Phenolics have been considered classic defence compounds for protecting plants from herbivores, ever since plant secondary metabolites were suggested to have evolved for that reason. The resource availability and carbon-nutrient balance hypotheses proposed that variation in phenolic levels between and within plant species reflects environmental availability of nutrients and light, and represents a trade-off in allocation by plants to growth and defence against herbivores. In contrast to these concepts, we suggest that (1) the main role of many plant phenolics may be to protect leaves from photodamage, not herbivores; (2) they can achieve this by acting as antioxidants; and (3) their levels may vary with environmental conditions in order to counteract this potential photodamage. We therefore suggest that patterns in phenolic levels, often used to support the concept of trade-off between growth and herbivore defence in relation to resource availability, may actually reflect different risks of photodamage. We suggest that the level of many phenolics is low under some environmental conditions, not because resources to produce them are limited, but simply because the risk of photodamage is low and they are not required. If our photodamage hypothesis is correct, a reassessment of the ecological and evolutionary role of many phenolics in plant defence theory is required.

Item Type:	Refereed Article
Research Division:	Biological Sciences
Research Group:	Plant Biology
Research Field:	Plant Biology not elsewhere classified
Objective Division:	Expanding Knowledge
Objective Group:	Expanding Knowledge
Objective Field:	Expanding Knowledge in the Environmental Sciences
Author:	Close, DC (Associate Professor Dugald Close)
Author:	McArthur, C (Dr Clare McArthur)
ID Code:	24621
Year Published:	2002
Web of Science® Times Cited:	285
Deposited By:	Zoology
Deposited On:	2002-08-01
Last Modified:	2011-08-02
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