Decreased Ethylene Production Research Articles

PpeERF115 regulates peach fruit ripening by increasing polyamine turnover through up-regulation of genes involved in polyamine synthesis and catabolism

Polyamines (PAs) are anti-senescence agents that promote maintenance of fruit quality after harvesting. Many studies have reported increases in PA synthesis and catabolism and decreases in PA levels during fruit ripening. However, few reports have addressed the modulation mechanisms of PA metabolism during fruit maturation. In this report, we found that the peach (Prunus persica L.) transcription factor PpeERF115 directly bound to the PpeADC1 and PpePAO1 promoters, activating these genes. Silencing PpeERF115 enhanced spermidine (Spd) and spermine (Spm) accumulation, reduced putrescine (Put) content, decreased ethylene production, suppressed the respiratory rate, promoted maintenance of fruit firmness, and delayed peach ripening. Conversely, fruit over-expressing PpeERF115 showed significantly reduced Spd and Spm accumulation and clear increases in Put levels. RNA-sequencing analysis indicated that PpeADC1, PpeCuAO2, and PpePAO1 were dramatically down-regulated in PpeERF115-known out fruit, whereas PpeSAMDC1 was significantly up-regulated. This study is the first to show that PpeERF115 regulates peach ripening by increasing PA turnover through up-regulation of PA synthesis and catabolism. These results extend our comprehension of the coordination between ethylene and PAs during regulation of fruit maturation.

The involvement of nitric oxide and ethylene on the formation of endodermal barriers in response to Cd in hyperaccumulator Sedum alfredii

Nitric oxide (NO) and ethylene are both important signaling molecules which participate in numerous plant development processes and environmental stress resistance. Here, we investigate whether and how NO interacts with ethylene during the development of endodermal barriers that have major consequences for the apoplastic uptake of cadmium (Cd) in the hyperaccumulator Sedum alfredii. In response to Cd, an increased NO accumulation, while a decrease in ethylene production was observed in the roots of S. alfredii. Exogenous supplementation of NO donor SNP (sodium nitroprusside) decreased the ethylene production in roots, while NO scavenger cPTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) had the opposite effect. The exogenous addition of NO affected the ethylene production through regulating the expression of genes related to ethylene synthesis. However, upon exogenous ethylene addition, roots retained their NO accumulation. The abovementioned results suggest that ethylene is downstream of the NO signaling pathway in S. alfredii. Regardless of Cd, addition of SNP promoted the deposition of endodermal barriers via regulating the genes related to Casparian strips deposition and suberization. Correlation analyses indicate that NO positively modifies the formation of endodermal barriers via the NO-ethylene signaling pathway, Cd-induced NO accumulation interferes with the synthesis of ethylene, leading to a deposition of endodermal barriers in S. alfredii.

Involvement of ethylene in glutamate-mediated tomato fruit resistance to Alternaria alternata

Recent progress showed the potential of glutamate to regulate stress responses by affecting phytohormones homeostasis, but much remains to be explored. To decipher the role of ethylene in glutamate-induced resistance to Alternaria alternata, ethephon application, ethylene perception inhibitor (1-MCP) experiment and ethylene measurement were pursued. Concurrently, temporal alteration in ethylene biosynthesis and signaling pathways were transcriptionally analyzed in tomato fruit. Our data exhibited that ethylene conferred tomato fruit susceptibility rather than resistance to Alternaria alternata. The enhanced resistance in glutamate treatment was related to decreased ethylene production during the early stages of interaction, accompanied by lower expression levels of SlACS1, SlACS2 and SlACO1 relative to the control. Interestingly, 1-MCP induced amounts of resistance similar to that observed in glutamate treatment, while ethylene receptors (SlETR3 and SlETR4), mitogen-activated protein kinase SlMPK3 and ethylene response factor SlERF1 were down-regulated by glutamate during infection. Collectively, antagonizing the ethylene biosynthesis or signaling might play a pivotal role in glutamate-induced resistance to the necrotrophic pathogen Alternaria alternata.

1-MCP extends the shelf life of ready-to-eat ‘Hayward’ and ‘Qihong’ kiwifruit stored at room temperature

Near eating-stage fruit of ‘Hayward’ and ‘Qihong’ kiwifruit (firmness 20 N) were treated with 0.5 µL L −1 1-Methylcyclopropene (1-MCP) for 12 h at room temperature (23 ±1 °C), and then stored at 23 ± 1 °C for several days. Compared with control fruit, 1-MCP greatly delayed loss of firmness, and extended the room-temperature shelf life of ready-to-eat kiwifruit by an extra 8 d (‘Hayward’) or 10 d (‘Qihong’). The 1-MCP treatment also slowed the declines in titratable acidity and color, but had no significant effects on soluble solids content (p < 0.05). Although in the 1-MCP treated fruit the amounts of total volatiles increased during room-temperature storage, the concentration of total volatiles was lower in the treated fruit compared with the untreated controls. Treatment with 1-MCP inhibited ester production and aldehyde degradation. At edible firmness, kiwifruit treated with 1-MCP showed similar fruit quality compared with the untreated controls, with similar mean values in soluble solids content, titratable acidity and color (p > 0.05). 1-MCP also decreased ethylene production and respiration rate. Moreover, the activities of superoxide (SOD), catalase (CAT) and peroxidase (POD) were increased in the treated fruit compared with the controls. The results indicate treatment with 1-MCP is a potentially effective way of prolonging the room-temperature (23 ± 1 °C) shelf life of ready-to-eat kiwifruit and maintaining their eating quality under commercial conditions.

The isolated or combined effects of dynamic controlled atmosphere (DCA) and 1-MCP on the chemical composition of cuticular wax and metabolism of ‘Maxi Gala’ apples after long-term storage

Apples have a continuous hydrophobic layer that covers the surface of the fruit, which is called the cuticle. The effects of 1-methylcyclopropene (1-MCP) on the cuticular wax layer of apples were reported after cold storage, although the interaction between 1-MCP and dynamic controlled atmosphere (DCA) is not yet known. Therefore, this study aimed to analyze the effects of 1-MCP on the wax composition and metabolism of ‘Maxi Gala’ apples after storage in a controlled atmosphere (CA) and dynamic controlled atmosphere based on chlorophyll fluorescence (DCA-CF) and respiratory quotient (DCA-RQ; RQ = 1.3 and 1.5). The 1-MCP treatment effectively decreased ethylene production for CA and DCA-CF treatments, while in DCA-RQ treatments produced no effect. The average extracted cuticular wax content of ‘Maxi Gala’ apples was 16.65 g m−2 and no differences in storage conditions or 1-MCP application were observed. Alkanes, alcohols, fatty acids, aldehydes, and terpenoids were identified in the chemical composition of the cuticular waxes, being alkanes and fatty acids the predominant ones. Moreover, 1-MCP decreased fatty acid and 10-nonacosanol concentrations in the fruit. Fruit with the 1-MCP application and stored in DCA had lower α-farnesene concentrations. The wax compositions of the DCA-stored apples with and without 1-MCP were similar. However, 1-MCP treatment resulted in a greater mass loss in fruit stored in DCA.

Transcriptomic analysis of a near-isogenic line of melon with high fruit flesh firmness during ripening.

A near-isogenic line (NIL) of melon (SC10-2) with introgression in linkage group X was studied from harvest (at firm-ripe stage of maturity) until day 18 of postharvest storage at 20.5 °C together with its parental control ('Piel de Sapo', PS). SC10-2 showed higher flesh firmness and whole fruit hardness but lower juiciness than its parental. SC10-2 showed a decrease in respiration rate accompanied by a decrease in ethylene production during ripening, both of which fell to a greater extent than in PS. The introgression affected 11 volatile organic compounds (VOCs), the levels of which during ripening were generally higher in SC10-2 than in PS. Transcriptomic analysis from RNA-Seq revealed differentially expressed genes (DEGs) associated with the effects studied. For example, 909 DEGs were exclusive to the introgression, and only 23 DEGs were exclusive to postharvest ripening time. Major functions of the DEGs associated with introgression or ripening time were identified by cluster analysis. About 37 genes directly and/or indirectly affected the delay in ripening of SC10-2 compared with PS in general and, more particularly, the physiological and quality traits measured and, probably, the differential non-climacteric response. Of the former genes, we studied in more detail at least five that mapped in the introgression in linkage group (LG) X, and 32 outside it. There is an apparent control of textural changes, VOCs and fruit ripening by an expression quantitative trait locus located in LG X together with a direct control on them due to genes presented in the introgression (CmTrpD, CmNADH1, CmTCP15, CmGDSL esterase/lipase, and CmHK4-like) and CmNAC18. © 2020 Society of Chemical Industry.

Effects of calcium treatment on malate metabolism and γ-aminobutyric acid (GABA) pathway in postharvest apple fruit

Calcium treatment effects on malate metabolism and the GABA pathway in ‘Cripps Pink’ apple fruit during storage were investigated. Postharvest apple fruit treated with 1% and 4% calcium chloride solutions were stored at 25 ± 1 °C. The 4% calcium treatment suppressed declines in titratable acidity and malate content and increased succinate and oxalate concentrations. Calcium treatment also reduced the respiration rate and decreased ethylene production peak during storage. Moreover, 4% calcium treatment significantly enhanced cyNAD-MDH and PEPC activities and upregulated MdMDH1, MdMDH2, MdPEPC1 and MdPEPC2 expression while inhibiting cyNADP-ME and PEPCK activities and downregulating MdME1, MdME4 and MdPEPCK2 expression. Surprisingly, calcium treatment changed the content of some free amino acids (GABA, proline, alanine, aspartic acid and glutamate), two of which (glutamate and GABA) are primary metabolites of the GABA pathway. Furthermore, calcium application enhanced GABA pathway activity by increasing MdGAD1, MdGAD2, MdGABA-T1/2 and MdSSADH transcript levels.

Phytohormone profile and CiFL1 expression in young seedlings of Cichorium intybus L. var sativum exposed to high temperature in relation to vernalization and de-vernalization processes

Cichorium intybus is a biennial plant species forming a taproot and a leaf rosette during the first year and which requires low temperature during vernalization to flower during the second year of its cycle. Heat stress, however, is known to induce premature flowering during the first year. The present work aims to compare the effect of heat treatment (38 °C during 3 days) and vernalization (4 °C during 6 weeks) on the phytohormonal profile and the expression of two chicory genes (CiFL1 and CiFT) homologous to the Arabidopsis flowering genes FLOWERING LOCUS C (FLC) and FLOWERING LOCUS T (FT). In Arabidopsis, FLC and FT code, respectively, for a repressor and an activator of flowering. Although CiFL1 was inhibited by vernalization, its expression was increased by heat treatment in both vernalized and non-vernalized seedlings while high temperature unexpectedly inhibited FT expression in vernalized seedlings. Vernalization induced a modification in the hormonal profile of C. intybus (cv. Melci) in a sense of a decrease in ethylene production, abscisic acid and total jasmonates content, while the level of salicylic and benzoic acids as well as polyamine spermidine increased. A limited effect on the gibberellins’ profile was observed. The subsequent impact of heat stress on phytohormone content was different in non-vernalized and vernalized seedlings, with a higher abscisic acid and jasmonates and a lower 1-aminocyclopropane-1-carboxylic acid concentration in the former than in the latter. These data are discussed in relation to the putative involvement of phytohormones in stress-induced flowering. It appears that heat stress implies different pathways than vernalization to hasten flowering process.

Structural and functional characterization of Solanum lycopersicum phosphatidylinositol 3-kinase C2 domain

Phosphatidylinositol 3-kinases (PI3Ks) are characterized by the presence of a C2 domain at the N-terminal end (class I, III); or at both the N-terminal and C-terminal ends (class II), sometimes including a Plextrin homology domain and/or a Ras domain. Plant PI3Ks are analogous to the class III mammalian PI3K. An N-terminal fragment (~170 aa) of the tomato PI3K regulatory domain including the C2 domain, was cloned and expressed in a bacterial system. This protein was purified to homogeneity and its physicochemical properties analyzed. The purified protein showed strong binding with monophosphorylated phosphatidylinositols, and the binding was dependent on calcium ion concentration and pH. In the overall tertiary structure of PI3K, C2 domain showed unique characteristics, having three antiparallel beta-sheets, hydrophobic regions, acidic as well as alkaline motifs, that can enable its membrane binding upon activation. To elucidate the functional significance of C2 domain, transgenic tobacco plants expressing the C2 domain of PI3K were generated. Transgenic plants showed defective pollen development and disrupted seed set. Flowers from the PI3K–C2 transgenic plants showed delayed wilting, and a decrease in ethylene production. It is likely that introduction of the PI3K–C2 segment may have interfered with the normal binding of PI3K to the membrane, delaying the onset of membrane lipid catabolism that lead to senescence.

Manipulation of β-carotene levels in tomato fruits results in increased ABA content and extended shelf life.

SummaryTomato fruit ripening is controlled by the hormone ethylene and by a group of transcription factors, acting upstream of ethylene. During ripening, the linear carotene lycopene accumulates at the expense of cyclic carotenoids. Fruit‐specific overexpression of LYCOPENE β‐CYCLASE (LCYb) resulted in increased β‐carotene (provitamin A) content. Unexpectedly, LCYb‐overexpressing fruits also exhibited a diverse array of ripening phenotypes, including delayed softening and extended shelf life. These phenotypes were accompanied, at the biochemical level, by an increase in abscisic acid (ABA) content, decreased ethylene production, increased density of cell wall material containing linear pectins with a low degree of methylation, and a thicker cuticle with a higher content of cutin monomers and triterpenoids. The levels of several primary metabolites and phenylpropanoid compounds were also altered in the transgenic fruits, which could be attributed to delayed fruit ripening and/or to ABA. Network correlation analysis and pharmacological experiments with the ABA biosynthesis inhibitor, abamine, indicated that altered ABA levels were a direct effect of the increased β‐carotene content and were in turn responsible for the extended shelf life phenotype. Thus, manipulation of β‐carotene levels results in an improvement not only of the nutritional value of tomato fruits, but also of their shelf life.

The TuMYB46L‐TuACO3 module regulates ethylene biosynthesis in einkorn wheat defense to powdery mildew

Summary Powdery mildew disease, elicited by the obligate fungal pathogen Blumeria graminis f.sp. tritici (Bgt), causes widespread yield losses in global wheat crop. However, the molecular mechanisms governing wheat defense to Bgt are still not well understood.Here we found that TuACO3, encoding the 1‐aminocyclopropane‐1‐carboxylic acid (ACC) oxidase functioning in ethylene (ET) biosynthesis, was induced by Bgt infection of the einkorn wheat Triticum urartu, which was accompanied by increased ET content. Silencing TuACO3 decreased ET production and compromised wheat defense to Bgt, whereas both processes were enhanced in the transgenic wheat overexpressing TuACO3.TuMYB46L, phylogenetically related to Arabidopsis MYB transcription factor AtMYB46, was found to bind to the TuACO3 promoter region in yeast‐one‐hybrid and EMSA experiments. TuMYB46L expression decreased rapidly following Bgt infection. Silencing TuMYB46L promoted ET content and Bgt defense, but the reverse was observed when TuMYB46L was overexpressed.Hence, decreased expression of TuMYB46L permits elevated function of TuACO3 in ET biosynthesis in Bgt‐infected wheat. The TuMYB46L‐TuACO3 module regulates ET biosynthesis to promote einkorn wheat defense against Bgt. Furthermore, we found four chitinase genes acting downstream of the TuMYB46L‐TuACO3 module. Collectively, our data shed a new light on the molecular mechanisms underlying wheat defense to Bgt.

Effects of postharvest polyamine application and edible coating on maintaining quality of mango (Mangifera indica L.) cv. Langra during cold storage.

Mango is a tropical fruit which is sensitive to chilling injury. The present work investigated the potential of edible coatings of chitosan and polyamine spermidine in increasing shelf life and quality of mango. The control fruits (treated with distilled water) and the mango fruits treated with different concentrations of chitosan (0.5%, 1.0%, and 2.0%) and spermidine (0.5, 1.0, and 2.0 mM) were studied to improve postharvest characteristics and quality maintenance during cold storage. Parameters such as firmness, weight loss, fungal contamination, total phenol, antioxidant activity, vitamin C, pH, total soluble solids (TSS), titratable acidity (TA), flavor index, color index, and ethylene production were measured after at harvest (0), 8, 16, and 24 days of storage at 15 ± 2°C and relative humidity of 85%–90%. Chitosan and spermidine delayed water loss, firmness, and fungal contamination. Application of chitosan containing ascorbic acid significantly increased phenolic content and antioxidant activity compared to the control plants. It also changed soluble solid content, TA, pH of pulp, and sugar content and decreased ethylene production. The obtained results suggested that chitosan (2%) and spermidine (2 mM) had potential to improve firmness and delay deterioration processes of “Langra” mango after harvest.

A simplex lattice design to optimise active modified atmosphere for storing pomegranate (cv. Wonderful) arils: Part 1, determining optimum gas for physiological responses

Understanding the experimental design and principles guiding gas mixture selection are important in the development of an optimal produce-specific modified atmosphere (MA) system. Exposure to gas combinations below or above the tolerance limit of fresh produce may result in subsequent undesirable changes in product quality and shortened shelf life. Therefore, this study investigated the design of an optimal gas combination for storage of pomegranate (cv. Wonderful) arils using the simplex lattice mixture design approach, and quantified the effects of temperature on the respiration rate of arils stored under an optimal gas atmosphere. The impact of initial gas composition was also determined by evaluating the physiological response and microbial quality (aerobic mesophilic bacteria, yeast and mould). The correlation of simplex lattice design experimental data to the predicted response parameters were explained effectively by Scheffé’s special cubic model (R2 > 94%). Parameter estimates showed a significant (p ≤ 0.05) synergetic effect of single model components for all the response variables. The use of high CO2 concentration (>10 kPa) decreased ethylene production rate and microbial load, while reducing O2 to an acceptable level reduced respiration rate (RR). Based on the results obtained, the optimal gas composition was established as 4.67 kPa O2 +12.67 kPa CO2 + 82.67 kPa N2. Under this optimal atmosphere condition, increasing storage temperature by 10 °C resulted in a threefold increase in RR. These results demonstrate that optimum storage temperature also plays a critical role in the success of MA systems.

Effect of 1-MCP on the production of volatiles and biosynthesis-related gene expression in peach fruit during cold storage

As an effective ethylene action inhibitor, 1-Methylcyclopropene (1-MCP) can delay fruit ripening and senescence. However, little is known about the effect of 1-MCP on peach fruit aroma-related volatiles and their biosynthesis-related gene expression during cold storage. Peaches (cv. Xiahui 6) were treated with 1-MCP (10 μL L−1 for 12 h) to investigate the influence of 1-MCP on aromatic volatile biosynthesis and involved genes expression during cold storage. 1-MCP treatment significantly decreased ethylene production and delayed the ripening and senescence of peach at cold storage. A lower production of esters was found in 1-MCP treated fruit, while there were higher alcohol acyltransferase (AAT) activity and PpaAAT1/2 expression in treated fruit during the early storage. The performance patterns of both aldehydes and alcohols were different between 1-MCP and control fruit accompanied by lower lipoxygenase (LOX), alcohol dehydrogenase (ADH), hydroperoxide lyase (HPL) activities in accordance with the expression of PpaLOX3, PpaADH1 and PpaHPL1 in 1-MCP treated fruit compared with the control in the late storage. All in all, the role of 1-MCP on the volatiles and its related genes expression in peach fruits was discussed, and 1-MCP affected the formation of aroma volatile by functioning in the expression of pivotal enzyme genes including LOX, HPL, ADH and AAT.

Breeding of carnations (Dianthus caryophyllus L.) for long vase life.

Carnation (Dianthus caryophyllus L.) is one of the main floricultural crops in Japan and worldwide. The vase life of cut ornamental flowers, including carnations, is important in determining their quality and consumers’ preference. To improve the vase life of carnation flowers, my group started a breeding research program in 1992 using conventional cross-breeding techniques. We repeatedly crossed and selected promising offspring with long vase life for seven generations, from 1992 to 2008. In 2005, we developed two cultivars, ‘Miracle Rouge’ and ‘Miracle Symphony’, with genetically determined long vase lives of 17.7 to 20.7 days (3.2 to 3.6 times that of ‘White Sim’) under standard conditions (23°C, 70% RH, 12-h photoperiod). Line 532-6 showed an ultra-long vase life averaging 27.8 to 32.7 days (4.6 to 5.4 times that of ‘White Sim’). We evaluated changes in ethylene sensitivity with flower senescence simply and accurately using a time-lapse video recorder. In 2010, we selected line 806-46b with both ultra-long vase life (27.1 days, 4.4 times that of ‘White Sim’) and ethylene resistance. Analyses using six cultivars and 123 selected lines from the 1st to the 7th generations revealed that the long vase life was strongly associated with a decrease in ethylene production.

Pectic and Galacturonic Acid Oligosaccharides on the Postharvest Performance of Citrus Fruits

Orange [Citrus sinensis (L.) Osbeck] and grapefruit (Citrus paradisi Macfad) citrus fruits are prone to develop different peel physiological disorders caused by storage at both chilling and nonchilling temperatures. The effect of galacturonic acid oligosaccharides (GAOs) and pectic oligosaccharides (POs) in reducing postharvest nonchilling peel pitting (NCPP), decay, and chilling injury (CI) in orange cv. Navelina and the effect of POs in reducing CI in grapefruit cv. Rio Red, were investigated. The incidence of these disorders was examined in fruits stored at chilling and nonchilling temperatures and at 90% to 95% relative humidity (RH). POs showed a better efficacy than GAOs in reducing postharvest losses in orange. The POs were able to reduce NCPP and decay in ‘Navelina’ fruits stored at 20 °C, irrespective of the fruit maturity stage. The application of 10 g·L−1 POs also reduced CI and the chilling-induced ethylene production in oranges and grapefruits maintained at the chilling temperature. Likewise, the decrease in ethylene production found in ‘Navelina’ fruits that developed NCPP during storage at the nonchilling temperature was related to lower peel damage. Moreover, results showed that POs do not induce an increase in ethylene when fruit are stored under conditions that do not cause stress-related injury to fruit. Therefore, POs efficacy in reducing postharvest physiological disorders is not likely mediated by ethylene. Overall results indicate that the application of POs may be an acceptable alternative to mitigate postharvest losses of citrus fruits.

Transcriptomic Analysis Implies That GA Regulates Sex Expression via Ethylene-Dependent and Ethylene-Independent Pathways in Cucumber (Cucumis sativus L.).

Sex differentiation of flower buds is an important developmental process that directly affects fruit yield of cucumber (Cucumis sativus L.). Plant hormones, such as gibberellins (GAs) and ethylene can promote development of male and female flowers, respectively, however, the regulatory mechanisms of GA-induced male flower formation and potential involvement of ethylene in this process still remain unknown. In this study, to unravel the genes and gene networks involved in GA-regulated cucumber sexual development, we performed high throughout RNA-Seq analyses that compared the transcriptomes of shoot tips between GA3 treated and untreated gynoecious cucumber plants. Results showed that GA3 application markedly induced male flowers but decreased ethylene production in shoot tips. Furthermore, the transcript levels of M (CsACS2) gene, ethylene receptor CsETR1 and some ethylene-responsive transcription factors were dramatically changed after GA3 treatment, suggesting a potential involvement of ethylene in GA-regulated sex expression of cucumber. Interestingly, GA3 down-regulated transcript of a C-class floral homeotic gene, CAG2, indicating that GA may also influence cucumber sex determination through an ethylene-independent process. These results suggest a novel model for hormone-mediated sex differentiation and provide a theoretical basis for further dissection of the regulatory mechanism of male flower formation in cucumber.Statement: We reveal that GA can regulate sex expression of cucumber via an ethylene-dependent manner, and the M (CsACS2), CsETR1, and ERFs are probably involved in this process. Moreover, CAG2, a C-class floral homeotic gene, may also participate in GA-modulated cucumber sex determination, but this pathway is ethylene-independent.

Selenium delays tomato fruit ripening by inhibiting ethylene biosynthesis and enhancing the antioxidant defense system.

The antioxidant activity of selenium (Se) detoxifies reactive oxygen species (ROS) in plants and animals. In the present study, we elucidated the mechanism underlying Se induced fruit development and ripening. Our study showed that foliar pretreatment with 1mgL-1 sodium selenate effectively delayed fruit ripening and maintained fruit quality. Gene expression studies revealed that the repression of ethylene biosynthetic genes 1-aminocyclopropane-1-carboxylic acid (ACC) synthase and ACC oxidase decreased ethylene production and respiration rate. Moreover, Se treatment probably boosted the antioxidant defense system to reduce ROS generation and membrane damage. The enhanced antioxidative effect was attributed to higher glutathione content and increased activity of enzymes such as glutathione peroxidase and glutathione reductase. The upregulation of respiratory burst oxidase homologue genes in tomato fruit may also contribute to the enhanced antioxidative effect. Selenium treatment represents a promising strategy for delaying ripening and extending the shelf life of tomato fruit.

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.

Inhibition of ethylene production by putrescine alleviates aluminium-induced root inhibition in wheat plants.

Inhibition of root elongation is one of the most distinct symptoms of aluminium (Al) toxicity. Although putrescine (Put) has been identified as an important signaling molecule involved in Al tolerance, it is yet unknown how Put mitigates Al-induced root inhibition. Here, the possible mechanism was investigated by using two wheat genotypes differing in Al resistance: Al-tolerant Xi Aimai-1 and Al-sensitive Yangmai-5. Aluminium caused more root inhibition in Yangmai-5 and increased ethylene production at the root apices compared to Xi Aimai-1, whereas the effects were significantly reversed by ethylene biosynthesis inhibitors. The simultaneous exposure of wheat seedlings to Al and ethylene donor, ethephon, or ethylene biosynthesis precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), increased ethylene production and aggravated root inhibition, which was more pronounced in Xi Aimai-1. In contrast, Put treatment decreased ethylene production and alleviated Al-induced root inhibition in both genotypes, and the effects were more conspicuous in Yangmai-5. Furthermore, our results indicated that Al-induced ethylene production was mediated by ACC synthase (ACS) and ACC oxidase, and that Put decreased ethylene production by inhibiting ACS. Altogether, these findings indicate that ethylene is involved in Al-induced root inhibition and this process could be alleviated by Put through inhibiting ACS activity.