Abstract
Amino acids represent an important component in the diet of the Venus flytrap (Dionaea muscipula), and supply plants with much needed nitrogen resources upon capture of insect prey. Little is known about the significance of prey-derived carbon backbones of amino acids for the success of Dionaea's carnivorous life-style. The present study aimed at characterizing the metabolic fate of N-15 and C-13 in amino acids acquired from double-labeled insect powder. We tracked changes in plant amino acid pools and their C-13- and N-15-signatures over a period of five weeks after feeding, as affected by contrasting feeding intensity and tissue type (i.e., fed and non-fed traps and attached petioles of Dionaea). Isotope signatures (i.e., C-13 and N-15) of plant amino acid pools were strongly correlated, explaining 60% of observed variation. Residual variation was related to contrasting effects of tissue type, feeding intensity and elapsed time since feeding. Synthesis of nitrogen-rich transport compounds (i.e., amides) during peak time of prey digestion increased N-15- relative to C-13- abundances in amino acid pools. After completion of prey digestion, C-13 in amino acid pools was progressively exchanged for newly fixed C-12. The latter process was most evident for non-fed traps and attached petioles of plants that had received ample insect powder. We argue that prey-derived amino acids contribute to respiratory energy gain and loss of (CO2)-C-13 during conversion into transport compounds (i.e., 2days after feeding), and that amino-nitrogen helps boost photosynthetic carbon gain later on (i.e., 5weeks after feeding).