Tocopherols are lipophilic antioxidants known as vitamin E and synthesized from the condensation of two metabolic pathways leading to the formation of homogentisate and phytyl diphosphate. While homogentisate is derived from tyrosine metabolism, phytyl diphosphate may be formed from geranylgeranyl diphosphate or phytol recycling from chlorophyll degradation. Here, we hypothesized that abscisic acid (ABA) could induce tocopherol biosynthesis in sweet cherries by modifying the expression of genes involved in vitamin E biosynthesis, including those from the phytol recycling pathway. Hence, the expression of key tocopherol biosynthesis genes was determined together with vitamin E and chlorophyll contents during the natural development of sweet cherries on the tree. Moreover, the effects of exogenously applied ABA on the expression of key tocopherol biosynthesis genes were also investigated during on-tree fruit development, and tocopherols and chlorophylls contents were analyzed. Results showed that the expression of tocopherol biosynthesis genes, including VTE5, VTE6, HPPD and HPT showed contrasting patterns of variation, but in all cases, increased by 2- and 3-fold over time during fruit de-greening. This was not the case for GGDR and VTE4, the first showing constitutive expression during fruit development and the second with marked down-regulation at ripening onset. Furthermore, exogenous ABA stimulated the production of both α- and γ-tocopherols by 60% and 30%, respectively, promoted chlorophyll degradation and significantly enhanced VTE5 and VTE6 expression, and also that of HPPD and VTE4, altogether increasing total tocopherol accumulation. In conclusion, ABA increases promote the transcription of phytol recycling enzymes, which may contribute to vitamin E biosynthesis during fruit development in stone fruits like sweet cherries.

中文翻译：

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甜樱桃果实中脱落酸通过 VTE5 和 VTE6 的瞬时转录激活触发维生素 E 积累

生育酚是一种亲脂性抗氧化剂，称为维生素 E，由两种代谢途径缩合合成，导致尿黑酸和植基二磷酸的形成。黑黑酸源自酪氨酸代谢，而植基二磷酸可以由香叶基香叶基二磷酸或叶绿素降解回收的叶绿醇形成。在这里，我们假设脱落酸 (ABA) 可以通过改变参与维生素 E 生物合成的基因（包括来自植醇回收途径的基因）的表达来诱导甜樱桃中的生育酚生物合成。因此，在甜樱桃在树上自然发育过程中，关键生育酚生物合成基因的表达与维生素 E 和叶绿素含量一起被确定。此外，还研究了外源施加ABA对树上果实发育过程中关键生育酚生物合成基因表达的影响，并分析了生育酚和叶绿素含量。结果表明，生育酚生物合成基因（包括 VTE5、VTE6、HPPD 和 HPT）的表达呈现出对比鲜明的变化模式，但在所有情况下，在果实脱绿过程中，随着时间的推移，生育酚生物合成基因的表达增加了 2 倍和 3 倍。 GGDR 和 VTE4 的情况并非如此，第一个在果实发育过程中表现出组成型表达，第二个在成熟开始时表现出明显的下调。此外，外源ABA分别刺激α-和γ-生育酚的产生60%和30%，促进叶绿素降解并显着增强VTE5和VTE6以及HPPD和VTE4的表达，共同增加总生育酚的积累。总之，ABA 的增加促进了植醇回收酶的转录，这可能有助于甜樱桃等核果发育过程中维生素 E 的生物合成。