Taylor Richard B, Sotka Erik, Hay Mark E
Institute of Marine Sciences, University of North Carolina at Chapel Hill, 3431 Arendell Street, Morehead City, NC 28557, USA.
Department of Biology, University of North Carolina at Chapel Hill, 3431 Arendell Street, Morehead City, NC 28557, USA.
Oecologia. 2002 Jun;132(1):68-76. doi: 10.1007/s00442-002-0944-2. Epub 2002 Jun 1.
Tissues within individual plants can vary greatly in the strength of their constitutive (i.e., permanent) and induced resistance to herbivores. Optimal defense theory predicts that defenses should be allocated among tissues in proportion to the value of the tissues to the plant and the tissue-specific risk of attack by grazers. We examined the relationship between tissue value and defense in the highly-differentiated brown seaweed Sargassum filipendula. Tissues within S. filipendula varied widely in palatability to the herbivorous amphipod Ampithoe longimana, with younger tissues preferred over older tissues and blades preferred over stipes. Old stipes (at the base of the plant), which linked the other tissues to the seafloor and were thus the most valuable tissue to the plant, were defended constitutively and resisted amphipod grazing by virtue of their toughness rather than via deterrent chemistry. Induction of resistance as a result of amphipod grazing occurred only in the top stipes, which contain the meristematic tissue responsible for future growth. Induction in the top stipes was not due to toughness or other structural properties, as the unpalatability persisted when top stipes were dried, ground to a fine powder, and reconstituted into an agar matrix. This suggests that the induced resistance to grazing resulted from an increase in chemical defenses. The demonstration of constitutive or induced defenses in only the more valuable tissues of the seaweed is consistent with predictions of optimal defense theory. Our finding of induction due to mesograzer (amphipod) feeding is also consistent with the notion that it is these small, more sedentary, herbivores that are most likely to induce defenses in seaweeds.
单个植物体内的组织对食草动物的组成型（即永久性）抗性和诱导抗性强度可能有很大差异。最佳防御理论预测，防御应根据组织对植物的价值以及食草动物攻击各组织的特定风险，按比例分配到各个组织中。我们研究了高度分化的褐藻绳藻中组织价值与防御之间的关系。绳藻体内的组织对食草性双足虾长指长臂虾的适口性差异很大，较嫩的组织比较老的组织更受青睐，叶片比叶柄更受青睐。老叶柄（在植物基部）将其他组织与海底相连，因此是对植物最有价值的组织，它具有组成型防御，凭借其坚韧度而非通过化学威慑来抵抗双足虾的啃食。双足虾啃食导致的抗性诱导仅发生在顶部叶柄，顶部叶柄含有负责未来生长的分生组织。顶部叶柄的诱导并非由于坚韧度或其他结构特性，因为当顶部叶柄干燥、磨成细粉并重新制成琼脂基质时，其不可口性依然存在。这表明对啃食的诱导抗性是由化学防御的增加导致的。仅在海藻更有价值的组织中表现出组成型或诱导型防御，这与最佳防御理论的预测一致。我们发现中食草动物（双足虾）取食会诱导抗性，这也与以下观点一致，即正是这些体型较小、活动较少的食草动物最有可能诱导海藻产生防御。
