Exogenous abscisic acid mitigates chilling injury in zucchini during cold storage by eliciting a time-dependent shaping of specialized metabolites

Chilling injury is a physiological disorder that appears when zucchini fruit is stored at low temperatures, causing a severe diminution of the quality and nutraceutical value. Abscisic acid (ABA) has been proven to be a key natural agent preventing low-temperature damage. This work aimed to elucidate the changes in exocarp metabolites of zucchini fruit during cold storage and the mechanisms underlying the protective effects of ABA through an untargeted metabolomics approach. A time-dependent metabolic modulation could be observed in response to cold storage, where exogenously applied ABA elicited distinct metabolomic signatures. Supervised statistics were then used to identify methyl jasmonate, heliespirone C, and (indol-3-yl)acetyl-L-phenylalanine as the key compounds in the fruit exocarp having the highest discriminant ability. Noteworthy, the untargeted phenolic profile of zucchini exocarps was also distinctively modulated amid the different treatments. Overall, the implication of ABA in accumulating specialized metabolites, having a dual role in chilling injury mitigation during cold stress and increasing the nutraceutical properties of zucchini fruits, was observed.Grants (AGL2017-82885-C2-2-R and PID2020-118080RB-C22) of the Ministry of Science and Innovation (Spanish Government)Contrato-Puente from the Plan Propio of the University of Granad

The promoters of two CpMYB106-like paralog genes respond to abiotic stresses and phytohormones and drive differential expression in contrasting cultivars of Cucurbita pepo

Zucchini fruit (Cucurbita pepo L.) is susceptible to chilling injury (CI) during its postharvest life, with this response being cultivar-dependent. A previous transcriptomic analysis comparing cold-tolerant fruit from the cultivar ‘Natura’ with cold-sensitive fruit from the cultivar ‘Sinatra’, revealed the transcription factor (TF) CpMYB106-like as a relevant candidate gene for the acquisition of postharvest low-temperature tolerance. C. pepo has two CpMYB106-like paralogs, which are differentially present in the ‘Natura’ (CpMYB106-likeA) and ‘Sinatra’ (CpMYB106-likeB) cultivars due to gene and promoter deletions. The aim of this study was to investigate the transcriptional regulation of the CpMYB106-like paralogs to unravel their role in the postharvest life of zucchini fruit. For this, gene expression was analyzed and promoter sequences and their activities were studied through reporter β-glucuronidase (GUS) gene analysis in heterologous systems. An expression analysis showed that CpMYB106-like mRNA levels were induced only in the cold-stored fruit of ‘Natura’. The analysis of the promoter sequences showed numerous cis-regulatory elements (CREs), many of which have a differential distribution or frequency between the two paralogs. Promoter basal activity was determined by transient transformation of Nicotiana benthamiana leaves, which showed a higher expression driven by the promoter from the coldtolerant cultivar ‘Natura’, which could be explained by the presence of three additional copies of the enhancer element EECCRCAH1 in proMYB106A. The tissue-specific expression pattern, and the response to abiotic stresses and phytohormones controlled by CpMYB106-like promoters was analyzed in transgenic Arabidopsis thaliana plants. GUS activity was mainly detected in the vascular system, leaves, and inflorescences, especially in siliques. With respect to abiotic stresses, low temperature decreased GUS expression in Arabidopsis, but increased it in plants carrying the ‘Natura’ promoter after a 24-h acclimation period at 22 ºC. Salt treatment induced GUS activity driven by both promoters in Arabidopsis seedlings, but it was higher with the ‘Natura’ promoter. Furthermore, methyl jasmonate (MeJA) also induced a sharp increase of GUS controlled by proMYB106A. These results suggest that the regulation of CpMYB106- like TFs in zucchini is promoter-driven, and reveal the involvement of these genes in the acquisition of cold tolerance in fruit during postharvest stress conditions

Postharvest abscisic acid treatment modulates the primary metabolism and the biosynthesis of t-zeatin and ribofavin in zucchini fruit exposed to chilling stress

Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at doi:10.1016/j.postharvbio.2023.112457Abscisic acid (ABA) plays an important role in the regulation of several stress responses such as drought, high salinity and low temperature being also proved as a key phytohormone for the acquisition of postharvest cold tolerance in zucchini fruit. Therefore, it would be of great interest to unravel the mechanisms implicated in the ABA response, using a metabolomic approach. The aim of this work has been to use a combination of metabolomic tools to identify the main metabolic pathways involved in ABA-mediated regulation of chilling tolerance in zucchini fruit. As a result of this study, it was found that ABA modulates the primary metabolism inducing the accumulation of some sugars, organic acids such as succinic acid and amino acids including histidine, serine, phenylalanine, glutamic acid and γ-aminobutyric acid, and that are involved in low-temperature tolerance. ABA treatment also activates the t-zeatin and riboflavin biosynthesis during the first days of cold storage which can be important signals in the ABA-mediated cold response to induce tolerance in zucchini fruit.Departamento Fisiología Vegetal. Universidad de Granada. Grupo AGR-209Grants (AGL2017- 82885-C2–2-R and PID2020-118080RB-C22) funded by MCIN/AEI/10.13039/501100011033FPI grant EEBB-PRE-C-2018-0057 Funded by MCIN/AEI/ 10.13039/ 501100011033European Union NextGenerationEU/PRTRFunding for open access charge: Universidad de Granada / CBU

Postharvest Treatment with Abscisic Acid Alleviates Chilling Injury in Zucchini Fruit by Regulating Phenolic Metabolism and Non-Enzymatic Antioxidant System

Reports show that phytohormone abscisic acid (ABA) is involved in reducing zucchini postharvest chilling injury. During the storage of harvested fruit at low temperatures, chilling injury symptoms were associated with cell damage through the production of reactive oxygen species. In this work, we have studied the importance of different non-enzymatic antioxidants on tolerance to cold stress in zucchini fruit treated with ABA. The application of ABA increases the antioxidant capacity of zucchini fruit during storage through the accumulation of ascorbate, carotenoids and polyphenolic compounds. The quantification of specific phenols was performed by UPLC/MS-MS, observing that exogenous ABA mainly activated the production of flavonoids. The rise in all these non-enzymatic antioxidants due to ABA correlates with a reduction in oxidative stress in treated fruit during cold stress. The results showed that the ABA mainly induces antioxidant metabolism during the first day of exposure to low temperatures, and this response is key to avoiding the occurrence of chilling injury. This work suggests an important protective role of non-enzymatic antioxidants and polyphenolic metabolism in the prevention of chilling injury in zucchini fruit

Postharvest Treatment with Abscisic Acid Alleviates Chilling Injury in Zucchini Fruit by Regulating Phenolic Metabolism and Non-Enzymatic Antioxidant System

Reports show that phytohormone abscisic acid (ABA) is involved in reducing zucchini postharvest chilling injury. During the storage of harvested fruit at low temperatures, chilling injury symptoms were associated with cell damage through the production of reactive oxygen species. In this work, we have studied the importance of different non-enzymatic antioxidants on tolerance to cold stress in zucchini fruit treated with ABA. The application of ABA increases the antioxidant capacity of zucchini fruit during storage through the accumulation of ascorbate, carotenoids and polyphenolic compounds. The quantification of specific phenols was performed by UPLC/MS-MS, observing that exogenous ABA mainly activated the production of flavonoids. The rise in all these non-enzymatic antioxidants due to ABA correlates with a reduction in oxidative stress in treated fruit during cold stress. The results showed that the ABA mainly induces antioxidant metabolism during the first day of exposure to low temperatures, and this response is key to avoiding the occurrence of chilling injury. This work suggests an important protective role of non-enzymatic antioxidants and polyphenolic metabolism in the prevention of chilling injury in zucchini fruit.Ministry of Science and Innovation, Spain (MICINN)Spanish Government AGL2017-82885-C2-2-R PID2020-118080RB-C22Spanish Governmen

Application of polysaccharide-based edible coatings to improve the quality of zucchini fruit during postharvest cold storage

The use of edible coatings has surged as a response to the ever-increasing demand for ecologically-friendly methods for maintaining fruit quality during storage. This study analyses the application of different polysaccharide-based coatings, carboxymethylcellulose, chitosan, dextrin and starch, and the use of a plasticizer agent, glycerol, with dextrin shown to be the most effective in maintaining the postharvest quality of zucchini fruit during cold storage. Subsequently, to improve these results, the nutraceutical additives oleuropein and olive oil, were tested in combination with dextrin. Results showed that dextrin coatings reduced weight loss, chilling injury, and oxidative stress in zucchini fruit at low temperature, maintaining fruit quality. The natural additives obtained from the olive tree showed a higher induction of antioxidant enzymes as well as a greater accumulation of ascorbate and total phenolics, with the dextrin coating with olive oil being even more effective in maintaining the chilling injury low until the end of storage, associated to phenolic metabolism. This type of preservation could be implemented for extending postharvest life and enhancing the overall quality of zucchini fruit.Programa Operativo FEDER Andalucía 2014-2020 (Project BAGR-296-UGR20)FPI grants (MEC) (Project AGL2017-82885-C2-2-R): Universidad de Granada / CBU