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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. [ABSTRACT FROM AUTHOR]

Cuticle composition is an important economic trait in agriculture, as it is the first protective barrier of the plant against environmental conditions. The main goal of this work was to study the role of the cuticular wax in maintaining the postharvest quality of zucchini fruit, by comparing two commercial varieties with contrasting behavior against low temperatures; the cold-tolerant variety 'Natura', and the cold-sensitive 'Sinatra', as well as 'Sinatra' fruit with induced-chilling tolerance through a preconditioning treatment (15°C for 48 h). The freshly-harvested 'Natura' fruit had a well-detectable cuticle with a significant lower permeability and a subset of 15 up-regulated cuticle-related genes. SEM showed that zucchini epicuticular waxes mainly consisted of round-shaped crystals and clusters of them, and areas with more dense crystal deposition were found in fruit of 'Natura' and of preconditioned 'Sinatra'. The cuticular wax load per surface was higher in 'Natura' than in 'Sinatra' fruit at harvest and after 14 days at 4°C. In addition, total cuticular wax load only increased in 'Natura' and preconditioned 'Sinatra' fruit with cold storage. With respect to the chemical composition of the waxes, the most abundant components were alkanes, in both 'Natura' and 'Sinatra', with similar values at harvest. The total alkane content only increased in 'Natura' fruit and in the preconditioned 'Sinatra' fruit after cold storage, whereas the amount of total acids decreased, with the lowest values observed in the fruit that showed less chilling injury (CI) and weight loss. Two esters were detected, and their content also decreased with the storage in both varieties, with a greater reduction observed in the cold-tolerant variety in response to low temperature. Gene expression analysis showed significant differences between varieties, especially in CpCER1-like and CpCER3-like genes, involved in alkane production, as well as in the transcription factors CpWIN1-like and CpFUL1-like , associated with cuticle development and epidermal wax accumulation in other species. These results suggest an important role of the alkane biosynthetic pathway and cuticle morphology in maintaining the postharvest quality of zucchini fruit during the storage at low temperatures. [ABSTRACT FROM AUTHOR]

Abscisic acid (ABA) is a key phytohormone in the regulation of most stress responses, which especially involve dehydration such as drought, high salinity, and low temperature. Under these stress conditions, plants accumulate ABA that triggers a response to cope with the adverse environment. In this study, we investigated the implication of ABA in the acquisition of chilling tolerance in zucchini during fruit postharvest. For that, we have analyzed ABA biosynthesis and response in fruit of two varieties with different chilling tolerance, ‘Natura’ (cold tolerant) and ‘Sinatra’ (cold sensitive). The results have showed that the biosynthesis of ABA was induced in ‘Natura’ fruit, with an increase of the abscisic aldehyde oxidase activity (AAO), and consequently an accumulation of ABA during the first day of exposition to cold. The levels of ABA showed a significant negative correlation with weight loss and chilling damage, and a positive correlation with firmness. Transcriptional analysis of some genes involved in ABA signaling and response, such as the ABA receptors PYL1 and PYL4, the transcription factors AI5L2/ABF3, NAC072/RD26, ATHB7, bHLH112, and the enzymes KAT2 as well as HDA6, a deacetylase involved in histone modification, presented different expression levels between varieties, showing ‘Natura’ the highest expression in most cases at least at short-term storage. Finally, to corroborate the role of ABA in cold tolerance, 5 mM of sodium tungstate (an inhibitor of ABA biosynthesis) was applied to ‘Natura’ fruit and 0.5 mM of ABA was applied to ‘Sinatra’ fruit and their postharvest behaviour at low temperature was followed. The treatment with tungstate induced cold-sensitivity in ‘Natura’ fruit, whereas ABA-treated ‘Sinatra’ fruit improved their quality during the storage at 4 °C. The results obtained point to ABA as a phytohormone responsible for the acquisition of postharvest cold tolerance. [ABSTRACT FROM AUTHOR]

Highlights: [•] Carbohydrate content was determined in zucchini fruits during postharvest storage. [•] The raffinose is more likely related to dehydration than to chilling susceptibility. [•] Glucose, fructose, and pinitol could be involved in the adaptation to cold storage. [ABSTRACT FROM AUTHOR]

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. • Exogenous abscisic acid (ABA) was applied to zucchini fruits prior to cold storage. • Untargeted metabolomics approach showed the metabolic changes on zucchini exocarps. • Time-dependent modulation of specialized metabolites and polyphenols was reported. • Methyl jasmonate led the ABA-mediated response facing chilling injury mitigation. [ABSTRACT FROM AUTHOR]

• Low temperature induces CpMYB106-like in the cold-tolerant 'Natura' fruit. • 'Natura' promoter, proMYB106A, shows higher basal expression. • Acclimation after cold stress increases GUS expression driven by proMYB106A. • Salt and MeJA upregulate both promoters, but most prominently proMYB106A. • CREs occurrence and distribution in 'Natura' promoter could lead to higher expression. 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 cold-tolerant 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 °C. 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. [Display omitted] [ABSTRACT FROM AUTHOR]

Abscisic 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. [Display omitted] • Abscisic acid (ABA) improves postharvest quality of zucchini fruit. • Targeted metabolomics reveals an ABA modulation of the primary metabolism. • An accumulation of sugars, organic acids and amino acids induced chilling tolerance. • Secondary metabolism was also affected by ABA treatment. • ABA activates the t-zeatin and riboflavin biosynthesis at first day of cold stress. [ABSTRACT FROM AUTHOR]

Given that external treatments with ABA had been proved to alleviate chilling injury in the immature zucchini fruit, an RNAseq analysis was conducted to gain insight into the molecular mechanisms that are involved in ABA-induced postharvest cold tolerance. Fruit from the cold sensitive cultivar Sinatra were treated with ABA and then stored for 14 d at 4 ºC. Exocarp samples from control and ABA-treated fruit were taken at 1, 5 and 14 d of cold storage, assessing the transcriptional changes during postharvest storage relative to freshly harvested fruit. The RNAseq analysis produced 229 million high-quality reads from a total of about 23,000 unigenes. Pairwise comparisons of differentially expressed genes (DEGs) in treated and untreated samples at each cold storage time resulted in 852, 793 and 1120 DEGs that were specifically found in the ABA-treated but not in the control fruit at either 1, 5 or 14 d of cold storage. This ABA-specific DEG list was subjected to a GO and KEGG enrichment analysis, as well as to a clusterization of gene expression profiles. This revealed the significance of certain metabolic and signaling pathways participating in ABA-induced postharvest cold tolerance, highlighting the relevance of the Ca2+ signaling pathway, as well as the positive regulation mediated by certain hormones such as ethylene and jasmonate, and the negative regulation mediated by others like auxins and brassinosteroids. A number of DEGs were also found in the ABA-treated fruit that code for transcription factors, as well as for genes involved in oxidative stress response and in membrane and cell wall metabolism. Data indicates that ABA-induced cold tolerance is not mediated by CBF-like genes but involve the up- and down-regulation of several transcription factors in the BZIP , GRAS , MYB , MYC , NAC and ZAT families that are known to participate as positive and negative regulators in the cold defensive response. Moreover, ABA regulates different genes responsible for reducing oxidative stress damage, inducing the biosynthesis of cuticular wax and repressing the biosynthesis of lignin, as well as protecting membrane and cell wall integrity in fruit cells during postharvest cold storage. • ABA induces postharvest cold tolerance in zucchini fruit independently of CBF pathway. • Specific roles of TFs and membrane and cell wall enzymes in postharvest cold response. • Ethylene, jasmonate, auxin and brassinosteroid mediate the ABA-induced cold tolerance. • Signaling genes for Ca2+ and MAPK are regulating zucchini postharvest cold tolerance. • Revealed genes could improve postharvest cold tolerance in zucchini fruit. [ABSTRACT FROM AUTHOR]