Co-occurrence of cyanogenic glucosides and their derivatives as a common feature in metabolic profiles of almond and cassava

Almond (Prunus dulcis L.) and cassava (Manihot esculenta Crantz) are two important food crops and representatives of more than 2600 plants species known to produce amino acid-derived cyanogenic glucosides. Cyanogenic glucosides function as effective phytoanticipins, responsible for a sophisticated defence mechanism: the release of toxic HCN (cyanogenesis) upon tissue disruption [1]. However, cyanogenic glucosides are not only stagnant defence compounds. Increasing evidence points towards a dynamic endogenous turnover to provide plant primary metabolism with a supply of reduced nitrogen [2 – 4]. In order to investigate the presence of putative turnover products of cyanogenic glucosides, metabolite profiling using LC-MS/MS and HR-MS has been carried out in almond and cassava. In total, 21 structural derivatives of the aromatic cyanogenic glucosides prunasin and amygdalin in almond, and of the aliphatic cyanogenic glucosides linamarin and lotaustralin in cassava, have been identified, including di- and triglucosides and apiosides derived from a number of the aforementioned compounds. The relative amounts of the compounds were determined in different tissues and at various developmental stages.

Fig. 1: Proposed endogenous turnover pathway of cyanogenic glycosides without any release of HCN; instead, ammonia and carbon dioxide are recovered to be utilized in primary metabolism.

The co-occurrence of cyanogenic glycosides with their corresponding amides, acids and “anitriles” strongly suggests that an endogenous “unified” turnover pathway of cyanogenic glucosides operates in cyanogenic plants, thus enabling remobilization of reduced nitrogen and carbon for primary metabolism with no liberation of free HCN (Fig. 1). Elucidating this new catabolic route in the metabolism of cyanogenic glucosides has great potential for regulating the content of these toxic compounds in crops without disrupting plant vital functions.

Acknowledgement: The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme FP7/2007 – 2013/under REA grant agreement n° 289217.

Keywords: Almond, cassava, cyanogenic glucosides, endogenous turnover

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