Baldwin I T
Max-Planck-Institute für Chemische Okologie, Tatzendpromenade 1A, 07745 Jena, Germany.
Proc Natl Acad Sci U S A. 1998 Jul 7;95(14):8113-8. doi: 10.1073/pnas.95.14.8113.
Herbivore attack is widely known to reduce food quality and to increase chemical defenses and other traits responsible for herbivore resistance. Inducible defenses are commonly thought to allow plants to forgo the costs of defense when not needed; however, neither their defensive function (increasing a plant's fitness) nor their cost-savings function have been demonstrated in nature. The root-produced toxin nicotine increases after herbivore attack in the native, postfire annual Nicotiana attenuata and is internally activated by the wound hormone, jasmonic acid. I treated the roots of plants with the methyl ester of this hormone (MeJA) to elicit a response in one member of each of 745 matched pairs of plants growing in native populations with different probabilities of attack from herbivores, and measured the lifetime production of viable seed. In populations with intermediate rates of attack, induced plants were attacked less often by herbivores and survived to produce more seed than did their uninduced counterparts. Previous induction did not significantly increase the fitness of plants suffering high rates of attack. However, if plants had not been attacked, induced plants produced less seed than did their uninduced counterparts. Jasmonate-induced responses function as defenses but are costly, and inducibility allows this species to forgo these costs when the defenses are unnecessary.
食草动物的攻击会降低食物质量，并增加化学防御以及其他与抗食草动物相关的特性，这是广为人知的。诱导防御通常被认为能让植物在不需要时避免防御成本；然而，它们的防御功能（提高植物的适合度）和节省成本的功能在自然界中都尚未得到证实。在原生的、火灾后一年生的弱光烟草中，食草动物攻击后根部产生的毒素尼古丁会增加，并且它会被创伤激素茉莉酸在植物体内激活。我用这种激素的甲酯（茉莉酸甲酯，MeJA）处理植物的根部，以引发在自然种群中生长的745对匹配植物中每对中的一株的反应，这些植物遭受食草动物攻击的概率不同，然后测量其存活种子的终生产量。在攻击率中等的种群中，诱导植物受到食草动物攻击的频率较低，并且比未诱导的同类植物存活下来产生更多的种子。先前的诱导并没有显著提高遭受高攻击率的植物的适合度。然而，如果植物没有受到攻击，诱导植物产生的种子比未诱导的同类植物少。茉莉酸诱导的反应起到防御作用，但代价高昂，而诱导性使该物种在不需要防御时能够避免这些成本。
