Acyl-acyl carrier protein (ACP) thioesterase (TE) catalyze the hydrolysis of the thioester bond that links the acyl chain to the sulfhydryl group of the phosphopantetheine prosthetic group of ACP. This reaction terminates acyl chain elongation of fatty acid biosynthesis, and in plant seeds it is the biochemical determinant of the fatty acid compositions of storage lipids. A full-length cDNA of an acyl-ACP thioesterase, named CvFatB, was isolated from oil plant Cuphea viscosissima accumulating up to 90% caprylate (8:0) and caprate (10:0) in its seed oil. This cDNA contains a 1,245-bp open reading frame that encodes a protein of 415 amino acids. The deduced sequence also contains two essential residues (H317 and C352) for TE catalytic activity and a putative chloroplast transit peptide at the N-terminal. Overexpression of the CvFatB cDNA in Arabidopsis resulted in increased levels of saturated fatty acid, especially palmitate, and reduced levels of unsaturated fatty acids. The findings suggest that CvFatB from oil plant C. viscosissima can function as a saturated acyl-ACP TE and can potentially be used to diversify the fatty acid biosynthesis pathway to produce novel fatty acids.

The influences of ethylene inhibitors (AgNO3 and silver thiosulfate) and cytokinins (BAP and TDZ) on shoot regeneration from cotyledon and hypocotyl explants of B. napus cv. Youngsan were investigated. The presence of 50 μM Silver thiosulfate (STS) in shoot regeneration medium formed shoots at 60-68% after 3-4 weeks of culture, which was enhanced by 2-fold compared to that of Silver nitrate (AgNO3). Moreover, cotyledon explants were more regenerative than hypocotyls; shoots from cotyledon explants began to occur 4-5 days earlier than that of hypocotyl explants. TDZ at a concentration of 8-10 μM was effective for shoot regeneration, compared with BAP. Consequently, the optimal shoot regeneration response was observed in medium supplemented with 50 μM STS + 8 μM TDZ. In transmission electron microscopy (TEM) analysis, higher density of silver nanoparticles was shown to be accumulated widely inside the cell wall and plasmodesmata of regenerating leaf cultured in medium supplemented with AgNO3. By contrast, in the cell cultured in medium with STS, fine-grained deposits were partly observed in the surroundings of the cell wall.