Seasonal variation in the production of tannins and cyanogenic glucosides in the chaparral shrub, Heteromeles arbutifolia

Abstract

The seasonal quantitative variation in tannin and cyanogenic glucoside levels was examined in a population of Heteromeles arbutifolia, an evergreen sclerophyll shrub, during the growing seasons of 1972 and 1973. The seasonal syntheses of these presumed herbivore defensive compounds relates to patterns of carbon gain and allocation as well as nutrient status in this plant: 1. Leaves exhibit high levels of both tannins and cyanogenic glucosides at the time of their initiation. It is postulated that these high levels are possible because of favorable balance of carbon and nutrients prior to leaf initiation. 2. Levels of the nitrogen-containing cyanogenic glucosides in the leaves correlate positively with available nitrogen in this plant which varies seasonally. 3. Fruits exhibit a long maturation period characterized by low levels of predation. On maturation the fruits are rapidly removed by birds. Natural products seem to play a role in this system. Immature fruit exhibits extremely high tannin levels as well as puly cyanogenic glucosides. On maturation the tannin levels decline and the glucosides are shifted from the pulp to the seeds.