Tocochromanols: Rancid lipids, seed longevity, and beyond
Abstract
Lipid peroxidation is a chain reaction in which unsaturated fatty acids in lipids of various types are oxidized, producing highly reactive products that can cause further cellular damage. Polyunsaturated fatty acids (PUFAs) are particularly susceptible to peroxidation, a chain reaction initiated by hydroxyl radicals ( Fig. 1 ). The first reasonably stable products, fatty acyl hydroperoxides, are still sufficiently reactive to produce aldehydes (reactive electrophiles) that cause cellular damage and induce the expression of defense-related genes ( 2, 3). This process is seen in the rancidification of fats and oils stored in the air. Chain reactions are minimized by preventing initiation or propagation. Initiation is minimized by antioxidant systems that decrease hydroxyl radical production ( 4). The tocochromanols are effective in preventing the propagation of peroxidation. Of these, α-tocopherol and γ-tocopherol ( 1) are the most common in plants ( 5, 6). Tocochromanols consist of a hydrophobic isoprenoid tail that is anchored into membrane bilayers, whereas a more hydrophilic hydroxychroman ring sits nearer the surface. To prevent propagation of fatty acid peroxidation, the hydroxyl group on the …