Chlorophyll Catabolites in Senescent Leaves of Lima Bean (Phaseolus Lunatus) and in the Frass of Spodoptera Littoralis After Defecation

Abstract

Chlorophylls (Chls), the green pigments responsible for photosynthesis in plants, algae and bacteria, are also part of the daily diet of herbivorous feeders. Chl degradation occurs during leaf senescence and fruit ripening but is also noticed as a response to biotic and abiotic stresses. Besides the programmed degradation during senescence different factors such as high temperature, extreme pH values, enzymatic actions, molecular oxygen, and light initiate the degradation of Chl. To gain more information on Chl degradation in the gut of plant-feeding insects, regurgitate and frass of Spodoptera littoralis caterpillars were analysed for late Chl catabolites by using LC-MS, UV, Fluorescence and NMR spectroscopy. The major metabolites were determined in fresh leaves of the food plant lima bean (Phaseoluslunatus), and were compared with digestive products. The observed spectrum of metabolites can be attributed to the combined action of esterolytic gut enzymes and the strongly alkaline milieu in the digestive tract. Interestingly, linear Chl catabolites were not detected in the gut of the larvae of S. littoralis. Substantial amounts of Chl catabolites were found to be macrocyclic rings opened in the senescent food plants, but also in the aged frass. We studied two primary fluorescent chlorophyll catabolites in senescent leaves of lima bean. One of the primary fluorescent chlorophyll catabolites that have been found in the frass of S. littoralis might be generating opened tetrapyrroles of Chl, only after being exposed to the air and light.