Nighttime Temperatures and Sunlight Intensities Interact to Influence Anthocyanin Biosynthesis and Photooxidative Sunburn in “Fuji” Apple

Xiaomin Xue,Pengmin Li,Jinzheng Wang,Fengwang Ma,Ying Duan

doi:10.3389/fpls.2021.694954

Abstract

Light and low temperatures induce anthocyanin accumulation, but intense sunlight causes photooxidative sunburn. Nonetheless, there have been few studies of anthocyanin synthesis under different sunlight intensities and low nighttime temperatures. Here, low nighttime temperatures followed by low light intensity were associated with greater anthocyanin accumulation and the expression of anthocyanin biosynthesis genes in “Fuji” apple peel. UDP-glucose flavonoid-3-O-glucosyltransferase (UFGT) activity was positively associated with anthocyanin enrichment. Ascorbic acid can be used as an electron donor of APX to scavenge H2O2 in plants, which makes it play an important role in oxidative defense. Exogenous ascorbate altered the anthocyanin accumulation and reduced the occurrence of high light–induced photooxidative sunburn by removing hydrogen peroxide from the peel. Overall, low light intensity was beneficial for the accumulation of anthocyanin and did not cause photooxidative sunburn, whereas natural light had the opposite effect on the apple peel at low nighttime temperatures. This study provides an insight into the mechanisms by which low temperatures induce apple coloration and high light intensity causes photooxidative sunburn.

Highlights

Apples (Malus domestica Borkh.) are appreciated by consumers worldwide and provide nutrition in the form of sugars, acids, vitamins, flavonoids, pectin, amino acids, and other components (Boyer and Liu, 2004; Hecke et al, 2006; Zhang et al, 2010)
Anthocyanin and Flavonoid Concentrations To explore the influence of low nighttime temperature and sunlight on phenolic compounds, anthocyanins and flavonoids were measured at different time periods
Because cyanidin-3-galactoside accounts for about 99% of the anthocyanin in apple peel (Chen et al, 2013), the 15◦C treatment had no substantive effect on overall anthocyanin content relative to the natural nighttime temperature

Summary

Introduction

Apples (Malus domestica Borkh.) are appreciated by consumers worldwide and provide nutrition in the form of sugars, acids, vitamins, flavonoids, pectin, amino acids, and other components (Boyer and Liu, 2004; Hecke et al, 2006; Zhang et al, 2010). Anthocyanin biosynthesis begins with 4-coumaroyl CoA from phenylalanine metabolism, and Nighttime Temperatures and Anthocyanin Biosynthesis phenylalanine ammonia lyase (PAL) is the key enzyme in phenylalanine metabolism The genes encoding these enzymes (PAL, CHS, DFR, ANS, and UFGT) are regulated primarily by the MYB-bHLH-WD40 (MBW) complex (Lloyd et al, 2017; An et al, 2019). In this complex, MYB transcription factors are regarded as the dominant components that regulate the anthocyanin biosynthetic genes (Dubos et al, 2010; Lai et al, 2013). Other MYB transcription factors such as MdMYB9, MdMYB11, MdMYB12, MdMYB22, MdbHLH3, and MdbHLH33 play important roles in the positive regulation of anthocyanin synthesis (An et al, 2012, 2014; Xie et al, 2012; Wang N. et al, 2018)

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Conclusion