Tannin assays in ecological studies Precipitation of ribulose-1,5-bisphosphate carboxylase/oxygenase by tannic acid, quebracho, and oak foliage extracts

Tannic acid and quebracho precipitate many times their weight of the abundant leaf protein, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPC). The use of this protein in protein precipitation assays for tannin content is described. Extracts of mature foliage of pin, bur, and black oak precipitate 2.01, 0.69, and 0.09 mg RuBPC/ mg (dry wt) of leaf powder extracted, respectively, at pH 6.1. From these measurements it can be calculated that all three of these oak species have sufficient tannins to precipitate all of the RuBPC present in their foliage. At mildly alkaline pHs, however (pH ⩾ 7.5), RuBPC is not precipitated by tannins. Since RuBPCis the most abundant protein present in photosynthetic tissues, often constituting as much as 50% of the soluble proteins and 25% of the total proteins in leaf tissue, the interactions of this protein with tannins are highly relevant to an evaluation of the role of tannins as antiherbivore, digestibility-reducing substances. Our measurements provide no basis for arguing that differences in tannin levels in different species reflect differences in the digestibility of leaf proteins or that tannins have any effect whatsoever upon the digestibility of leaf protein under conditions which normally prevail in most insects' guts. These findings emphasize the need to test more of the assumptions underlying contemporary interpretations of the importance of tannins in plant herbivore interactions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44903/1/10886_2004_Article_BF00988046.pd

Protein-precipitating capacity of tannins in Shorea (Dipterocarpaceae) seedling leaves

The protein-precipitating capacities of tanniferous extracts from immature and mature leaves of three Shorea spp. (Dipterocarpaceae) seedlings were measured by an adaptation of Goldstein and Swain's β-glucosidase precipitation assay. Protein precipitation by the extracts was not correlated with total phenolics (Folin-Denis assay) or proanthocyanidin content (BuOH-HCl assay) as measured in an earlier study. Extracts of S. maxwelliana mature leaves had much lower protein-precipitating capacity than those of S. acuminata and S. leprosula , but fewer insect species feed on and cause less damage to the foliage of S. maxwelliana compared with the other species' foliage. Immature leaf extracts of S. leprosula and S. acuminata had substantial protein-precipitating capacities which in the latter species exceeded that of its mature leaf extracts. Leaf extracts precipitated less protein when initial protein concentration was reduced, although not limiting, but no effect or the reverse effect occurred with quebracho tannin and tannic acid. Problems in the characterization of foliage astringency and the interpretation of its role as a potential antiherbivore defense are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44902/1/10886_2005_Article_BF01403099.pd