From acidity to sweetness: a comprehensive review of carbon accumulation in grape berries

Most of the carbon found in fruits at harvest is imported by the phloem. Imported carbon provide the material needed for the accumulation of sugars, organic acids, secondary compounds, in addition to the material needed for the synthesis of cell walls. The accumulation of sugars during fruit development influences not only sweetness but also various parameters controlling fruit composition (fruit "quality"). The accumulation of organic acids and sugar in grape berry flesh cells is a key process for berry development and ripening. The present review presents an update of the research on grape berry development, anatomical structure, sugar and acid metabolism, sugar transporters, and regulatory factors.

Eat the fruit earlier: Sakis (Pithecia chrysocephala) show enhanced temporal fruit resource access compared with squirrel monkeys (Saimiri sciureus) in an urban forest fragment in Brazil

Fruit availability experienced by different primate species is likely to vary due to species-specific fruit use, even within the same habitat and timeframe. Pitheciines, primates of the subfamily Pitheciinae, particularly favor the seeds of unripe fruits. Researchers consider this dietary characteristic an adaptation to increase access to fruit resources. However, the relative advantages of pitheciines over sympatric non-pitheciine non-seed-eating primates regarding species-specific fruit availability is not well studied. In a 26-ha forest within the city of Manaus, Amazonian Brazil, we assessed the wild-food feeding behavior of free-ranging groups of golden-faced sakis (Pithecia chrysocephala) and sympatric common squirrel monkeys (Saimiri sciureus). We hypothesized that sakis would have greater and more consistent access to wild fruit due to (1) a wider variety of fruit species in their diet, and (2) longer consumption periods per fruit species. We recorded the plant species, part (pulp or seed), and developmental stage (ripe or unripe) of wild fruit consumed by both species. We also conducted monthly fruit censuses of 1000 trees and vines to estimate overall wild fruit abundance. As an indicator of fruit availability, we calculated the proportion of available fruiting trees and vines for each primate species separately based on their observed diet. Throughout the year, the proportion of available trees and vines was significantly higher and more temporally stable for sakis than for squirrel monkeys. This was because sakis used shared fruit species longer than squirrel monkeys by consuming both ripe and unripe fruit. Although sakis had a broader fruit repertoire than squirrel monkeys, it did not contribute to the higher fruit availability. Thus, the fruit feeding system of sakis identifies aspects of a niche that is less restricted in the timing of fruit consumption, which led to a relative advantage in fruit availability.

Effect of Crown Layers on Reproductive Effort and Success in Andromonoecious Aesculus indica (Wall. ex Camb.) Hook (Sapindaceae) in a Temperate Forest of Garhwal Himalaya

The andromonoecy is an unusual sex expression in trees in which an individual plant bears both functionally staminate and hermaphrodite flowers on the inflorescences. This study aims to investigate the effect of crown layers on the floral biology and reproductive effort of Aesculus indica (Wall. ex Camb.) Hook. The results revealed that the peak period of anthesis was between 06:00 and 08:00 h of the day. Male flower production was predominantly higher as compared to the perfect flowers on the inflorescences. There was no significant variation between total pollen production in staminate and perfect flowers. Features like protogyny and inter-level asynchrony promote xenogamy; however, intra-level asynchrony results in geitonogamy. Controlled pollination treatments revealed the existence of self-incompatibility in flowers. Pollination syndromes in flowers support ambophily. A trend of consistent improvement in reproductive success from lower canopy layers to upper crown layers in the analyzed trees was recorded. The crown layers have a significant impact on flower production, fruit, and seed set. An increase in male flower production due to the increment in the crown is a mechanism of reproductive assurance as a pollen donor and pollinator recipient and also due to the differential cost of expenditure of reproduction in crown layers. Andromonoecy in A. indica promotes self-incompatibility, and there was a tapering trend of reproductive success in the crown layers.

Uncovering genetic and metabolite markers associated with resistance against anthracnose fruit rot in northern highbush blueberry

Anthracnose fruit rot (AFR), caused by the fungal pathogen Colletotrichum fioriniae, is among the most destructive and widespread fruit disease of blueberry, impacting both yield and overall fruit quality. Blueberry cultivars have highly variable resistance against AFR. To date, this pathogen is largely controlled by applying various fungicides; thus, a more cost-effective and environmentally conscious solution for AFR is needed. Here we report three quantitative trait loci associated with AFR resistance in northern highbush blueberry (Vaccinium corymbosum). Candidate genes within these genomic regions are associated with the biosynthesis of flavonoids (e.g. anthocyanins) and resistance against pathogens. Furthermore, we examined gene expression changes in fruits following inoculation with Colletotrichum in a resistant cultivar, which revealed an enrichment of significantly differentially expressed genes associated with certain specialized metabolic pathways (e.g. flavonol biosynthesis) and pathogen resistance. Using non-targeted metabolite profiling, we identified a flavonol glycoside with properties consistent with a quercetin rhamnoside as a compound exhibiting significant abundance differences among the most resistant and susceptible individuals from the genetic mapping population. Further analysis revealed that this compound exhibits significant abundance differences among the most resistant and susceptible individuals when analyzed as two groups. However, individuals within each group displayed considerable overlapping variation in this compound, suggesting that its abundance may only be partially associated with resistance against C. fioriniae. These findings should serve as a powerful resource that will enable breeding programs to more easily develop new cultivars with superior resistance to AFR and as the basis of future research studies.

Calcium carbide-ripened plantain induced alterations in plasma electrolytes concentration and kidney function in rats

INTRODUCTION

Artificial fruit ripening agents such as ethanol, ethylene, ethephon, and calcium carbide (CaC2) is usually employed in stimulating the fruit ripening process. Currently, there is a paucity of information regarding the effects of various artificial fruits ripening methods on the health status of consumers. In this study, the physiological effects and possible health hazards associated with the consumption of plantain ripened by CaC2 and other non-chemical methods on the kidneys were investigated.

METHODS

Artificially ripened plantain was mixed with rat feed and fed to Wistar albino rats for four weeks, and the levels of plasma electrolytes (Na+, HCO3-, K+, and Cl-), urea, creatinine, as well as histological changes in the kidneys were determined.

RESULTS

Results indicated that rats fed with carbide-ripened plantain had a significantly high level of plasma bicarbonate (HCO3-) compared to control rats., but there was no difference in the level of plasma sodium (Na+). However, the levels of plasma potassium (K+) and chloride (Cl-) were significantly low in rats fed with CaC2-ripened plantain as compared to the control rats. Furthermore, the levels of urea and creatinine were significantly high in rats fed with CaC2-ripened plantain compared to the control animals. Histological analyses showed glomeruli atrophy and tubular necrosis in kidneys of rats fed with CaC2-ripened plantain, thereby further indicating toxicity to the kidneys.

CONCLUSIONS

Histological evidence and alterations in the level of the plasma electrolytes, urea, and creatinine suggest that consumption of fruits ripened with calcium carbide may be harmful to the kidneys.

Alterações induzidas por plátano maturado com carbureto de cálcio na concentração plasmática de eletrólitos e na função renal em ratos

Resumo Introdução: Agentes de maturação artificial como etanol, etileno, etefon e carbureto de cálcio (CaC2) são comumente empregados para estimular o amadurecimento de frutas. Atualmente, há uma escassez de informações a respeito dos efeitos de diversos métodos artificiais de maturação de frutas no estado de saúde dos consumidores. Neste estudo, investigaram-se os efeitos fisiológicos e possíveis riscos à saúde associados ao consumo de plátano maturado por CaC2 e outros métodos não químicos nos rins. Métodos: O plátano artificialmente amadurecido foi misturado com ração de rato e fornecido a ratos albinos Wistar por quatro semanas, e determinaram-se os níveis de eletrólitos plasmáticos (Na+, HCO3−, K+, e Cl−), ureia, creatinina, bem como alterações histológicas nos rins. Resultados: Ratos alimentados com plátano amadurecido com carbureto apresentaram um nível significativamente maior de bicarbonato plasmático (HCO3−) em comparação com ratos controle, mas não houve diferença no nível plasmático de sódio (Na+). Entretanto, os níveis plasmáticos de potássio (K+) e cloreto (Cl−) foram significativamente baixos em ratos alimentados com plátano maturado com CaC2 comparados com ratos controle. Além disso, os níveis de ureia e creatinina foram significativamente mais elevados em ratos alimentados com plátano amadurecido com CaC2, em comparação com os animais controle. Análises histológicas mostraram atrofia glomerular e necrose tubular em rins de ratos alimentados com plátano amadurecido com CaC2, indicando assim ainda mais toxicidade aos rins. Conclusões: Evidências histológicas e alterações nos eletrólitos plasmáticos, ureia e creatinina sugerem que o consumo de frutas amadurecidas com carbureto de cálcio pode ser prejudicial aos rins.

From the First to Third Generation of Neonicotinoids: Implication for Saving the Loss of Fruit Quality and Flavor by Pesticide Applications

Neonicotinoids can control crop pests with high efficiency and low cost and have quickly swept one-fourth of the global insecticide market since the launch of imidacloprid in 1991. Imidacloprid and acetamiprid, the first generation of neonicotinoids, and dinotefuran, the representative of third generation of neonicotinoids, were applied on tomato plants individually to investigate neonicotinoid effects on tomato fruit quality, especially on appearance parameters, sugar, acid, and aroma compounds. Compared with the control, fewer differences in the transcriptome profile, sugar, acid, and volatile organic compound (VOC) contents, and sensory analysis results were shown in dinotefuran treatments than in the other two treatments. Therefore, dinotefuran was more recommended to control pests of tomatoes with less loss of fruit flavor and quality as well as lower ecological risks.

Non-visual senses in fruit selection by the mantled howler monkey (Alouatta palliata)

There is extensive knowledge about the visual system and the implications of the evolution of trichromatic color vision in howler monkeys (genus Alouatta) related to food selection; however, information about the other sensory systems is limited. In this study we assessed the use of touch, sniffing, and taste in fruit evaluation by 20 adult mantled howler monkeys (Alouatta palliata) on Agaltepec Island, Mexico. During 9 months of observation, we recorded the frequency that each monkey used touch, sniffing, and taste in evaluating cryptic fruits (that remain green during their ripening process) and conspicuous fruits (with red, yellow, or orange colorations when they are ripe). Sucrose content and hardness measurements were made to establish the degree of ripeness of the fruits. We found that mantled howler monkeys used long behavioral sequences during conspicuous fruit investigations. Sniffing was used infrequently, but significantly more often in the evaluation of conspicuous-ripe and unripe fruits compared to cryptic-ripe and unripe fruits. During the evaluation of cryptic-ripe fruits, mantled howler monkeys increased the use of touch compared to evaluating cryptic-unripe fruits. We did not find significant differences in the use of taste in the evaluation of cryptic and conspicuous fruits (both ripe and unripe). Our results suggest that the non-visual senses play an essential role in fruit selection by howler monkeys, with differences in the behavioral strategy according to the fruit's conspicuity. The multimodal signals of ripe and unripe fruits allow the howler monkeys to assess their palatability before being consumed.

Fruit Quality Attributes of ‘Arisoo’ and ‘Picnic’ Apples as Influenced by 1-Methylcyclopropene Concentration and Its Application Frequency during Cold Storage

The efficacy of 1-methylcyclopropene (1-MCP) in maintenance of apple fruit quality can differ depending on apple cultivar, ethylene content at harvest, 1-MCP concentration, the interval between harvest and 1-MCP application, and the number of applications. In this study, we investigated whether the 1-MCP concentration and its application frequency differently affected fruit quality attributes of the two new apple cultivars ‘Arisoo’ and ‘Picnic’. The fruits were treated with 1-MCP (as single or double treatments) at the rate of 0 μL L−1 (control), 0.5 μL L−1, 1 μL L−1, 0.5 + 0.5 μL L−1, and 1 + 1 μL L−1 for 18 h, and they were stored at 0 °C up to six months. Comparatively, the fruit qualities of 1-MCP treated fruits were higher than that of the control during cold storage, with a higher suppression of internal ethylene content and a slower reduction of titratable acidity in 1-MCP treatments than the controls throughout the cold storage in both cultivars, regardless of the concentration and number of applications. Reduction of fruit firmness and soluble solid contents were maintained by single application of 0.5 μL L−1 1-MCP in ‘Arisoo’ apple, while double application of 0.5 + 0.5 μL L−1 was needed in ‘Picnic’ cultivar. The effective concentration for weight-loss reduction was found to be the single application of 1 μL L−1 1-MCP in both ‘Arisoo’ and ‘Picnic’. Conclusively, 1-MCP as single treatment at the rate of 0.5 μL L−1 could be sufficient in inhibiting ethylene action and maintaining fruit quality losses during cold storage, particularly in ‘Arisoo’. However, double application of 1-MCP might be necessary for some quality attributes in ‘Picnic’ apple.

Unravelling the Molecular Regulation Mechanisms of Slow Ripening Trait in Prunus persica

Fruit development is a complex process that involves the interplay of cell division, expansion, and differentiation. As a model to study fruit development, nectarines incapable of ripening were described as slow ripening. Slow ripening fruits remained firm and exhibited no rise in CO₂ or ethylene production rates for one month or more at 20 °C. Different studies suggest that this trait is controlled by a single gene (NAC072). Transcriptome analysis between normal and slow ripening fruits showed a total of 157, 269, 976, and 5.224 differentially expressed genes in each fruit developmental stage analyzed (T1, T2, T3, and T7, respectively), and no expression of NAC072 was found in the slow ripening individuals. Using this transcriptomic information, we identified a correlation of NAC072 with auxin-related genes and two genes associated with terpene biosynthesis. On the other hand, significant differences were observed in hormonal biosynthetic pathways during fruit development between the normal and slow ripening individuals (gibberellin, ethylene, jasmonic acid and abscisic acid). These results suggest that the absence of NAC072 by the direct or indirect expression control of auxins or terpene-related genes prevents normal peach fruit development.

Enhance Fruit Ripening Uniformity and Accelerate the Rutab Stage by Using ATP in 'Zaghloul' Dates during the Shelf Life

The Rutab date involves a physiological process by which the fruit turns completely ripe. The objective of this study was to research the effect of ATP-treated fruit to improve their biologically active compounds of the Rutab process of the 'Zagloul' date during shelf-life. Fruits at full color (red) were dipped in 0, 1, 1.5 mmol L^-1 ATP solution for 10 min, and then stored at room temperature (27 ± 1 °C) with a relative humidity of (67 ± 4 RH%) for 12 d. We found that ATP treatment, especially at 1.5 mM, enhances the Rutab stage of date fruit, and certain biologically active compounds such as total phenols and flavonoids, in all ATP treatments compared to untreated fruits. ATP enhanced the loss of tannin compounds in fruit but had no impact on the change in fruit moisture percentage of fruit during storage. The treatments did affect the changes in total sugar content and activated the sucrose enzymes, i.e., acid invertase (AI), neutral invertase (NI), sucrose synthase-cleavage (SS-c), and sucrose synthase-synthesis (SS-s) during storage. Interestingly, immersion in 1.5 mM ATP forced the date fruit to reach the Rutab stage during storage. These results indicated that the dose of ATP (1.5 mM) is a new potential tool that pushes the fruits to regular ripening after harvest, thus reducing the losses in the fruits during the production process. A linear model could be satisfactorily used for predicting the properties of the treated date with ATP 1.5 mM at different shelf-life durations.

Machine Learning for Automatic Classification of Tomato Ripening Stages Using Electrophysiological Recordings

The physiological processes underlying fruit ripening can lead to different electrical signatures at each ripening stage, making it possible to classify tomato fruit through the analysis of electrical signals. Here, the electrical activity of tomato fruit (Solanum lycopersicum var. cerasiforme) during ripening was investigated as tissue voltage variations, and Machine Learning (ML) techniques were used for the classification of different ripening stages. Tomato fruit was harvested at the mature green stage and placed in a Faraday's cage under laboratory-controlled conditions. Two electrodes per fruit were inserted 1 cm apart from each other. The measures were carried out continuously until the entire fruits reached the light red stage. The time series were analyzed by the following techniques: Fast Fourier Transform (FFT), Wavelet Transform, Power Spectral Density (PSD), and Approximate Entropy. Descriptive analysis from FFT, PSD, and Wavelet Transform were used for PCA (Principal Component Analysis). Finally, ApEn, PCA1, PCA2, and PCA3 were obtained. These features were used in ML analyses for looking for classifiable patterns of the three different ripening stages: mature green, breaker, and light red. The results showed that it is possible to classify the ripening stages using the fruit's electrical activity. It was also observed, using precision, sensitivity, and F1-score techniques, that the breaker stage was the most classifiable among all stages. It was found a more accurate distinction between mature green × breaker than between breaker × light red. The ML techniques used seem to be a novel tool for classifying ripening stages. The features obtained from electrophysiological time series have the potential to be used for supervised training, being able to help in more accurate classification of fruit ripening stages.

Evolutionary ecology of climacteric and non-climacteric fruits

Fleshy fruits can be divided between climacteric (CL, showing a typical rise in respiration and ethylene production with ripening after harvest) and non-climacteric (NC, showing no rise). However, despite the importance of the CL/NC traits in horticulture and the fruit industry, the evolutionary significance of the distinction remains untested. In this study, we tested the hypothesis that NC fruits, which ripen only on the plant, are adapted to tree dispersers (feeding in the tree), and CL fruits, which ripen after falling from the plant, are adapted to ground dispersers. A literature review of 276 reports of 80 edible fruits found a strong correlation between CL/NC traits and the type of seed disperser: fruits dispersed by tree dispersers are more likely to be NC, and those dispersed by ground dispersers are more likely to be CL. NC fruits are more likely to have red-black skin and smaller seeds (preferred by birds), and CL fruits to have green-brownish skin and larger seeds (preferred by large mammals). These results suggest that the CL/NC traits have an important but overlooked seed dispersal function, and CL fruits may have an adaptive advantage in reducing ineffective frugivory by tree dispersers by falling before ripening.

Mutations in tomato 1-aminocyclopropane carboxylic acid synthase2 uncover its role in development beside fruit ripening

The role of ethylene in plant development is mostly inferred from its exogenous application. The usage of mutants affecting ethylene biosynthesis proffers a better alternative to decipher its role. In tomato (Solanum lycopersicum), 1-aminocyclopropane carboxylic acid synthase2 (ACS2) is a key enzyme regulating ripening-specific ethylene biosynthesis. We characterised two contrasting acs2 mutants; acs2-1 overproduces ethylene, has higher ACS activity, and has increased protein levels, while acs2-2 is an ethylene underproducer, displays lower ACS activity, and has lower protein levels than wild type. Consistent with high/low ethylene emission, the mutants show opposite phenotypes, physiological responses, and metabolomic profiles compared with the wild type. The acs2-1 mutant shows early seed germination, faster leaf senescence, and accelerated fruit ripening. Conversely, acs2-2 has delayed seed germination, slower leaf senescence, and prolonged fruit ripening. The phytohormone profiles of mutants were mostly opposite in the leaves and fruits. The faster/slower senescence of acs2-1/acs2-2 leaves correlated with the endogenous ethylene/zeatin ratio. The genetic analysis showed that the metabolite profiles of respective mutants co-segregated with the homozygous mutant progeny. Our results uncover that besides ripening, ACS2 participates in the vegetative and reproductive development of tomato. The distinct influence of ethylene on phytohormone profiles indicates the intertwining of ethylene action with other phytohormones in regulating plant development.

A chromosome-level genome assembly provides insights into ascorbic acid accumulation and fruit softening in guava (Psidium guajava)

Guava (Psidium guajava) is an important fleshy-fruited tree of the Myrtaceae family that is widely cultivated in tropical and subtropical areas of the world and has attracted considerable attention for the richness of ascorbic acid in its fruits. However, studies on the evolution and genetic breeding potential of guava are hindered by the lack of a reference genome. Here, we present a chromosome-level genomic assembly of guava using PacBio sequencing and Hi-C technology. We found that the genome assembly size was 443.8 Mb with a contig N50 of ~15.8 Mb. We annotated a total of 25 601 genes and 193.2 Mb of repetitive sequences for this genome. Comparative genomic analysis revealed that guava has undergone a recent whole-genome duplication (WGD) event shared by all species in Myrtaceae. In addition, through metabolic analysis, we determined that the L-galactose pathway plays a major role in ascorbic acid biosynthesis in guava fruits. Moreover, the softening of fruits of guava may result from both starch and cell wall degradation according to analyses of gene expression profiles and positively selected genes. Our data provide a foundational resource to support molecular breeding of guava and represent new insights into the evolution of soft, fleshy fruits in Myrtaceae.

Cell Wall Calcium and Hemicellulose Have a Role in the Fruit Firmness during Storage of Blueberry (Vaccinium spp.)

The firmness of blueberry is one of its most significant quality attributes. Modifications in the composition of the cell wall have been associated with changes in the fruit firmness. In this work, cell wall components and calcium concentration in two blueberry cultivars with contrasting firmness phenotypes were evaluated at harvest and 30 days cold storage (0 °C). High performance anion-exchange chromatography with pulse amperometric detector (HPAEC-PAD) analysis was performed using the "Emerald" (firmer) and "Jewel" (softer) blueberry cultivars, showing increased glucose in the firmer cultivar after cold storage. Moreover, the LM15 antibody, which recognizes xyloglucan domains, displayed an increased signal in the Emerald cultivar after 30 d cold storage. Additionally, the antibody 2F4, recognizing a homogalacturonan calcium-binding domain, showed a greater signal in the firmer Emerald blueberries, which correlates with a higher calcium concentration in the cell wall. These findings suggest that xyloglucan metabolism and a higher concentration of cell wall calcium influenced the firmness of the blueberry fruit. These results open new perspectives regarding the role of cell wall components as xyloglucans and calcium in blueberry firmness.

An effector-reporter system to study cellular signal transduction in strawberry fruit (Fragaria ananassa)

An effector-reporter system is a powerful tool used to study cellular signal transduction, but this technique has been traditionally used in protoplasts. A similar system to study cellular signal transduction in fruits has not yet been established. In this study, we aimed to establish an effector-reporter system for strawberry fruit, a model nonclimacteric fruit. We first investigated the characteristics of transient gene expression in strawberry fruits and found marked variation in gene expression levels among individual fruits, and this variation has complicated the establishment of a technical system. To overcome this difficulty, we investigated a sampling strategy based on a statistical analysis of the activity pattern of four different reporters (GUS, GFP, FLuc, and RLuc) among individual fruits and combinations of pairs of reporters (GUS/GFP and RLuc/FLuc). Based on an optimized sampling strategy, we finally established a step-by step protocol for the effector/reporter assay. Using FaMYB10 and FaWRKY71 as the effectors and GUS driven by the FaCHS promoter as the reporter, we demonstrated that this effector/reporter system was practical and reliable. This effector/reporter technique will contribute to an in-depth exploration of the signaling mechanism for the regulation of strawberry fruit ripening.

Emerging approaches to determine maturity of citrus fruit

Owing to their health-boosting properties and other appreciable properties, citrus fruit is widely consumed and commercialized worldwide. Destination markets around the world vary in their fruit quality requirements and are also highly influenced by climatic conditions, agronomical and postharvest practices. Hence, harvesting decisions are arduous. Maturity indices in citrus fruit are highly variable and dependent on the species and varieties, growing regions, and destination markets. For decades, determination of the maturity of citrus fruit and predicting the near time of harvesting was a challenge for producers, researchers, and food safety agencies. Thus, the current review provides a correlation between maturity and internal components and an overview of techniques of maturity determination for citrus fruits. Also, stress has been given to the destructive and nondestructive methods to determine the maturity level of different citrus species. The techniques presented in this review portray continuous productiveness as an excellent quality assessment, particularly as ripening and maturity analysis tools for citrus fruits. Traditional techniques are time-consuming, laborious, costly, destructive, and tedious. Thus, these nondestructive techniques hold great potential to replace conventional procedures.

Molecular Bases of Fruit Quality in Prunus Species: An Integrated Genomic, Transcriptomic, and Metabolic Review with a Breeding Perspective

In plants, fruit ripening is a coordinated developmental process that requires the change in expression of hundreds to thousands of genes to modify many biochemical and physiological signal cascades such as carbohydrate and organic acid metabolism, cell wall restructuring, ethylene production, stress response, and organoleptic compound formation. In Prunus species (including peaches, apricots, plums, and cherries), fruit ripening leads to the breakdown of complex carbohydrates into sugars, fruit firmness reductions (softening by cell wall degradation and cuticle properties alteration), color changes (loss of green color by chlorophylls degradation and increase in non-photosynthetic pigments like anthocyanins and carotenoids), acidity decreases, and aroma increases (the production and release of organic volatile compounds). Actually, the level of information of molecular events at the transcriptional, biochemical, hormonal, and metabolite levels underlying ripening in Prunus fruits has increased considerably. However, we still poorly understand the molecular switch that occurs during the transition from unripe to ripe fruits. The objective of this review was to analyze of the molecular bases of fruit quality in Prunus species through an integrated metabolic, genomic, transcriptomic, and epigenetic approach to better understand the molecular switch involved in the ripening process with important consequences from a breeding point of view.

3-D microstructural changes in relation to the evolution of quality during ripening of mango (Mangifera indica L. cv. Carabao)

BACKGROUND

The ripening of mango involves changes in texture, flavor, and color, affecting the quality of the fruit. Previous studies have investigated the physiology on the evolution of quality during ripening but only a few have looked at microstructural changes during ripening. None of them has provided an insight into the relationhip between 3-D microstructure and the evolution of quality during ripening. As the 3-D microstructure of fruit tissue determines its mechanical and gas-transport properties, it is likely to affect fruit texture, respiratory metabolism, and other ripening processes.

RESULTS

The present study focuses on the role of 3-D microstructural changes in relation to quality changes during mango ripening. Microstructural imaging using X-ray micro-computed tomography suggested the incidence of cell leakage, which was confirmed by the measurement of electrolyte leakage from the fruit peel. Due to cell leakage, porosity, pore connectivity, and pore local diameter were decreased whereas the tissue local diameter and pore specific area were increased. The decline in respiration and respiratory quotient during ripening followed the microstructural changes observed. Meanwhile, changes in aroma were observed such as a decrease in monoterpenes and an increase in esters and other fermentative metabolites.

CONCLUSION

Overall, the results provide a complete, integrated picture of microstructural changes during ripening accompanying the evolution of fruit quality, suggesting functional relationships between the two. © 2020 Society of Chemical Industry.

Secondary metabolites in a neotropical shrub: spatiotemporal allocation and role in fruit defense and dispersal

Deciphering the ecological roles of plant secondary metabolites requires integrative studies that assess both the allocation patterns of compounds and their bioactivity in ecological interactions. Secondary metabolites have been primarily studied in leaves, but many are unique to fruits and can have numerous potential roles in interactions with both mutualists (seed dispersers) and antagonists (pathogens and predators). We described 10 alkenylphenol compounds from the plant species Piper sancti-felicis (Piperaceae), quantified their patterns of intraplant allocation across tissues and fruit development, and examined their ecological role in fruit interactions. We found that unripe and ripe fruit pulp had the highest concentrations and diversity of alkenylphenols, followed by flowers; leaves and seeds had only a few compounds at detectable concentrations. We observed a nonlinear pattern of alkenylphenol allocation across fruit development, increasing as flowers developed into unripe pulp then decreasing as pulp ripened. This pattern is consistent with the hypothesis that alkenylphenols function to defend fruits from pre-dispersal antagonists and are allocated based on the contribution of the tissue to the plant's fitness, but could also be explained by non-adaptive constraints. To assess the impacts of alkenylphenols in interactions with antagonists and mutualists, we performed fungal bioassays, field observations, and vertebrate feeding experiments. In fungal bioassays, we found that alkenylphenols had a negative effect on the growth of most fungal taxa. In field observations, nocturnal dispersers (bats) removed the majority of infructescences, and diurnal dispersers (birds) removed a larger proportion of unripe infructescences. In feeding experiments, bats exhibited an aversion to alkenylphenols, but birds did not. This observed behavior in bats, combined with our results showing a decrease in alkenylphenols during ripening, suggests that alkenylphenols in fruits represent a trade-off (defending against pathogens but reducing disperser preference). These results provide insight into the ecological significance of a little studied class of secondary metabolites in seed dispersal and fruit defense. More generally, documenting intraplant spatiotemporal allocation patterns in angiosperms and examining mechanisms behind these patterns with ecological experiments is likely to further our understanding of the evolutionary ecology of plant chemical traits.

Effects of Horseradish Oil and Eight Isothiocyanates Vapour Treatment on Postharvest Disease Control and Their Efficacy as Preservatives of Mature Green Tomato

This study evaluated the potential of horseradish (Armoracia rusticana) oil (ARO) and eight isothiocyanates (propyl ITC [ProITC], isopropyl ITC [IsoproITC], n-butyl ITC [n-BuITC], 3-butenyl ITC [3-BeITC], phenyl ITC [PhITC], benzyl ITC [BzITC], 2-phenylethyl ITC [PhEITC], and allyl ITC [AITC]) as preservatives and antifungal agents for postharvest tomato disease control. Results showed that ARO and eight ITCs demonstrated antifungal activities against Botrytis cinerea, Alternaria alternata, Rhizopus stolonifer, and Geotrichum candidum, which can cause the decay of mature green tomato during storage. Allyl-ITC (AITC) had the lowest EC₅₀ values of mycelia growth suppression, with 0.18, 0.44, 0.29, and 0.43 μg/ml air for B. cinerea, A. alternata, R. stolonifer, and G. candidum, respectively. ARO, 2-PhEITC, BzITC, and AITC exhibited better efficacy as preservatives of mature green tomato than other ITCs on the basis of some parameters, such as low decay rate, slow reduction in weight loss, slight change in hardness, slow decrease in acidity, and total soluble solid content of treated tomatoes. GC-MS revealed that 2-PhEITC (77.78%) and AITC (15.87%) were the major components of ARO. These results can be used as a basis to develop preservative products composed of ITCs.

Visual detection and fruit selection by the mantled howler monkey (Alouatta palliata)

Howler monkeys (platyrrhini) have evolved routine trichromatic color vision independently from catarrhines, which presents an opportunity to test hypotheses concerning the adaptive value of distinguishing reddish from greenish hues. A longstanding hypothesis posits that trichromacy aids in the efficient detection of reddish-ripe fruits, which could be an advantage for the detection of the nutritional content of the fruit, such as sugars. In the present study, we assessed fruit visual conspicuity and selection based on color and sucrose content by wild mantled howler monkeys (Alouatta palliata) on Agaltepec Island, Mexico. We used colorimetry to classify dietary fruits as cryptic (greenish) or conspicuous (reddish) against their background leaves. Species-specific color models indicate that trichromatic howler monkeys should be more efficient in discriminating the conspicuous ripe fruits from leaves compared to detecting cryptic ripe fruits from leaves. We found howler monkeys consume more cryptic fruits compared to conspicuous fruits, and that they consume more unripe fruits than ripe fruits. The consumption (acceptance) of fruit was independent of sucrose content, and thus this disaccharide may not play an essential role in mantled howler food selection. Our findings suggest that routine trichromatic color vision may aid in the detection and discrimination of conspicuously colored fruits, but that the final decision whether to accept or reject a fruit probably involves the use of other senses in addition to vision.

A contradictory action of procoagulant ficin by a fibrinolytic serine protease from Egyptian Ficus carica latex

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We purified a serine protease from Ficus carica latex.

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Serine protease had a high tendency to hydrolyze fibrinogin.

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Serine protease inhibited blood coagulation.

Ficus carica is one of the most popular and edible plants. Its trees emanate latex of high medical importance. The well-studied procoagulant effect of ficin is a hallmark of this latex which protrudes an interesting question of how can the plant control this effect? In the present work, we purified and characterized a serine protease (FPIII) with fibrinolytic activity from F. carica latex and study the anticoagulant character of the latex. FPIII was inhibited by PMSF and its molecular weight was 48 kDa. The optimum pH and temperature of FPIII were detected at 8.5 and 60 °C, respectively. The activation energy of FPIII was 7 kcal/mol and was thermal stable up to 60 °C. FPIII tended to hydrolyze different protein substrates and showed a good catalytic efficiency (K_cat/K_m). The anticoagulant effects and fibrinogenolytic activities of latex crude extract and FPIII were detected, which controls the procoagulant effect of ficin.

Frugivory and seed dispersal by chelonians: a review and synthesis

In recent years, it has become clear that frugivory and seed dispersal (FSD) by turtles and tortoises is much more common than previously thought. We here review published and unpublished records of chelonian FSD, and assess the role of chelonians as seed dispersers, from individual species to the community level. We first discuss the distribution of chelonian FSD and the characteristics of the fruit and/or seed species eaten and dispersed by chelonians. We then use the seed dispersal efficiency framework to explore the quantitative and qualitative components of seed dispersal by tortoises and turtles, embarking on a journey from when the fruits and/or seeds are consumed, to when and where they are deposited, and assess how efficient chelonians are as seed dispersers. We finally discuss chelonian FSD in the context of communities and of chelonians as megafauna. A substantial proportion of the world's aquatic and terrestrial turtles and a major part of testudinid tortoises (71 species in 12 families) include fruits and/or seeds in their diet; fruits of at least 588 plant species in 121 families are ingested and/or dispersed by chelonians. For some chelonians, overall or in certain seasons, fruit may even form the largest part of their diet. Contrary to seed dispersal by lizards, the other major reptilian frugivores, chelonian FSD is not an island phenomenon in terms of geographic distribution. Nevertheless, on islands tortoises are often among the largest native terrestrial vertebrates - or were until humans arrived. We synthesise our knowledge of chelonian FSD, and discuss the relevance of our findings for conservation and restoration, especially in relation to rewilding with large and giant tortoises.

ABA and sucrose co-regulate strawberry fruit ripening and show inhibition of glycolysis

Abscisic acid (ABA) and sucrose play an important role in strawberry fruit ripening, but how ABA and sucrose co-regulate this ripening progress remains unclear. The intention of this study was to examine the effect of ABA and sucrose on strawberry fruit ripening and to evaluate the ABA/sucrose interaction mechanism on the strawberry fruit ripening process. Here, we report that there is an acute synergistic effect between ABA and sucrose in accelerating strawberry fruit ripening. The time frame of fruit development and ripening was shortened after the application of ABA, sucrose, and ABA + sucrose, but most of the major quality parameters in treated-ripe fruit, including fruit weight, total soluble solids, anthocyanin, ascorbic acid, the total phenolic content, lightness (L*), chroma (C*), and hue angle (h°) values were not affected. Meanwhile, the endogenous ABA and sucrose levels, and the expression of ABA and sucrose signaling genes and ripening-related genes, such as NCED1, NCED2, SnRK2.2, SuSy, MYB5, CEL1, and CEL2, was all significantly enhanced by ABA or sucrose treatment alone, but in particular, by the ABA + sucrose treatment. Therefore, improving the ripening regulation efficiency is one synergetic action of ABA/sucrose. Another synergetic action of ABA/sucrose shows that a short inhibition of glycolysis occurs during accelerated strawberry ripening. ABA and sucrose can induce higher accumulation of H₂O₂, leading to a transient decrease in glycolysis. Conversely, lower endogenous H₂O₂ levels caused by reduced glutathione (GSH) treatment resulted in a transient increase in glycolysis while delaying strawberry fruit ripening. Collectively, this study demonstrates that the ABA/sucrose interaction affects the ripening regulation efficiency and shows inhibition of glycolysis.

Disruptions in the female reproductive system on consumption of calcium carbide ripened fruit in mouse models

This study investigated for the first time the outcome of ingestion of calcium carbide-ripened fruit on some female reproductive parameters. A set of unripe mature bananas ripened with calcium carbide (CCRB) and another set ripened via non-artificial means (NARB) were fed orally to prepubertal female mice for three days using the uterotrophic assay procedure. A distilled water group and oestradiol group (10 mg/kg) were also assigned. Food intake, body weights, vaginal openings and cytology were analysed. Samples of blood, uteri, ovaries and cervices were additionally collected and analysed. Increased serum oestrogen level and uterus weight were detected in the CCRB and oestradiol treated groups. Histopathology showed increased numbers of myometrial cells, presence of secondary follicles and regressing corpus lutea as well as thickened cervix epithelia which were evidence of oestrogenic disruptions. This study has shown that consumption of fruits ripened with calcium carbide negatively alters the female reproductive physiology, accelerates puberty onset and increases serum oestrogen levels. Caution must therefore be exercised by fruit sellers in the use of calcium carbide and policies set in place for strict regulation of its use worldwide.

Primary Metabolism in Avocado Fruit

Avocado (Persea americana Mill) is rich in a variety of essential nutrients and phytochemicals; thus, consumption has drastically increased in the last 10 years. Avocado unlike other fruit is characterized by oil accumulation during growth and development and presents a unique carbohydrate pattern. There are few previous and current studies related to primary metabolism. The fruit is also quite unique since it contains large amounts of C7 sugars (mannoheptulose and perseitol) acting as transportable and storage sugars and as potential regulators of fruit ripening. These C7 sugars play a central role during fruit growth and development, but still confirmation is needed regarding the biosynthetic routes and the physiological function during growth and development of avocado fruit. Relatively recent transcriptome studies on avocado mesocarp during development and ripening have revealed that most of the oil is synthesized during early stages of development and that oil synthesis is halted when the fruit is harvested (pre-climacteric stage). Most of the oil is accumulated in the form of triacylglycerol (TAG) representing 60-70% in dry basis of the mesocarp tissue. During early stages of fruit development, high expression of transcripts related to fatty acid and TAG biosynthesis has been reported and downregulation of same genes in more advanced stages but without cessation of the process until harvest. The increased expression of fatty acid key genes and regulators such as PaWRI1, PaACP4-2, and PapPK-β-1 has also been reported to be consistent with the total fatty acid increase and fatty acid composition during avocado fruit development. During postharvest, there is minimal change in the fatty acid composition of the fruit. Almost inexistent information regarding the role of organic acid and amino acid metabolism during growth, development, and ripening of avocado is available. Cell wall metabolism understanding in avocado, even though crucial in terms of fruit quality, still presents severe gaps regarding the interactions between cell wall remodeling, fruit development, and postharvest modifications.

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.

Sound perception in plants

Can plants perceive sound? And what sounds are they likely to be "listening" to? The environment of plants includes many informative sounds, produced by biotic and abiotic sources. An ability to respond to these sounds could thus have a significant adaptive value for plants. We suggest the term phytoacoustics to describe the emerging field exploring sound emission and sound detection in plants, and review the recent studies published on these topics. We describe evidence of plant responses to sounds, varying from changes in gene expression to changes in pathogen resistance and nectar composition. The main focus of this review is the effect of airborne sounds on living plants. We also review work on sound emissions by plants, and plant morphological adaptations to sound. Finally, we discuss the ecological contexts where response to sound would be most advantageous to plants.

Deciphering the nutritive and antioxidant properties of Malay cherry (Lepisanthes alata) fruit dominated by ripening effects

In this study, Malay cherry fruit were explored for the changes in their nutritive and phenolic compositions upon ripening (unripe and ripe stages).

Modifications in Organic Acid Profiles During Fruit Development and Ripening: Correlation or Causation?

The pivotal role of phytohormones during fruit development and ripening is considered established knowledge in plant biology. Perhaps less well-known is the growing body of evidence suggesting that organic acids play a key function in plant development and, in particular, in fruit development, maturation and ripening. Here, we critically review the connection between organic acids and the development of both climacteric and non-climacteric fruits. By analyzing the metabolic content of different fruits during their ontogenetic trajectory, we noticed that the content of organic acids in the early stages of fruit development is directly related to the supply of substrates for respiratory processes. Although different organic acid species can be found during fruit development in general, it appears that citrate and malate play major roles in this process, as they accumulate on a broad range of climacteric and non-climacteric fruits. We further highlight the functional significance of changes in organic acid profile in fruits due to either the manipulation of fruit-specific genes or the use of fruit-specific promoters. Despite the complexity behind the fluctuation in organic acid content during fruit development and ripening, we extend our understanding on the importance of organic acids on fruit metabolism and the need to further boost future research. We suggest that engineering organic acid metabolism could improve both qualitative and quantitative traits of crop fruits.

Characterization of the hot pepper (Capsicum frutescens) fruit ripening regulated by ethylene and ABA

BACKGROUND

Ripening of fleshy fruits has been classically defined as climacteric or non-climacteric. Both types of ripening are controlled by plant hormones, notably by ethylene in climacteric ripening and by abscisic acid (ABA) in non-climacteric ripening. In pepper (Capsicum), fruit ripening has been widely classified as non-climacteric, but the ripening of the hot pepper fruit appears to be climacteric. To date, how to regulate the hot pepper fruit ripening through ethylene and ABA remains unclear.

RESULTS

Here, we examined ripening of the hot pepper (Capsicum frutescens) fruit during large green (LG), initial colouring (IC), brown (Br), and full red (FR) stages. We found a peak of ethylene emission at the IC stage, followed by a peak respiratory quotient at the Br stage. By contrast, ABA levels increased slowly before the Br stage, then increased sharply and reached a maximum level at the FR stage. Exogenous ethylene promoted colouration, but exogenous ABA did not. Unexpectedly, fluridone, an inhibitor of ABA biosynthesis, promoted colouration. RNA-sequencing data obtained from the four stages around ripening showed that ACO3 and NCED1/3 gene expression determined ethylene and ABA levels, respectively. Downregulation of ACO3 and NCED1/3 expression by virus-induced gene silencing (VIGS) inhibited and promoted colouration, respectively, as evidenced by changes in carotenoid, ABA, and ethylene levels, as well as carotenoid biosynthesis-related gene expression. Importantly, the retarded colouration in ACO3-VIGS fruits was rescued by exogenous ethylene.

CONCLUSIONS

Ethylene positively regulates the hot pepper fruit colouration, while inhibition of ABA biosynthesis promotes colouration, suggesting a role of ABA in de-greening. Our findings provide new insights into processes of fleshy fruit ripening regulated by ABA and ethylene, focusing on ethylene in carotenoid biosynthesis and ABA in chlorophyll degradation.

Characterization of the hot pepper (Capsicum frutescens) fruit ripening regulated by ethylene and ABA

BACKGROUND

Ripening of fleshy fruits has been classically defined as climacteric or non-climacteric. Both types of ripening are controlled by plant hormones, notably by ethylene in climacteric ripening and by abscisic acid (ABA) in non-climacteric ripening. In pepper (Capsicum), fruit ripening has been widely classified as non-climacteric, but the ripening of the hot pepper fruit appears to be climacteric. To date, how to regulate the hot pepper fruit ripening through ethylene and ABA remains unclear.

RESULTS

Here, we examined ripening of the hot pepper (Capsicum frutescens) fruit during large green (LG), initial colouring (IC), brown (Br), and full red (FR) stages. We found a peak of ethylene emission at the IC stage, followed by a peak respiratory quotient at the Br stage. By contrast, ABA levels increased slowly before the Br stage, then increased sharply and reached a maximum level at the FR stage. Exogenous ethylene promoted colouration, but exogenous ABA did not. Unexpectedly, fluridone, an inhibitor of ABA biosynthesis, promoted colouration. RNA-sequencing data obtained from the four stages around ripening showed that ACO3 and NCED1/3 gene expression determined ethylene and ABA levels, respectively. Downregulation of ACO3 and NCED1/3 expression by virus-induced gene silencing (VIGS) inhibited and promoted colouration, respectively, as evidenced by changes in carotenoid, ABA, and ethylene levels, as well as carotenoid biosynthesis-related gene expression. Importantly, the retarded colouration in ACO3-VIGS fruits was rescued by exogenous ethylene.

CONCLUSIONS

Ethylene positively regulates the hot pepper fruit colouration, while inhibition of ABA biosynthesis promotes colouration, suggesting a role of ABA in de-greening. Our findings provide new insights into processes of fleshy fruit ripening regulated by ABA and ethylene, focusing on ethylene in carotenoid biosynthesis and ABA in chlorophyll degradation.

Putting primary metabolism into perspective to obtain better fruits

Background

One of the key goals of fruit biology is to understand the factors that influence fruit growth and quality, ultimately with a view to manipulating them for improvement of fruit traits.

Scope

Primary metabolism, which is not only essential for growth but is also a major component of fruit quality, is an obvious target for improvement. However, metabolism is a moving target that undergoes marked changes throughout fruit growth and ripening.

Conclusions

Agricultural practice and breeding have successfully improved fruit metabolic traits, but both face the complexity of the interplay between development, metabolism and the environment. Thus, more fundamental knowledge is needed to identify further strategies for the manipulation of fruit metabolism. Nearly two decades of post-genomics approaches involving transcriptomics, proteomics and/or metabolomics have generated a lot of information about the behaviour of fruit metabolic networks. Today, the emergence of modelling tools is providing the opportunity to turn this information into a mechanistic understanding of fruits, and ultimately to design better fruits. Since high-quality data are a key requirement in modelling, a range of must-have parameters and variables is proposed.

Exploring a volatomic-based strategy for a fingerprinting approach of Vaccinium padifolium L. berries at different ripening stages

The effect of ripening on the evolution of the volatomic pattern from endemic Vaccinium padifolium L. (Uveira) berries was investigated using headspace-solid phase microextraction (HS-SPME) followed by gas chromatography/quadrupole-mass spectrometry (GC-qMS) and multivariate statistical analysis (MVA). The most significant HS-SPME parameters, namely fibre polymer, ionic strength and extraction time, were optimized in order to improve extraction efficiency. Under optimal experimental conditions (DVB/CAR/PDMS fibre coating, 40°C, 30min extraction time and 5g of sample amount), a total of 72 volatiles of different functionalities were isolated and identified. Terpenes followed by higher alcohols and esters were the predominant classes in the ripening stages - green, break and ripe. Although significant differences in the volatomic profiles at the three stages were obtained, cis-β-ocimene (2.0-40.0%), trans-2-hexenol (2.4-19.4%), cis-3-hexenol (2.5.16.4%), β-myrcene (1.9-13.8%), 1-hexanol (1.7-13.6%), 2-hexenal (0.7-8.0%), 2-heptanone (0.7-7.7%), and linalool (1.9-6.1%) were the main volatile compounds identified. Higher alcohols, carboxylic acids and ketones gradually increased during ripening, whereas monoterpenes significantly decreased. These trends were dominated by the higher alcohols (1-hexanol, cis-3-hexenol, trans-2-hexenol) and monoterpenes (β-myrcene, cis-β-ocimene and trans-β-ocimene). Partial least squares regression (PLSR) revealed that ethyl caprylate (1.000), trans-geraniol (0.995), ethyl isovalerate (-0.994) and benzyl carbinol (0.993) are the key variables that most contributed to the successful differentiation of Uveira berries according to ripening stage. To the best of our knowledge, no study has carried out on the volatomic composition of berries from endemic Uveira.

A Transcriptome Approach Toward Understanding Fruit Softening in Persimmon

Persimmon (Diospyros kaki Thunb.), which is a climacteric fruit, softens in 3-5 weeks after harvest. However, little is known regarding the transcriptional changes that underlie persimmon ripening. In this study, high-throughput de novo RNA sequencing was performed to examine differential expression between freshly harvested (FH) and softened (ST) persimmon fruit peels. Using the Illumina HiSeq platform, we obtained 259,483,704 high quality reads and 94,856 transcripts. After the removal of redundant sequences, a total of 31,258 unigenes were predicted, 1,790 of which were differentially expressed between FH and ST persimmon (1,284 up-regulated and 506 down-regulated in ST compared with FH). The differentially expressed genes (DEGs) were further subjected to KEGG pathway analysis. Several pathways were found to be up-regulated in ST persimmon, including "amino sugar and nucleotide sugar metabolism." Pathways down-regulated in ST persimmon included "photosynthesis" and "carbon fixation in photosynthetic organisms." Expression patterns of genes in these pathways were further confirmed using quantitative real-time RT-PCR. Ethylene gas production during persimmon softening was monitored with gas chromatography and found to be correlated with the fruit softening. Transcription involved in ethylene biosynthesis, perception and signaling was up-regulated. On the whole, this study investigated the key genes involved in metabolic pathways of persimmon fruit softening, especially implicated in increased sugar metabolism, decreased photosynthetic capability, and increased ethylene production and other ethylene-related functions. This transcriptome analysis provides baseline information on the identity and modulation of genes involved in softening of persimmon fruits and can underpin the future development of technologies to delay softening in persimmon.

Two FERONIA-Like Receptor Kinases Regulate Apple Fruit Ripening by Modulating Ethylene Production

Ethylene has long been known to be a critical signal controlling the ripening of climacteric fruits; however, the signaling mechanism underlying ethylene production during fruit development is unknown. Here, we report that two FERONIA-like receptor kinases (FERLs) regulate fruit ripening by modulating ethylene production in the climacteric fruit, apple (Malus×domestica). Bioinformatic analysis indicated that the apple genome contains 14 members of the FER family (MdFERL1-17), of these 17 FERLs, MdFERL6 was expressed at the highest level in fruit. Heterologous expression of MdFERL6 or MdFERL1, the apple homolog of Arabidopsis FER, in another climacteric fruit, tomato (Solanum lycopersicum) fruit delayed ripening and suppressed ethylene production. Overexpression and antisense expression of MdFERL6 in apple fruit calli inhibited and promoted ethylene production, respectively. Additionally, virus-induced gene silencing (VIGS) of SlFERL1, the tomato homolog of FER, promoted tomato fruit ripening and ethylene production. Both MdFERL6 and MdFERL1 physically interacted with MdSAMS (S-adenosylmethionine synthase), a key enzyme in the ethylene biosynthesis pathway. MdFERL6 was expressed at high levels during early fruit development, but dramatically declined when fruit ripening commenced, implying that MdFERL6 might limit ethylene production prior to fruit development and the ethylene production burst during fruit ripening. These results indicate that FERLs regulate apple and tomato fruit ripening, shedding light on the molecular mechanisms underlying ripening in climacteric fruit.

A FERONIA-Like Receptor Kinase Regulates Strawberry (Fragaria × ananassa) Fruit Ripening and Quality Formation

Ripening of fleshy fruits is controlled by a series of intricate signaling processes. Here, we report a FERONIA/FER-like receptor kinase, FaMRLK47, that regulates both strawberry (Fragaria × ananassa) fruit ripening and quality formation. Overexpression and RNAi-mediated downregulation of FaMRLK47 delayed and accelerated fruit ripening, respectively. We showed that FaMRLK47 physically interacts with FaABI1, a negative regulator of abscisic acid (ABA) signaling, and demonstrated that FaMRLK47 regulates fruit ripening by modulating ABA signaling, a major pathway governing strawberry fruit ripening. In accordance with these findings, overexpression and RNAi-mediated downregulation of FaMRLK47 caused a decrease and increase, respectively, in the ABA-induced expression of a series of ripening-related genes. Additionally, overexpression and RNAi-mediated downregulation of FaMRLK47 resulted in an increase and decrease in sucrose content, respectively, as compared with control fruits, and respectively promoted and inhibited the expression of genes in the sucrose biosynthesis pathway (FaSS and FaSPS). Collectively, this study demonstrates that FaMRLK47 is an important regulator of strawberry fruit ripening and quality formation, and sheds light on the signaling mechanisms underlying strawberry fruit development and ripening.

Respiration climacteric in tomato fruits elucidated by constraint-based modelling

Tomato is a model organism to study the development of fleshy fruit including ripening initiation. Unfortunately, few studies deal with the brief phase of accelerated ripening associated with the respiration climacteric because of practical problems involved in measuring fruit respiration. Because constraint-based modelling allows predicting accurate metabolic fluxes, we investigated the respiration and energy dissipation of fruit pericarp at the breaker stage using a detailed stoichiometric model of the respiratory pathway, including alternative oxidase and uncoupling proteins. Assuming steady-state, a metabolic dataset was transformed into constraints to solve the model on a daily basis throughout tomato fruit development. We detected a peak of CO₂ released and an excess of energy dissipated at 40 d post anthesis (DPA) just before the onset of ripening coinciding with the respiration climacteric. We demonstrated the unbalanced carbon allocation with the sharp slowdown of accumulation (for syntheses and storage) and the beginning of the degradation of starch and cell wall polysaccharides. Experiments with fruits harvested from plants cultivated under stress conditions confirmed the concept. We conclude that modelling with an accurate metabolic dataset is an efficient tool to bypass the difficulty of measuring fruit respiration and to elucidate the underlying mechanisms of ripening.

Novel Protein-Protein Inhibitor Based Approach to Control Plant Ethylene Responses: Synthetic Peptides for Ripening Control

Ethylene signaling is decisive for many plant developmental processes. Among these, control of senescence, abscission and fruit ripening are of fundamental relevance for global agriculture. Consequently, detailed knowledge of the signaling network along with the molecular processes of signal perception and transfer are expected to have high impact on future food production and agriculture. Recent advances in ethylene research have demonstrated that signaling of the plant hormone critically depends on the interaction of the ethylene receptor family with the NRAMP-like membrane protein ETHYLENE INSENSITIVE 2 (EIN2) at the ER membrane, phosphorylation-dependent proteolytic processing of ER-localized EIN2 and subsequent translocation of the cleaved EIN2 C-terminal polypeptide (EIN2-CEND) to the nucleus. EIN2 nuclear transport, but also interaction with the receptors sensing the ethylene signal, both, depend on a nuclear localization signal (NLS) located at the EIN2 C-terminus. Loss of the tight interaction between receptors and EIN2 affects ethylene signaling and impairs plant ethylene responses. Synthetic peptides derived from the NLS sequence interfere with the EIN2-receptor interaction and have utility in controlling plant ethylene responses such as ripening. Here, we report that a synthetic peptide (NOP-1) corresponding to the NLS motif of Arabidopsis EIN2 (aa 1262-1269) efficiently binds to tomato ethylene receptors LeETR4 and NR and delays ripening in the post-harvest phase when applied to the surface of sampled green fruits pre-harvest. In particular, degradation of chlorophylls was delayed by several days, as monitored by optical sensors and confirmed by analytical methods. Similarly, accumulation of β-carotene and lycopene in the fruit pulp after NOP-1 application was delayed, without having impact on the total pigment concentration in the completely ripe fruits. Likewise, the peptide had no negative effects on fruit quality. Our molecular and phenotypic studies reveal that peptide biologicals could contribute to the development of a novel family of ripening inhibitors and innovative ripening control in climacteric fruit.

Transcriptome Analysis Provides a Preliminary Regulation Route of the Ethylene Signal Transduction Component, SlEIN2, during Tomato Ripening

Ethylene is crucial in climacteric fruit ripening. The ethylene signal pathway regulates several physiological alterations such as softening, carotenoid accumulation and sugar level reduction, and production of volatile compounds. All these physiological processes are controlled by numerous genes and their expression simultaneously changes at the onset of ripening. Ethylene insensitive 2 (EIN2) is a key component for ethylene signal transduction, and its mutation causes ethylene insensitivity. In tomato, silencing SlEIN2 resulted in a non-ripening phenotype and low ethylene production. RNA sequencing of SlEIN2-silenced and wild type tomato, and differential gene expression analyses, indicated that silencing SlEIN2 caused changes in more than 4,000 genes, including those related to photosynthesis, defense, and secondary metabolism. The relative expression level of 28 genes covering ripening-associated transcription factors, ethylene biosynthesis, ethylene signal pathway, chlorophyll binding proteins, lycopene and aroma biosynthesis, and defense pathway, showed that SlEIN2 influences ripening inhibitor (RIN) in a feedback loop, thus controlling the expression of several other genes. SlEIN2 regulates many aspects of fruit ripening, and is a key factor in the ethylene signal transduction pathway. Silencing SlEIN2 ultimately results in lycopene biosynthesis inhibition, which is the reason why tomato does not turn red, and this gene also affects the expression of several defense-associated genes. Although SlEIN2-silenced and green wild type fruits are similar in appearance, their metabolism is significantly different at the molecular level.

Polymeric Supports for Controlled Release of Ethylene for Food Industry

In modern fruit supply chain a common method to trigger ripening is to keep fruits inside special chambers and initiate the ripening process through administration of ethylene. Ethylene is usually administered through cylinders with inadequate control of its final concentration in the chamber. The aim of this study is the development of intelligent polymeric supports able to accurately regulate ethylene concentration in the atmosphere where fruits are preserved. Two different technologies were proposed: a polymeric (PEGDA) film and a polymeric (PLA) bag filled with inclusion complex of ethylene/α-cyclodextrin. The complex was prepared by molecular encapsulation which allows the entrapment of ethylene into the cavity of α-cyclodextrin. After encapsulation, ethylene can be gradually released from the inclusion complex and its release rate can be regulated by temperature and humidity. Intelligent polymeric film was prepared by dispersing inclusion complex into a thin polymeric film produced by UV-curing. Intelligent polymeric bag was made by inserting inclusion complex into heat sealed bag. The kinetics of ethylene release was studied for both systems, showing that it can effectively possible to control the release of ethylene within confined volume. Furthermore, modelling and simulations of ethylene release in a food container were made, demonstrating that it is possible to modulate release rate and, thus, control ripening.

Note. The ripening of Prunus persica fruits with a dominant flat allele Nota. Maduración de frutos de Prunus persica con un alelo dominante de la forma achatada

The changes of peaches ( Prunus persica, L.) with a predominant flat allele were studied during their ripening on the tree. Physicochemical and physiological parameters were analyzed between days 101 and 121 after fruit set. During this period, the weight ranged from 65 g (corresponding to fruit growth stage III) up to a stabilized weight of 90 g when the fruit was ripe. The color changes that characterized fruit ripening began to appear on day 112 after fruit set, with a decrease in the hue angle value both in the skin and pulp. Firmness diminished along the experience from 6.75 to 3.03 Monet units in ripe state. Ripened fruit was also characterized by a soluble solid content of 13.43 °Brix and 0.178% malic acid as titratable acidity. The ripeness index increased throughout maturation from 25.41 at the outset to 44.42 on day 112 after fruit set, and 75.45 at the end of the experiment. The fruit showed a clear climacteric behavior with increased ethylene production and respiration rate. The onset in both processes started on day 112 after fruit set, reached a maximum on day 116, and decreased thereafter. Changes in the content of free and conjugated 1-aminocyclopropane-1-carboxy lic acid (ACC) were coincident with those of ethylene evolution throughout ripening. In regard to polyamine levels, putrescine showed a peak slightly later than that of ethylene and ACC.