In the leaves ofCoffea arabicaL., purine alkaloid formation was estimated by analyzing the theobromine and caffeine content and by measuring the methylation rate of 2-14Ctheobromine to 2-14Ccaffeine in short-term experiments (6–24 h). At the same time, growth (in terms of dry weight and area), net photosynthesis (NPS), and dark respiration were determined. During leaf development, which was considered to be terminated when NPS was at a maximum (60–80 μmol g-1s-1) and dark respiration at a minimum (5–7.5 μmol g-1s-1), the content of theobromine and the velocity of caffeine formation were both found to decrease by a factor of more than 100. The close correlation between the theobromine content and the methylation rate is suspended when purine alkaloid formation is influenced by factors other than leaf development. Among these factors, temperature is the most effective: the velocity of caffeine biosynthesis is increased by raising the temperature and vice versa. Although the plants were well irrigated, a drastic decrease of NPS in the afternoon was observed under all environmental conditions tested. Light saturation was reached between 170–360 μmol m-2s-1. The temperature optimum of NPS was shown to be very broad (24–33°C)m provided the adaptation time was suff
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