Changes in triacylglycerol composition in the mesocarp of developing sea buckthorn fruit

The content of separate positional types and individual positional species of triacylglycerols (TAGs) in sea buckthorn fruit mesocarp from the 53rd to the 107th day after pollination was determined. The amount of most types and species of TAGs increased during fruit growth, and their composition at all stages of maturation found experimentally was close to that calculated according to the theory of 1,3-Random, 2-Random Distribution of fatty acids (FAs) between the respective hydroxy groups of glycerol. The rate constant of biosynthesis of Group A TAGs (S-3 + SSU + USU) during the period of maturation studied here exceeded the respective constant for Group B (SUS + SUU + U-3); the relative content of Group B in total TAGs was higher than 98%. In turn, this group could be divided, according to its positional-species composition, into four more groups (I-IV); their TAGs include residues of individual FA species, viz., palmitic, hexadecenoic, octadecenoic, and Linoleic (P, H, O, and L, respectively). Group I TAGs (PHH + PHP + HHH + PHO + HHO) were synthesized at a higher rate than those of Group II (POH + POP + HOH + POO + HOG) and Group III (PLH + PLP + HLH + PLO + HLO), and the TAGs of Group III, in turn, were synthesized more intensively than those of Group ZI. Such a pattern of TAG dynamics was brought about both by the quantitative type and species FA composition of total TAGs at each developmental stage, and by the affinity of separate FA species to the sn-2 and rac-1 positions of TAGs during biosynthesis. A possible mechanism of TAG formation in mesocarp is discussed.