Anthocyanin Accumulation Mechanism in Highbush Blueberry Fruit by UV Radiation

Abstract

The aim of this work was to better understand the molecular mechanism of increasing anthocyanin contents in highbush blueberry fruit (Vaccinium corymbosum L.)after UV-B radiation at 6.0 kJ m-2 for 20 min. Blueberry fruits were applied by three kinds of UV lights (A, B and C) to find out UV-B and UV-C are the good radiations to maintain the quality and anthocyanin of blueberry fruit. Most of individual anthocyanins, namely Delphinidine-3-galactoside, Delphinidin-3-glucoside, Delphinidine-3-arabinoside, Petunidine-3-galactoside, Petunidine-3-glucoside, Petunidine-3-arabinoside, Malvidine-3-galactoside, Malvidine-3-glucoside and Malvidine-3-arabinoside increased after 3 h by UV-B and UV-C radiation treatments. Then, the analysis on effects of UV-B radiation on the gene expressions of anthocyanin and ethylene related genes and transcription factors (TFs) of VcBBX, VcMYB21, VcWD40, VcR2R3MYB, VcEIL4, and VcTDR4 in tissues of Duke and Nelson highbush blueberry fruitwere investigated. Beside of that, the ethylene production and the main individual anthocyanin also were analyzed. These findings showed that the UV-B and UV-C radiation can improve the quality and anthocyanin in Duke blueberry fruit. UV-B radiation increased transcript levels of anthocyanin biosynthesis genes such as VcPAL,VcCHS, VcF3H, VcDFR, and VcUFGTand also up-regulated about transcript levels on TFs of VcR2R3 MYB, VcMYB21, VcWD40, VcBBX, and VcEIL4inthe peels of Duke blueberry fruit. This increasing was found in immediately after UV-B treatment (20 min) and became maximized within 3 h. However, UV-B radiation reduced the transcript levels of VcTDR4, VcACO, VcETR1 in Duke blueberry fruit. UV-B radiation also induces the reduction of ethylene production in Nelson blueberry fruit. The contents of main individual anthocyanin (Delphinidin-3-Galactoside, Malvidin-3-Galactoside, and Malvidin-3-Arabinoside) were increased significantly after UV-B immediately or within 3 h depending on the analyzed tissues. The results indicated that UV-B radiation stimulates the increase of anthocyanin biosynthesis which could be up-regulated by the anthocyanin related TFs and down-regulated by the ethylene related genes in Duke blueberry fruit. This study supports that the pre-storage treatment of UV-B increases the phytochemical accumulation of the full-ripe highbush blueberry fruit after being picked.