The Sesquiterpenes(E)-ß-Farnesene and (E)-α-Bergamotene Quench Ozone but Fail to Protect the Wild Tobacco Nicotiana attenuata from Ozone, UVB, and Drought Stresses

Among the terpenes, isoprene (C5) and monoterpene hydrocarbons (C10) have been shown to ameliorate abiotic stress in a number of plant species via two proposed mechanisms: membrane stabilization and direct antioxidant effects. Sesquiterpene hydrocarbons (C15) not only share the structural properties thought to lend protective qualities to isoprene and monoterpene hydrocarbons, but also react rapidly with ozone, suggesting that sesquiterpenes may similarly enhance tolerance of abiotic stresses. To test whether sesquiterpenes protect plants against ozone, UVB light, or drought, we used transgenic lines of the wild tobacco Nicotiana attenuata. The transgenic plants expressed a maize terpene synthase gene (ZmTPS10) which produced a blend of (E)-ß-farnesene and (E)-α-bergamotene, or a point mutant of the same gene (ZmTPS10M) which produced (E)-ß-farnesene alone,. (E)-ß-farnesene exerted a local, external, and transient ozone-quenching effect in ozone-fumigated chambers, but we found no evidence that enhanced sesquiterpene production by the plant inhibited oxidative damage, or maintained photosynthetic function or plant fitness under acute or chronic stress. Although the sesquiterpenes (E)-ß-farnesene and (E)-α-bergamotene might confer benefits under intermittent heat stress, which was not tested, any roles in relieving abiotic stress may be secondary to their previously demonstrated functions in biotic interactions.

在萜类化合物（terpenes）中，异戊二烯（isoprene）(C5)与单萜烃（monoterpene hydrocarbons）(C10)已被证实可通过两种已提出的机制缓解多种植物的非生物胁迫（abiotic stress）：膜稳定作用（membrane stabilization）与直接抗氧化作用（direct antioxidant effects）。倍半萜烃（sesquiterpene hydrocarbons）(C15)不仅具备被认为可赋予异戊二烯和单萜烃保护特性的结构属性，还能快速与臭氧发生反应，这提示倍半萜或许同样能增强植物对非生物胁迫的耐受性。
为验证倍半萜是否能保护植物抵御臭氧、UVB辐射或干旱胁迫，我们以野生烟草渐狭烟草（Nicotiana attenuata）的转基因株系为实验材料。该实验包含两类转基因植株：一类表达玉米萜合酶基因（ZmTPS10），可合成(E)-β-法尼烯与(E)-α-香柠檬烯的混合物；另一类为该基因的点突变体（ZmTPS10M），仅能合成单一的(E)-β-法尼烯。
(E)-β-法尼烯可在臭氧熏蒸的培养箱中发挥局部、外部且瞬时的臭氧淬灭效应（ozone-quenching effect），但研究团队未发现证据表明，植株增强的倍半萜生成能够抑制氧化损伤（oxidative damage），或是在急性或慢性胁迫（acute or chronic stress）下维持光合功能（photosynthetic function）与植物适合度（plant fitness）。
尽管倍半萜(E)-β-法尼烯与(E)-α-香柠檬烯或许能在间歇性热胁迫（intermittent heat stress）下为植株带来益处（该效应未在本研究中检测），但其在缓解非生物胁迫中所发挥的任何作用，可能都次于此前已证实的其在生物互作（biotic interactions）中的功能。