title: Regulation of On-Tree Vitamin E Biosynthesis in Olive Fruit during Successive Growing Years: The Impact of Fruit Development and Environmental Cues.
abstract: The term vitamin E refers to a group of eight lipophilic compounds known as tocochromanols. The tocochromanols are divided into two groups, that is, tocopherols and tocotrienols, with four forms each, namely α-, β-, γ-, and δ-. In order to explore the temporal biosynthesis of tocochromanols in olive (Olea europaeacv. 'Koroneiki') fruit during on-tree development and ripening over successive growing years, a combined array of analytical, molecular, bioinformatic, immunoblotting, and antioxidant techniques were employed. Fruits were harvested at eight successive developmental stages [10-30 weeks after flowering (WAF)], over three consecutive years. Intriguingly, climatic conditions affected relative transcription levels of vitamin E biosynthetic enzymes; a general suppression to induction pattern (excludingVTE5) was monitored moving from the 1stto the 3rdgrowing year, probably correlated to decreasing rainfall levels and higher temperature, particularly at the fruit ripening stage. A gradual diminution of VTE5 protein content was detected during the fruit development of each year, with a marked decrease occurring after 16 WAF. Alpha-tocopherol was the most abundant metabolite with an average percentage of 96.82 ± 0.23%, 91.13 ± 0.95%, and 88.53 ± 0.96% (during the 1st, 2nd, and 3rdyear, respectively) of total vitamin E content in 10-30 WAF. The concentrations of α-tocopherol revealed a generally declining pattern, both during the on-tree ripening of the olive fruit and across the 3 years, accompanied by a parallel decline of the total antioxidant capacity of the drupe. Contrarily, all other tocochromanols demonstrated an inverse pattern with lowest levels being recorded during the 1styear. It is likely that, in a defense attempt against water deficit conditions and increased air temperature, transcription of genes involved in vitamin E biosynthesis (excludingVTE5) is up-regulated in olive fruit, probably leading to the blocking/deactivating of the pathway through a negative feedback regulatory mechanism.
authors.affiliation: Department of Agricultural Sciences, Biotechnology and Food Science, Cyprus University of Technology Lemesos, Cyprus.
authors.forename: Egli C
authors.initials: EC
authors.lastname: Georgiadou
authors.affiliation: Department of Agricultural Sciences, Biotechnology and Food Science, Cyprus University of Technology Lemesos, Cyprus.
authors.forename: Vlasios
authors.initials: V
authors.lastname: Goulas
authors.affiliation: Department of Horticultural Genetics and Biotechnology, Mediterranean Agronomic Institute of Chania Chania, Greece.
authors.forename: Thessaloniki
authors.initials: T
authors.lastname: Ntourou
authors.affiliation: Department of Agricultural Sciences, Biotechnology and Food Science, Cyprus University of Technology Lemesos, Cyprus.
authors.forename: George A
authors.initials: GA
authors.lastname: Manganaris
authors.affiliation: Department of Horticultural Genetics and Biotechnology, Mediterranean Agronomic Institute of Chania Chania, Greece.
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Kalaitzis
authors.affiliation: Department of Agricultural Sciences, Biotechnology and Food Science, Cyprus University of Technology Lemesos, Cyprus.
authors.forename: Vasileios
authors.initials: V
authors.lastname: Fotopoulos
keywords: VTE5; Western blot; antioxidant capacity; relative transcription levels; tocopherols; tocotrienols; vitamin E