Phenolics, alkaloids, saponins and cyanogenic glycosides.pdf

S. Mali, R.M. Borges / Biochemical Systematics and Ecology 31 (2003) 1221–12461231each year (June through September/October). The need for protection against fungiat this time appears to be high and this may explain the ubiquitous presence oftannins in leaves, which is further evidenced by the low leaf litter decay (R.M.Borges, personal observation). The poor, acidic, leached soils (data from IndianBureau of Soil Sciences) and the high levels of insolation at this site may havefurther resulted in phenolics such as condensed tannins being laid down in leavesand even in other plant parts due to overflow (Haslam, 1985) or a pluralistic combinationof the various resource-related defence hypotheses (Berenbaum, 1995).Owing to the dearth of work on hydrolysable tannins in tropical rainforests weare unable to compare our results with other studies but hope that our results willbe useful for further comparisons. Despite their powerful free-radical scavengingactivity and alleged anti-carcinogenic effects (e.g. Sawa et al., 1999), virtually noinformation is available on the effect of hydrolysable tannins on various types ofherbivores in natural systems (but see Whitten and Whitten, 1987; Clifford and Scalbert,2000) although their effect on large arboreal herbivores like the giant squirrelR. indica has been investigated (Borges and Mali, in preparation).Since we have used the Folin–Ciocalteu method for estimating total phenolics,which is recommended by Waterman and Mole (1994) as being better than the earlierFolin–Denis assay, and since all the earlier studies on community-wide distributionof secondary compounds in tropical forests have used the Folin–Denis method (e.g.Gartlan et al., 1980), our levels of total phenolics cannot be compared with otherstudies. However, as we have used the widely applied proanthocyanidin method forcondensed tannins, our condensed tannin levels can be compared (Table 5) and werefound to be nearly identical with the values found for another evergreen forest atKakachi in southern India (Oates et al., 1980) despite the complete non-overlap ofspecies between Bhimashankar and Kakachi. Furthermore, these condensed tanninlevels were also found to be close to the values found for the two African andthe two south-east Asian forests that have been most extensively studied (Table 5).Interestingly, the fibre levels (ADF) of the mature trees at Bhimashankar were alsofound to be nearly the same as those measured at Kakachi (Table 5).Immature leaves, flowers, and petioles had high astringency while lower levelswere found in fruit. It is possible that either immature leaves, flowers and petiolesactually do have greater protection by biologically active tannins as measured bytheir astringency or that the extractability of phenolics is greater in these tissues.High gallotannin levels were also found by Ossipov et al. (1997) in immature leaves;these levels declined as the leaves matured. Low astringency may be present in fruitas it is known that astringency levels decrease as fruit ripen (Goldstein and Swain,1963). We cannot compare astringency levels between various stages of the samefruit owing to lack of sample sizes. Tree twigs had the lowest levels of astringency,condensed and hydrolysable tannins but the highest levels of fibre. Tree twigs haverarely been analysed chemically (Waterman and Kool, 1994). This pattern of allocationof secondary compounds to tree twigs may be a general strategy as twigs areprotected by high lignin levels and therefore do not require protection from othercompounds. Inner bark had astringency levels and condensed tannin levels comparableto those of mature leaves while fibre levels were lower than those of twigs. As