Changes in content and biosynthetic activity of caffeine and trigonelline during growth and ripening of Coffea arabica and Coffea canephora fruits

Caffeine and trigonelline are major nitrogenous alkaloids found in coffee seeds. Accumulation of these alkaloids in two cultivars of Coffea arabica and in a cultivar of Coffea canephora seeds was monitored. Growth stages are specified by letters, A to G. They correspond to the pinhead and small (A), rapid expansion and pericarp growth (B), endosperm formation (C), early dry matter accumulation (D), mature (green) (E), ripening (pink) (F) and fully ripened (red) (G) stages. Caffeine and trigonelline content increased at stages D and E. The concentrations of caffeine in ripe seeds (stage G) of the two cultivars of C. arabica and C. canephora seeds were respectively 1.0% and 1.9% dry weight. A high biosynthetic activity of caffeine, which was estimated via the incorporation of [8-14C]adenine into purine alkaloids, was found in whole fruits (perisperm and pericarp) in stages B and C, and in developing seeds (endosperm) in stages D and E. The biosynthetic activities of caffeine were reduced in both pericarp and seeds in stages F and G. In C. arabica cv. Mokka and in C. canephora, the transcripts of CmXRS1, CTS2 and CCS1, three N-methyltransferase genes for caffeine biosynthesis, and of methionine synthase gene (MS) were detected in every stage of growth, although the amounts of these transcripts were significantly less in stage G. The pattern of expression of genes for caffeine synthesis during growth is roughly related to the in situ synthesis of caffeine from adenine nucleotides, although exceptions were found in the very early and later stages of fruit growth. The amounts of the transcripts of CmXRS1, CTS2 and CCS1 were higher in seeds than in pericarp, but reverse was true for MS transcripts in developing coffee fruits. Similarly, caffeine synthase (N3-methyltransferase) activity was also higher in seeds than in pericarp. Concentrations of trigonelline in ripe seeds (stage G) of C. arabica cv. Mokka, C. arabica cv. Catimor and C. canephora were ca. 1.3%, 1.0% and 1.4% of dry weight, respectively. High biosynthetic activity of trigonelline was found in young fruits (stages A–C) and in the pericarp of developing fruits (stage E). The biosynthetic activity was reduced markedly in seeds at stages F and G. These results suggest that active trigonelline biosynthesis occurs in the pericarp of coffee fruits. Although the final concentration of caffeine and trigonelline varies in the three Coffea plants, the patterns of fluctuations of the caffeine and trigonelline biosynthetic activity in all Coffea plants are all similar.