Integrative Analysis of Terpenoid Profiles and Hormones from Fruits of Red-Flesh Citrus Mutants and Their Wild Types.

Cuihua Liu,Min He,Juan Xu,Zhuang Wang

doi:10.3390/molecules24193456

Abstract

In citrus color mutants, the levels of carotenoid constituents and other secondary metabolites are different in their corresponding wild types. Terpenoids are closely related to coloration, bitterness, and flavor. In this study, terpenoid profiles and hormones in citrus fruits of two red-flesh mutants—Red Anliu orange and Red-flesh Guanxi pummelo—and their corresponding wild types were investigated using GC/MS, HPLC, and LC-MS/MS. Results showed that Red Anliu orange (high in carotenoids) and Anliu orange (low in carotenoids) accumulated low levels of limonoid aglycones but high levels of monoterpenoids; conversely, Red-flesh Guanxi pummelo (high in carotenoids) and Guanxi pummelo (deficient in carotenoids) accumulated high levels of limonoid aglycones but low levels of monoterpenoids. However, isopentenyl diphosphate was present at similar levels. A correlation analysis indicated that jasmonic and salicylic acids might play important roles in regulating terpenoid biosynthesis. Additionally, the similarities of carotenoid and volatile profiles between each mutant and its corresponding wild type were greater than those between the two mutants or the two wild types. The flux balance of terpenoid metabolism in citrus fruit tends toward stability among various citrus genera that have different terpenoid profiles. Bud mutations could influence metabolite profiles of citrus fruit to a limited extent.

Highlights

In citrus, the ability to accumulate anthocyanins is not a universal feature [1]; blood orange (Citrus sinensis) and purple pummelo (Citrus maxima) are two rare citrus accessions characterized by high anthocyanin accumulation in mature fruits [1]
Two red-flesh citrus varieties and their respective wild types were used to explore the characteristics of phytohormones and terpenoid metabolites, including carotenoids, volatiles, and limonoid aglycones
Two different citrus species of fruits, sweet oranges of Red Anliu orange (R-An) and An (Citrus sinensis), together with pummelos of Red-flesh Guanxi pummelo (R-Guanxi pummelo (GX)) and GX (Citrus maxima), were employed in the study and their terpenoid profiles were very different. Both R-An and An accumulated low levels of Limonoid aglycones (LAs) but high levels of monoterpenoids; R-GX and GX accumulated high levels of LAs but low levels of monoterpenoids

Summary

Introduction

The ability to accumulate anthocyanins is not a universal feature [1]; blood orange (Citrus sinensis) and purple pummelo (Citrus maxima) are two rare citrus accessions characterized by high anthocyanin accumulation in mature fruits [1]. The main pigments of citrus fruit are carotenoids [1,2]. Fruit color is an important indicator of exterior and inner quality levels, including nutrition and flavor [3]. The juice sacs of citrus fruit are yellow or orange; an increase in color mutants of citrus has been reported—for example, Shara orange [4], Cara Cara navel orange [5], Red Anliu orange (R-An) [6], Chuhong pummelo [7], and Red-flesh Guanxi pummelo (R-GX) [8]. In addition to tetraterpenoid carotenoids, monoterpenoid and sesquiterpenoid volatiles, and triterpenoid bitter compounds are important secondary metabolites of citrus fruit [7] Carotenoid and primary and secondary metabolite (e.g., sugars, acids, and flavonoids) constituents in color mutants are different from those of wild types [6,9].

Methods

Results

Conclusion