ANALYSIS OF ANTIOXIDANTS IN RIPENING TOMATO FRUITS SYNTHESIZING RESVERATROL

Many phytochemicals, with antioxidant activity, have significant consequences for human health and are thought to prevent some diseases greatly. The manipulation of plant secondary metabolism offers the opportunity to develop transgenic plants with increased health-promoting phytochemicals content. One such pathway with potential for manipulation is flavonoid metabolism where derivatives of cinnamic acid are converted to a wide array of phenolic compounds with various functions in plants. Trans-resveratrol is a polyphenolic compound produced from a reaction catalysed by the enzyme stilbene synthase which is closely related to chalcone synthase, the first enzyme of the flavonoid pathway. Resveratrol is believed to play a significant role in the pharmacological property of several plants through antioxidant, antileukaemic, or chemopreventive activities. Expression of stilbene synthase in heterologous plant species is considered an attractive option because the synthesis of resveratrol as a foreign antioxidant requires the addition of only a single gene. A stilbene synthase cDNA from grape was utilised to transform tomato (Lycopersicon esculentum Mill., cv Money maker) tissues by A. tumefaciens. Transgenic plants accumulate new compounds, not present in wild-type or vector transformed plants, that were identified as trans-resveratrol and trans-resveratrol-glucopyranoside by RP-HPLC analysis. The level synthesis of trans-resveratrol during fruit ripening was evaluated and the accumulation of the metabolite is likely to be dependent upon a combination of sufficient stilbene synthase levels and the availability of substrates (coumaroil-CoA and malonyl CoA). Fruit ripening is considered an oxidative phenomenon which requires enzymatic activity together with low-molecular-weight antioxidant molecules. Here we analyse the consequence of trans-resveratrol accumulation on synthesis of ascorbate and glutathione in transgenic ripening fruits.