解析四种化学型香樟单萜VOCs合成、释放与抗高温胁迫机制

High temperature weather caused by an intensifying greenhouse effect has gained close attention in the world. Under high temperature, plant growth and development are impacted seriously, and abundance of volatile organic compounds (VOCs) are released from plants, which closely relate to plant thermoresistance. Cinnamomum camphora (L.) Presl. is an excellent and multipurpose tree species, and mainly grows in the regions harmed by high temperature frequently. This species mainly released monoterpenes, and can be divided into 4 chemotypes such as eucalyptol-type, camphor-type, linalool-type and borneol-type, according to the uppermost compound. However, the exact mechanism for their formation is unclear. High temperature stress promoted monoterpene emission from C. camphora. However, obvious increases were found in the levels of reactive oxygen species, and remarkable decreases in photosynthetic abilities, after monoterpene synthesis was blocked (see the research basis). This indicates that monoterpenes play an important role in C. camphora resisting high temperature stress, but the exact mechanism is unclear. Therefore, we will investigate the difference of monoterpene synthesis and emission mechanism in the 4 chemotype C. camphora, response mechanism of monoterpenes to high temperature stress, resistance abilities to high temperature and fuctions of monoterpenes in the 4 chemotypes, and the main functional components. The results of this study are very meaningful and valuable for uncovering the response mechanism of tree VOCs to high temperature stress and improving tree resistance abilities to high temperature from adjusting the secondary metabolism.

温室效应加剧导致的高温天气已被全世界广为关注。高温不仅影响植物生长发育，还诱导释放大量的挥发性有机化合物(VOCs)，这些VOCs与植物抗高温胁迫密切相关。香樟是优良的多用途树种，生长地多为高温危害多发地区。香樟主要释放单萜VOCs，根据其最主要化合物可分为桉叶油素型、樟脑型、芳樟醇型和龙脑型4种化学型，然而何种机制导致了不同化学型出现尚不清楚。高温胁迫可诱导香樟单萜大量释放，当抑制其释放后，活性氧大量产生、光合性能降低(见研究基础)，这表明单萜在香樟抗高温胁迫中具有重要作用，然而作用机制尚不清楚。因此，本项目拟从4种化学型香樟单萜VOCs的合成与释放差异、对高温胁迫的响应机制、抵抗高温胁迫的能力差异与作用机制、以及主要功能成分进行研究，这对深入认识树木VOCs对高温胁迫的响应机制以及通过调节次生代谢提高树木抗高温能力均具有重要价值与意义。

萜烯类挥发性有机化合物(VOCs)在植物抵抗高温胁迫中具有重要作用，香樟主要释放单萜并且在生长过程中不可避免的经历高温胁迫。本项目以樟脑型、桉叶油素型、芳樟醇型和龙脑型香樟为材料，研究了4种化学型香樟叶片生长与光合性能差异、单萜VOCs合成与释放差异、单萜VOCs释放对高温胁迫响应机制、单萜VOCs抵抗高温胁迫能力差异与作用机制以及主要功能成分。樟脑型、桉叶油素型、芳樟醇型和龙脑型香樟均主要释放单萜，其中樟脑、桉叶油素、芳樟醇和龙脑分别为其典型成分，释放量均在相应化学型单萜总释放量的50%以上。首次揭示了MEP途径和单萜合酶表达差异导致了4种化学型香樟单萜释放差异，高温可通过上调这些基因表达以促进单萜释放；油细胞为香樟液态单萜储存结构，香樟所释放的单萜主要来自直接合成，而非储存单萜释放。在高温胁迫时，单萜VOCs可通过降低ROS含量、维持光合性能以提高香樟抗高温胁迫能力，然而其在不同化学型香樟中的抗高温胁迫能力存在一定差异。4种典型单萜为主要抗高温胁迫单萜，其可通过诱导非酶抗氧化物形成相关基因表达以猝灭ROS，通过诱导光合色素形成、光合电子传递链、CO2固定等相关基因表达以维持光合性能，通过诱导膜脂分子代谢相关基因表达以维持膜脂稳定。这表明典型单萜可作为信号分子以提高香樟抗高温胁迫能力，然而其所传递的抗高温胁迫信号存在一定差异。4种化学型香樟萜烯提取液及其主要成分在体外均具有一定的抗氧化活性，然而其有效浓度较高。由于植物体内很难达到此高浓度，因此单萜不可能通过直接猝灭ROS以提高香樟抗高温胁迫能力，而应是作为信号分子通过诱导基因表达以发挥抗高温胁迫作用。此外，还利用藻细胞验证了萜烯VOCs的信号功能，同时发现香樟提取液及其主要单萜具有抑藻作用，具有开发为除藻剂以防治水华藻类的潜在价值。