Halitschke R, Keßler A, Kahl J, Lorenz A, Baldwin I T
Max-Planck-Institut für Chemische Ökologie, Carl-Zeiss-Promenade 10, 07745 Jena, Germany e-mail:
Oecologia. 2000 Aug;124(3):408-417. doi: 10.1007/s004420000389.
After herbivore attack, plants launch a suite of direct and indirect defense responses that must be coordinated if plants are to realize a fitness benefit from these responses. Here we characterize the volatile emissions in the native tobacco plant, Nicotiana attenuata Torr. ex Wats., that are elicited by tobacco hornworm (Manduca sexta L.) attack and are known to function as attractants for parasitoids. To provide the first ecophysiological comparison of examples of both types of defense in the same species, we characterize the elicitation and signaling mechanisms, the resources required, and the potential costs and benefits of the volatile release and compare these traits with those of the well-described induced direct defense in this species, nicotine production. The release of (E)-β-ocimene, cis-α-bergamotene and linalool is dramatically induced within 24 h by application of methyl jasmonate (MeJA), caterpillar feeding, and the treatment of mechanical wounds with larval oral secretions (OS), but not by mechanical damage alone. Plants from different geographic locations produce volatile blends that differ in composition. The most consistently released component from all genotypes, cis-α-berga-motene, is positively related to the amount of MeJA and the level of wounding if OS are applied to the wounds. The volatile release is strongly light dependent, dropping to undetectable quantities during dark periods, even when temperatures are elevated to match those of the light period. Inhibitors of wound-induced jasmonate accumulation (salicylates and auxins), which are known to inhibit wound-induced nicotine production, do not inhibit the release of volatiles. By individually inducing different leaf positions with OS and, on other plants, excising them after induction, we demonstrate that the emission is largely a systemic, whole-plant response, which is maximally triggered when the second fully expanded leaf is induced. We conclude that while both are whole-plant, systemic responses that utilize recently acquired resources for their production and are activated by the jasmonate cascade, the elicitation of the volatile release exhibits greater tissue sensitivity and utilizes additional signaling components than does nicotine production. In contrast to the large investment of fitness-limiting resources required for induced nicotine production or the resources used in benzyl acetone release from flowers for pollinator attraction, the resource requirements for the volatile release are minor. Hence the argument that the volatile release incurs comparatively large physiological costs cannot be supported in this system.
在遭受食草动物攻击后，植物会启动一系列直接和间接的防御反应，若要从这些反应中获得适合度益处，这些反应必须相互协调。在此，我们描述了野生烟草植物——黄花烟草（Nicotiana attenuata Torr. ex Wats.）遭受烟草天蛾（Manduca sexta L.）攻击后引发的挥发性物质排放情况，已知这些挥发性物质可作为寄生蜂的引诱剂。为了对同一物种中这两种防御类型的实例进行首次生态生理学比较，我们描述了诱导和信号传导机制、所需资源以及挥发性物质释放的潜在成本和收益，并将这些特征与该物种中已充分描述的诱导直接防御——尼古丁产生的特征进行比较。茉莉酸甲酯（MeJA）处理、毛虫取食以及用幼虫口腔分泌物（OS）处理机械伤口后，（E）-β-罗勒烯、顺式-α-佛手柑油烯和芳樟醇的释放在24小时内会显著诱导，但仅机械损伤不会诱导。来自不同地理位置的植物产生的挥发性混合物在组成上有所不同。所有基因型中最持续释放的成分——顺式-α-佛手柑油烯，若将OS应用于伤口，其与MeJA的量和伤口程度呈正相关。挥发性物质的释放强烈依赖光照，在黑暗时期会降至无法检测的量，即使温度升高至与光照时期相同。已知能抑制伤口诱导的茉莉酸积累的抑制剂（水杨酸酯和生长素），它们能抑制伤口诱导的尼古丁产生，但不会抑制挥发性物质的释放。通过用OS分别诱导不同的叶位，并在其他植物上诱导后切除这些叶位，我们证明这种排放很大程度上是一种系统性的全株反应，当第二片完全展开的叶子被诱导时，这种反应会被最大程度地触发。我们得出结论，虽然挥发性物质释放和尼古丁产生都是利用最近获取的资源进行生产且由茉莉酸级联反应激活的全株系统性反应，但挥发性物质释放的诱导表现出更高的组织敏感性，并且比尼古丁产生利用了更多的信号成分。与诱导尼古丁产生所需的限制适合度的大量资源投入或花朵中用于吸引传粉者而释放苄基丙酮所使用的资源相比，挥发性物质释放所需的资源较少。因此，在这个系统中，挥发性物质释放会带来相对较大生理成本的观点是不成立的。
