Induction of phenolic compounds in Populus tremuloides as a function of leaf age.

Abstract

The co-evolution of plants and herbivores has resulted in a wide range of defensive adaptations in plants. Phenolic glycosides form one of the largest groups of defensive chemicals and are found in trembling aspen (Populus tremuloides). Not only are these compounds constitutively present, but they are known to be induced following an herbivorous or microbial attack in mature leaves; however, it is not currently known if this ability is present in young leaves. The focus of this study was to determine if levels of induction change during foliar maturation. We tested for variable constitutive and induced phenolic levels in leaves of P. tremuloides near the UMBS during a two-week period in late May and early June 2003. Also, our study examined the possibility that the carbon to nitrogen ratio of leaf tissue afects either constitutive or induced levels of phenolic glycosides. We found that the carbon to nitrogen ratio does indeed increase as a leaf matures (p<0.0005); however, neigher constitutive nor induced phenolic levels coincided with this trend (p=0.478, p=0.555). These results suggest that defensive priorities change as a leaf matures.