cis-3-Hexenal production in tobacco is stimulated by 16-carbon monounsaturated fatty acids.
Transgenic tobacco plants O9 and T16 expressing the yeast acyl-CoA Delta9 desaturase and an insect acyl-CoA Delta11 desaturase, respectively, displayed altered profiles of fatty acids compared to wild-type tobacco plants and marked increases in cis-3-hexenal, a major leaf volatile derived from alpha-linolenic acid (18:3). As expected, O9 and T16 plants had increased levels of the major unsaturated fatty acid products formed by the transgenic desaturases they expressed, viz., palmitoleic acid (16:1(Delta9)) and palmitvaccenic acid (16:1(Delta11)), respectively. In addition, levels of 18:3 lipid declined slightly and the pool of free 18:3, which accounts for about 30% of free fatty acids in wild-type plants, disappeared completely in both transgenics. Both O9 and T16 plants were found to have a two-fold increase in 13-lipoxygenase (13-LOX) activity, which catalyzes the first of two steps leading to hexenal production from 18:3. In O9 and T16 plants, the activity of 9-lipoxygenase and hydroperoxide lyase, the latter catalyzing the formation of cis-3-hexenal from alpha-linolenic acid hydroperoxide, was significantly different from that of the wild-type plants. Although 16:1(Delta9) and 16:1(Delta11) had no direct effects on 13-LOX activity in vitro, cis-3-hexenal production increased in tobacco leaves treated with these fatty acids, suggesting that they may act in vivo by stimulating 13-LOX gene expression.
Hong
Mei
M
Department of Plant Biology and Pathology, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901-8520, USA.
Zilinskas
Barbara A
BA
Knipple
Douglas C
DC
Chin
Chee Kok
CK
D000446:Aldehyde-Lyases / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004952:Esters; D044943:Fatty Acid Desaturases / Q000235:genetics / Q000378:metabolism; D005227:Fatty Acids / Q000032:analysis / Q000737:chemistry / Q000494:pharmacology; D005231:Fatty Acids, Unsaturated / Q000737:chemistry / Q000494:pharmacology*; D006591:Hexobarbital / Q000031:analogs & derivatives / Q000378:metabolism*; D006838:Hydrocarbons / Q000032:analysis / Q000737:chemistry; D008084:Lipoxygenase / Q000378:metabolism; D013058:Mass Spectrometry / Q000379:methods; D018515:Plant Leaves / Q000737:chemistry / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism*; D013237:Stereoisomerism; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014835:Volatilization
D004952:Esters; D005227:Fatty Acids; D005231:Fatty Acids, Unsaturated; D006838:Hydrocarbons; D003577:Cytochrome P-450 Enzyme System; D006591:Hexobarbital; C117433:13-lipoxygenase; D008084:Lipoxygenase; D044943:Fatty Acid Desaturases; D000446:Aldehyde-Lyases; C054540:hydroperoxide lyase