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

In addition to direct ecological functions in the interaction of plants wit h the environment, the emission of monoterpenes, especially from the foliag e of evergreen trees, is of great importance for the production of ozone an d photochemical oxidants in the troposphere. In the present work, we establ ished a reproducible non-radioactive standard enzyme assay and characterize d monoterpene synthase activities in needles of Norway spruce (Picea abies (L.) Karst.) and in leaves of helm oak (Quercus ilex L.). In Norway spruce, the dominant monoterpenes formed were alpha-pinene, camphene, and to a les ser extent beta-pinene and limonene. In helm oak. alpha-pinene, sabinene, a nd beta-pinene were the main products. while limonene was a minor component . Under optimum conditions, in both Norway spruce and helm oak, monoterpene formation remained constant up to 180 min and 90 min. respectively, and va ried with the buffer and Mg2+ and Mn2+ concentrations used. Optimum tempera ture for monoterpene synthase activity was 40 degrees C in both species: op timal pH ranged between 6.5 and 7.5 in both species. Apparent Michaelis-con stants for the substrate GDP were ca. 17.9 +/- 5.1 mu M for Norway spruce a nd ca. 69.4 +/- 22.1 mu M for holm oak. Molecular weight determination by F PLC indicated that the monoterpene synthases in Norway spruce and helm oak have native molecular weights of ca. 59 and 50 kDa, respectively. (C) 2000 Elsevier Science Ltd. All rights reserved.