Induced Plant Responses to Herbivory - Terrestrial Systems Ecology
Induced Plant Responses to Herbivory - Terrestrial Systems Ecology
Induced Plant Responses to Herbivory - Terrestrial Systems Ecology
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332 KARBAN & MYERS<br />
Table 1<br />
A dicho<strong>to</strong>mous key for induced responses<br />
Does stress or injury change plant quality?<br />
1 NO: No response<br />
l' YES: INDUCED RESPONSE (proceed <strong>to</strong> 2)<br />
Annu. Rev. Ecol. Syst. 1989.20:331-348. Downloaded from www.annualreviews.org<br />
by ETH- Eidgenossische Technische Hochschule Zurich - BIBLIOTHEK on 03/29/11. For personal use only.<br />
Does the induced response decrease herbivore preference or performance?<br />
2 NO: No effect or induced susceptibility<br />
2' YES: INDUCED RESISTANCE (proceed <strong>to</strong> 3)<br />
Does reduced herbivore preference/performance increase plant fitness?<br />
3 NO: The plant is not defended by the response<br />
3' YES: INDUCED DEFENSE<br />
in plant quality following injury caused by drought (104), nutrient deficiency<br />
(70), solar radiation (66), low temperature (46), high temperature (94), air<br />
pollution (20), and previous damage caused by herbivory (107). Much of the<br />
evidence for changes in resistance associated with induced responses comes<br />
from bioassays of induced foliage under labora<strong>to</strong>ry or artificial field conditions<br />
(reviewed in 28, 84). While the proportion of cases in which induced<br />
responses act as defenses against herbivores may be uncertain, we would like<br />
<strong>to</strong> consider in this review the characteristics of changes that relate <strong>to</strong> their role<br />
as defenses. What are the changes, why and how might they occur, and what<br />
might be done <strong>to</strong> further understand their influence on plant-herbivore interactions?<br />
Specifically, which changes are likely <strong>to</strong> act as effective defenses<br />
and how might they work? Which herbivores are likely <strong>to</strong> be affected? Have<br />
these responses evolved as defenses against herbivores? Under what conditions<br />
might selection favor facultative induced defenses rather than preformed<br />
constitutive defenses?<br />
WHAT CHANGES FOLLOW DAMAGE?<br />
Secondary Metabolites and Phy<strong>to</strong>alexins<br />
Injuries <strong>to</strong> plant tissues cause a wide array of plant responses. The nature of<br />
the response varies with plant type. One area of progress has been <strong>to</strong> recognize<br />
that the way trees respond is associated with their growth pattern and<br />
nutrient status (14). A cataloging of plant responses is beyond the scope of<br />
this review, although a few representative examples are provided. Many<br />
studies of induced responses have considered changes in tannins and phenols,<br />
products of the shikimic acid pathway. Relative activity of the enzyme<br />
phenylalanine ammonia lyase (PAL) can determine the production of phenolics,<br />
including lignin (19). Induction of the phy<strong>to</strong>hormone ethylene by tissue<br />
damage may influence the production of PAL and therefore the concentration