The effects of long‐term water stress on water and terpene contents of the foliage of Cupressus sempervirens were studied. A great deal of water was lost over 2 months before a remarkable stabilization. A strong decrease of all the classes of terpenes accompanied this dehydration. Mono‐ and sesquiterpene hydrocarbons and free terpenols were almost entirely metabolized, whereas esters and terpene glycosides rose slightly and remained at a constant level when the water content had stabilized. Although a significant part of the mono‐ and sesquiterpene hydrocarbons was emitted in the early stage of stress application, the major part was used by the plant in response to the drought conditions.
The biosynthesis of terpene hydrocarbons has been investigated in maritime pine (Pinus pinaster Ait.) seedling primary leaves under light and darkness and with different precursors. Impossible in darkness, the synthesis of monoterpenes (mainly α‐ and β‐pinene) is strongly activated by light. Only 14C‐carbonate and 14C‐acetate can be incorporated into monoterpenes. Activation by light is comparatively much more effective for seedling leaves previously cultivated under short days than in leaves from seedlings given long days. The spectral bands which are efficient for the synthesis of monoterpenes are located around 480 and 685 nm with 14C‐carbonate and 480 and 630 nm with l‐14C‐acetate. Furthermore, this light activation does not occur if leaf pieces instead of whole leaves are used for the incorporation experiments. When 2‐14C‐mevalonic acid and 1‐14C‐isopentenyl pyrosphosphate are applied as precursors, no radioactivity is recorded in monoterpene hydrocarbons even after light exposures. In contrast, sesquiterpene hydrocarbons (caryophyllene and humulene) are easily synthesized under light or darkness in intact or fragmented leaves from the different precursors of photosynthetic or exogenous origin. From these results the compartmentalization in the synthesis of C10 and C15 hydrocarbons appears clear. There is a metabolic cooperation between the photosynthetic tissues and the specific site of elaboration of C10 hydrocarbons, which site is located in the parts where the epithelial cells of resin ducts are functional. The synthesis of sesquiterpene hydrocarbons takes place in the whole leaf without activation by light.
A plastid vesicle preparation isolated from exocarpium of young Citrofortunella mitis (calamondin) fruits was able to synthesise monoterpene hydrocarbons when incubated with isopentenyl pyrophosphate. The electron-microscope comparison between this organelle fraction and the various plastid classes present in the peel tissues has shown the structural identity between these plastid vesicles and the leucoplasts of the epithelial cells lining the secretory pockets. The monoterpene biosynthesis required the presence of dimethylallyl pyrophosphate, Mn(2+) or Mg(2+) and was increased by addition of 2-mercaptoethanol. Evidence is provided that the leucoplast vesicles act as a complete system in which occur all the successive steps involved in monoterpene hydrocarbon elaboration from isopentenyl pyrophosphate.
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