Comment: hydrogen cyanide produced in genetically altered grasses

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hydrogen cyanide produced in genetically altered grasses

"Grape has also been genetically modified to resist insects by making them produce hydrogen cyanide when attacked by insects. Cyanogenic plants are characterized by the liberation of HCN in the course of tissue injury, due to the hydrolysis of cyanogenic glucosides. Most of our knowledge of cyanogenicity comes from Sorghum bicolor , which contains large quantities of the cyanogenic glucoside, dhurrin. Prussic acid, a derivative of cyanide, is also a serious potential problem. Crop species most commonly associated with prussic acid poisoning are sorghum, Johnsongrass, and Sudangrass. Grain sorghum typically has more potential for toxic levels of prussic acid than forage sorghum or Sudangrass. Young, rapidly growing plants are the most likely to contain high levels of prussic acid. Cyanide is more concentrated in young leaves than in older leaves or stems. New sorghum growth following drought or frost is dangerously high in cyanide. Generally, any stress condition that retards normal plant growth may increase prussic acid content. Hydrogen cyanide is released when plant leaves are damaged by trampling, cutting, crushing, chewing, or wilting. Drought-stunted plants accumulate cyanide and can possess toxic levels at maturity. Prussic acid poisoning is most commonly associated with regrowth following a drought-ending rain, or the first fall frost. New growth from frosted or drought-stressed plants is palatable, but dangerously high in cyanide. After a killing frost, at least four days should pass before grazing to allow released hydrogen cyanide to dissipate.

A multigenic trait responsible for biosynthesis of the secondary metabolite, dhurrin cyanogenic glucoside was engineered in grapevine with three genes sequences from sorghum ( Sorghum bicolor ): two cytochrome P450s (CYP79A1 and CYP71E1) and a UDPG-glucosyltransferase (sbHMNGT). The grapevine was modified using a two-step process involving whole plant transformation followed by hairy root transformation. The two step process make sure that the whole plant could be transformed with the dhurrin pathway, while the secondary transformation of the hairy root culture allowed fuller study of the dhurrin produced in roots which had been challenged with the root pathogenic insect Phyloxera .

One dhurrin-positive line was tested and found to release cyanide upon maceration. Co-culture of a cyanogenic hairy root line or a non-cyanogenic line with the specialist rootsucking, gall-forming, aphid-like insect, grapevine phylloxera ( Daktulosphaira vitifoliae ) gave no evidence that the cyanogenic plant tissue was protected from insect infestation. Consistently high levels of dhurrin accumulation may be required for that to occur [17]. We are not sure at all about the ultimate purpose of the modified grape but will certainly avoid drinking juice and wine made from it, provided that it is labeled as such. If it is not labeled, we may all have no choice over cyanide poisoning."

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