Phenolics, fibre, alkaloids, saponins, and cyanogenic glycosides in a seasonal cloud forest in India

Abstract

We investigated secondary compounds in ephemeral and non-ephemeral parts of trees and lianas of a seasonal cloud forest in the Western Ghats of India. We measured astringency, phenolic content, condensed tannins, gallotannins, ellagitannins, and fibre, and also screened for alkaloids, saponins and cyanogenic glycosides in 271 plant parts across 33 tree and 10 liana species which constituted more than 90% of the tree and liana species of this species-poor forest. Cyanogenic glycosides occurred only in the young leaves of Bridelia retusa (Euphorbiaceae), i.e. in 2.3% of species examined. Alkaloids were absent from petioles, ripe fruit and mature seeds examined. Saponins were found in all types of plant parts. Condensed tannins occurred in almost all plant parts examined (93.6%), while hydrolysable tannins were less ubiquitous (gallotannins in 31.2% of samples, and ellagitannins in 18.9%). Astringency levels were significantly correlated with total phenolic, condensed tannin, and hydrolysable tannin contents. Condensed tannin and hydrolysable tannin contents were not related. Immature leaves, flowers, and petioles had high astringency while lower levels were found in fruit. Flowers and fruit had the lowest fibre levels. There was no relationship between relative dominance of a species in the forest and the fibre or phenolic contents of its mature leaves. In each plant part category, the frequency of species containing tannins together with alkaloids or saponins was significantly lower than the frequency of species containing tannins alone. There was, however, no segregation between alkaloids and saponins.