Factors influencing α-tocopherol synthesis in pepper fruits

Determination of vitamin E in the fruit pericarp of green, yellow and red varieties of Capsicum annuum L. from the local market points to a parallel accumulation in pepper fruits of α-tocopherol with secondary carotenoids and triacylglycerols enriched in unsaturated fatty acids. Highest α-tocopherol concentrations of about 400 nmol per g of dry weight have been found in red fruits. Ripe yellow and red pepper fruits grown under greenhouse conditions were smaller and contained lower α-tocopherol contents than corresponding ones from the local market. An approximation to the α-tocopherol levels in market fruits has been observed, however, if the green plants had been treated with the bleaching herbicide norflurazone before fruit ripening, affecting the carotenoid pathway. Optimum herbicide efficiency has been obtained via watering of the green plants. In ripe fruits of the yellow and red varieties α-tocopherol contents were paralleled by increasing γ-tocopherol methyltransferase activities. In chromoplast preparations from pepper, methylation capacities have been found for γ- and δ-tocopherol as well as for the structurally related tocotrienols, the diterpene side chain of which consists of a geranylgeranyl- instead of the reduced phytyl residue found in tocopherols. β-Tocopherol was not methylated, which supports the position-specific methylation of prenylquinones at the 5 position of the tocopherol aromatic headgroup.