| Foliage sesquiterpenoids of 133 Cupressus macnabiana A. Murr. trees from ten native populations in California were analyzed using gas chromatography. The constitutive sesquiterpenoid composition was found to be quite different from all other North American Cupressus species, mainly consisting of a great diversity of compounds with a cadinane structure. Two distinct chemotypes were identified, one high in α-cadinol, the other high in γ-cadinene.; Variation in the level and distribution of sesquiterpenoid cyclase activities from several of the wild trees was investigated. In vitro assays, with farnesyl diphosphate as substrate, revealed that two distinct types of sesquiterpenoid biosynthesis take place. One is constitutive sesquiterpenoid biosynthesis, which persists throughout the year, though with varying level of cyclase activity, in foliage of all ages. The other is developmentally controlled sesquiterpenoid biosynthesis, which is only present in the early development stage of new foliage and produces unique sesquiterpenoids including carota-1,4-diene, isodaucene, β-bisabolene, thujopsan-2α-ol and α- and β-acorenols. The developmentally controlled sesquiterpenoids showed marked structural diversity, and their biosynthesis apparently was under tight genetic control. Implications of developmentally controlled biosynthesis for defense of newly formed foliage are considered.; One constitutive sesquiterpenoid cyclase, 4-hydroxygermacra-1(10),5-diene cyclase, was partially purified by a combination of DEAE-cellulose and hydroxyapatite fractionation, strong and weak anion-exchange chromatography, and hydroxyapatite chromatography. The partially purified enzyme is similar to other reported sesquiterpenoid cyclases in substrate specificity and Mg2+ cofactor requirement. The pH optimum for 4HGD cyclase is between 8.0–8.5, significantly higher than that reported for most other terpene cyclases including conifer sesquiterpenoid cyclases, but is close to that for gymnosperm monoterpene cyclases. All efforts to recover the cadinane cyclase activities were unsuccessful; some of the most likely possibilities for this failure were explored and ruled out. Other avenues to recover these elusive activities are discussed. |
