously due to low temperatures of both the air and the root layer of soil in a permafrost region. Awakening from exogenous dormancy was accompanied by a rise in the activity of ω9- and ω6-desaturases, as evidenced by high values of the indices representing stearoyl- (SDR) and oleoyl- (ODR) desaturase ratios, respectively.
A sharp rise in the LDR (linoleoyl-desaturase ratio) at the onset of the growing season suggests that an increase in the share of linolenic acid (induced by higher ω3-desaturase activity) is a factor that promotes the resistance of primordial shoot tissues both to abrupt air temperature variations in spring and to the change in the light conditions during bud break. Where in Karelia a rise in linolenic FA in glycolipids was observed already in April, in Yakutia in only happened in May. Having analyzed the new data and the literature, the authors have come to the conclusion that desaturase activity in winter is mainly governed by the overall physiological status of the tree, while the determinant in spring is the phase of primordia development inside the bud.