Tissue-specific transcriptional analysis outlines calcium-induced core metabolic changes in sweet cherry fruit.

The role of calcium in fruit ripening has been established, however knowledge regarding the molecular analysis at fruit tissue-level is still lacking. To address this, we examined the impact of foliar-applied calcium (0.5% CaCl2) in the ripening metabolism in skin and flesh tissues of the sweet cherry 'Tragana Edessis' fruit at the harvest stage. Exogenously applied calcium increased endogenous calcium level in flesh tissue and reduced fruit respiration rate and cracking traits. Fruit metabolomic along with transcriptomic analysis unraveled common and tissue-specific metabolic pathways associated with calcium feeding. Treatment with calcium diminished several alcohols (arabitol, sorbitol), sugars (fructose, maltose), acids (glyceric acid, threonic acid) and increased ribose and proline in both fruit tissues. Moreover, numerous primary metabolites, such as proline and galacturonic acid, were differentially accumulated in calcium-exposed tissues. Calcium-affected genes that involved in ubiquitin/ubl conjugation and cell wall biogenesis/degradation were differentially expressed between skin and flesh samples. Notably, skin and flesh tissues shared common calcium-responsive genes and exhibited substantial similarity in their expression patterns. In both tissues, calcium activated gene expression, most strongly those involved in plant-pathogen interaction, plant hormone signaling and MAPK signaling pathway, thus affecting related metabolic processes. By contrast, calcium depressed the expression of genes related to TCA cycle, oxidative phosphorylation, and starch/sucrose metabolism in both tissues. This work established both calcium-driven common and specialized metabolic suites in skin and flesh cherry tissues, demonstrating the utility of this approach to characterize fundamental aspects of calcium in fruit physiology.

Identification of genes and metabolic pathways involved in wounding-induced kiwifruit ripening.

Fruit is constantly challenged by wounding events, inducing accelerated ripening and irreversible metabolic changes. However, cognate mechanisms that regulate this process are little known. To expand our knowledge of ripening metabolism induced by wounding, an artificial-wound global transcriptome investigation combined with metabolite profiling study was conducted in postharvest kiwifruit (Actinidia chinensis var. deliciosa (A. Chev.) A. Chev. 'Hayward'). Wounding treatment promoted fruit ripening, as demonstrated by changes in fruit firmness, ethylene production and respiration activity determined periodically during a ripening period of 8 d at room temperature. Calcium imaging using fluorescent probe Fluo-3 AM revealed spatial dynamics of Ca2+ signaling in the wounding area following 8d ripening. Several sugars including fructose, glucose, and sucrose as well as organic acids such as citric, succinic and galacturonic acid were increased by wounding. Changes of various amino acids in wounded-treated fruit, especially 5-oxoproline and valine along with alternations of soluble alcohols, like myo-inositol were detected. Gene expression analysis of the wounded fruit showed increased expression of genes that are mainly involved in defense response (e.g., AdTLP.1-3, AdPP2C.1-2, AdMALD1), calcium ion binding (e.g., AdCbEFh, AdCLR, AdANX), TCA cycle (e.g., AdMDH.1, AdMDH.2, AdCS), sugars (e.g., AdSUSA.1, AdSPS4, AdABFr), secondary metabolism (e.g., AdPAL.1-3, AdCCR, AdHCT.1-2), lipid processing (e.g., AdGELP.1-4, AdGELP) and pectin degradation (e.g., AdPE.1-2, AdPAE.1-2, AdPG.1-2) as well as in ethylene (AdERF7, AdERF1B, AdACO.1-4) and auxin (AdICE, AdAEFc, AdASII) synthesis and perception. Moreover, genes related to aquaporins, such as AdAQP2, AdAQP4 and AdAQP7 were down-regulated in fruit exposed to wounding. These results demonstrate multiple metabolic points of wounding regulatory control during kiwifruit ripening and provide insights into the molecular basis of wounding-mediated ripening.

The perennial fruit tree proteogenomics atlas: a spatial map of the sweet cherry proteome and transcriptome.

Genome-wide transcriptome analysis provides systems-level insights into plant biology. Due to the limited depth of quantitative proteomics our understanding of gene-protein-complex stoichiometry is largely unknown in plants. Recently, the complexity of the proteome and its cell-/tissue-specific distribution have boosted the research community to the integration of transcriptomics and proteomics landscapes in a proteogenomic approach. Herein, we generated a quantitative proteome and transcriptome abundance atlas of 15 major sweet cherry (Prunus avium L., cv 'Tragana Edessis') tissues represented by 29 247 genes and 7584 proteins. Additionally, 199 984 alternative splicing events, particularly exon skipping and alternative 3' splicing, were identified in 23 383 transcribed regions of the analyzed tissues. Common signatures as well as differences between mRNA and protein quantities, including genes encoding transcription factors and allergens, within and across the different tissues are reported. Using our integrated dataset, we identified key putative regulators of fruit development, notably genes involved in the biosynthesis of anthocyanins and flavonoids. We also provide proteogenomic-based evidence for the involvement of ethylene signaling and pectin degradation in cherry fruit ripening. Moreover, clusters of genes and proteins with similar and different expression and suppression trends across diverse tissues and developmental stages revealed a relatively low RNA abundance-to-protein correlation. The present proteogenomic analysis allows us to identify 17 novel sweet cherry proteins without prior protein-level annotation evidenced in the currently available databases. To facilitate use by the community, we also developed the Sweet Cherry Atlas Database (https://grcherrydb.com/) for viewing and data mining these resources. This work provides new insights into the proteogenomics workflow in plants and a rich knowledge resource for future investigation of gene and protein functions in Prunus species.

Genotype- and tissue-specific metabolic networks and hub genes involved in water-induced distinct sweet cherry fruit cracking phenotypes.

Sweet cherry fruit cracking is a complex physiological disorder that causes significant economic losses. Despite many years of research there is a lack of understanding of the mechanisms involved in cracking. Here, skin and flesh tissue from the cracking susceptible 'Early Bigi' and the cracking tolerant 'Regina' cultivars were sampled prior and just after water dipping treatment to identify water-affected metabolic networks that putatively involved in fruit cracking. Primary metabolites, most strongly those involved in sugars and amino acid metabolism, such as glucose and asparagine, shifted in 'Early Bigi' compared with 'Regina' tissues following water exposure. Comparisons between cultivars, tissues and dipping points identified significant differentially expressed genes. Particularly, genes related to abscisic acid, ethylene biosynthesis, pectin metabolism, expansins and aquaporins were altered in water-exposed tissues. To further characterize the role of these genes in cracking, their single nucleotide variants of the coding regions was studied in another eight sweet cherry cultivars, which differ in their sensitivity to cracking, revealing a strong link mainly between pectin metabolism-related genes and cracking-phenotypes. Integrated metabolomic and transcriptomic profiling uncovered genotypic- and tissue-specific metabolic pathways, including tricarboxylic acid cycle, cell enlargement, lipid and ethanol biosynthesis, and plant defense that putatively are involved in fruit cracking. Based on these results, a model which describes the skin and flesh metabolic reprogramming during water-induced fruit cracking in the susceptible 'Early Bigi' cultivar is presented. Τhis study can help to explore novel candidate genes and metabolic pathways for cracking tolerance in sweet cherry.

Comparative Transcriptomics and Metabolomics Reveal an Intricate Priming Mechanism Involved in PGPR-Mediated Salt Tolerance in Tomato.

Plant-associated beneficial strains inhabiting plants grown under harsh ecosystems can help them cope with abiotic stress factors by positively influencing plant physiology, development, and environmental adaptation. Previously, we isolated a potential plant growth promoting strain (AXSa06) identified as Pseudomonas oryzihabitans, possessing 1-aminocyclopropane-1-carboxylate deaminase activity, producing indole-3-acetic acid and siderophores, as well as solubilizing inorganic phosphorus. In this study, we aimed to further evaluate the effects of AXSa06 seed inoculation on the growth of tomato seedlings under excess salt (200 mM NaCl) by deciphering their transcriptomic and metabolomic profiles. Differences in transcript levels and metabolites following AXSa06 inoculation seem likely to have contributed to the observed difference in salt adaptation of inoculated plants. In particular, inoculations exerted a positive effect on plant growth and photosynthetic parameters, imposing plants to a primed state, at which they were able to respond more robustly to salt stress probably by efficiently activating antioxidant metabolism, by dampening stress signals, by detoxifying Na+, as well as by effectively assimilating carbon and nitrogen. The primed state of AXSa06-inoculated plants is supported by the increased leaf lipid peroxidation, ascorbate content, as well as the enhanced activities of antioxidant enzymes, prior to stress treatment. The identified signatory molecules of AXSa06-mediated salt tolerance included the amino acids aspartate, threonine, serine, and glutamate, as well as key genes related to ethylene or abscisic acid homeostasis and perception, and ion antiporters. Our findings represent a promising sustainable solution to improve agricultural production under the forthcoming climate change conditions.

Pre- and Post-harvest Melatonin Application Boosted Phenolic Compounds Accumulation and Altered Respiratory Characters in Sweet Cherry Fruit.

The aim of the present study was to investigate the impact of exogenous melatonin (0. 5 mM) application through pre-harvest foliar spray and postharvest immersion, alone or in combination, on ripening parameters of sweet cherry (cv. Ferrovia) fruit and their relationship with bioactive compounds and gene expression at harvest as well after cold storage (0°C) for 12 days and subsequent room temperature (20°C) exposure for 8 h. Although several ripening traits were not influenced by melatonin, the combining pre- and post-harvest treatments delayed fruit softening at post-cold period. Preharvest spray with melatonin depressed fruit respiration at time of harvest while all applied treatments induced respiratory activity following cold, indicating that this anti-ripening action of melatonin is reversed by cold. Several genes related to the tricarboxylic acid cycle, such as PaFUM, PaOGDH, PaIDH, and PaPDHA1 were upregulated in fruit exposed to melatonin, particularly following combined pre- and post-harvest application. The accumulation of phenolic compounds, such as neochlorogenic acid, chlorogenic acid, epicatechin, procyanidin B1, procyanidin B2+B4, cyanidin-3-O-galactoside, and cyanidin-3-O-rutinoside along with the expression of several genes involved in phenols biosynthesis, such as PaSK, PaPAL, Pa4CL, PaC4H, and PaFNR were at higher levels in melatonin-treated cherries at harvest and after cold exposure, the highest effects being observed in fruits subjected to both pre- and post-harvest treatments. This study provides a comprehensive understanding of melatonin-responsive ripening framework at different melatonin application conditions and sweet cherry stages, thereby helps to understand the action of this molecule in fruit physiology.

Silicon influenced ripening metabolism and improved fruit quality traits in apples.

The benefits of silicon against abiotic stress in different annual plant species have been described in many studies, however the regulation of ripening of fruit tree crops by silicon remains largely uncharacterized. Therefore, the present study aimed to explore the impact of foliar silicon application in the apple (cv. 'Fuji') fruit ripening traits along with the effect of silicon in the nutrient and metabolic changes in the fully expanded leaves, annual shoots, fruit outer pericarp (peel) and fruit mesocarp (skin) tissues. Data indicated that fruit firmness and apple peel color attributes, such as redness (a*) and percentage of red-blushed surface were induced by silicon application. Moreover, several fruit ripening traits, such as titratable acidity, soluble solid content and respiration rate were unaffected by silicon. Endogenous silicon level in leaves shoots and peel tissues were increased by exogenously applied silicon while several elements (i.e., P, Mg, Mn, Fe and Cu) were altered in the tested tissues that exposed to silicon. In addition, silicon increased the accumulation of total phenolic and total anthocyanin compounds in the various apple tissues. The level of various primary metabolites including sorbitol, fructose, maltose cellobiose, malic acid, phosphoric acid and gluconic acid was also notably affected by silicon in a tissue-specific manner. Overall, this study provides a valuable resource for future research, aiming in the elucidation of the role of silicon in fruit tree physiology.

Proteo-metabolomic journey across olive drupe development and maturation.

Maturity is one of the most important factors associated with the quality of olive products, however the molecular events underlying olive drupe development remain poorly characterized. Using proteomic and metabolomic approaches, this study investigated the changes in the olive drupes (cv. Chondrolia Chalkidikis) across six developmental stages (S1-S6) that characterize the dynamics of fruit growth and color. Primary metabolites, including carbohydrates and organic acids (i.e., xylose, malic acid), showed significant accumulation in the black maturation stage. Temporal changes in various secondary metabolites (e.g., oleuropein, oleacin and tyrosol) were also observed. Proteins involved in oxidation-reduction (i.e., LOX1/5), carbohydrate metabolism (i.e., GLUA, PG) and photosynthesis (i.e., chlorophyll a-b binding proteins) significantly altered in the turning black compared to the green mature stage. By providing the first proteometabolomic study of olive drupe development, this investigation offers a novel framework for further studies on this economically relevant crop.

Fruit quality trait discovery and metabolic profiling in sweet cherry genebank collection in Greece.

The current study characterizes the physicochemical, sensory and bioactive compound traits of twenty-two sweet cherry accessions, namely breeding lines, landraces and modern cultivars, embodying the majority of Greek germplasm. The evaluated accessions differ in several quality traits including colour parameters and textural properties as well as sensory attributes, such as taste intensity and overall acceptance. Significant differences in primary metabolites, including fructose, glucose, sorbitol, malic acid were recorded among tested accessions. All genotypes were rich in polyphenols, primarily in quercetin-3,4-O-diglucoside, esculetin, rutin and neochlorogenic acid. An anthocyanins-related discrimination among accessions was also obtained based on cyanidin-3-O-rutinoside and peonidin glycosides content. Overall, the cultivars 'Tsolakeika' and 'Bakirtzeika' exhibited the higher consumer acceptance while the cultivars 'Vasiliadi' and 'Tragana Edessis-Naousis' and especially the breeding line 'TxAg33' contained high polyphenol levels. These results represent a valuable resource for future breeding efforts for sweet cherry cultivars with improved nutritional quality traits.

Novel insights into the calcium action in cherry fruit development revealed by high-throughput mapping.

KEY MESSAGE: This work provides the first system-wide datasets concerning metabolic changes in calcium-treated fruits, which reveal that exogenously applied calcium may specifically reprogram sweet cherry development and ripening physiognomy. Calcium modulates a wide range of plant developmental processes; however, the regulation of fruit ripening by calcium remains largely uncharacterized. In this study, transcriptome, proteome and metabolome profiling was used to document the responses of sweet cherry fruit to external calcium application (0.5% CaCl2) at 15, 27 and 37 days after full blossom. Endogenous calcium loading in fruit across development following external calcium feeding was accompanied by a reduction in respiration rate. Calcium treatment strongly impaired water-induced fruit cracking tested by two different assays, and this effect depended on the fruit size, water temperature and light/dark conditions. Substantial changes in the levels of numerous polar/non-polar primary and secondary metabolites, including malic acid, glucose, cysteine, epicatechin and neochlorogenic acid were noticed in fruits exposed to calcium. At the onset of ripening, we identified various calcium-affected genes, including those involved in ubiquitin and cysteine signaling, that had not been associated previously with calcium function in fruit biology. Calcium specifically increased the abundance of a significant number of proteins that classified as oxidoreductases, transferases, hydrolases, lyases, and ligases. The overview of temporal changes in gene expression and corresponding protein abundance provided by interlinked analysis revealed that oxidative phosphorylation, hypersensitive response, DNA repair, stomata closure, biosynthesis of secondary metabolites, and proton-pump activity were mainly affected by calcium. This report provides the fullest characterization of expression patterns in calcium-responsive genes, proteins and metabolites currently available in fruit ripening and will serve as a blueprint for future biological endeavors.

Decoding altitude-activated regulatory mechanisms occurring during apple peel ripening.

Apple (Malus domestica Borkh) is an important fruit crop cultivated in a broad range of environmental conditions. Apple fruit ripening is a physiological process, whose molecular regulatory network response to different environments is still not sufficiently investigated and this is particularly true of the peel tissue. In this study, the influence of environmental conditions associated with low (20 m) and high (750 m) altitude on peel tissue ripening was assessed by physiological measurements combined with metabolomic and proteomic analyses during apple fruit development and ripening. Although apple fruit ripening was itself not affected by the different environmental conditions, several key color parameters, such as redness and color index, were notably induced by high altitude. Consistent with this observation, increased levels of anthocyanin and other phenolic compounds, including cyanidin-3-O-galactoside, quercetin-3-O-rhamnoside, quercetin-3-O-rutinoside, and chlorogenic acid were identified in the peel of apple grown at high altitude. Moreover, the high-altitude environment was characterized by elevated abundance of various carbohydrates (e.g., arabinose, xylose, and sucrose) but decreased levels of glutamic acid and several related proteins, such as glycine hydroxymethyltransferase and glutamate-glyoxylate aminotransferase. Other processes affected by high altitude were the TCA cycle, the synthesis of oxidative/defense enzymes, and the accumulation of photosynthetic proteins. From the obtained data we were able to construct a metabolite-protein network depicting the impact of altitude on peel ripening. The combined analyses presented here provide new insights into physiological processes linking apple peel ripening with the prevailing environmental conditions.

Whole genome re-sequencing of sweet cherry (Prunus avium L.) yields insights into genomic diversity of a fruit species.

Sweet cherries, Prunus avium L. (Rosaceae), are gaining importance due to their perenniallity and nutritional attributes beneficial for human health. Interestingly, sweet cherry cultivars exhibit a wide range of phenotypic diversity in important agronomic traits, such as flowering time and defense reactions against pathogens. In this study, whole-genome resequencing (WGRS) was employed to characterize genetic variation, population structure and allelic variants in a panel of 20 sweet cherry and one wild cherry genotypes, embodying the majority of cultivated Greek germplasm and a representative of a local wild cherry elite phenotype. The 21 genotypes were sequenced in an average depth of coverage of 33.91×. and effective mapping depth, to the genomic reference sequence of 'Satonishiki' cultivar, between 22.21× to 36.62×. Discriminant analysis of principal components (DAPC) with SNPs revealed two clusters of genotypes. There was a rapid linkage disequilibrium decay, as the majority of SNP pairs with r2 in near complete disequilibrium (>0.8) were found at physical distances less than 10 kb. Functional analysis of the variants showed that the genomic ratio of non-synonymous/synonymous (dN/dS) changes was 1.78. The higher dN frequency in the Greek cohort of sweet cherry could be the result of artificial selection pressure imposed by breeding, in combination with the vegetative propagation of domesticated cultivars through grafting. The majority of SNPs with high impact (e.g., stop codon gaining, frameshift), were identified in genes involved in flowering time, dormancy and defense reactions against pathogens, providing promising resources for future breeding programs. Our study has established the foundation for further large scale characterization of sweet cherry germplasm, enabling breeders to incorporate diverse germplasm and allelic variants to fine tune flowering and maturity time and disease resistance in sweet cherry cultivars.

Sweet cherry fruit cracking: follow-up testing methods and cultivar-metabolic screening.

BACKGROUND: Rain-induced fruit cracking is a major physiological problem in most sweet cherry cultivars. For an in vivo cracking assay, the 'Christensen method' (cracking evaluation following fruit immersion in water) is commonly used; however, this test does not adequately simulate environmental conditions. Herein, we have designed and evaluated a cracking protocol, named 'Waterfall method', in which fruits are continuously wetted under controlled conditions. RESULTS: The application of this method alone, or in combination with 'Christensen method, was shown to be a reliable approach to characterize sweet cherry cracking behavior. Seventeen cherry cultivars were tested for their cracking behavior using both protocols, and primary as well as secondary metabolites identification was performed in skin tissue using a combined GC-MS and UPLC-MS/MS platform. Significant variations of some of the detected metabolites were discovered and important cracking index-metabolite correlations were identified. CONCLUSIONS: We have established an alternative/complementary method of cherry cracking characterization alongside to Christiansen assay.

Systems-Based Approaches to Unravel Networks and Individual Elements Involved in Apple Superficial Scald.

Superficial scald is a major physiological disorder in apple fruit that is induced by cold storage and is mainly expressed as brown necrotic patches on peel tissue. However, a global view of the gene-protein-metabolite interactome underlying scald prevention/sensitivity is currently missing. Herein, we have found for the first time that cold storage in an atmosphere enriched with ozone (O3) induced scald symptoms in 'Granny Smith' apple fruits during subsequent ripening at room temperature. In contrast, treatment with the ethylene perception inhibitor 1-methylcyclopropene (1-MCP) reversed this O3-induced scald effect. Amino acids, including branched-chain amino acids, were the most strongly induced metabolites in peel tissue of 1-MCP treated fruits. Proteins involved in oxidative stress and protein trafficking were differentially accumulated prior to and during scald development. Genes involved in photosynthesis, flavonoid biosynthesis and ethylene signaling displayed significant alterations in response to 1-MCP and O3. Analysis of regulatory module networks identified putative transcription factors (TFs) that could be involved in scald. Subsequently, a transcriptional network of the genes-proteins-metabolites and the connected TFs was constructed. This approach enabled identification of several genes coregulated by TFs, notably encoding glutathione S-transferase (GST) protein(s) with distinct signatures following 1-MCP and O3 treatments. Overall, this study is an important contribution to future functional studies and breeding programs for this fruit, aiding to the development of improved apple cultivars to superficial scald.

Proteomic and metabolic analysis reveals novel sweet cherry fruit development regulatory points influenced by girdling.

Despite the application of girdling technique for several centuries, its impact on the metabolic shifts that underly fruit biology remains fragmentary. To characterize the influence of girdling on sweet cherry (Prunus avium L.) fruit development and ripening, second-year-old shoots of the cultivars 'Lapins' and 'Skeena' were girdled before full blossom. Fruit characteristics were evaluated across six developmental stages (S), from green-small fruit (stage S1) to full ripe stage (stage S6). In both cultivars, girdling significantly altered the fruit ripening physiognomy. Time course fruit metabolomic along with proteomic approaches unraveled common and cultivar-specific responses to girdling. Notably, several primary and secondary metabolites, such as soluble sugars (glucose, trehalose), alcohol (mannitol), phenolic compounds (rutin, naringenin-7-O-glucoside), including anthocyanins (cyanidin-3-O-rutinoside, cyanidin-3-O-galactoside, cyanidin-3.5-O-diglucoside) were accumulated by girdling, while various amino acids (glycine, threonine, asparagine) were decreased in both cultivars. Proteins predominantly associated with ribosome, DNA repair and recombination, chromosome, membrane trafficking, RNA transport, oxidative phosphorylation, and redox homeostasis were depressed in fruits of both girdled cultivars. This study provides the first system-wide datasets concerning metabolomic and proteomic changes in girdled fruits, which reveal that shoot girdling may induce long-term changes in sweet cherry metabolism.

An integrated metabolomic and gene expression analysis identifies heat and calcium metabolic networks underlying postharvest sweet cherry fruit senescence.

MAIN CONCLUSION: Ηeat and calcium treatments reprogram sweet cherry fruit metabolism during postharvest senescence as evidenced by changes in respiration, amino acid metabolism, sugars, and secondary metabolites shift. Heat and calcium treatments are used to improve postharvest fruit longevity; however, the exact mechanism remains poorly understood. To characterize the impact of these treatments on sweet cherries metabolism, 'Lapins' fruits were treated with heat or CaCl2 solutions and their combination and subsequently were exposed at room temperature, for up to 4 days, defined as senescence period. Single and combined heat and calcium treatments partially delayed fruit senescence, as evidenced by changes in fruit colour darkening, skin penetration force, and respiration activity. Calcium content was noticeably increased by heat in Ca-treated fruit. Several primary metabolites, including amino acids, organic acids, and alcohols, were decreased in response to both treatments, while many soluble sugars and secondary metabolites were increased within 1 day post-treatment. Changes of several metabolites in heat-treated fruits, especially esculetin, peonidin 3-O-glucoside and peonidin 3-O-galactoside, ribose, pyroglutamate, and isorhamnetin-3-O-rutinoside, were detected. The metabolome of fruit exposed to calcium also displayed substantial modulations, particularly in the levels of galactose, glycerate, aspartate, tryptophan, phospharate rutin, and peonidin 3-O-glucoside. The expression of several genes involved in TCA cycle (MDH1, IDH1, OGDH, SUCLA2, and SDH1-1), pectin degradation (ADPG1) as well as secondary (SK1, 4CL1, HCT, and BAN), amino acids (ALDH18A1, ALDH4A1, GS, GAD, GOT2, OPLAH, HSDH, and SDS), and sugar (PDHA1 and DLAT) metabolism were affected by both treatments. Pathway-specific analysis further revealed the regulation of fruit metabolic programming by heat and calcium. This work provides a comprehensive understanding of metabolic regulation in response to heat and calcium during fruit senescence.

Metabolic features underlying the response of sweet cherry fruit to postharvest UV-C irradiation.

The impact of ultraviolet-C (UV-C) irradiation on sweet cherry fruit was studied. Following harvest, fruits (cv. Sweetheart) were exposed to different doses of UV-C (0, 1.2, 3.0 or 6.0 kJ m-2) and then cold stored (0 °C) for 10 days. Treatments with UV-C delayed most ripening features and reduced pitting symptoms, particularly following prolonged UV-C application. Also, application of the highest UV-C dose inhibited pectin degradation and delayed skin resistance to penetration. An activation of antioxidants capacity and bioactive compounds, such as flavonoids and phenolics was observed. Illumination with UV-C diminished respiration and altered metabolite profile in whole fruit and skin samples. Several amino acids (eg., threonine and aspartate), sugars, (eg., glucose and fructose) and alcohols (e.g., inositol and mannitol) were modulated by long-term UV-C treatment in whole cherry fruit. Various metabolites, including malate, galacturonate, oxoproline and glutamine were also modulated by UV-C skin tissue. These data enhance our understanding of UV-C function in fruit biology.

Ozone-induced inhibition of kiwifruit ripening is amplified by 1-methylcyclopropene and reversed by exogenous ethylene.

BACKGROUND: Understanding the mechanisms involved in climacteric fruit ripening is key to improve fruit harvest quality and postharvest performance. Kiwifruit (Actinidia deliciosa cv. 'Hayward') ripening involves a series of metabolic changes regulated by ethylene. Although 1-methylcyclopropene (1-MCP, inhibitor of ethylene action) or ozone (O3) exposure suppresses ethylene-related kiwifruit ripening, how these molecules interact during ripening is unknown. RESULTS: Harvested 'Hayward' kiwifruits were treated with 1-MCP and exposed to ethylene-free cold storage (0 °C, RH 95%) with ambient atmosphere (control) or atmosphere enriched with O3 (0.3 µL L- 1) for up to 6 months. Their subsequent ripening performance at 20 °C (90% RH) was characterized. Treatment with either 1-MCP or O3 inhibited endogenous ethylene biosynthesis and delayed fruit ripening at 20 °C. 1-MCP and O3 in combination severely inhibited kiwifruit ripening, significantly extending fruit storage potential. To characterize ethylene sensitivity of kiwifruit following 1-MCP and O3 treatments, fruit were exposed to exogenous ethylene (100 µL L- 1, 24 h) upon transfer to 20 °C following 4 and 6 months of cold storage. Exogenous ethylene treatment restored ethylene biosynthesis in fruit previously exposed in an O3-enriched atmosphere. Comparative proteomics analysis showed separate kiwifruit ripening responses, unraveled common 1-MCP- and O3-dependent metabolic pathways and identified specific proteins associated with these different ripening behaviors. Protein components that were differentially expressed following exogenous ethylene exposure after 1-MCP or O3 treatment were identified and their protein-protein interaction networks were determined. The expression of several kiwifruit ripening related genes, such as 1-aminocyclopropane-1-carboxylic acid oxidase (ACO1), ethylene receptor (ETR1), lipoxygenase (LOX1), geranylgeranyl diphosphate synthase (GGP1), and expansin (EXP2), was strongly affected by O3, 1-MCP, their combination, and exogenously applied ethylene. CONCLUSIONS: Our findings suggest that the combination of 1-MCP and O3 functions as a robust repressive modulator of kiwifruit ripening and provide new insight into the metabolic events underlying ethylene-induced and ethylene-independent ripening outcomes.

Ethylene -dependent and -independent superficial scald resistance mechanisms in 'Granny Smith' apple fruit.

Superficial scald is a major physiological disorder of apple fruit (Malus domestica Borkh.) characterized by skin browning following cold storage; however, knowledge regarding the downstream processes that modulate scald phenomenon is unclear. To gain insight into the mechanisms underlying scald resistance, 'Granny Smith' apples after harvest were treated with diphenylamine (DPA) or 1-methylcyclopropene (1-MCP), then cold stored (0 °C for 3 months) and subsequently were ripened at room temperature (20 °C for 8 days). Phenotypic and physiological data indicated that both chemical treatments induced scald resistance while 1-MCP inhibited the ethylene-dependent ripening. A combination of multi-omic analysis in apple skin tissue enabled characterization of potential genes, proteins and metabolites that were regulated by DPA and 1-MCP at pro-symptomatic and scald-symptomatic period. Specifically, we characterized strata of scald resistance responses, among which we focus on selected pathways including dehydroabietic acid biosynthesis and UDP-D-glucose regulation. Through this approach, we revealed scald-associated transcriptional, proteomic and metabolic signatures and identified pathways modulated by the common or distinct functions of DPA and 1-MCP. Also, evidence is presented supporting that cytosine methylation-based epigenetic regulation is involved in scald resistance. Results allow a greater comprehension of the ethylene-dependent and -independent metabolic events controlling scald resistance.

Postharvest responses of sweet cherry fruit and stem tissues revealed by metabolomic profiling.

Sweet cherry, a non-climacteric and highly perishable fruit, is usually cold-stored during post-harvest period to prevent senescence; therefore, metabolic profiling in response to cold storage in sweet cherry is of economic and scientific interest. In the present work, metabolic analysis was performed in fruit and stem tissues to determine the metabolic dynamics associated with cold storage in response to 1-methylcyclopropene (1-MCP), an ethylene-action inhibitor, and modified atmosphere packaging (MAP). Fruit (cv. Regina) following harvest were treated with 1-MCP and then cold-stored (0 °C, relative humidity 95%) for 1 month in the presence or in the absence of MAP and subsequently maintained at 20 °C for up to 2 days. Physiological analysis suggested that cold storage stimulated anthocyanin production, respiration rate and stem browning. Cherry stem exposed to 1-MCP displayed senescence symptoms as demonstrated by the higher stem browning and the lower stem traction force while MAP treatment considerably altered these features. The metabolic profile of fruits and stems just following cold storage was distinctly different from those analyzed at harvest. Marked tissue-specific differences were also detected among sweet cherries exposed to individual and to combined 1-MCP and MAP treatments, notably for amino acid biosynthesis. The significance of some of these metabolites as cold storage hallmarks is discussed in the context of the limited knowledge on the 1-MCP and MAP response mechanisms at the level of cherry fruit and stem tissues. Overall, this study provides the first steps toward understanding tissue-specific postharvest behavior in sweet cherry under various conditions.