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Acyl-CoA binding protein (ACBP) ubiquitously found in eukaryotic organisms fulfills important functions of solubilisation, protection and transport of acyl-CoA esters, a major intermediate of lipid metabolism. This thesis presents an investigation of the physiological role of the small cytosolic ACBP in seed oil biosynthesis. The second important objective of this study was to evaluate the use of ACBP as a molecular tool for modification of seed oil content and/or fatty acid (FA) composition. Agrobacterium-mediated transformation of Arabidopsis thaliana and Brassica napus was performed with a number of genetic constructs designed for seed-specific expression of the B. napus cDNA encoding a small cytosolic ACBP. Protein level and subcellular localization of BnACBP in A. thaliana transgenic seeds depended on the structure of the genetic constructs mainly, the presence of additional in-frame sequences, encoding a protein fusion partners or signal peptides. Seed oil from A. thaliana T2 and T3 seeds had increased polyunsaturated fatty acid (PUFA) percentage (18:2cis delta9,12 and, in some lines, 18:3cis delta9,12,15) at the expense of very-long-chain monounsaturated (20:1cis delta11) and saturated (18:0) fatty acids. An increase in PUFA levels in seed oil was due to enhanced acyl channeling from the acyl-CoA pool to phosphatidylcholine, the substrate for extraplastidial FA desaturation. The activity of A. thaliana acyl-CoA: lysophosphatidylcholine acyltransferase (AthLPCAT), an enzyme involved in acyl exchange between acyl-CoA and PC, was significantly increased in the presence of the recombinant B. napus ACBP (rBnACBP) in the reaction mixture. rBnACBP also modulated enzymatic activities of glycerol-3-phosphate acyltransferase and diacylglycerol acyltransferase in vitro. Finally, the effect of constitutive or seed-specific gene silencing of ACBP on seed oil formation was examined. A. thaliana transformation with RNAi constructs resulted in partial suppression of ACBP expression and changes in FA composition of seed oil which included an increase in the percentage of 18:1cis delta9 and 18:2cis delta9,12 and, decrease of 18:3cis delta9,12,15. Overall, the results of this study demonstrate that the small cytosolic ACBP plays an important role in acyl exchange between acyl-CoA and PC metabolic pools. Overexpression of ACBP during seed development can be useful in genetic engineering strategies aimed at modifying the FA composition of seed oils. / Plant Science