Submitted to: Phytochemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/11/2006
Publication Date: 12/6/2006
Citation: Bushman, B.S., Scholte, A.A., Cornish, K., Scott, D.J., Brichta, J.L., Vederas, J.C., Ochoa, O., Michelmore, R.W., Shintani, D., Knapp, S.J. 2006. Identification and comparison of natural rubber from two lactuca species. Phytochemistry. Interpretive Summary: Natural rubber is an essential and strategic commodity. Sources of natural rubber alternative to Hevea brasiliensis have been investigated for decades, but few plants produce high molecular weight rubber that is correlated to the high quality characteristics. In this report, we characterized high molecular weight rubber in the latex of two closely related lettuce species. We found that latex from lettuce has high molecular weight rubber in it, has a narrow polydispersity range, and has variation in rubber transferase enzyme activity. Additionally, as lettuce has extensive agronomic and genomic resources available, it could be used as an experimental system to dissect genetic, molecular, and biochemical biosynthesis of rubber.
Technical Abstract: Renewed interest in the identification of alternative sources of natural rubber to Hevea brasiliensis has focused on the Compositae family. In our search for Compositae models for rubber synthesis, we extracted latex from stems of two lettuce species: Lactuca serriola, prickly lettuce, and Lactuca sativa cv. Salinas, crisphead lettuce. Both species contained cis-1,4-polyisoprene rubber in the dichloromethane-soluble portions of their latex, and sesquiterpene lactones in their acetone-soluble portions. The rubber from both species and their progeny had molecular weights in excess of 1,000,000 g/mol, and polydispersity values of 1.1. Rubber transferase activity was detected across a range of farnesyl diphosphate initiator concentrations, with decreased activity as initiator concentrations exceeded putative saturation. These results add lettuce to the short list of plant species that produce high molecular weight rubber in their latex. Due to the genomic and agronomic resources available in lettuce species, they provide the opportunity for further dissection of natural rubber biosynthesis in plants.