The Unusual Acid-Accumulating Behavior during Ripening of Cherimoya (Annona cherimola Mill.) is Linked to Changes in Transcription and Enzyme Activity Related to Citric and Malic Acid Metabolism.

Mauricio González-Agüero,María Zamudio,Bruno Defilippi,Carolina Contreras,Pedro Undurraga,Luis Tejerina Pardo

doi:10.3390/molecules21050398

Abstract

Cherimoya (Annona cherimola Mill.) is a subtropical fruit characterized by a significant increase in organic acid levels during ripening, making it an interesting model for studying the relationship between acidity and fruit flavor. In this work, we focused on understanding the balance between the concentration of organic acids and the gene expression and activity of enzymes involved in the synthesis and degradation of these metabolites during the development and ripening of cherimoya cv. “Concha Lisa”. Our results showed an early accumulation of citric acid and other changes associated with the accumulation of transcripts encoding citrate catabolism enzymes. During ripening, a 2-fold increase in malic acid and a 6-fold increase in citric acid were detected. By comparing the contents of these compounds with gene expression and enzymatic activity levels, we determined that cytoplasmic NAD-dependent malate dehydrogenase (cyNAD-MDH) and mitochondrial citrate synthase (mCS) play important regulatory roles in the malic and citric acid biosynthetic pathways.

Highlights

During ripening, fruits are transformed into palatable consumer products, and consumer preference for a specific fruit or variety is determined by its organoleptic attributes
We focused on understanding the balance between organic acid levels during cherimoya development and ripening and enzymatic activity/gene expression related to the synthesis and degradation of these metabolites
In relation to the organic acid content, our analysis revealed almost no changes in ascorbic, tartaric and succinic acid levels during cherimoya ripening (Table 3); this was similar to what was found by Manríquez et al [23] in “Concha Lisa” and “Bronceada”, where the tartaric acid concentration was very low from harvest to the last stages of ripening

Summary

Introduction

Fruits are transformed into palatable consumer products, and consumer preference for a specific fruit or variety is determined by its organoleptic attributes. Organoleptic qualities are related to many other characteristics such as firmness, color, aroma, sweetness and acidity, which are associated with specific metabolic pathways that are coordinated during fruit development and ripening [1] Throughout this process, a series of changes in fruit composition occur, including the synthesis and degradation of pigments, volatile compound accumulation, and changes in the concentration of sugars and organic acids [2]. One of the most important traits affecting fruit quality, is a complicated attribute that is mainly controlled by the level and ratio of different sugars and organic acids [3] In fruits, these components are involved in both primary metabolism and in the biosynthesis of secondary metabolites, including amino acids, vitamins and aroma volatiles, which further influence quality [4]. The traits most commonly associated with fruit taste, are mainly measured as total

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