Regulation of on-tree vitamin E biosynthesis in olive fruit during successive growing years: The impact of fruit development and environmental cues

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Abstract

� 2016 Georgiadou,Goulas,Ntourou,Manganaris,Kalaitzis and Fotopoulos. 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 europaea cv. ‘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 (excluding VTE5) was monitored moving from the 1 st to the 3 rd growing 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 1 st ,2 nd ,and 3 rd year,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 1 st year. It is likely that,in a defense attempt against water deficit conditions and increased air temperature,transcription of genes involved in vitamin E biosynthesis (excluding VTE5) is up-regulated in olive fruit,probably leading to the blocking/deactivating of the pathway through a negative feedback regulatory mechanism.

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Georgiadou, E. C., Goulas, V., Ntourou, T., Manganaris, G. A., Kalaitzis, P., & Fotopoulos, V. (2016). Regulation of on-tree vitamin E biosynthesis in olive fruit during successive growing years: The impact of fruit development and environmental cues. Frontiers in Plant Science, 7(NOVEMBER2016). https://doi.org/10.3389/fpls.2016.01656

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