The accumulation of the acylic sesquiterpene, α-farnesene, and its subsequent oxidation into conjugate trienols (CTols), leading to the production of the ketone 6-methyl-5-hepten-2-one (MHO Rowan et al., 1995), is widely considered to be a principal cause of superficial scald (Huelin and Murray, 1966 Anet, 1969 Whitaker et al., 2000 Lurie et al., 2005 Lurie and Watkins, 2012). This post-harvest disorder arises as a chilling injury following cold storage (Whitaker and Saftner, 2000 Tsantili et al., 2007 Rudell et al., 2009 Pesis et al., 2009), and is associated with structural disorganization of mitochondria and chloroplasts (Kratsch and Wise, 2000 Sevillano et al., 2009). However, cold storage can also promote the occurrence of several physiological disorders, such as superficial scald in apple, which manifests as necrosis in the epidermis and hypodermal cortical tissues (Watkins et al., 1995 Tsantili et al., 2007 Lurie and Watkins, 2012).
Post-harvest quality and shelf life can be extended by storage in low-temperature conditions, which slows down general fruit cell metabolism (McGlasson et al., 1979 Sevillano et al., 2009). The pattern of sorbitol accumulation was consistent with the expression profile of a sorbitol 6-phosphate dehydrogenase, MdS6PDH, the overexpression of which in transgenic Arabidopsis thaliana plants confirmed its involvement in the cold acclimation and freezing tolerance.įleshy fruits, after harvest, are often stored in order to guarantee long-term availability and marketability. Specifically, the inhibition of ethylene perception stimulated the production of antioxidant compounds to scavenge reactive oxygen species, the synthesis of fatty acids to stabilize plastid and vacuole membranes against cold temperature, and the accumulation of the sorbitol, which can act as a cryoprotectant. We also determined that prevention of superficial scald, through the use of an ethylene action inhibitor, is associated with the triggering of cold acclimation-related processes. To elucidate the mechanism of superficial scald development and possible means of prevention, we performed an integrated metabolite screen, including an analysis of volatiles, phenols and lipids, together with a large-scale transcriptome study.
Although this phenomenon is widely ascribed to the oxidation of α-farnesene, its physiology is not yet fully understood. In apple, one of the most serious physiological disorders is superficial scald, which is characterized by discoloration and brown necrotic patches on the fruit exocarp. Fruits stored at low temperature can exhibit different types of chilling injury.