Genotypic differences in metabolomic changes during storage induced-degreening of chrysanthemum disk florets

Selecting chrysanthemum cultivars with long storability and vase life is a major challenge for breeders. The rate of degreening of disk florets during the postharvest phase is an important determinant of vase life. There is large genotypic variation in susceptibility to disk floret degreening. Our aim was to understand these genotypic differences at the physiological level. Carbohydrate starvation seemed to play a role, since application of sugars prevented degreening and degreening only occurred if florets had a long-term low carbohydrate content. In order to find out which metabolic processes could explain genotypic differences, we used 1H Nuclear Magnetic Resonance (NMR) spectroscopy profiling, High Performance Anion Exchange Chromatography (HPAEC) and respiration measurements to compare metabolic responses of three genotypes to carbohydrate starvation. HPAEC and NMR measurements showed that carbohydrate content could not fully explain genotypic differences. A genotype with intermediate sensitivity to degreening showed similar carbohydrate content compared to an insensitive one. However, respiration rate declined faster under carbohydrate starvation in a sensitive and intermediate sensitive genotype compared to an insensitive genotype, suggesting a more abrupt constraint on the mitochondrial electron transport chain and with that oxidative stress. Changes in the metabolic profile under carbohydrate starvation were diverse and revealed candidate processes associated with disk floret degreening. Camphor content increased and correlated positively with degreening insensitivity. Phenylpropanoids and flavonoids also increased upon carbohydrate starvation and the response was genotype specific. We propose the upregulation of the phenylpropanoid metabolism as important source of nitrogen in the form of harmful ammonia during carbohydrate starvation. Our results provide a framework to identify processes associated with genotypic differences in the response to carbohydrate starvation and susceptibility to floret degreening.