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

Abstract

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.