Rubber and other hydrocarbons produced in tissue cultures of guayule ( Parthenium argentatum)

Abstract

Callus cultures were initiated in leaf and influorescence explants from mature guayule rubber plants ( Parthenium argentatum). Initial cultures were morphologically heterogeneous and contained leaf and shoot primordia. These structures were substantially eliminated by serially subculturing only the least organized callus-like tissues. The selected calli from inflorescences have exhibited stable morphogenetic properties and growth rates for over one year. These cultures produced chlorophyll when grown under illumination and chemical analyses of both light- and dark-grown calli showed the presence of alkanes, sesquiterpenoids and cis-1,4-polyisoprene (rubber). Callus contained the same alkane species that were previously found in leaves of mature plants. Similarly, the predominant n-alkanes in both callus and plants had the carbon chain lengths C 29 and C 31. The proportions of alkane size classes differed between tissue sources. A change in pattern from longer to shorter alkanes was found according to the order: mature leaves, light-grown callus and dark-grown callus. Two sesquiterpene phenolic esters (guayulin-A and -B), allergenic compounds found in guayule plants, were present in guayule callus at about 4% of levels found in whole plants. Light had a negligible influence on production of the guayulins but showed a larger effect on rubber synthesis; light-grown callus produced about ten times the amount of rubber produced by dark-grown callus. The appearance of these important secondary hydrocarbons in long-term guayule tissue cultures represents a useful system for further studies of the regulation of these chemicals.