Fruit quality in organic and conventional farming: advantages and limitations

Fruit quality is essential for nutrition and human health and needs urgent attention in current agricultural practices. Organic farming is not as productive as conventional agriculture, but it can provide higher quality in some fruit crops, thanks to the absence of synthetic fertilizers and pesticides, enhanced pollination, and the reduction of protection treatments, hence boosting antioxidant compound production. Although organic farming does not always provide healthier food than conventional farming, some lessons from organic farming can be extrapolated to new sustainable production models. Exploiting natural resources and an adequate knowledge transfer will undoubtedly help improve the quality of climacteric and nonclimacteric fruits in new agricultural systems.

Identification and Profiling Analysis of microRNAs in Guava Fruit (Psidium guajava L.) and Their Role during Ripening

The guava (Psidium guajava L.) is a climacteric fruit with an accelerated post-harvest overripening. miRNAs are small RNA sequences that function as gene regulators in eukaryotes and are essential for their survival and development. In this study, miRNA libraries were constructed, sequenced and analyzed from the breaker and ripe stages of guava fruit cv. Siglo XXI. One hundred and seventy-four mature miRNA sequences from 28 miRNA families were identified. The taxonomic distribution of the guava miRNAs showed a high level of conservation among the dicotyledonous plants. Most of the predicted miRNA target genes were transcription factors and genes involved in the metabolism of phytohormones such as abscisic acid, auxins, and ethylene, as revealed through an ontology enrichment analysis. The miRNA families miR168, miR169, miR396, miR397, and miR482 were classified as being directly associated with maturation, whereas the miRNA families miR160, miR165, miR167, miR3930, miR395, miR398, and miR535 were classified as being indirectly associated. With this study, we intended to increase our knowledge and understanding of the regulatory process involved in the ripening process, thereby providing valuable information for future research on the ripening of guava fruit.

Effect of Potassium Permanganate, Ultraviolet Radiation and Titanium Oxide as Ethylene Scavengers on Preservation of Postharvest Quality and Sensory Attributes of Broccoli Stored with Tomatoes

This study introduces an effective solution to enhance the postharvest preservation of broccoli, a vegetable highly sensitive to ethylene, a hormone produced by climacteric fruits such as tomatoes. The proposed method involves a triple combination of ethylene elimination techniques: potassium permanganate (KMnO₄) filters combined with ultraviolet radiation (UV-C) and titanium oxide (TiO₂), along with a continuous airflow to facilitate contact between ethylene and these oxidizing agents. The effectiveness of this approach was evaluated using various analytical techniques, including measurements of weight, soluble solids content, total acidity, maturity index, color, chlorophyll, total phenolic compounds, and sensory analysis conducted by experts. The results demonstrated a significant improvement in the physicochemical quality of postharvest broccoli when treated with the complete system. Notably, broccoli subjected to this innovative method exhibited enhanced organoleptic quality, with heightened flavors and aromas associated with fresh green produce. The implementation of this novel technique holds great potential for the food industry as it reduces postharvest losses, extends the shelf life of broccoli, and ultimately enhances product quality while minimizing waste. The successful development and implementation of this new technique can significantly improve the sustainability of the food industry while ensuring the provision of high-quality food to consumers.

Natural variation in the NAC transcription factor NONRIPENING contributes to melon fruit ripening

The NAC transcription factor NONRIPENING (NOR) is a master regulator of climacteric fruit ripening. Melon (Cucumis melo L.) has climacteric and non-climacteric fruit ripening varieties and is an ideal model to study fruit ripening. Two natural CmNAC-NOR variants, the climacteric haplotype CmNAC-NOR^S,N and the non-climacteric haplotype CmNAC-NOR^A,S , have effects on fruit ripening; however, their regulatory mechanisms have not been elucidated. Here, we report that a natural mutation in the transcriptional activation domain of CmNAC-NOR^S,N contributes to climacteric melon fruit ripening. CmNAC-NOR knockout in the climacteric-type melon cultivar "BYJH" completely inhibited fruit ripening, while ripening was delayed by 5-8 d in heterozygous cmnac-nor mutant fruits. CmNAC-NOR directly activated carotenoid, ethylene, and abscisic acid biosynthetic genes to promote fruit coloration and ripening. Furthermore, CmNAC-NOR mediated the transcription of the "CmNAC-NOR-CmNAC73-CmCWINV2" module to enhance flesh sweetness. The transcriptional activation activity of the climacteric haplotype CmNAC-NOR^S,N on these target genes was significantly higher than that of the non-climacteric haplotype CmNAC-NOR^A,S . Moreover, CmNAC-NOR^S,N complementation fully rescued the non-ripening phenotype of the tomato (Solanum lycopersicum) cr-nor mutant, while CmNAC-NOR^A,S did not. Our results provide insight into the molecular mechanism of climacteric and non-climacteric fruit ripening in melon.

Systems Biology Applied to the Study of Papaya Fruit Ripening: The Influence of Ethylene on Pulp Softening

Papaya is a fleshy fruit that undergoes fast ethylene-induced modifications. The fruit becomes edible, but the fast pulp softening is the main factor that limits the post-harvest period. Papaya fast pulp softening occurs due to cell wall disassembling coordinated by ethylene triggering that massively expresses pectinases. In this work, RNA-seq analysis of ethylene-treated and non-treated papayas enabled a wide transcriptome overview that indicated the role of ethylene during ripening at the gene expression level. Several families of transcription factors (AP2/ERF, NAC, and MADS-box) were differentially expressed. ACO, ACS, and SAM-Mtase genes were upregulated, indicating a high rate of ethylene biosynthesis after ethylene treatment. The correlation among gene expression and physiological data demonstrated ethylene treatment can indeed simulate ripening, and regulation of changes in fruit color, aroma, and flavor could be attributed to the coordinated expression of several related genes. Especially about pulp firmness, the identification of 157 expressed genes related to cell wall metabolism demonstrated that pulp softening is accomplished by a coordinated action of several different cell wall-related enzymes. The mechanism is different from other commercially important fruits, such as strawberry, tomato, kiwifruit, and apple. The observed behavior of this new transcriptomic data confirms ethylene triggering is the main event that elicits fast pulp softening in papayas.

Ethylene and Auxin: Hormonal Regulation of Volatile Compound Production During Tomato (Solanum lycopersicum L.) Fruit Ripening

As the auxin-ethylene interaction in climacteric fruit ripening has been highlighted, the hormonal regulation of aroma changes in climacteric fruits requires clarification. The influence of both phytohormones on the volatile organic compound (VOC) metabolism was evaluated during tomato (Solanum lycopersicum L.) fruit ripening. Tomato fruits cv. Micro-Tom and Sweet Grape at the mature green stage were randomly grouped according to treatment with ethylene (ETHY), auxin (IAA), or both (ETHY + IAA). At middle ripening, Micro-Tom ETHY + IAA fruits present VOC profiles similar to those of ETHY fruits, while Sweet Grape presents VOC profiles closer to those of IAA fruits. At full ripeness, Micro-Tom and Sweet Grape ETHY + IAA fruits show profiles closer to those of IAA fruits, suggesting that the auxin overlaps the ethylene effects. Aroma compounds positively correlated with consumer preferences (2-isobutylthiazole, 6-methyl-5-hepten-2-one, and others) are identified in both cultivars and have their contents affected by both hormone treatments. The transcription of genes related to the biosynthesis of important tomato VOCs that have fatty-acid and carotenoid precursors evidences their regulation by both plant hormones. Additionally, the results indicate that the observed effects on the VOC metabolism are not restricted to the Micro-Tom cultivar, as these are also observed in the Sweet Grape cultivar. In conclusion, ethylene and auxin directly regulate the metabolic pathways related to VOC formation, impacting tomato aroma formation during ripening since Micro-Tom fruits apparently at the same maturation stage have different aromas.

Influence of the ethylene-related signal-inhibiting octapeptide NOP-1 on postharvest ripening and quality of 'Golden Delicious' apples

BACKGROUND

Processes extending the shelf life of climacteric fruit play an important role in terms of a sustainable global food supply. In a previous study, a synthetic octapeptide (NOP-1) was shown to inhibit the interaction between ethylene receptor (ETR) and ethylene insensitive-2 (EIN2), and in consequence delay tomato ripening. We investigated for the first time the effect of NOP-1 on inhibiting the ripening of apples ('Golden Delicious') during postharvest.

RESULTS

Using purified recombinant proteins from a bacterial expression system, we demonstrate here that EIN2 also interacts tightly (K_d  = 136 ± 29 nmol L^-1 ) with the corresponding apple ETR MdETR1. In line with previous binding studies on tomato ETRs, the ripening-delaying peptide NOP-1 clearly binds to the purified apple ETR. An NOP-1 solution (1000 µmol L^-1 ) was applied with a brush or microdispenser and compared with apples treated with 1-methylcyclopropene (1-MCP) (SmartFresh™, Agrofresh) applied as gaseous treatment or untreated control fruits. NOP-1 inhibited colour development and chlorophyll degradation during shelf life. These effects were more pronounced with the brush application (surface film) than with microdroplets application (mimicking a sprayable formulation). NOP-1 did not alter ethylene release or respiration rate, whereas 1-MCP expectedly strongly suppressed both. There were no differences in quality parameters evaluated.

CONCLUSION

Our study shows that NOP-1 binds to MdETR1 which results in delaying of ethylene-dependent ripening developments of skin colour and chlorophyll. Besides application methods, possible reasons for the weak effect of NOP-1 in comparison with previous tomato experiments could be different receptor affinity and penetration differences. © 2019 Society of Chemical Industry.

Fruit ripening: the role of hormones, cell wall modifications, and their relationship with pathogens

Fruits result from complex biological processes that begin soon after fertilization. Among these processes are cell division and expansion, accumulation of secondary metabolites, and an increase in carbohydrate biosynthesis. Later fruit ripening is accomplished by chlorophyll degradation and cell wall lysis. Fruit maturation is an essential step to optimize seed dispersal, and is controlled by a complex network of transcription factors and genetic regulators that are strongly influenced by phytohormones. Abscisic acid (ABA) and ethylene are the major regulators of ripening and senescence in both dry and fleshy fruits, as demonstrated by numerous ripening-defective mutants, effects of exogenous hormone application, and transcriptome analyses. While ethylene is the best characterized player in the final step of a fruit's life, ABA also has a key regulatory role, promoting ethylene production and acting as a stress-related hormone in response to drought and pathogen attack. In this review, we focus on the role of ABA and ethylene in relation to the interconnected biotic and abiotic phenomena that affect ripening and senescence. We integrate and discuss the most recent data available regarding these biological processes, which are crucial for post-harvest fruit conservation and for food safety.

'Movers and shakers' in the regulation of fruit ripening: a cross-dissection of climacteric versus non-climacteric fruit

Fruit ripening is a complex and highly coordinated developmental process involving the expression of many ripening-related genes under the control of a network of signalling pathways. The hormonal control of climacteric fruit ripening, especially ethylene perception and signalling transduction in tomato has been well characterized. Additionally, great strides have been made in understanding some of the major regulatory switches (transcription factors such as RIPENING-INHIBITOR and other transcriptional regulators such as COLOURLESS NON-RIPENING, TOMATO AGAMOUS-LIKE1 and ETHYLENE RESPONSE FACTORs), that are involved in tomato fruit ripening. In contrast, the regulatory network related to non-climacteric fruit ripening remains poorly understood. However, some of the most recent breakthrough research data have provided several lines of evidences for abscisic acid- and sucrose-mediated ripening of strawberry, a non-climacteric fruit model. In this review, we discuss the most recent research findings concerning the hormonal regulation of fleshy fruit ripening and their cross-talk and the future challenges taking tomato as a climacteric fruit model and strawberry as a non-climacteric fruit model. We also highlight the possible contribution of epigenetic changes including the role of plant microRNAs, which is opening new avenues and great possibilities in the fields of fruit-ripening research and postharvest biology.

Molecular regulation of fruit ripening

Fruit ripening is a highly coordinated developmental process that coincides with seed maturation. The ripening process is regulated by thousands of genes that control progressive softening and/or lignification of pericarp layers, accumulation of sugars, acids, pigments, and release of volatiles. Key to crop improvement is a deeper understanding of the processes underlying fruit ripening. In tomato, mutations blocking the transition to ripe fruits have provided insights into the role of ethylene and its associated molecular networks involved in the control of ripening. However, the role of other plant hormones is still poorly understood. In this review, we describe how plant hormones, transcription factors, and epigenetic changes are intimately related to provide a tight control of the ripening process. Recent findings from comparative genomics and system biology approaches are discussed.