Extending cassava root shelf life via reduction of reactive oxygen species production

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cassava shelf life postharvest
Plant Physiology, online
One of the major constraints facing the large scale production of cassava roots is the rapid postharvest physiological deterioration (PPD) that occurs within 72 hours following harvest. One of the earliest recognized biochemical events during the initiation of PPD is a rapid burst of reactive oxygen species (ROS) accumulation. We have investigated the source of this oxidative burst to identify possible strategies to limit its extent and to extend cassava root shelf life. We provide evidence for a causal link between cyanogenesis and the onset of the oxidative burst that triggers PPD. By measuring ROS accumulation in transgenic low cyanogen plants with and without cyanide complementation, we show that PPD is cyanide dependent, presumably resulting from cyanide-dependent inhibition of respiration. To reduce cyanide-dependent ROS production in cassava root mitochondria, we generated transgenic plants expressing a codon-optimized Arabidopsis mitochondrial alternative oxidase (AOX 1A) gene. Unlike cytochrome C oxidase, AOX is cyanide insensitive. Transgenic plants overexpressing AOX exhibited over a 10-fold reduction in ROS accumulation compared to wild-type plants. The reduction in ROS accumulation was associated with delayed onset of PPD by 14-21 days after harvest of greenhouse-grown plants. The delay in PPD in transgenic plants was also observed under field conditions but with a root biomass yield loss in the highest AOX expressing lines. These data reveal a mechanism for postharvest physiological deterioration in cassava based on cyanide-induced oxidative stress, and PPD control strategies involving inhibition of ROS production or its sequestration.

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