Histochemical Studies of Bracken Fern: Localization of Phenolic and Tannin Defences in Bracken Accessions along an Altitudinal Gradient in the Neotropics

摘要

Bracken fern (Pteridium aquilinum) synthesizes and accumulates a variety of toxins belonging to different compound families (Fenwick, 1988; Alonso-Amelot, 2002) which amount to over 100 known compounds. These materials contribute, each one in its ownway, to fending off invertebrate and vertebrate predators. Particularly, quantitative studies of phenolics and tannins (P/T) in bracken are limited in number but nevertheless they suggest that a negative correlation between total phenolics and insect herbivory exists (Tempel, 1981). Also, there is abundant evidence in connection with the role of tannins as feeding deterrents and their part in the disruption of digestive processes in mammals. At least two additional aspects in bracken chemistry need to be addressed for a better understanding of the ecological role of P/T accumulated at considerable metabolic cost. Firstly, if preliminary quantitative analyses of P/T show considerable variance with season (Graham, 1991; Vogt et al., 1991; Chaves et al.,1993), it is not entirely clear how this variation correlates with the biotic and abiotic variables encountered in ecological gradients. Secondly, the particular part within the segments where specific compounds are located has not been determined and might provide information in assigning a specific role as toxicants according to the attacking species.