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）：膜稳定作用与直接抗氧化效应。倍半萜烃（sesquiterpene hydrocarbons，C15）不仅具备被认为可赋予异戊二烯与单萜烃保护特性的结构属性，还能与臭氧（ozone）快速发生反应，这表明倍半萜或许同样能够提升植物对非生物胁迫的耐受性。为验证倍半萜是否能够保护植物抵御臭氧、UVB紫外线（UVB light）或干旱胁迫，本研究使用了野生烟草花烟草（Nicotiana attenuata）的转基因株系。这些转基因植株分为两类：一类表达玉米萜烯合酶基因（maize terpene synthase gene，ZmTPS10），该基因可合成(E)-β-法尼烯与(E)-α-香柠檬烯的混合产物；另一类表达该基因的点突变体（point mutant，ZmTPS10M），该突变体仅能合成(E)-β-法尼烯。(E)-β-法尼烯在臭氧熏蒸箱中可发挥局部、外源且瞬时的臭氧淬灭效应，但本研究未发现证据表明，植株体内倍半萜合成的增强能够抑制氧化损伤（oxidative damage），或是在急性或慢性胁迫下维持光合功能（photosynthetic function）与植株适合度（plant fitness）。尽管倍半萜(E)-β-法尼烯与(E)-α-香柠檬烯或许能够在间歇性热胁迫（intermittent heat stress）下赋予植株益处（该场景未在本研究中得到验证），但其在缓解非生物胁迫中发挥的任何作用，或许都次于此前已被证实的其在生物互作（biotic interactions）中的功能。