Isolation of Cell Compartments Involved in the Biosynthesis of Lower Terpenoids of Citrofortunella Mitis Fruits
The biosynthesis of mono- and sesquiterpene hydrocarbons takes place in different cell compartments of plant producing essential oils (Croteau and Loomis, 1972 ; Bernard-Dagan et al., 1982). Gleizes et al. (1983) have isolated the organelles involved in monoterpene hydrocarbon synthesis from the epicarp of young fruits of calamondin (Citrofortunella mitis). These colorless organelles devoid of plastoribosomes (Carde, 1984) are leucoplasts characterized by a dense stroma surrounded by a double membrane. Their inner membrane system is a peripheral reticulum connected with the envelope. In the presence of [1-14C] isopentenyl pyrophosphate (IPP), leucoplasts elaborate limonene, the main monoterpene hydrocarbon, with some traces of α- and β-pinene. They are also able to realize the isoprenoid chain elongation with formation of C15 and C20 pyrophosphates which, however, do not lead to the corresponding terpenoid derivatives (Gleizes et al., 1987). Nevertheless sesquiterpene hydrocarbons are present in small amounts in the epicarp of fruits and it was established recently (Belingheri et al., 1988) that they are synthesized by endoplasmic reticulum. In the present report this result is completed by electron microscope investigations after zinc iodide-osmium tetroxide impregnation made in situ and on membranes isolated from the epicarp of calamondin.
KeywordsMonoterpene Hydrocarbon Sesquiterpene Hydrocarbon Isopentenyl Pyrophosphate Plastid Envelope Peripheral Reticulum
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