Manipulation of nitric oxide levels and its impacts on tomato fruit physiology and nutritional quality

Author(s)

Rafael Zuccarelli

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
• Defense date: 2022-08-05

Examining board members

Luciano Freschi; Marília Gaspar; Halley Caixeta de Oliveira; Ivan Sestari

• Advisor: Luciano Freschi; Maria Magdalena Rossi

Abstract

The ripening of fleshy fruits is a phenomenon controlled by a complex network of hormones and signaling molecules, and nitric oxide (NO) has been recognized as an important mediator of this process. However, the molecular mechanisms behind NO action in fruits and their consequences on the events leading to ripening-associated changes in fruit color, flavor, aroma and nutritional value remain poorly elucidated. Therefore, in this work, we conducted a detailed characterization of the transcriptome and metabolome in NO-treated tomato (Solanum lycopersicum) fruits under physiologically relevant concentrations. The treatment was performed in a NO-enriched atmosphere under continuous flow and normoxia during the pre-climacteric stage of detached fruits. The NO-treated fruits exhibited a late-ripening phenotype, with the preservation of the greenish coloration of the pedicellar region at advanced stages of ripening. These changes occurred without causing injuries or damage to the external appearance of the fruits. Approximately one-third of the transcripts detected during ripening displayed alterations in their abundance in response to NO, with relevant repression of several genes encoding ripening master regulators. This resulted in repression in both the fruit production and sensitivity to ethylene. In vitro activity assays of key antioxidant enzymes and quantification of hydrogen peroxide content revealed significant changes in the redox metabolism of NO-treated fruits. Such imbalance in fruit redox status resulted, in turn, in nitro-oxidative stress, as evidenced by the higher frequency of S-nitrosation and nitration events in proteins. Interestingly, increased S-nitrosoglutathione reductase (GSNOR) activity was also observed, which is the enzyme responsible for removing S-nitrosoglutathione (GSNO), one of the main metabolites derived from NO. Furthermore, flavonoids and ascorbate accumulation in NO-treated fruits presented an increase of 60% and 25%, respectively. Consistently, the abundance of gene transcripts related to flavonoid and ascorbate biosynthesis was also up-regulated. On the other hand, the carotenoid content in NO-treated fruits was only 70% of the concentration found in the untreated control group. In agreement, NO treatment repressed the transcript abundance of several genes related to lycopene biosynthesis, which is the main carotenoid responsible for giving the red color of tomato fruits. Finally, other compounds responsible for flavor and aroma, such as sugars, organic acids, amino acids and volatile compounds, were only marginally affected by the NO treatment. Together, our results indicated that the NO treatment at the early stages of ripening can prolong fruit shelflife, with significant impacts on the antioxidant composition and minimal changes in attributes associated with fruit flavor and aroma. (AU)

• FAPESP's process: 16/02033-1 - Manipulation of nitric oxide levels and its impacts on tomato fruit physiology, hormonal balance and nutritional quality
• Grantee: Rafael Zuccarelli
• Support Opportunities: Scholarships in Brazil - Doctorate