Loreto Francesco, Barta Csengele, Brilli Federico, Nogues Isabel
Consiglio Nazionale delle Ricerche, Istituto di Biologia Agroambientale e Forestale, Monterotondo Scalo, Roma, Italy.
Plant Cell Environ. 2006 Sep;29(9):1820-8. doi: 10.1111/j.1365-3040.2006.01561.x.
Among the volatile organic compounds (VOCs) emitted by plants, some are characteristic of stress conditions, but their biosynthesis and the metabolic and environmental control over the emission are still unclear. We performed experiments to clarify whether (1) the emission following wounding can occur at distance from the wounding site, from VOC pools subjected to metabolic signals; and (2) the emission of biogenic VOCs generated by membrane damage (e.g. consequent to wounding or ozone exposure) can also be induced by exposure to high light and high temperature, recurrent in nature. In Phragmites australis, leaf cutting caused large and rapid bursts of acetaldehyde both at the cutting site and on parts of the cut leaf distant from the cutting site. This emission was preceded by a transient stomatal opening and did not occur in conditions preventing stomatal opening. This suggests the presence of a large pool of leaf acetaldehyde whose release is under stomatal control. VOCs other than isoprene, particularly acetaldehyde and (E)-2-hexenal, one of the C-6 compounds formed by the denaturation of membrane lipids, were released by leaves exposed to high temperature and high light. The high-temperature treatment (45 degrees C) also caused a rapid stimulation and then a decay of isoprene emission in Phragmites leaves. Isoprene recovered to the original emission level after suspending the high-temperature treatment, suggesting a temporary deficit of photosynthetically formed substrate under high temperature. Emission of C-6 compounds was slowly induced by high temperature, and remained high, indicating that membrane denaturation occurs also after suspending the high-temperature treatment. Conversely, the emission of C-6 compounds was limited to the high-light episode in Phragmites. This suggests that a membrane denaturation may also occur in conditions that do not damage other important plant processes such as the photochemistry of photosynthesis of photoinhibition-insensitive plants. In the photoinhibition-sensitive Arabidopsis thaliana mutant NPQ1, a large but transient emission of (E)-2-hexenal was also observed a few minutes after the high-light treatment, indicating extensive damage to the membranes. However, (E)-2-hexenal emission was not observed in Arabidopsis plants fumigated with isoprene during the high-light treatment. This confirms that isoprene can effectively protect cellular membranes from denaturation. Our study indicates that large, though often transient, VOC emissions by plants occur in nature. In particular, we demonstrate that VOCs can be released by much larger tissues than those wounded and that even fluctuations of light and temperature regularly observed in nature can induce their emissions. This knowledge adds information that is useful for the parameterization of the emissions and for the estimate of biogenic VOC load in the atmosphere.
在植物释放的挥发性有机化合物（VOCs）中，有些是胁迫条件下的特征性物质，但其生物合成以及排放的代谢和环境控制仍不清楚。我们进行了实验，以阐明：（1）受伤后的排放是否能在远离受伤部位的地方，从受到代谢信号影响的VOC库中发生；（2）由膜损伤（如受伤或暴露于臭氧后）产生的生物源VOCs的排放，是否也能由高光和高温诱导，而高光和高温在自然界中经常出现。在芦苇中，叶片切割在切割部位以及切割叶片上远离切割部位的部分都引发了大量且迅速的乙醛释放。这种释放之前有短暂的气孔开放，在阻止气孔开放的条件下则不会发生。这表明存在大量的叶片乙醛库，其释放受气孔控制。除异戊二烯外的VOCs，特别是乙醛和（E）-2-己烯醛（膜脂变性形成的C-6化合物之一），由暴露于高温和高光的叶片释放。高温处理（45摄氏度）也导致芦苇叶片中异戊二烯排放迅速增加，随后下降。暂停高温处理后，异戊二烯恢复到原始排放水平，这表明高温下光合形成的底物暂时不足。C-6化合物的排放由高温缓慢诱导，并保持在较高水平，这表明在暂停高温处理后膜变性仍会发生。相反，芦苇中C-6化合物的排放仅限于高光时段。这表明在不损害其他重要植物过程（如光抑制不敏感植物的光合作用光化学）的条件下，膜变性也可能发生。在对光抑制敏感的拟南芥突变体NPQ1中，高光处理几分钟后也观察到大量但短暂的（E）-2-己烯醛排放，表明膜受到广泛损伤。然而，在高光处理期间用异戊二烯熏蒸的拟南芥植株中未观察到（E）-2-己烯醛排放。这证实异戊二烯能有效保护细胞膜免予变性。我们的研究表明，植物在自然界中会发生大量（尽管通常是短暂的）VOC排放。特别是，我们证明VOCs可以由比受伤组织大得多的组织释放，而且自然界中经常观察到的光和温度波动也能诱导其排放。这些知识为排放参数化和大气中生物源VOC负荷估算提供了有用信息。
