Leaf chemistry in response to herbivory in puttyroot, Apectrum hyemale (Orchidaceae)

Background/Question/Methods: Apectrum hyemale is a perennial forest herb of eastern North American deciduous forest. Its wintergreen phenology makes it unique among temperate forest herbs: a single striated blue-green leaf emerges in early fall, photosynthesizes through the winter, and senesces in the spring as the canopy closes. Although it is considered globally secure (G5), this species is uncommon throughout much of its range and populations are highly fragmented.  Plants are vulnerable to insect and mammalian herbivores shortly after shoot emergence.  Because there is no published literature on the leaf chemistry of this species, we conducted exploratory assays of insect damaged (n = 10) and undamaged leaves (n = 10).  We collected specimens in January 2008 from a 75 ha woodlot on the Wright State campus (Greene Co., OH), 2-3 months following damage by insect herbivores, and analyzed nutrients (total sugars and total proteins) and putative defense compounds (peroxidase, polyphenol oxidase, chitinase and trypsin inhibitor) using spectrophotometric techniques.  We compared leaves damaged by insect herbivores to undamaged leaves using Wilcoxon signed rank tests. 
Results/Conclusions: Sugar content (51.4 ± 5.2 mg/g) and total protein content  (3.8 ± 1.6 mg/g) did not differ between damaged and undamaged leaves.   Among defense proteins, only peroxidase activity was greater in damaged (56.8 ± 12.6 SE mg/g fresh weight) than undamaged leaves (16.7 ± 5.6 SE mg/g; n = 20; Z = 2.15; P = 0.028). Chitinase activity (33.0 ± 2.4 mg/g) and polyphenol oxidases (0.13 ± 0.042 mg/g) did not differ significantly between damaged and undamaged leaves, and trypsin inhibitor was undetected.