Monoterpene synthase activities in leaves of Picea abies (L.) Karst. and Quercus ilex L.

摘要

In addition to direct ecological functions in the interaction of plants with the environment, the emission of monoterpenes, especially from the foliage of evergreen trees, is of great importance for the production of ozone and photochemical oxidantsin the troposphere. In the present work, a reproducible non-radioactive standard enzyme assay was established, and the monoterpene synthase activities in needles of Norway spruce (Picea abies (L.) Karst.) and in leaves of holm oak (Quercus ilex L.) werecharacterized. In Norway spruce, the dominant monoterpenes formed were alpha-pinene, camphene, and to a lesser extent beta-pinene and limonene. In holm oak, alpha-pinene, sabinene, and beta-pinene were the main products, while limonene was a minor component. Under optimum conditions, in both Norway spruce and holm oak, monoterpene formation remained constant up to 180 min and 90 min, respectively, and varied with the buffer and Mg2+ and Mn2+ concentrations used. Optimum temperature for monoterpene synthase activity was 40deg C in both species; optimal pH ranged between 6.5 and 7.5 in both species. Apparent Michaelis-constants for the substrate GDP were ca. 17.9±5.1μM for Norway spruce and ca. 69.4±22.1μM for holm oak. Molecular weight determination byFPLC indicated that the monoterpene synthases in Norway spruce and holm oak have native molecular weights of ca. 59 and 50 kDa, respectively.