摘要：Caffeine is the most abundant and important purine alkaloid derived from several important crop, such as coffee, tea, cocoa, guarana, and other plants. In tea and coffee plants, caffeine is predominantly produced in the young buds of leaves and in immature fruits. The effect of light-stimulating caffeine biosynthesis is uncertain, but our results clearly show that light, independent of N-availability, increases caffeine (26%), allantoin (47%), and theophylline (8%) content in plants compared with those grown in a shaded (50% solar irradiation) environment. Caffeine is the major low-molecular-weight nitrogenous compound in coffee plants, and at times, it functions as a chemical defense for new bud leaves. Therefore, the primary question that remains is whether caffeine can serve as a nitrogen source for other metabolic pathways. If so, plants grown under a low nitrogen concentration should promote caffeine degradation, with the consequent use of nitrogen atoms (e.g . , in NH3) for the construction of other nitrogen compounds that are used for the plant's metabolism. Our results provide strong evidence that caffeine is degraded into allantoin at low rates in N-deficient plants but not in N-enriched ones. By contrast, this degradation may represent a significant N-source in N-deficient plants.
关键词：Coffea arabica L.; nitrogen compounds; nitrogen starvation; sun and shade plants
