Ascorbate and glutathione metabolism in two sunflower cell lines of differing α-tocopherol biosynthetic capability

The natural antioxidants, tocopherols and ascorbate (ASC), are of great interest in terms of human health, because of their role in the prevention of chronic diseases. In cell metabolism, tocopherols are the major lipid-soluble antioxidants, whereas ASC and glutathione (GSH) are hydro-soluble antioxidants. These three metabolites cooperate in scavenging for oxygen radicals and protecting cell membranes. ASC and GSH are required in the process of regeneration of tocopherol from its α-cromanoxyl radical, while, GSH donates electrons for the reduction of dehydroascorbate (DHA), the fully oxidised form of ASC. Two cell lines of sunflower (Helianthus annuus L. cv Gloriasol) with differing capability to synthesise α-tocopherol were identified. In spite of the differing content of α-tocopherol (almost threefold higher in the high synthesising cell line, HT, than in the low synthesising one, LT), the cell lines have comparable growth curves. In the cells collected in the stationary phase, the ASC and GSH pools are also significantly higher in the HT cells than in the LT cells. On the other hand, the enzymes responsible for H2O2 scavenging and ASC and GSH recycling had higher activity in the LT than in the HT cells. The cooperation between the three antioxidant systems in the maintenance of the cellular redox balance is discussed, as well as the possible utilisation of the HT cell line for the in vitro production of natural antioxidants.