Accumulation of hydroxycoumarins during post-harvest deterioration of tuberous roots of Cassava (Manihot esculenta Crantz)

The use of the root crop Cassava (Manihot esculenta Crantz) is constrained by its rapid deterioration after harvest. Chemical and spectroscopic examination revealed the accumulation of four hydroxycoumarins (esculin, esculetin, scopolin and scopoletin), compounds derived from the phenylpropanoid pathway, during the time course of post-harvest deterioration. Fluorescence-microscopy revealed their localization in the apoplast of the parenchyma. Scopoletin and scopolin showed the most dramatic increases in concentration, peaking by day 2 after harvesting. A smaller secondary peak of scopoletin tended to be more pronounced in cultivars showing lower susceptibility to deterioration. Evidence for the metabolism of scopoletin to an insoluble coloured product by means of a peroxidase is presented. This product may be the cause of the discolouration of the vascular tissue during storage.