Fatty Acids Composition of Brachyblast and Auxiblast Lipids in Siberian Larch (Larix sibirica Ledeb.) Needles

The changes in the fatty acids (FAs) composition and the activity of acyl-lipid desaturases in lipids of needles formed on perennial shortened shoots—brachyblasts and annual elongated shoots—auxiblasts of Siberian larch ( Larix sibirica Ledeb.) during their spring–summer–autumn growth and development in the Irkutsk region were studied. It was found that in the lipids of brachyblast needles at the leaf-out stage (early May), the unsaturation indices (U/S and DBI) are characterized by the lowest values (0.16 and 0.25, respectively). With an increase in air temperature, they increase significantly and become close in value to those of auxiblast needles, regardless of the development phase of the latter (about 3.0 and 2.0 U/S and DBI, respectively). During the growing season, the ODR index was the highest and relatively stable in the needles of both shoot types. In the shoot stems, its values were lower but equal to the SDR index (0.75–0.85), which gradually increased from June to October. Significant differences were observed in the LDR index, which was at least four times higher in the needles than in the stems. Among the rare FAs characteristic of conifers, pinole FA stands out; its content in auxiblast stems varies from 10 to 16%, while in the needles of both shoot types, its values are half as much. The combined data revealed both similarities and differences in the FAs composition and activity of acyl-lipid desaturases in the needles of different shoot types—brachyblasts and auxiblasts. At the same time, their FAs composition differs significantly from that of auxiblast stems, which is likely due to different but complementary functions: needle lipids promote active photosynthetic function, while auxiblast stem lipids facilitate successful preparation for survival in the low, subzero temperatures of the upcoming winter.