To investigate the physiological role of the purine alkaloids during germination, seeds of Coffea arabica were allowed to germinate under aseptic conditions on agar at 26°C, either in the dark or in the light. After imbibition for 7 days less than 1 % of the seed caffeine is found in the agar, indicating a strong diffusion barrier at the surface of the coffee bean. After 56 days, when the radicle has grown deep into the agar support, a considerable amount (22%) of caffeine is excreted. The total caffeine content increases during germination for 56 days by 83% in the dark and by 51 % in the light, whereas the soluble protein falls drastically. We propose that caffeine is not a nitrogen reserve for germination and acts against competitors (release into the soil) and against predators (concentration increase in the tissue).Key words: Caffeine -Coffea arabica •-Excretion -Germination -Nitrogen metabolism -Purine alkaloid -Theobromine.There is a large body of information on the actual aspect of purine alkaloid physiology, published fifty or more years ago, which is difficult of access and in certain instances requires a re-examination with subtle methods allowing an improved insight into the physiological role of these alkaloids. At the beginning of this century U. Suzuki expressed clearly that in the tea plant "the processes of metabolism show more connection with the production of coffein than those of assimilation and synthesis do" (cited by Weevers 1930, p. 123). Later, Weevers (1907, 1930 carried out a detailed study on this topic in all caffeine-containing plant species consumed by man, i.e. tea {Camellia sinensis (L.) O. Kuntze), coffee (different species of Coffea), mate (Ilex paraguariensis St. Hil.), guarana (Paullinia cupanaH.B.K..), cocoa (Theobroma cacao L.) and cola (Cola acuminata Schott et Endl.). He analyzed detached leaves and, where possible, seedlings, and always observed an increase in protein accompanied by a decrease in purine alkaloids or vice versa depending on the experimental conditions selected. As regards these events during seedling development of Coffea arabica, Weevers reported results from experiments in the dark only.We decided therefore to examine the changes in different nitrogen fractions during germination of Coffea arabica L. under controlled environmental conditions and to make a comparison on the physiology of caffeine between the coffee plant and other caffeine-containing plant species.
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