Ascorbic Acid Content and Transcriptional Profiling of Genes Involved in Its Metabolism during Development of Petals, Leaves, and Fruits of Orange (Citrus sinensis cv. Valencia Late).

Enriqueta Alós,Lorenzo Zacarias,Florencia Rey,María Jesús Rodrigo,José Vicente Gil

doi:10.3390/plants10122590

Abstract

Citrus fruit is one of the most important contributors to the ascorbic acid (AsA) intake in humans. Here, we report a comparative analysis of AsA content and transcriptional changes of genes related to its metabolism during development of petals, leaves and fruits of Valencia Late oranges (Citrus sinensis). Petals of close flowers and at anthesis contained the highest concentration of AsA. In fruits, AsA content in the flavedo reached a maximum at color break, whereas the pulp accumulated lower levels and experienced minor fluctuations during development. AsA levels in leaves were similar to those in the flavedo at breaker stage. The transcriptional profiling of AsA biosynthetic, degradation, and recycling genes revealed a complex and specific interplay of the different pathways for each tissue. The D-galacturonic acid pathway appeared to be relevant in petals, whereas in leaves the L-galactose pathway (GGP and GME) also contributed to AsA accumulation. In the flavedo, AsA content was positively correlated with the expression of GGP of the L-galactose pathway and negatively with DHAR1 gene of the recycling pathway. In the pulp, AsA appeared to be mainly controlled by the coordination among the D-galacturonic acid pathway and the MIOX and GalDH genes. Analysis of the promoters of AsA metabolism genes revealed a number of cis-acting elements related to developmental signals, but their functionalities remain to be investigated.

Highlights

Accepted: 24 November 2021L-ascorbic acid (AsA), known as vitamin C, is an essential component of the human diet, and fruits and vegetables are the main sources of this compound [1]
The AsA and DHA concentration in petals and leaves of Valencia Late at two developmental stages were assessed. Both tissues accumulated high levels of AsA, contents were higher in petals than in leaves (Figure 2)
Accumulation of AsA was similar in petals of closed flowers and at anthesis (~430 mg/100 g FW), but DHA increased by nearly 4-times during petal development (Figure 2A,B)

Summary

Introduction

L-ascorbic acid (AsA), known as vitamin C, is an essential component of the human diet, and fruits and vegetables are the main sources of this compound [1]. AsA is a powerful antioxidant that may decrease the incidence of several illnesses such as cancer or cardiovascular diseases [2]. The elucidation of AsA accumulation and the factors regulating its concentration in horticultural crops has been a topic of interest, and many studies have focused on assessing AsA concentrations in the edible parts of plants [3,4]. AsA is the most abundant low molecular weight antioxidant present in plant cells and participates in numerous physiological processes, including photosynthesis, growth, and senescence [5]. AsA levels have been associated with improved fruit postharvest properties [8,9,10]

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