The influence of virus infections on antioxidant levels in the genetically modified plum variety "Honeysweet" (Prunus domestica L.)

It is well-known that polyphenolic compounds are found abundantly in fruit, but various kinds of diseases  lower these levels. This work measures total polyphenolic content, antioxidant activity and the levels of specific important antioxidants in fruits of the genetically modified (GM) plum variety HoneySweet, trees  which were previously inoculated with a range of different virus infections.  These were the Plum Pox virus (PPV), Prune Dwarf virus (PDV) and Apple Chlorotic Leaf-Spot virus (ACLSV). Uninoculated trees were used as controls. Antioxidant activity was measured using four different photometric  methods – DPPH (2,2-diphenyl-1-picrylhydrazyl), DMPD (N-dimethyl-p-phenylenediamine), ABTS (2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid) and FRAP (Ferric reducing antioxidant power). Total polyphenol content was measured using the Folin–Ciocalteau method. The profiles of 10 specific antioxidant constituents in the fruits of the GM plum variety HoneySweet were detected and analyzed, since these are of interest for their role in human diets and could play a role in the resistance of plants to viruses. Detection was made using HPLC with UV-VIS detection.  They were: gallic acid, p-coumaric acid, 4-aminobenzoic acid, chlorogenic acid, caffeic acid, ferulic acid, vanillin, rutin and quercetin. The compound with the highest concentration was chlorogenic acid (587 mg/100 g), and that with the lowest was p-coumaric acid (0.95 mg/100 g). Of the four methods of antioxidant activity used, in three the lowest levels of antioxidant activity were seen where the PPV virus was combined with ACLSV, and in three the highest levels were seen in the un-inoculated control without any infection. The highest values of total polyphenols were seen in the control (65.3 mg/100 g), followed by infection of PPV, then treatment PPV, PDV and ACLSV, then treatment PPV and PDV and finally the lowest levels were seen in treatment PPV and ACLSV (44.2 mg/100 g), which was also that with the lowest antioxidant activity.