Effect of infiltrated polyamines on polygalacturonase activity and chilling injury responses in zucchini squash (Cucurbita pepo L.)

A Synergistic Effect Based on the Combination of Melatonin with 1-Methylcyclopropene as a New Strategy to Increase Chilling Tolerance and General Quality in Zucchini Fruit

Zucchini fruit are highly sensitive to low temperatures leading to significant peel depressions, increasing weight loss and making them impossible to be commercialized. In this study the effect on the reduction of chilling injury (CI) assaying different postharvest treatments to cv. Cronos was evaluated. We have compared the application of substances such as 1-methylcyclopropene (1-MCP) with the application of a natural origin compound as melatonin (MT), both with demonstrated activity against CI in different vegetal products. The effects of MT (1 mM) by dipping treatment of 1 h and 1-MCP (2400 ppb) have been evaluated on zucchini fruit during 15 days of storage at 4 °C plus 2 days at 20 °C. Treatments applied independently improved some fruit quality parameters in comparison with control fruit but were not able to manage CI even though they mitigated the impact on several parameters. However, when these two separated strategies were combined, zucchini cold tolerance increased with a synergic trend. This synergic effect affected in general all parameters but specially CI, being also the only lot in which zucchini fruit were most effectively preserved. This is the first evidence in which a clear positive effect on zucchini chilling tolerance has been obtained combining these two different strategies. In this sense, the combined effect of 1-MCP and MT could be a suitable tool to reach high quality standards and increasing shelf life under suboptimal temperatures.

Alleviating Chilling Injury in Stored Pomegranate Using a Single Intermittent Warming Cycle: Fatty Acid and Polyamine Modifications

Pomegranate is a perishable superfruit with important human health-promoting phytochemicals. The use of cold storage is inevitable for its long-term preservation. As pomegranate is sensitive to temperatures below 5°C, it is therefore necessary and worthwhile to introduce a postharvest technique that is safe, applicable, and commercially acceptable to maintain the fruit quality under a cold storage condition. The efficacy of intermittent warming (IW) in the form of a single warming period (1 day at 20°C with 70% relative humidity (RH) before returning the treated fruit to storage) during the cold storage of ‘Rabab-e-Neyriz' pomegranate (70 days at 2 ± 0.5°C and 90 ± 5% RH) was evaluated. To find the best treatment time, warming was performed at 4 temporary interruption points in storage (after 15, 25, 35, or 45 days of storage). For each interruption date, the treated fruit were compared to the controls twice, once immediately after treatment and once at the end of the storage period. It was founded that a single warming period at the right time during cold storage (before irreversible damage occurs) activated multiple mechanisms and physiological responses in pomegranate fruit peel that are significantly responsible for alleviating the severity of chilling damage to this commodity. In other words, warming on the 15th day was the most efficient treatment, resulting in better preservation of unsaturated fatty acids from peroxidation, lower malondialdehyde (MDA) production, and preservation of the unsaturated/saturated fatty acids (UFAs/SFAs) ratio (membrane integrity index) in the peel during storage and lower chilling injury symptoms. Moreover, the content of spermine (Spm) and putrescine (Put) (as important antioxidants acting as membrane safety agents) was significantly increased immediately after treatment, followed by a continuous increase in Spm and a higher level of Put compared to control until the end of storage.

Near-saturated relative humidity alleviates chilling injury in zucchini fruit through its regulation of antioxidant response and energy metabolism

To investigate the effect of relative humidity (RH) on chilling injury (CI), zucchini fruit were stored in cold rooms (4 ± 0.4 ℃) with different RHs (near-saturated RH [NSH] with 96-100% and normal RH with 72-76% served as control). Storage in NSH delayed weight loss and CI, maintained firmness and skin color. Higher antioxidant enzyme activities and greater scavenging capacities of free radicals were found in NSH-fruit than in the control fruit. The decrease of the unsaturated fatty acids was delayed in NSH-fruit due to lower activities of related membrane lipid degrading enzymes as compared to the control fruit. NSH-fruit also maintained higher activities of energy metabolism-associated enzymes than control fruit, leading to high levels of adenosine triphosphate (ATP). Taken together, we attributed the alleviation of CI by NSH storage to its enhancement of antioxidant capacities and its effect on maintaining higher energy status in zucchini fruit.

Spermidine application reduces fluoride uptake and ameliorates physiological injuries in a susceptible rice cultivar by activating diverse regulators of the defense machinery

The manuscript illustrates the ameliorative effects of exogenously applied higher polyamine (PA), spermidine (Spd) in the susceptible indica rice cultivar IR-64 subjected to prolonged fluoride stress. The Spd treatment drastically reduced fluoride bioaccumulation by restricting entry of the anions through chloride channels and enabled better maintenance of the proton gradient via accumulation of P-H⁺/ATPase, thereby improving the root and shoot lengths, fresh and dry weights, RWC, chlorophyll content and activities of pyruvate dehydrogenase (PyrDH), α-amylase, and nitrate reductase (NR) in the Spd-treated, stressed plants. Expression of RuBisCo, PyrDH, α-amylase, and NR was stimulated. Spd supplementation reduced the molecular damage indices like malondialdehyde, lipoxygenase, protease activity, electrolyte leakage, protein carbonylation, H₂O₂, and methylglyoxal (detoxified by glyoxalase II). Mitigation of oxidative damage was facilitated by the accumulation and utilization of proline, glycine-betaine, total amino acids, higher PAs, anthocyanin, flavonoids, β-carotene, xanthophyll, and phenolics as verified from the expression of genes like P5CS, BADH1, SAMDC, SPDS, SPMS, DAO, PAO, and PAL. Spd treatment activated the ascorbate-glutathione cycle in the stressed seedlings. Expression and activities of enzymatic antioxidants showed that GPOX, APX, GPX, and GST were the chief ROS scavengers. Exogenous Spd promoted ABA accumulation by upregulating NCED3 and suppressing ABA8ox1 expression. ABA-dependent osmotic stress-responsive genes like Osem, WRKY71, and TRAB1 as well as ABA-independent transcription factor encoding gene DREB2A were induced by Spd. Thus, Spd treatment ameliorated fluoride-mediated injuries in IR-64 by restricting fluoride uptake, refining the defense machinery and activating the ABA-dependent as well as ABA-independent stress-responsive genes.

Exogenous γ-aminobutyric acid treatment improves the cold tolerance of zucchini fruit during postharvest storage

This work examines the effect of a treatment with 1 mM of γ-aminobutyric acid (GABA) on zucchini fruit during postharvest cold storage. Specifically, the effect of GABA on postharvest quality was measured, as well as its implication in the GABA shunt and other related metabolic pathways. The treatments were performed in Sinatra, a variety of zucchini highly sensitive to low-temperature storage. The application of GABA improved the quality of zucchini fruit stored at 4 °C, with a reduction of chilling-injury index, weight loss, and cell death, as well as a lower rate of electrolyte leakage. GABA content was significantly higher in the treated fruit than in the control fruit at all times analyzed. At the end of the storage period, GABA-treated fruit had higher contents of both proline and putrescine. The catabolism of this polyamine was not affected by exogenous GABA. Also, over the long term, the treatment induced the GABA shunt by increasing the activities of the enzymes GABA transaminase (GABA-T) and glutamate decarboxylase (GAD). GABA-treated fruit contained higher levels of fumarate and malate than did non-treated fruit, as well as higher ATP and NADH contents. These results imply that the GABA shunt is involved in providing metabolites to produce energy, reduce power, and help the fruit to cope with cold stress over the long term.

Characterisation and prediction of carbohydrate content in zucchini fruit using near infrared spectroscopy

BACKGROUND

Zucchini fruit plays an important part in healthy nutrition due to its high content of carbohydrates. Recent studies have demonstrated the feasibility of visible-NIRS to predict quality profile. However, this procedure has not been applied to determine carbohydrates.

RESULTS

Visible-NIR and wet chemical methods were used to determine individual sugars and starch in zucchini fruits. By applying a principal component analysis (PCA) with NIR spectral data a differentiation between the less sweet versus the sweetest zucchini accessions could be found. For the determination of carbohydrate content effective prediction models for individual sugars such as glucose, fructose, sucrose and starch by using partial least squares (PLS) regression have been developed.

CONCLUSION

The coefficients of determination in the external validation (R² VAL) ranged from 0.66 to 0.85. The standard deviation (SD) to standard error of prediction ratio (RPD) and SD to range (RER) were variable for different quality compounds and showed values that were characteristic of equations suitable for screening purposes. From the study of the MPLS loadings of the first three terms of the different equations for sugars and starch, it can be concluded that some major cell components such as pigments, cellulose, organic acids highly participated in modelling the equations for carbohydrates. © 2017 Society of Chemical Industry.

Transcriptomic changes in Cucurbita pepo fruit after cold storage: differential response between two cultivars contrasting in chilling sensitivity

Background

Zucchini fruit is susceptible to chilling injury (CI), but the response to low storage temperature is cultivar dependent. Previous reports about the response of zucchini fruit to chilling storage have been focused on the physiology and biochemistry of this process, with little information about the molecular mechanisms underlying it. In this work, we present a comprehensive analysis of transcriptomic changes that take place after cold storage in zucchini fruit of two commercial cultivars with contrasting response to chilling stress.

Results

RNA-Seq analysis was conducted in exocarp of fruit at harvest and after 14 days of storage at 4 and 20 °C. Differential expressed genes (DEGs) were obtained comparing fruit stored at 4 °C with their control at 20 °C, and then specific and common up and down-regulated DEGs of each cultivar were identified. Functional analysis of these DEGs identified similarities between the response of zucchini fruit to low temperature and other stresses, with an important number of GO terms related to biotic and abiotic stresses overrepresented in both cultivars. This study also revealed several molecular mechanisms that could be related to chilling tolerance, since they were up-regulated in cv. Natura (CI tolerant) or down-regulated in cv. Sinatra (CI sensitive). These mechanisms were mainly those related to carbohydrate and energy metabolism, transcription, signal transduction, and protein transport and degradation. Among DEGs belonging to these pathways, we selected candidate genes that could regulate or promote chilling tolerance in zucchini fruit including the transcription factors MYB76-like, ZAT10-like, DELLA protein GAIP, and AP2/ERF domain-containing protein.

Conclusions

This study provides a broader understanding of the important mechanisms and processes related to coping with low temperature stress in zucchini fruit and allowed the identification of some candidate genes that may be involved in the acquisition of chilling tolerance in this crop. These genes will be the basis of future studies aimed to identify markers involved in cold tolerance and aid in zucchini breeding programs.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4500-9) contains supplementary material, which is available to authorized users.

A Profusion of Molecular Scissors for Pectins: Classification, Expression, and Functions of Plant Polygalacturonases

In plants, the construction, differentiation, maturation, and degradation of the cell wall are essential for development. Pectins, which are major constituents of primary cell walls in eudicots, function in multiple developmental processes through their synthesis, modification, and degradation. Several pectin modifying enzymes regulate pectin degradation via different modes of action. Polygalacturonases (PGs), which function in the last step of pectin degradation, are a crucial class of pectin-modifying enzymes. Based on differences in their hydrolyzing activities, PGs can be divided into three main types: exo-PGs, endo-PGs, and rhamno-PGs. Their functions were initially investigated based on the expression patterns of PG genes and measurements of total PG activity in organs. In most plant species, PGs are encoded by a large, multigene family. However, due to the lack of genome sequencing data in early studies, the number of identified PG genes was initially limited. Little was initially known about the evolution and expression patterns of PG family members in different species. Furthermore, the functions of PGs in cell dynamics and developmental processes, as well as the regulatory pathways that govern these functions, are far from fully understood. In this review, we focus on how recent studies have begun to fill in these blanks. On the basis of identified PG family members in multiple species, we review their structural characteristics, classification, and molecular evolution in terms of plant phylogenetics. We also highlight the diverse expression patterns and biological functions of PGs during various developmental processes, as well as their mechanisms of action in cell dynamic processes. How PG functions are potentially regulated by hormones, transcription factors, environmental factors, pH and Ca²⁺ is discussed, indicating directions for future research into PG function and regulation.

Oxidative Stress Associated with Chilling Injury in Immature Fruit: Postharvest Technological and Biotechnological Solutions

Immature, vegetable-like fruits are produced by crops of great economic importance, including cucumbers, zucchini, eggplants and bell peppers, among others. Because of their high respiration rates, associated with high rates of dehydration and metabolism, and their susceptibility to chilling injury (CI), vegetable fruits are highly perishable commodities, requiring particular storage conditions to avoid postharvest losses. This review focuses on the oxidative stress that affects the postharvest quality of vegetable fruits under chilling storage. We define the physiological and biochemical factors that are associated with the oxidative stress and the development of CI symptoms in these commodities, and discuss the different physical, chemical and biotechnological approaches that have been proposed to reduce oxidative stress while enhancing the chilling tolerance of vegetable fruits.

Effect of Putrescine Treatment on Chilling Injury, Fatty Acid Composition and Antioxidant System in Kiwifruit

We investigated the effects of different concentrations (0, 1, 2 and 4 mM) of putrescine on chilling injury, fruit quality, ethylene production rate, fatty acid composition and the antioxidant system of cold-stored kiwifruit (Actinidia chinensis Planch. var. chinensis 'Hongyang'). We achieved a significant decrease in ethylene production, maintained fruit quality and alleviated chilling injury during storage via treatment with 2 mM putrescine. Furthermore, putrescine treatment inhibited increases in superoxide anion production rate and H2O2 concentration, while maintaining higher membrane lipid unsaturation as well as increased activities of superoxide dismutase and catalase. In addition, putrescine treatment enhanced the activities of antioxidant enzymes related to the ascorbate-glutathione cycle while causing higher levels of ascorbic acid and reduced glutathione. Our results suggest that induced tolerance against chilling injury via putrescine treatment in cold-stored kiwifruit may be due to enhanced antioxidant activity, increased unsaturation of membrane lipids, and inhibited ethylene production.

Pathogenesis-Related Protein 1b1 (PR1b1) Is a Major Tomato Fruit Protein Responsive to Chilling Temperature and Upregulated in High Polyamine Transgenic Genotypes

Plants execute an array of mechanisms in response to stress which include upregulation of defense-related proteins and changes in specific metabolites. Polyamines - putrescine (Put), spermidine (Spd), and spermine (Spm) - are metabolites commonly found associated with abiotic stresses such as chilling stress. We have generated two transgenic tomato lines (556HO and 579HO) that express yeast S-adenosylmethionine decarboxylase and specifically accumulate Spd and Spm in fruits in comparison to fruits from control (556AZ) plants (Mehta et al., 2002). Tomato fruits undergo chilling injury at temperatures below 13°C. The high Spd and Spm tomato together with the control azygous line were utilized to address role(s) of polyamines in chilling-injury signaling. Exposure to chilling temperature (2°C) led to several-fold increase in the Put content in all the lines. Upon re-warming of the fruits at 20°C, the levels of Spd and Spm increased further in the fruit of the two transgenic lines, the higher levels remaining stable for 15 days after re-warming as compared to the fruit from the control line. Profiling their steady state proteins before and after re-warming highlighted a protein of ∼14 kD. Using proteomics approach, protein sequencing and immunoblotting, the ∼14-kD protein was identified as the pathogenesis related protein 1b1 (PR1b1). The PR1b1 protein accumulated transiently in the control fruit whose level was barely detectable at d 15 post-warming while in the fruit from both the 556HO and 579HO transgenic lines PR1b1 abundance increased and remained stable till d 15 post warming. PR1b1 gene transcripts were found low in the control fruit with a visible accumulation only on d 15 post warming; however, in both the transgenic lines it accumulated and increased soon after rewarming being several-fold higher on day 2 while in 556HO line this increase continued until d 6 than the control fruit. The chilling-induced increase in PR1b1 protein seems independent of ethylene and methyl jasmonate signaling but may be linked to salicylic acid. We propose that polyamine-mediated sustained accumulation of PR1b1 protein in post-warmed chilled tomato fruit is a pre-emptive cold stress response and possibly a defense response mechanism related to Cold Stress-Induced Disease Resistance (SIDR) phenomenon.

Individual Shrink Wrapping of Zucchini Fruit Improves Postharvest Chilling Tolerance Associated with a Reduction in Ethylene Production and Oxidative Stress Metabolites

We have studied the effect of individual shrink wrapping (ISW) on the postharvest performance of refrigerated fruit from two zucchini cultivars that differ in their sensitivity to cold storage: Sinatra (more sensitive) and Natura (more tolerant). The fruit was individually shrink wrapped before storing at 4°C for 0, 7 and 14 days. Quality parameters, ethylene and CO2 productions, ethylene gene expression, and oxidative stress metabolites were assessed in shrink wrapped and non-wrapped fruit after conditioning the fruit for 6 hours at 20°C. ISW decreased significantly the postharvest deterioration of chilled zucchini in both cultivars. Weight loss was reduced to less than 1%, pitting symptoms were completely absent in ISW fruit at 7 days, and were less than 25% those of control fruits at 14 days of cold storage, and firmness loss was significantly reduced in the cultivar Sinatra. These enhancements in quality of ISW fruit were associated with a significant reduction in cold-induced ethylene production, in the respiration rate, and in the level of oxidative stress metabolites such as hydrogen peroxide and malonyldialdehyde (MDA). A detailed expression analysis of ethylene biosynthesis, perception and signaling genes demonstrated a downregulation of CpACS1 and CpACO1 genes in response to ISW, two genes that are upregulated by cold storage. However, the expression patterns of six other ethylene biosynthesis genes (CpACS2 to CpACS7) and five ethylene signal transduction pathway genes (CpCTR1, CpETR1, CpERS1, CpEIN3.1 and CpEN3.2), suggest that they do not play a major role in response to cold storage and ISW packaging. In conclusion, ISW zucchini packaging resulted in improved tolerance to chilling concomitantly with a reduction in oxidative stress, respiration rate and ethylene production, as well as in the expression of ethylene biosynthesis genes, but not of those involved in ethylene perception and sensitivity.

Contribution of polyamines and other related metabolites to the maintenance of zucchini fruit quality during cold storage

In order to investigate the contribution of polyamines and related amino acids in the maintenance of zucchini fruit quality during cold storage, two varieties of Cucurbita pepo with different degrees of chilling tolerance were used, Natura (more tolerant) and Sinatra (moresensitive). After harvest, free putrescine levels decreased during storage at 20 °C, whereas in fruit kept at 4 °C this polyamine accumulated in both varieties, but with higher levels in the sensitive variety (Sinatra). This behavior suggests that putrescine is accumulated as a response to low temperature in zucchini fruit by stress-induced chilling injury, and not due to the postharvest storage itself. ADC activity responds quickly to chilling but sharply decreases after 14 days, whereas its expression remains high in both varieties. ODC activity takes over when the cold stress is relatively severe, as this activity was found to be much higher in Sinatra. ODCexpression also correlated with ODC activity. DAO activity increased in Natura fruit, and conversely decreased in Sinatra fruit during storage at 4 °C, whereas the proline content was higher in Natura and lower in Sinatra. Therefore, we suggest that putrescine degradation and proline accumulation contribute to the acquisition of chilling tolerance in zucchini fruit. GABA content decreased in both varieties, with a greater reduction in Natura fruit and less in Sinatra fruit. In addition, GABA transaminase showed a higher activity in Natura fruit than in Sinatra fruit during cold storage, suggesting that GABA catabolism could be involved in the tolerance to postharvest cold storage in zucchini fruit.

Changes in carbohydrate content in zucchini fruit (Cucurbita pepo L.) under low temperature stress

The postharvest handling of zucchini fruit includes low-temperature storage, making cold stress unavoidable. We have investigated the changes of soluble carbohydrates under this stress and its relation with weight loss and chilling injury in zucchini fruit during postharvest storage at 4 °C and 20 °C for up to 14 days. Two varieties with different degrees of chilling tolerance were compared: Natura, the more tolerant variety, and Sinatra, the variety that suffered more severe chilling-injury symptoms and weight loss. In both varieties, total soluble carbohydrates, reducing soluble carbohydrates and polyols content was generally higher during storage at 4 °C than at 20 °C, thus these parameters are related to the physiological response of zucchini fruit to cold stress. However, the raffinose content increased in Natura and Sinatra fruits during storage at 4 °C and 20 °C, although at 20 °C the increase in raffinose was more remarkable than at 4 °C in both varieties, so that the role of raffinose could be more likely related to dehydration than to chilling susceptibility of zucchini fruit. Glucose, fructose, pinitol, and acid invertase activity registered opposite trends in both varieties against chilling, increasing in Natura and decreasing in Sinatra. The increase in acid invertase activity in Natura fruit during cold storage could contribute in part to the increase of these reducing sugars, whose metabolism could be involved in the adaptation to postharvest cold storage.

Postharvest polyamine application alleviates chilling injury and affects apricot storage ability

Fruit of two apricot cultivars 'Bagheri' and 'Asgarabadi' were treated with putrescine (Put) or spermidine (Spd) at 1 mM and then were stored at 1 °C for 21 days. Fruit were sampled weekly and stored 2 days at 20 °C for shelf-life study. The treatments reduced ethylene production and maintained the firmness and color of the fruit. Peroxidase (POX), catalase (CAT), superoxide dismutase (SOD), and polyphenol oxidase (PPO) activities and total phenol (TP) concentrations were measured during storage. Both cultivars showed chilling injury (CI) incidence, and the severity in control fruit was higher than either Put or Spd treatments. CI incidence in Spd-treated fruit was lower than that of Put-treated fruit. Polyamine (PA) treatment generally increased antioxidant enzyme activity of fruit during storage. PA treatments may help maintain the quality of apricot fruit during storage by inhibiting ripening and decreasing CI incidence.

Clover and ryegrass are tolerant species to ammonium nutrition

The application of nitrification inhibitors (NIs) together with nitrogen fertilizers in grasslands is an effective alternative to reduce nitrate leaching and nitrogenous gases emissions to the atmosphere. Nevertheless, the use of NIs increases the amount of ammonium available for the plant that, due to its reported toxic effect in plants, can have a direct effect on crop production. Grassland species have traditionally suffered from intensive grazing and urea deposition and, therefore, a tolerance to ammonium nutrition could be expected in these species. Plants of Trifolium repens L. var. huia and Lolium perenne L. var. Herbus were grown under two nitrogen nutrition regimes (nitrate or ammonium) and three different nitrogen concentrations (0.5, 2.5 and 5 mmol/L). The effect of nitrogen form was determined on biomass production parameters, gas-exchange and water relations parameters as well as polyamine (PA) and ion tissue contents. Both grassland species showed tolerance to ammonium nutrition due to their capacity to adjust several metabolic processes in a species-specific way. Gas exchange measurements and biomass production (expressed as dry weight (DW)) were unaffected by the nitrogen form or dose in both species except for a decrease in root total DW in ryegrass plants grown under ammonium nutrition. Hydraulic conductance (L(0)) increased in ryegrass with increasing ammonium doses but no change due to the nitrogen source was observed in water potential (Psi(w)) values. Both species, and specially ryegrass, accumulated free ammonium mainly in roots when grown under ammonium nutrition and its translocation to the shoot via xylem was also observed. A clear difference in cations and PAs pattern was observed in each species when comparing both nitrogen nutrition regimes.

Overexpression of Spermidine Synthase Enhances Tolerance to Multiple Environmental Stresses and Up-Regulates the Expression of Various Stress-Regulated Genes in Transgenic Arabidopsis thaliana

Polyamines play pivotal roles in plant defense to environmental stresses. However, stress tolerance of genetically engineered plants for polyamine biosynthesis has been little examined so far. We cloned spermidine synthase cDNA from Cucurbita ficifolia and the gene was introduced to Arabidopsis thaliana under the control of the cauliflower mosaic virus 35S promoter. The transgene was stably integrated and actively transcribed in the transgenic plants. As compared with the wild-type plants, the T2 and T3 transgenic plants exhibited a significant increase in spermidine synthase activity and spermidine content in leaves together with enhanced tolerance to various stresses including chilling, freezing, salinity, hyperosmosis, drought, and paraquat toxicity. During exposure to chilling stress (5 degrees C), the transgenics displayed a remarkable increase in arginine decarboxylase activity and conjugated spermidine contents in leaves compared to the wild type. A cDNA microarray analysis revealed that several genes were more abundantly transcribed in the transgenics than in the wild type under chilling stress. These genes included those for stress-responsive transcription factors such as DREB and stress-protective proteins like rd29A. These results strongly suggest an important role for spermidine as a signaling regulator in stress signaling pathways, leading to build-up of stress tolerance mechanisms in plants under stress conditions.