Fruit Peel Tissue Research Articles

Miracle Fruit Pulp Transcriptomes Identify Genetic Variants in Support of Discovery Research and Breeding

Miracle fruit (Synsepalum dulcificum) is the botanical source of miraculin, a natural, noncaloric sweetener. Miracle fruit plants have a bush-like architecture and produce multiple flushes of attractive red berries each year. The berries consist of a large seed, opaque pulp, and brilliant red peel. The pulp of the fruit contains a glycoprotein, miraculin, that binds to the tongue’s sweet receptors and induces a conformational change in response to acidic stimuli. Thus, a strong sweet sensation is imparted in the absence of sugars. The miracle fruit plant is becoming increasingly popular because of its taste-modifying properties, but the species lacks many of the breeding tools common to other crops. We report miracle fruit pulp transcriptomes from ‘Sangria’, ‘Vermilion’, ‘Flame’, and ‘Cherry’ morphotypes. A consensus transcriptome included 91,856 transcripts. Reads mapping to the miraculin gene had the highest representation in individual miracle fruit pulp transcriptomes. Other abundant transcripts primarily included Gene Ontology categories representing cellular components, nucleus and nucleic acid binding, and protein modification. The transcriptomes were used to design real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR) primers for actin, elongation factor 1α, and the miraculin gene. Analysis by qRT-PCR indicated that miracle fruit pulp and peel tissues had the highest abundance of miraculin transcripts, although other tissues such as leaf, root, and flower also had detectable levels of the target sequence. Overall, these results will support discovery research for miracle fruit and the eventual breeding of this species.

Blue mold control and volatile compounds in “Fuji” apples treated with chitosan emulsion combined with essential oils

The aim of this work was to evaluate the effects of chitosan emulsion (CE) in combination with essential oils (Eos) on blue mold control, as well as on aroma and quality attributes of “Fuji” apples after storage. Treatments evaluated were control, CE (1%) and CE (1%) combined with citronella, clove and copaiba EOs (all EOs at 500 μl L−1). Fruits treated with EC and EC + OEs showed lower total phenolic compounds in the peel in all treatments. Fruits treated with EC combined with citronella OEs (242.4 OD mg–1 of protein min–1) and clove (205.8 OD mg–1 of protein min–1) showed lower peroxidase activity in fruit peel tissue. Therefore, CE and CE combined with citronella, clove and copaiba essential oils reduced the development of blue mold in “Fuji” apples. In addition, the treatments with lower severity of blue mold showed lower peroxidase activity in the peel and pulp tissues of the fruit, indicating induction of resistance by essential oils. Novelty impact statement Chitosan biofilm reduces rot by P. expansum in “Fuji” apples, and when in addition to chitosan, essential oils of citronella, clove and copaiba are used, there was an increase in the reduction of disease severity. The aroma of the fruit did not present a characteristic aroma of the essential oils used with the method of application used. There were no changes in fruit quality attributes with the use of chitosan and chitosan biofilm with the addition of essential oils.

Effects of 1‐methylcyclopropene and abscisic acid treatments on texture properties and microstructures of postharvest tangerine ( Citrus reticulata cv. Orah)

This study aimed to investigate the effects of 1-methylcyclopropylene (1-MCP) and abscisic acid (ABA) treatments on the postharvest tangerine variety Orah. The whole fruit was treated separately with 0.6 μl/L 1-methylcyclopropylene and 20 mg/L abscisic acid. The fruit was subjected to texture analysis, whereas fruit peel was obtained for microstructure observation. Correlation and principal component analyses showed that 1-MCP treatment could maintain a good peel texture. ABA treatment accelerated fruit senescence and caused the deterioration of the textural properties of the fruit. The data showed that 1-MCP treatment maintained the integrity and compactness of the peel structure. The peel of the fruit treated with 1-methylcyclopropylene also had a uniform thickness after storing at ambient temperature for 20 days. The peel tissue of fruit treated with ABA was more prone to collapse and structural disorder. These findings suggested that 1-methylcyclopropylene treatment was an effective way to prevent the deterioration of Orah tangerines. Novelty impact statement This study compared the effect of 1-methylcyclopropylene (1-MCP) and abscisic acid (ABA) treatments on the postharvest tangerine variety Orah. The changes in texture and ultrastructure of the Orah tangerine during the postharvest storage were the first studied tangerine variety. 1-MCP maintained the texture characteristic and delayed softening of the Orah tangerine, whereas ABA treatment accelerated the fruit ripening and senescence.

Peach, Apple, and Pear Fruit Quality: To Peel or Not to Peel?

The nutritional value of the peeled and unpeeled fruit (peel plus flesh tissues) was studied using four peach (Prunus persica L.; Red Heaven, Maria Blanca, Big Top, and Queen Giant), two pear (Pyrus communis L.; Santa Maria, Pyrus pyrifolia N.; Nashi), and three apple (Malus domestica Borkh.; Gala, Granny Smith, and Red Chief) cultivars. Based on principal components analysis (PCA) models, there was a clear differentiation among the cultivars’ and the peeled fruits’ nutritional characteristics in comparison to the unpeeled ones. Increased antioxidant capacity and content of total phenols and flavonoids of peaches (Red Heaven and Maria Blanca) versus nectarines (Big Top and Queen Giant) were recorded. In contrast, nectarines were characterized by higher hydroxycinnamates and dry matter. The apples’ cultivar Granny Smith exhibited a high level of titratable acidity (TA), while the Gala displayed a high level of soluble solids concentration (SSC), carotenoids, dry matter, hydroxycinnamic acids, and flavonols at the unpeeled fruit, whereas the Red Chief by increased anthocyanins, antioxidant capacity, total phenols, and flavonoids. Nashi pears with peel were more beneficial due to the strong skin contribution in the fruits’ beneficial compounds content. The peel of the Granny Smith cultivar was associated with an increased level of P, K, Ca, and Mg, whereas that of Red Chief with increased anthocyanins and Mg content.

Evidence for pre-climacteric activation of AOX transcription during cold-induced conditioning to ripen in European pear (Pyrus communis L.).

European pears (Pyrus communis L.) require a range of cold-temperature exposure to induce ethylene biosynthesis and fruit ripening. Physiological and hormonal responses to cold temperature storage in pear have been well characterized, but the molecular underpinnings of these phenomena remain unclear. An established low-temperature conditioning model was used to induce ripening of 'D'Anjou' and 'Bartlett' pear cultivars and quantify the expression of key genes representing ripening-related metabolic pathways in comparison to non-conditioned fruit. Physiological indicators of pear ripening were recorded, and fruit peel tissue sampled in parallel, during the cold-conditioning and ripening time-course experiment to correlate gene expression to ontogeny. Two complementary approaches, Nonparametric Multi-Dimensional Scaling and efficiency-corrected 2-(ΔΔCt), were used to identify genes exhibiting the most variability in expression. Interestingly, the enhanced alternative oxidase (AOX) transcript abundance at the pre-climacteric stage in 'Bartlett' and 'D'Anjou' at the peak of the conditioning treatments suggests that AOX may play a key and a novel role in the achievement of ripening competency. There were indications that cold-sensing and signaling elements from ABA and auxin pathways modulate the S1-S2 ethylene transition in European pears, and that the S1-S2 ethylene biosynthesis transition is more pronounced in 'Bartlett' as compared to 'D'Anjou' pear. This information has implications in preventing post-harvest losses of this important crop.

Transcriptomic and biochemical analysis of highlighted induction of phenylpropanoid pathway metabolism of citrus fruit in response to salicylic acid, Pichia membranaefaciens and oligochitosan

The effects of salicylic acid (SA), Pichia membranaefaciens and oligochitosan on induction of disease resistance in citrus fruit were investigated using transcriptomic and biochemical analysis in this study. The results of disease incidence and lesion diameter showed that application of exogenous elicitors SA (2.5 mmol L−1), P. membranaefaciens (1 × 108 cells mL−1) or oligochitosan (15 g L−1) were all effective in inhibiting blue and green molds in citrus fruit. Transcript profiling analysis of citrus fruit peel tissues revealed more differentially expressed genes in phenylpropanoid pathway metabolism induced by the three elicitors compared with other biological pathways. Moreover, biochemical analysis demonstrated that the three elicitors effectively enhanced phenylpropanoid pathway-related enzyme activities and stimulated the synthesis of phenolic acids and their subsequent metabolite lignin. Therefore, global results indicated that the activation of the phenylpropanoid biosynthesis pathway plays an important role in the induction of resistance in citrus fruit by the three elicitors.

Metabolic and transcriptional elucidation of the carotenoid biosynthesis pathway in peel and flesh tissue of loquat fruit during on-tree development

BackgroundCarotenoids are the main colouring substances found in orange-fleshed loquat fruits. The aim of this study was to unravel the carotenoid biosynthetic pathway of loquat fruit (cv. ‘Obusa’) in peel and flesh tissue during distinct on-tree developmental stages through a targeted analytical and molecular approach.ResultsSubstantial changes regarding colour parameters, both between peel and flesh and among the different developmental stages, were monitored, concomitant with a significant increment in carotenoid content. Key genes and individual compounds that are implicated in the carotenoid biosynthetic pathway were further dissected with the employment of molecular (RT-qPCR) and advanced analytical techniques (LC-MS). Results revealed significant differences in carotenoid composition between peel and flesh. Thirty-two carotenoids were found in the peel, while only eighteen carotenoids were identified in the flesh. Trans-lutein and trans-β-carotene were the major carotenoids in the peel; the content of the former decreased with the progress of ripening, while the latter registered a 7.2-fold increase. However, carotenoid profiling of loquat flesh indicated trans-β-cryptoxanthin, followed by trans-β-carotene and 5,8-epoxy-β-carotene to be the most predominant carotenoids. High amounts of trans-β-carotene in both tissues were supported by significant induction in a chromoplast-specific lycopene β-cyclase (CYCB) transcript levels. PSY1, ZDS, CYCB and BCH were up-regulated and CRTISO, LCYE, ECH and VDE were down-regulated in most of the developmental stages compared with the immature stage in both peel and flesh tissue. Overall, differential regulation of expression levels with the progress of on-tree fruit development was more evident in the middle and downstream genes of carotenoid biosynthetic pathway.ConclusionsCarotenoid composition is greatly affected during on-tree loquat development with striking differences between peel and flesh tissue. A link between gene up- or down-regulation during the developmental stages of the loquat fruit, and how their expression affects carotenoid content per tissue (peel or flesh) was established.

MaCDPK7, a calcium-dependent protein kinase gene from banana is involved in fruit ripening and temperature stress responses

ABSTRACTCalcium-dependent protein kinase (CDPK) is an important Ca2+ sensor in plant development and responses to stress stimuli. Banana fruit is a typical climacteric- and chilling-sensitive fruit. The roles of CDPK genes in the ripening and chilling response of banana fruit are unclear. We isolated a cDNA fragment with full-length coding MaCDPK7 (HM061075) from fruit peel tissue. Induction of MaCDPK7 expression in fruit peel was observed 0.5 h after phytohormone ethylene treatment, earlier than the up-regulation of MaACO1 and MaACS1, coding a 1-aminocyclopropane-1-carboxylate oxidase and 1-aminocyclopropane-1-carboxylate synthase, respectively. Penetration of calcium signaling blockers, EGTA, or LaCl3 inhibited the ripening and gene expression of MaCDPK7, MaACO1, and MaACS1 in the in vitro cultured peel pieces, but Ca2+ application removed the inhibitory effect of EGTA and LaCl3. This suggested that MaCDPK7 might be a positive regulator involved in the calcium signaling in banana fruit ripening. Under temperature stresses, we found that MaCDPK7 gene expression increased 3 h after hot water dipping (HWD). The HWD-treated fruits exhibited markedly less chilling injury (CI) than control fruits in cold storage. Stored at 7°C (CI temperature) dramatically increased MaCDPK7 gene expression, while pre-treatment of HWD repressed the induction in cold storage. These results show that the MaCDPK7 gene is involved in regulating banana fruit ripening and chilling resistance induced by heat treatment.

A comparative method for protein extraction and proteome analysis by two-dimensional gel electrophoresis from banana fruit

<p>Bananas and plantains are a major staple food and export product in many countries.<strong> </strong>Banana fruit tissues contain large amounts of secondary compounds, polysaccharides and other plant polymers which will interfere with protein extraction for gel-based proteomic analysis. Due to presence of very small amount of proteins (approximately 1%) in a large matrix of fruit tissues, it classified as ‘recalcitrant’. In this connection, assessment of different protein extraction protocols and extraction of high quality proteins from banana fruit tissues is crucial for successful gel-based proteome analysis. In this study, two different protein extraction protocols were validated to isolate proteins from banana (cv.Grand Naine) fruit peel and pulp tissues, and proteins were resolved by using SDS-PAGE. A comparative study showed that phenol based method is effective in extracting proteins over TCA-acetone method. Isolated proteins were further subjected to two-dimensional gel electrophoresis separation and stained with colloidal coomassie blue to visualize protein spots. On average 380 protein spots could be detected on coomassie stained two-dimensional gel and our study clearly demonstrated the differential protein accumulation during pre-climacteric and climacteric stages of banana fruit. <strong></strong></p>

Proteome changes in banana fruit peel tissue in response to ethylene and high-temperature treatments.

Banana (Musa AAA group) is one of the most consumed fruits in the world due to its flavor and nutritional value. As a typical climacteric fruit, banana responds to ethylene treatment, which induces rapid changes of color, flavor (aroma and taste), sweetness and nutritional composition. It has also been reported that ripening bananas at temperatures above 24 °C inhibits chlorophyll breakdown and color formation but increases the rate of senescence. To gain fundamental knowledge about the effects of high temperature and ethylene on banana ripening, a quantitative proteomic study employing multiplex peptide stable isotope dimethyl labeling was conducted. In this study, green (immature) untreated banana fruit were subjected to treatment with 10 μL L−1 of ethylene for 24 h. After ethylene treatment, treated and untreated fruit were stored at 20 or 30 °C for 24 h. Fruit peel tissues were then sampled after 0 and 1 day of storage, and peel color and chlorophyll fluorescence were evaluated. Quantitative proteomic analysis was conducted on the fruit peels after 1 day of storage. In total, 413 common proteins were identified and quantified from two biological replicates. Among these proteins, 91 changed significantly in response to ethylene and high-temperature treatments. Cluster analysis on these 91 proteins identified 7 groups of changed proteins. Ethylene treatment and storage at 20 °C induced 40 proteins that are correlated with pathogen resistance, cell wall metabolism, ethylene biosynthesis, allergens and ribosomal proteins, and it repressed 36 proteins that are associated with fatty acid and lipid metabolism, redox–oxidative responses, and protein biosynthesis and modification. Ethylene treatment and storage at 30 °C induced 32 proteins, which were mainly similar to those in group 1 but also included 8 proteins in group 3 (identified as chitinase, cinnamyl alcohol dehydrogenase 1, cysteine synthase, villin-2, leucine-transfer RNA ligase, CP47 protein and calmodulin) and repressed 43 proteins in 4 groups (groups 4–7), of which 6 were associated with photosynthesis II oxygen-evolving protein, the photosynthesis I reaction center, sugar metabolism, the redox–oxidative system and fatty acid metabolism. Differences in the response to ethylene and holding temperature at 30 °C were also revealed and have been discussed. The identities and quantities of the proteins found were linked with quality changes. This study demonstrates that ethylene and high temperature influence banana fruit ripening and senescence at the proteomic level and reveals the mechanisms by which high temperature accelerates banana fruit ripening.

Transcriptome changes in apple peel tissues during CO2 injurysymptom development under controlled atmosphere storage regimens.

Apple (Malus × domestica Borkh.) is one of the most widely cultivated tree crops, and fruit storability is vital to the profitability of the apple fruit industry. Fruit of many apple cultivars can be stored for an extended period due to the introduction of advanced storage technologies, such as controlled atmosphere (CA) and 1-methylcyclopropane (1-MCP). However, CA storage can cause external CO2 injury for some apple cultivars. The molecular changes associated with the development of CO2 injury are not well elucidated. In this study, the global transcriptional regulations were investigated under different storage conditions and during development of CO2 injury symptoms on ‘Golden Delicious’ fruit. Fruit peel tissues under three different storage regimens, regular cold atmosphere, CA and CA storage and 1-MCP application were sampled at four storage durations over a 12-week period. Fruit physiological changes were affected differently under these storage regimens, and CO2 injury symptoms were detectable 2 weeks after CA storage. Identification of the differentially expressed genes and a gene ontology enrichment analysis revealed the specific transcriptome changes associated with each storage regimen. Overall, a profound transcriptome change was associated with CA storage regimen as indicated by the large number of differentially expressed genes. The lighter symptom was accompanied by reduced transcriptome changes under the CA storage and 1-MCP application regimen. Furthermore, the higher enrichment levels in the functional categories of oxidative stress response, glycolysis and protein post-translational modification were only associated with CA storage regime; therefore, these processes potentially contribute to the development of external CO2 injury or its symptom in apple.

Postharvest dip treatment with a natural lysophospholipid plus soy lecithin extended the shelf life of banana fruit

Lysophosphatidylethanolamine (LPE), a natural phospholipid, has been investigated for retarding senescence and promoting the shelf life of fruit and other plant tissues. LPE is a water insoluble phospholipid. For most experimental purposes, LPE is dispersed in water prior to treatment of fruit using sonication. In this study, the water solubility of LPE was improved by mixing it with soy lecithin prior to mixing with water. A combination of LPE and lecithin was used for a dip treatment of banana fruit. Banana fruit at ripening stage 2 (3/4 green) were dipped in this solution for 30min and then stored at room temperature for 10d. A combination of 200mgL−1 LPE and lecithin gave the best shelf life. In this treatment over 75% of the fruit were marketable 7d after treatment. While only about 20% and 28% of the fruit were marketable in the water (control) and lecithin treated-fruit respectively. Fruit treated with lecithin alone had better shelf life as compared to the control. Furthermore, the LPE+lecithin treatment gave better shelf life as compared to the LPE alone treatment. At 7d after dip, fruit treated with LPE+lecithin had lower ion leakage from peel tissue, higher pulp firmness, and thicker peel as compare to the control and lecithin treatments. A dip treatment with NAA (1-naphthalene acetic acid) was compared with LPE+lecithin for fruit marketability and changes in various fruit properties during ripening. Although NAA improved shelf life and retarded fruit softening as compared to the control, this treatment resulted in abnormal de-greening of fruit peel tissue. Fruit treated with LPE+lecithin had normal yellow color development and had lower ethylene production as compared to NAA and control treatments. The results of this study suggest that a dip treatment with a combination of LPE and lecithin may have potential for improving shelf life of banana fruit.

Transcriptomic profiling of citrus fruit peel tissues reveals fundamental effects of phenylpropanoids and ethylene on induced resistance.

Penicillium spp. are the major postharvest pathogens of citrus fruit in Mediterranean climatic regions. The induction of natural resistance constitutes one of the most promising alternatives to avoid the environmental contamination and health problems caused by chemical fungicides. To understand the bases of the induction of resistance in citrus fruit against Penicillium digitatum, we have used a 12k citrus cDNA microarray to study transcriptional changes in the outer and inner parts of the peel (flavedo and albedo, respectively) of elicited fruits. The elicitor treatment led to an over-representation of biological processes associated with secondary metabolism, mainly phenylpropanoids and cellular amino acid biosynthesis and methionine metabolism, and the down-regulation of genes related to biotic and abiotic stresses. Among phenylpropanoids, we detected the over-expression of a large subset of genes important for the synthesis of flavonoids, coumarins and lignin, especially in the internal tissue. Furthermore, these genes and those of ethylene biosynthesis showed the highest induction. The involvement of both phenylpropanoid and ethylene pathways was confirmed by examining changes in gene expression and ethylene production in elicited citrus fruit. Therefore, global results indicate that secondary metabolism, mainly phenylpropanoids, and ethylene play important roles in the induction of resistance in citrus fruit.

EFFECT OF SUPERATMOSPHERIC OXYGEN CONCENTRATIONS ON PHYSIOLOGICAL AND QUALITATIVE ASPECTS OF COLD STORED POMEGRANATE FRUIT

Exposure to high concentrations of O 2 can positively affect the quality of different commodities during their postharvest life. The objective of this experiment was to assess the physiological and qualitative response of 'Primosole' pomegranates exposed to normal atmosphere (NA; 21 kPa O 2 and + 79 kPa N 2 ) or to atmospheres with high concentrations of O 2 (SAO; 50 kPa O 2 and + 50 kPa N 2 or 97 kPa O 2 + 3 kPa N 2 ). Fruit were stored at 2°C in NA or SAO for 4 weeks plus 1 week at 20°C in NA to simulate the marketing conditions (SMC). At the end of cold storage no significant differences were detected in respiration between fruit exposed to NA and 50 kPa O 2 , while significantly lower values were detected in those held at 97 kPa O 2 . However, upon transfer to SMC, respiration increased to the same level as at harvest in all treatments. 24h after transfer to 20°C, the seeds of fruit exposed to high O 2 produced less CO 2 than those of controls, but after 1 week of storage there was no difference amongst the treatments. During storage electrolyte leakage increased in peel tissue of fruit exposed to 50 and 97 kPa O 2 , showing higher and lower values, respectively, than NA stored fruit. In contrast, electrolyte leakage of seeds was similar in NA and 50 kPa O 2 stored fruit and higher in those stored at 97 kPa O 2 . Exposure to SAO had no important effect on the main chemical parameters (pH, titratable acidity, total soluble solids) of the juice, although at the end of the SMC the concentrations of total soluble solids and titratable acidity were slightly lower in fruit stored at 97 kPa O 2 . Chilling injury appeared only sporadically, regardless of the treatments, but browning of the husk was very severe at 97 kPa O 2 , especially after SMC. Decay was inhibited during fruit exposure to SAO. Throughout cold storage only fruit exposed to NA showed some decay; however at the end of SMC the highest decay was detected in fruit stored at 97 kPa O 2 . The presented results indicate minor effects on the overall quality of pomegranates stored at 2°C in superatmospheric oxygen concentrations, especially at 97 kPa O 2 .

A modified chemiluminescence method for hydrogen peroxide determination in apple fruit tissues

Hydrogen peroxide (H 2O 2) is one of the important by-products produced by plant and fruit tissues during normal metabolism as well as under stress conditions. Evidence suggests that it is actively involved in many physiological activities in plants, including ripening, senescence and the development of disorders. Quantitative measurement of H 2O 2 in fruit has been a challenge due to variations in methodologies, and their sensitivities and interferences present in plant samples. Among the currently used methodologies, chemiluminescence (CL) is one of the most promising, due to its high specificity and sensitivity. However, direct application of CL methods developed for leaf analysis is not suitable for fruit, especially fruit peel tissues, possibly due to interfering compounds in fruit tissues. In this study, evaluation of the efficiency of removal of interfering compounds by PVP, PVPP and activated charcoal revealed that the PVPP is the most effective compound to remove the interference. This modified protocol can measure H 2O 2 content in apple peel and flesh tissues. ‘Red Delicious’ apple peel and flesh tissues were measured with amount of 1.48 and 1.03 μmol/g FW, respectively. The established protocol can also be used for a wide variety of tissues in addition to apple fruit, including strawberry tissues (fruit, calyx and leaves) and spinach leaves. This protocol was applied to determine the H 2O 2 concentration in 1-MCP and DPA treated apples after 5 months of storage, but no significant difference in H 2O 2 in those samples was found. Direct comparison of CL with a commercial hydrogen peroxide measurement OXIS kit was also made. The challenges to accurately assay H 2O 2 in fruit/plant tissue were discussed.

CsPLDalpha1 and CsPLDgamma1 are differentially induced during leaf and fruit abscission and diurnally regulated in Citrus sinensis.

Understanding leaf and fruit abscission is essential in order to develop strategies for controlling the process in fruit crops. Mechanisms involved in signalling leaf and fruit abscission upon induction by abscission agents were investigated in Citrus sinensis cv. ‘Valencia’. Previous studies have suggested a role for phospholipid signalling; hence, two phospholipase D cDNA sequences, CsPLDα1 and CsPLDγ1, were isolated and their role was examined. CsPLDα1 expression was reduced in leaves but unaltered in fruit peel tissue treated with an ethylene-releasing compound (ethephon), or a fruit-specific abscission agent, 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP). By contrast, CsPLDγ1 expression was up-regulated within 6 h (leaves) and 24 h (fruit peel) after treatment with ethephon or CMNP, respectively. CsPLDα1 expression was diurnally regulated in leaf blade but not fruit peel. CsPLDγ1 exhibited strong diurnal oscillation in expression in leaves and fruit peel with peak expression around midday. While diurnal fluctuation in CsPLDα1 expression appeared to be light-entrained in leaves, CsPLDγ1 expression was regulated by light and the circadian clock. The diurnal expression of both genes was modulated by ethylene-signalling. The ethephon-induced leaf abscission and the ethephon- and CMNP-induced decrease in fruit detachment force were enhanced by application during rising diurnal expression of CsPLDγ1. The results indicate differential regulation of CsPLDα1 and CsPLDγ1 in leaves and fruit, and suggest possible roles for PLD-dependent signalling in regulating abscission responses in citrus.

Citrus Chlorophyllase Dynamics at Ethylene-Induced Fruit Color-Break: A Study of Chlorophyllase Expression, Posttranslational Processing Kinetics, and in Situ Intracellular Localization

Fruit color-break is the visual manifestation of the developmentally regulated transition of chloroplasts to chromoplasts during fruit ripening and often involves biosynthesis of copious amounts of carotenoids concomitant with massive breakdown of chlorophyll. Regulation of chlorophyll breakdown at different physiological and developmental stages of the plant life cycle, particularly at fruit color-break, is still not well understood. Here, we present the dynamics of native chlorophyllase (Chlase) and chlorophyll breakdown in lemon (Citrus limon) fruit during ethylene-induced color-break. We show, using in situ immunofluorescence on ethylene-treated fruit peel (flavedo) tissue, that citrus Chlase is located in the plastid, in contrast to recent reports suggesting cytoplasmic localization of Arabidopsis (Arabidopsis thaliana) Chlases. At the intra-organellar level, Chlase signal was found to overlap mostly with chlorophyll fluorescence, suggesting association of most of the Chlase protein with the photosynthetic membranes. Confocal microscopy analysis showed that the kinetics of chlorophyll breakdown was not uniform in the flavedo cells. Chlorophyll quantity at the cellular level was negatively correlated with plastid Chlase accumulation; plastids with reduced chlorophyll content were found by in situ immunofluorescence to contain significant levels of Chlase, while plastids containing still-intact chlorophyll lacked any Chlase signal. Immunoblot and protein-mass spectrometry analyses were used to demonstrate that citrus Chlase initially accumulates as an approximately 35-kD precursor, which is subsequently N-terminally processed to approximately 33-kD mature forms by cleavage at either of three consecutive amino acid positions. Chlase plastid localization, expression kinetics, and the negative correlation with chlorophyll levels support the central role of the enzyme in chlorophyll breakdown during citrus fruit color-break.

Ultraviolet radiation effects on fruit surface respiration and chlorophyll fluorescence

SummaryHigh-value fruit crops are exposed to a range of environmental conditions that can reduce fruit quality. Solar injury (SI) or sunburn is a common disorder in tropical, sub-tropical, and temperate climates and is related to: 1) high fruit surface temperature; 2) high visible light intensity; and, 3) ultraviolet radiation (UV). Positional changes in fruit that are caused by increased weight or abrupt changes that result from Summer pruning, limb breakage, or other damage to the canopy can expose fruit to high solar radiation levels, increased fruit surface temperatures, and increased UV exposure that are higher than the conditions to which they are adapted. In our studies, we examined the effects of high fruit surface temperature, saturating photosynthetically-active radiation (PAR), and short-term UV exposure on chlorophyll fluorescence, respiration, and photosynthesis of fruit peel tissues from tropical and temperate fruit in a simulation of these acute environmental changes. All tropical fruits (citrus, macadamia, avocado, pineapple, and custard apple) and the apple cultivars ‘Gala’, ‘Gold Rush’, and ‘Granny Smith’ increased dark respiration (A0) when exposed to UV, suggesting that UV repair mechanisms were induced. The maximum quantum efficiency of photosystem II (Fv/Fm) and the quantum efficiency of photosystem II ( II) were unaffected, indicating no adverse effects on photosystem II (PSII). In contrast, ‘Braeburn’ apple had a reduced Fv/Fm with no increase in A0 on all sampling dates.There was a consistent pattern in all studies.When Fv/Fm was unaffected by UV treatment, A0 increased significantly. Conversely, when Fv/Fm was reduced by UV treatment, then A0 was unaffected. The pattern suggests that when UV repair mechanisms are effective, PSII is adequately protected, and that this protection occurs at the cost of higher respiration. However, when the UV repair mechanisms are ineffective, not only is PSII damaged, but there is additional short-term damage to the repair mechanisms, indicated by a lack of respiration to provide energy.

Effect of microenvironments and exogenous substance application on 5′-nucleotidase activities in apple peel

The present experiment was conducted to examine the effect of microenvironments and exogenous substance application on 5′-nucleotidase activity in apple peel tissue. By enclosing apple fruits in bags, treating them with exogenous active oxygen species and regulative agents or placing them under controlled conditions at different fruit temperatures or relative humidity, the 5′-nucleotidase activities were compared with the corresponding controls. The results indicated that, a considerable effect of the microenvironments was found on 5′-nucleotidase activities in fruit peel tissue. The highest enzymatic activity appeared in fruits on the southwest exposure of canopy, regardless of bagged or non-bagged fruits, significantly higher than those from any other exposures. Fruits with bags had a significantly higher 5′-nucleotidase activity than the exposed ones. A variation in enzymatic activities was observed in fruits enclosed with different types of bags, which were supposed to alter the microenvironments around them. Within a certain range, gradual or fluctuating rise of fruit temperatures could favor the increase of 5′-nucleotidase activities as a result of heat adaptation, whereas the activity would be inhibited if the temperature-rising period was too short or temperature differential was too large. No matter what temperatures fruits were subjected to, high relative humidity was favorable for stimulating the 5′-nucleotidase activities, which might partly explain why fruit sunburn would not happen in humid climates. Treatments with four kinds of exogenous active oxygen species could reduce the 5′-nucleotidase activities significantly but spraying with CaCl2 was able to enhance 5′-nucleotidase activities by 55.39%, reaching a 5% significant level.

Methods for the efficient quantification of fruit provitamin A contents

As part of a screening program to identify micronutrient-rich banana and plantain ( Musa) varieties, a simple, robust, and comparatively rapid protocol for the quantification of the provitamin A carotenoids contents of fruit pulp and peel tissues by HPLC and by spectrophotometry has been developed. Major points to note include the use lyophilisation and extensive tissue disruption procedures to ensure quantitative recoveries, and the avoidance of saponification and/or concentration steps which lead to significant losses of provitamin A carotenoids. The protocol showed excellent reproducibility between replicate extractions, without the need for an internal standard. Application of the methodology demonstrated that Musa fruit pulp has a relatively simple provitamin A carotenoids content, quite different from the overlying peel, and that the proportions of α- and β-carotene are characteristic for each genotype. The protocol was also used to profile the provitamin A carotenoids of several other fruits.