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Title: Magnesium affects rubber biosynthesis and particle stability in Ficus elastica, Hevea brasiliensis and Parthenium argentatum

Author
item XIE, WENSHUANG - OHIO AGRICULTURAL RESEARCH & DEVELOPMENT CENTER
item CORNISH, KATRINA - OHIO AGRICULTURAL RESEARCH & DEVELOPMENT CENTER
item McMahan, Colleen
item WHALEN, MAUREEN
item SHINTANI, DAVID - UNIVERSITY OF NEVADA
item COFFELT, TERRY
item MATTOSO, LUIS - EMBRAPA

Submitted to: Association for the Advancement of Industrial Crops Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/22/2015
Publication Date: 9/22/2015
Citation: Xie, W., Cornish, K., Mcmahan, C.M., Whalen, M.C., Shintani, D.K., Coffelt, T.A., Mattoso, L.H. 2015. Magnesium affects rubber biosynthesis and particle stability in Ficus elastica, Hevea brasiliensis and Parthenium argentatum. Association for the Advancement of Industrial Crops Conference. 7:292-299.

Interpretive Summary: More than 12,000 plant species produce latex. Natural rubber, cis-1.4-polyisoprene, is an important component in some lattices and a major industrial product harvested from the latex of Hevea brasiliensis. Natural rubber is produced in laticifers of Ficus elastica and H. brasiliensis, and in parenchyma cells of Parthenium argentatum. Rubber biosynthesis takes place via rubber transferase, a membrane bound protein complex on rubber particles, with isopentenyl pyrophosphate (IPP) as the monomer, an allylic pyrophosphate (farnesyl pyrophosphate, FPP) as an initiator, and magnesium ions as cofactor/activator. Previous studies demonstrated that the optimal concentrations of magnesium are different among the three natural rubber species. Our data indicates that magnesium concentration affects rubber particle stability and biosynthesis in F. elastica, H. brasiliensis and P. argentatum.

Technical Abstract: Natural rubber biosynthesis occurs in laticifers of Ficus elastica and Hevea brasiliensis, and in parenchyma cells of Parthenium argentatum. Natural rubber is synthesized by rubber transferase using allylic pyrophosphates as initiators, isopentenyl pyrophosphate as monomeric substrate and magnesium as co-factor. Magnesium concentration affects rubber transferase activity and rubber molecular weight in H. brasiliensis and P.argentatum in in vitro studies. Maximum rubber transferase activity occurred at about 1 mM magnesium and was inhibited by magnesium concentrations above 10 mM in all three species. Magnesium ions were more readily washed from the F. elastica rubber particles than from either H. brasiliensis or P. argentatum during the purification protocol. Rubber transferase activity, in latex tapped from individual F. elastica plants, varied among plants but was below the maximum activity determined in vitro, suggesting that the living plants might have inhibitory magnesium levels in their laticifer cytosol. When H. brasiliensis rubber particles were purified in the absence of magnesium, and then assayed (in the presence of magnesium), they had half the activity of particles purified in the presence of magnesium, possibly due to irreversible destabilization of some of the rubber transferase enzyme complexes.