Caffeine in Citrus flowers

The allocation of purine alkaloids within citrus flowers was studied and found to be linked to anthesis, with 99% of the total flower caffeine confined to the androecium. The main alkaloid is caffeine accompanied by considerable (up to 30% of caffeine) concentrations of theophylline. In the anther, these purine alkaloids reach altogether a concentration of 0.9% dry wt which is close to the caffeine content of the Arabica coffee bean. The pollen alkaloid concentration is in the same range. Much lower but still marked concentrations were found in the nectar. A considerable breakdown of alkaloids during honey production is assumed. The biological significance of this particular secondary compound allocation as well as possible effects on the key pollinator, the honey-bee, are discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.