1-Methylcyclopropene and extreme ULO inhibit superficial scald in a different way highlighting the physiological basis of this disorder in pear

Despite years of research on the biochemical basis of superficial scald in apples, relatively little is known about the specific regulatory processes involved in pears. To gain further knowledge on these processes, different storage scenarios, controlled atmosphere (CA), 1-methylcyclopropene treatment (1-MCP) and storage under very low O2 concentration (xULO) were used in the scald susceptible ‘Blanquilla’ pears. Ethylene production, α-farnesene (AF), conjugated trienols (CTols) content and changes in ethanol levels were evaluated during storage and further related to superficial scald development and changes in fruit quality upon removal. While 1-MCP completely inhibited ethylene production and fruit softening, only a partial and transient inhibition of these parameters was found for xULO-treated fruit. Both 1-MCP and xULO treatments completely controlled scald disorder, yet in different ways. The reduction in disorder incidence in 1-MCP treated fruit was the result of ethylene inhibition and reduced levels of α-farnesene and CTols. In contrast, xULO treatment only partially inhibited ethylene production and the levels of α-farnesene metabolites but led to increased ethanol levels that were directly related to the scald incidence inhibition. Collectively, these results highlight that superficial scald in pear is not strictly related to ethylene and α-farnesene metabolism and that other compounds, such as the weak antioxidant ethanol, play a determining role in ‘Blanquilla’ pear.info:eu-repo/semantics/acceptedVersio

Interplay between hormones and assimilates during pear development and ripening and its relationship with the fruit postharvest behaviour

The ability of European pears (Pyrus communis L.) to ripen immediately after harvest is cultivar-dependent and relies on a range of physiological and biochemical events occurring during fruit growth and development that remain largely unknown. To gain further knowledge on these events, changes in the content of sugars, acids, major hormones and ethylene precursors or related enzymes were studied in two pear varieties (‘Blanquilla’ and ‘Conference’) with known differences in their postharvest ripening behaviour. In both cultivars, low contents of abscisic acid (ABA) seemed to be a prerequisite to initiate on-tree fruit ripening including sugar accumulation and softening. In ‘Blanquilla’ pears, the enhanced potential to produce ethylene and thereby to ripen upon harvest was associated to a late increase in ABA content paralleled by an accumulation of indole 3-acetic acid (IAA). In turn, the inability of ‘Conference’ fruit to produce ethylene upon harvest appeared to be related to a coordinated action of gibberellins (more specifically GA1), salicylic acid (SA) and jasmonic acid (JA), which remained at high concentrations during the latest phases of fruit growth. Collectively, our results highlight that a complex hormonal cross-talk during the development and on-tree ripening of pear fruit may finally determine the ability of the fruit to ripen upon harvest.info:eu-repo/semantics/acceptedVersio

New insights on the ripening pattern of ‘Blanquilla’ pears: A comparison between on- and off-tree ripened fruit

To better understand the key processes involved in the ripening of attached fruit, we have investigated physico-chemical and biochemical changes occurring in ‘Blanquilla’ pear during on-tree (attached fruit) and off-tree ripening (harvested fruit). Flesh firmness, sugars, acids and the volatile profiles as well as ethylene metabolism, PG and PME enzyme activities and oxidative damage were measured. Firmness loss in detached ‘Blanquilla’ pear (off-tree), was initially mediated by oxidative stress (higher accumulation of malondialdehyde) and then by ethylene in a process in which 1-aminocyclopropene 1-carboxylic acid (ACC) synthase was the limiting factor. In contrast the progressive but slower softening observed during on-tree fruit ripening was not associated to oxidative damage but rather to a delayed production of ethylene limited, in turn, by the activity of ACC oxidase. An interesting association was found between the initiation of the ethylene production and a concomitant increase of sucrose levels during on-tree ripening also accompanied by a decline in hexanal. The putative role of these compounds as a tree-associated factor modulating on-tree pear ripening is discussed.info:eu-repo/semantics/acceptedVersio

New insights on the ripening pattern of ‘Blanquilla’ pears: A comparison between on- and off-tree ripened fruit

To better understand the key processes involved in the ripening of attached fruit, we have investigated physico-chemical and biochemical changes occurring in ‘Blanquilla’ pear during on-tree (attached fruit) and off-tree ripening (harvested fruit). Flesh firmness, sugars, acids and the volatile profiles as well as ethylene metabolism, PG and PME enzyme activities and oxidative damage were measured. Firmness loss in detached ‘Blanquilla’ pear (off-tree), was initially mediated by oxidative stress (higher accumulation of malondialdehyde) and then by ethylene in a process in which 1-aminocyclopropene 1-carboxylic acid (ACC) synthase was the limiting factor. In contrast the progressive but slower softening observed during on-tree fruit ripening was not associated to oxidative damage but rather to a delayed production of ethylene limited, in turn, by the activity of ACC oxidase. An interesting association was found between the initiation of the ethylene production and a concomitant increase of sucrose levels during on-tree ripening also accompanied by a decline in hexanal. The putative role of these compounds as a tree-associated factor modulating on-tree pear ripening is discussed.This work was supported by the CERCA Programme/ Generalitat de Catalunya and by the Ministerio de Economía y Competitividad / MINECO (grant AGL2017-87923-R)

PbSRT1 and PbSRT2 regulate pear growth and ripening yet displaying a species-specific regulation in comparison to other Rosaceae spp.

Epigenetic regulation is crucial to ensure a coordinated control of the different events that occur during fruit development and ripening. Sirtuins are NAD+-dependent histone deacetylases involved in the regulation of gene expression of many biological processes. However, their implications in the Rosaceae family remains unexplored. Accordingly, in this work, we demonstrated the phylogenetic divergence of both sirtuins among Rosaceae species. We then characterized the expression pattern of both SRT1 and SRT2 in selected pome and stone fruit species. Both SRT1 and SRT2 significantly changed during the fruit development and ripening of apple, nectarine and pear fruit, displaying a different expression profile. Such differences could explain in part their different ripening behaviour. To further unravel the role of sirtuins on the fruit development and ripening processes, a deeper analysis was performed using pear as a fruit model. In pear, PbSRT1 gene expression levels were negatively correlated with specific hormones (i.e. abscisic acid, indole-3-acetic acid, gibberellin A1 and zeatin) during the first phases of fruit development. PbSRT2 seemed to directly mediate pear ripening in an ethylene-independent manner. This hypothesis was further reinforced by treating the fruit with the ethylene inhibitor 1-methylcyclopropene (1-MCP). Instead, enhanced PbSRT2 along pear growth/ripening positively correlated with the accumulation of major sugars (R2 > 0.94), reinforcing the idea that sugar metabolism may be a target of epigenetic modifications during fruit ripening. Overall, the results from this study point out, for the first time, the importance that sirtuins have in the regulation of fruit growth and ripening of pear fruit by likely regulating hormonal and sugar metabolism.info:eu-repo/semantics/acceptedVersio

Investigation of the transcriptomic and metabolic changes associated with superficial scald physiology impaired by lovastatin and 1-methylcyclopropene in pear fruit (cv. “Blanquilla”)

To elucidate the physiology underlying the development of superficial scald in pears, susceptible “Blanquilla” fruit was treated with different compounds that either promoted (ethylene) or repressed (1-methylcyclopropene and lovastatin) the incidence of this disorder after 4 months of cold storage. Our data show that scald was negligible for the fruit treated with 1-methylcyclopropene or lovastatin, but highly manifested in untreated (78% incidence) or ethylene-treated fruit (97% incidence). The comparison between the fruit metabolomic profile and transcriptome evidenced a distinct reprogramming associated with each treatment. In all treated samples, cold storage led to an activation of a cold-acclimation-resistance mechanism, including the biosynthesis of very-long-chain fatty acids, which was especially evident in 1-methylcyclopropane-treated fruit. Among the treatments applied, only 1-methylcyclopropene inhibited ethylene production, hence supporting the involvement of this hormone in the development of scald. However, a common repression effect on the PPO gene combined with higher sorbitol content was found for both lovastatin and 1-methylcyclopropene-treated samples, suggesting also a non-ethylene-mediated process preventing the development of this disorder. The results presented in this work represent a step forward to better understand the physiological mechanisms governing the etiology of superficial scald in pears.info:eu-repo/semantics/publishedVersio

Estudio de las bases fisiológicas, bioquímicas y moleculares de la maduración en peras y su relación con la aparición del escaldado superficial

L'escaldat superficial és de les alteracions postcollita més importants en pera i, a pesar que els símptomes apareixen després de llargs períodes d'emmagatzematge en fred, s'indueix durant els primers mesos d'emmagatzematge i la susceptibilitat queda determinada en camp. L'objectiu principal d'aquesta tesi va ser estudiar les bases fisiològiques, bioquímiques i moleculars de la maduració en peres i veure quina relació tenien amb el desenvolupament de l'escaldat superficial. Els estudis en camp van permetre conèixer el cross-talk hormonal existent i l'exclusivitat de madurar en arbre de “Blanquilla”, mentre que la incapacitat de “Conference” i “Flor d’Hivern” van reforçar la hipòtesi del tree factor. Els resultats postcollita van mostrar que el metabolisme de l'etilè i el α-farneseno estan molt relacionats amb el desordre en “Blanquilla” mentre que en “Flor d’Hivern” sembla estar relacionat amb un dany per fred. Finalment, la ineficàcia del 1-MCP i la lovastatina en “Conference” suggereixen l'existència d'una alteració d'etiologia diferent a l'escaldat.El escaldado superficial es de las alteraciones poscosecha más importantes en pera y, a pesar de que los síntomas aparecen tras largos periodos de almacenamiento en frío, se induce durante los primeros meses de almacenamiento y la susceptibilidad queda determinada en campo. El objetivo principal de esta tesis fue estudiar las bases fisiológicas, bioquímicas y moleculares de la maduración en peras y ver qué relación tenían con el desarrollo del escaldado superficial. Los estudios en campo permitieron conocer el cross-talk hormonal existente y la exclusividad de madurar en árbol de “Blanquilla”, mientras que la incapacidad de “Conference” y “Flor d’Hivern” reforzaron la hipótesis del tree factor. Los resultados poscosecha mostraron que el metabolismo del etileno y el α-farneseno están muy relacionados con el desorden en “Blanquilla” mientras que en “Flor d’Hivern” parece estar relacionado con un daño por frío. Por último, la ineficacia del 1-MCP y la lovastatina en “Conference” sugieren la existencia de una alteración de etiología diferente al escaldado.Superficial scald is one of the main postharvest physiological disorders in pears. Despite symptoms appear after long-term cold storage, scald is induced during the first months of cold storage and the susceptibility of the fruit is determined pre-harvest. The main objective of this thesis was to study the physiological, biochemical and molecular basis of pear maturation and ripening and its relationship with superficial scald development. The pre-harvest studies let to know the existing hormonal ‘cross-talk’ and that ‘Blanquilla’ was the only cultivar able to ripen on-tree while the inability to ripen on-tree of ‘Conference’ and ‘Flor d’Hiverns’ pears reinforced the hypothesis of the ‘tree factor’. Postharvest results showed that ethylene and α-farnesene metabolisms were closely related with the disorder appearance in ‘Blanquilla’, while the disorder in ‘Flor d’Hivern’ seem to be related to a chilling injury. Finally, the inefficacy of 1-MCP and lovastatin in ‘Conference’ pear suggests a disorder with a complete different etiology than superficial scald

The relationship between ethylene- and oxidative-related markers at harvest with the susceptibility of pears to develop superficial scald

To better understand the specific biochemical pathways involved in superficial scald susceptibility, changes in ethylene biosynthesis, antioxidant, oxidative related processes and sugar metabolism were investigated for two scald sensitive pear cultivars (‘Blanquilla’ and ‘Flor d’Hivern’) with distinct postharvest ripening patterns at different harvest dates. Both cultivars developed symptoms of scald after 4 months of storage at -0.5 °C, but the biochemical basis underlying the fruit susceptibility were different. In the summer pear ‘Blanquilla’, capable of ripening even on the tree, scald susceptibility was higher in fruit of advanced maturity and was associated with the action of ethylene on triggering the expression of PcAFS1 gene. In this cultivar, the levels of ACC, ACS enzyme activity and PcAFS1 at harvest were strongly correlated to scald incidence. In contrast, in the winter pear, ‘Flor d’Hivern’, with little or no ethylene-production capacity even after cold storage, scald symptoms were already visible when fruit were removed from cold storage, regardless of the fruit maturity. In this pear cultivar, scald symptoms were not dependent on ethylene, but rather associated with higher lipoxygenase (LOX) activity at harvest, an enzyme often associated with responses to chilling injury, and lower content of sorbitol, a compound that may act as cryoprotectant preventing cell damage during cold storage.info:eu-repo/semantics/acceptedVersio

Unravelling the cold-induced regulation of ethylene and α-farnesene and its involvement with the development of scald-like disorders in different pear cultivars

To better understand the cold-induced regulation of scald-like disorders in pears and the specific roles played by ethylene and α-farnesene, three pear cultivars with different patterns of ethylene production and chilling requirement were used in this study. Fruit were treated with 1-MCP (ethylene inhibitor) and Lovastatin (α-farnesene inhibitor) and stored at -0.5 °C and 90 % RH during 6 months. Changes in targeted metabolites, enzymes and genes were monitored periodically up to 120 d of storage and superficial scald incidence was assessed after this time and after 180 d of cold storage. 1-MCP treatment induced in the three cultivars a down-regulation of PcACS1, PcACO1, PcERF1 and PcAFS1 gene expression, but also a significant up-regulation of PcETR1 and PcEIN2 that led in all cases to the inhibition of the disorder incidence. In contrast, Lovastatin treatment caused diverse molecular or biochemical responses depending on the cultivar. In ‘Blanquilla’ pears, this treatment completely inhibited superficial scald reinforcing the idea that ethylene-α-farnesene interaction plays a decisive role in this specific cultivar. In contrast to 1-MCP, Lovastatin treatment did not control the disorder incidence in ‘Flor d’Hivern’ pears. Inversely, 1-MCP inhibited the development of the disorder, showing then that the inhibition of ethylene biosynthetic and signalling pathway may control superficial scald even in cultivars producing very low or undetectable ethylene levels. Finally, the inefficacy of both treatments to prevent the disorder development in ‘Conference’ pears, suggests the existence of a disorder different from that observed for the other cultivars whose biochemical basis remain unknown. Collectively our results show that the regulatory processes triggered by cold stress in pears are complex and cultivar dependent.info:eu-repo/semantics/acceptedVersio

Elucidating the involvement of ethylene and oxidative stress during on- and off-tree ripening of two pear cultivars with different ripening patterns

Scarce information is available about the ripening process of European pears attached and detached from the tree. Accordingly, this study aimed to investigate the physiological and biochemical processes underlying both on- and off-tree fruit ripening in a summer (‘Conference’) vs. a winter (‘Flor d’Hivern’) pear cultivar. For each cultivar, a batch of fruit was harvested at the commercial harvest date and ripened at 20 °C and another batch was left to ripen on the tree. In both cultivars the inability of the fruit to soften on-tree, was related to a very limited ethylene metabolism but also associated to high content of H2O2 and low lipid peroxidation levels. In contrast, ripening in detached fruit was cultivar-dependent. In ‘Conference’ pears, the sharp firmness loss and colour changes observed during off-tree ripening were not strictly associated to an enhanced ethylene production but rather triggered by an oxidative related process preceding the climacteric rise. In contrast, ‘Flor d’Hivern’ pears experienced limited softening and degreening during off-tree ripening not being related to the action of ethylene or oxidative stress. Collectively our results showed that pear ripening was not exclusively dependent of ethylene production and that the fruit potential to limit oxidative damage may be involved with the inability of some European pear cultivars to ripen on-tree.info:eu-repo/semantics/acceptedVersio