Functional diversifications of cyanogenic glucosides

Searching for the bull’s eye: agents and targets of selection vary among geographically disparate cyanogenesis clines in white clover (Trifolium repens L.)

“…These observations raise the possibility that agents of selection other than herbivore pressure could be acting to maintain the cyanogenesis polymorphism. Consistent with this hypothesis, cyanogenic glucosides and their metabolites have been proposed to serve physiological functions unrelated to defense, including as nitrogen storage and transport compounds (Møller, 2010), and as signaling regulators that facilitate stress responses (Segień and Bogatek, 2006). If these physiological functions are favored under specific conditions, such as limited soil nitrogen or limited moisture, and if the conditions where they are favored tend to occur in warmer locations, then spatial variability in these conditions could serve as contributing factors in cyanogenesis cline evolution.…”

“…For example, cyanogenic plants may be less tolerant of freezing (Brighton and Horne, 1977; but see Olsen and Ungerer, 2008) or less resistant to fungal infection (Dirzo and Harper, 1982b, Lieberei et al, 1989, Ballhorn et al, 2010; both of these factors could contribute to geographical variation in cyanogenesis frequencies. In addition, there is evidence that cyanogenic glucosides and hydrogen cyanide can serve physiological functions unrelated to herbivore defense, including as mediators of stress response and as nitrogen storage or transport molecules (see reviews by Segień and Bogatek (2006) and Møller (2010)). Thus, geographical variation in nitrogen availability or other environmental factors relating to these functions might also have a role in cyanogenesis cline evolution.…”

“…Usable soil nitrogen is often highly limited during the beginning stages of water stress due to the reduced activity of nitrate reductase (Nilsen and Orcutt, 1996;Larcher, 2001), and it is plausible that cyanogenic glucosides could serve as a nitrogen source during these periods of acute nitrogen limitation (Møller, 2010). Studies to date have been inconclusive regarding the relative fitness of white clover cyanotypes under water stress.…”

A recycling pathway for cyanogenic glycosides evidenced by the comparative metabolic profiling in three cyanogenic plant species

“…The hidden power of cyanogenic plants resides in their ability to produce amino acid-derived cyanogenic glycosides, from which toxic hydrogen cyanide (HCN) may be released through the action of specific -glycosidases andhydroxynitrilases whenever plant tissue is disrupted for example by chewing herbivores or by humans preparing foods from cyanogenic crops [1,2] The generated HCN is toxic for the plants themselves and has to be detoxified. This entails two steps: (1) -cyanoalanine synthase-catalysed conversion of HCN and cysteine into -cyanoalanine and H 2 S; (2) NIT4 family nitrilase-catalysed conversion of the toxic -cyanoalanine into ammonia, aspartic acid and asparagine, all of which can be further utilized in plant metabolism ( Figure 1) [3][4][5][6][7].…”

“…Despite the established role of cyanogenic glycosides in plant chemical defence, it is apparent that they possess additional physiological functions which improve the plants phenotypic plasticity during specific developmental stages and under environmental stress [1,2,[7][8][9][10][11][12]. Studies on Olinia species suggest that cyanogenic glucosides may be involved in modulating oxidative stress by scavenging reactive oxygen species (e.g.…”