Impact of Postharvest Nitric Oxide Treatment on Lignin Biosynthesis-Related Genes in Wax Apple (Syzygium samarangense) Fruit

Nitric oxide mitigates cadmium stress by promoting the biosynthesis of cell walls in Robinia pseudoacacia roots

Cadmium (Cd) pollution is a growing concern worldwide, because it threatens human health through the food chain. Woody plants, such as the pioneer species black locust (Robinia pseudoacacia L.), are widely used in phytoremediation of Cd-contaminated soils, but strongly differ in Cd tolerance. Nitric oxide (NO), a highly reactive gas of biogenic and anthropogenic origin, has been shown to protect plants to Cd exposure. We investigated the protective mechanism of NO against Cd toxicity in black locust using physiological, transcriptomic and metabolomic approaches. We studied the correlation between cell wall traits, genes, and metabolites. The findings indicated that NO improved the growth of black locust under Cd exposure and elevated the fraction of Cd in the cell wall. NO increased cell wall thickness by stimulating the biosynthesis of pectin, cellulose, hemicellulose, and lignin. Transcriptomic and metabolomic analyses demonstrated that NO upregulated genes related to root cell wall biosynthesis and increased the accumulation of related metabolites, thereby increasing the Cd resistance of black locust. Our results elucidated a molecular mechanism underlying NO-mediated Cd tolerance in black locust and provided novel insights for phytoremediation of Cd-polluted soils by woody plants.

Roles of Nitric Oxide and Brassinosteroid in Improving Fruit Quality during Postharvest: Potential Regulators?

Most postharvest fruits are highly perishable, which directly impairs fruit taste and causes an economic loss of fresh products. Thus, it is necessary to find effective techniques to alleviate this issue. Recently, nitric oxide (NO) and brassinosteroid (BR) have been developed as postharvest alternatives to improve fruit quality. This work mainly reviews the recent processes of NO and BR in improving fruit quality during postharvest. Exogenous NO or BR treatments delayed fruit senescence, enhanced disease resistance, and alleviated chilling injury in postharvest fruit, and potential physiological and biochemical mechanisms mainly include (1) enhancing antioxidant and defense ability, (2) affecting ethylene biosynthesis, (3) regulating sugar and energy metabolism, (4) mediating plant hormone signaling, and (5) regulating protein S-nitrosylation and DNA methylation. This review concludes the functions and mechanisms of NO and BR in improving postharvest fruit quality. Additionally, a specific finding is the possible crosstalk of applications of NO and BR during postharvest fruit storage, which provides new insights into the applicability of NO and BR for delaying fruit senescence, enhancing disease resistances of fruit, and alleviating chilling injury in postharvest fruit.

The roles of nitric oxide in improving postharvest fruits quality: Crosstalk with phytohormones

Nowadays, improving the quality of postharvest fruits has become a hot research topic. Nitric oxide (NO) is often regarded as a signaling molecule that delays the postharvest senescence of fruits. Moreover, phytohormones affect the postharvest senescence of fruits. This review mainly describes how NO improves the postharvest quality of fruits by delaying postharvest fruit senescence, mitigating fruit cold damage and controlling postharvest diseases. Furthermore, the crosstalk of NO and multiple plant hormones effectively delays the postharvest senescence of fruits, and the major crosstalk mechanisms include (1) mediating phytohormone signaling. (2) inhibiting ETH production. (3) stimulating antioxidant enzyme activity. (4) decreasing membrane lipid peroxidation. (5) maintaining membrane integrity. (6) inhibiting respiration rate. (7) regulating gene expression related to fruit senescence. This review concluded the roles and mechanisms of NO in delaying postharvest fruit senescence. In addition, the crosstalk mechanisms between NO and various phytohormones on the regulation of postharvest fruit quality are also highlighted, which provides new ideas for the subsequent research.

Genome-wide identification of the AOMT gene family in wax apple and functional characterization of SsAOMTs to anthocyanin methylation

Introduction

Anthocyanins are major pigments in the peels of red-series wax apple fruits, and two principal components of them, namely, the cyanin and the peonidin, are non-methoxylated and methoxylated anthocyanins, respectively. Anthocyanin O-methyltransferases (AOMTs) are an important group of enzymes that have the ability to catalyze anthocyanins methylation to promote the solubility, stability, and bioactivity of anthocyanins. Although AOMT genes have been studied in a variety of plants, the function of them in wax apple is generally not well understood.

Methods

The anthocyanin composition in peels of two wax apple cultivars was determined by High Performance Liquid Chromatography Tandem Mass Spectrometry (HPLS-MS). The genome-wide analysis of the AOMT genes was performed with bioinformatics technology, and the expression patterns of different plant tissues, cultivars, fruit ripening stages, and exogenous abscisic acid (ABA) treatments were analyzed by transcriptome sequencing analysis and real-time quantitative PCR verification. An initial functional evaluation was carried out in vitro using recombinant the Anthocyanin O-methyltransferase Gene 5 of S. samarangense (SsAOMT5) protein.

Results

Only two main compositions of anthocyanin were found in peels of two wax apple cultivars, and it was worth noting that Tub Ting Jiang cultivar contained non-methoxylated anthocyanin (Cy3G) only, whereas Daye cultivar contained both non-methoxylated and methoxylated (Pn3G) anthocyanins. A total of six SsAOMT genes were identified in the whole genome of wax apple, randomly distributing on three chromosomes. A phylogenic analysis of the protein sequences divided the SsAOMT gene family into three subgroups, and all SsAOMTs had highly conserved domains of AOMT family. In total, four types of stress- related and five types of hormone- related cis-elements were discovered in the promoter region of the SsAOMTs. Expression pattern analysis showed that SsAOMT5 and SsAOMT6 were expressed in all tissues to varying degrees; notably, the expression of SsAOMT5 was high in the flower and fruit and significantly higher in Daye peels than those of other cultivars in the fruit ripening period. Exogenous ABA treatment significantly increased anthocyanin accumulation, but the increase of methoxylated anthocyanin content did not reach significant level compared with those without ABA treatment, whereas the expression of SsAOMT5 upregulated under ABA treatment. We identified two homologous SsAOMT5 genes from Daye cultivar (DSsAOMT5) and Tub Ting Jiang cultivar (TSsAOMT5); the results of functional analyses to two SsAOMT5 recombinant proteins in vitro demonstrated that DSsAOMT5 showed methylation modification activity, but TSsAOMT5 did not.

Conclusion

In conclusion, SsAOMT5 was responsible for methylated anthocyanin accumulation in the peels of wax apple and played an important role in red coloration in wax apple peels.

The MADS-box gene EjAGL15 positively regulates lignin deposition in the flesh of loquat fruit during its storage

Introduction

Lignification of fruit flesh is a common physiological disorder that occurs during post-harvest storage, resulting in the deterioration of fruit quality. Lignin deposition in loquat fruit flesh occurs due to chilling injury or senescence, at temperatures around 0°C or 20°C, respectively. Despite extensive research on the molecular mechanisms underlying chilling-induced lignification, the key genes responsible for the lignification process during senescence in loquat fruit remain unknown. MADS-box genes, an evolutionarily conserved transcription factor family, have been suggested to play a role in regulating senescence. However, it is still unclear whether MADS-box genes can regulate the lignin deposition that arises from fruit senescence.

Methods

Both senescence- and chilling-induced flesh lignification were simulated by applying temperature treatments on loquat fruits. The flesh lignin content during the storage was measured. Transcriptomic, quantitative reverse transcription PCR and correlation analysis were employed to identify key MADS-box genes that may be involved in flesh lignification. The Dual-luciferase assay was utilized to identify the potential interactions between MADS-box members and genes in phenylpropanoid pathway.

Results and Discussion

The lignin content of the flesh samples treated at 20°C or 0°C increased during storage, but at different rates. Results from transcriptome analysis, quantitative reverse transcription PCR, and correlation analysis led us to identify a senescence-specific MADS-box gene, EjAGL15, which correlated positively with the variation in lignin content of loquat fruit. Luciferase assay results confirmed that EjAGL15 activated multiple lignin biosynthesis-related genes. Our findings suggest that EjAGL15 functions as a positive regulator of senescence-induced flesh lignification in loquat fruit.

Nitric Oxide Acts as an Inhibitor of Postharvest Senescence in Horticultural Products

Horticultural products display fast senescence after harvest at ambient temperatures, resulting in decreased quality and shorter shelf life. As a gaseous signal molecule, nitric oxide (NO) has an important physiological effect on plants. Specifically, in the area of NO and its regulation of postharvest senescence, tremendous progress has been made. This review summarizes NO synthesis; the effect of NO in alleviating postharvest senescence; the mechanism of NO-alleviated senescence; and its interactions with other signaling molecules, such as ethylene (ETH), abscisic acid (ABA), melatonin (MT), hydrogen sulfide (H2S), hydrogen gas (H2), hydrogen peroxide (H2O2), and calcium ions (Ca2+). The aim of this review is to provide theoretical references for the application of NO in postharvest senescence in horticultural products.

Combined effect of Bacillus siamensis and chlorogenic acid on maintenance of quality, control of disease in stored wax apple fruit

Objectives

The purpose of this study was to evaluate the effect of combined postharvest use of Bacillus siamensis strain and chlorogenic acid on quality mainteance and disease control in wax apple fruit.

Materials and Methods

Wax apple fruit were treated with Bacillus siamensis strain (N1), chlorogenic acid (CHA) and N1+CHA and preserved at 25℃for 12 days. The appearance and quality parameters were evaluated, along with the disease index (DI), content of total soluble solids (TSS), total acid (TA), vitamin C (Vc), total phenolic, and flavonoids during cold storage. Meanwhile, the activities of β-1,3-glucanase (GLU) , phenylalanine ammonialyase (PAL), polyphenol oxidase (PPO), and peroxidase (POD) were determined. Furthermore, the transcriptome and the expression level of key defense enzyme genes were analyzed by RNA-seq and real-time quantitative reverse transcription PCR (qRT-PCR).

Results

N1+CHA treatment significantly lowered DI and delayed fruit quality deterioration by slowing TSS and TA loss and enhancing antioxidant capacity, including Vc, total phenolic, and flavonoids content. Meanwhile, the activities of GLU, PAL, PPO and POD were dramatically increased by N1+CHA treatment. Additionally, N1+CHA treatment modulated several metabolic pathways, including those involved in plant-hormone signal transduction and plant-pathogen interaction. The expression level of key defense enzyme genes were significantly up-regulated in stored wax apple fruit by the N1+CHA treatment, which were well coincided with the transcriptome data.

Conclusion

The combined use of N1+CHA significantly prevent disease and maintain fruit quality of wax apple during storage. These findings indicate that it could serve as a promising biological technique for preserving wax apple fruit.

Nitric Oxide Extends the Postharvest Life of Water Bamboo Shoots Partly by Maintaining Mitochondrial Structure and Energy Metabolism

Harvested water bamboo shoots can be stored for only a few days before they lose weight and become soft. Nitrogen oxide (NO) and modified atmosphere packaging (MAP) have previously been used to prolong horticultural crop storage. In the present study, we analyzed the joint effect of these two methods on extending the postharvest quality of water bamboo shoots. Water bamboo shoots were treated with (1) 30 μL L⁻¹ NO, (2) MAP, and (3) a combination of NO and MAP. The NO treatment delayed the softness and weight loss through maintaining the integrity of the mitochondrial ultrastructure and enhancing the ATP level by activating the expressions and activities of succinic dehydrogenase, malic acid dehydrogenase, and cytochrome oxidase. MAP improved the effect of NO on the mitochondrial energy metabolism. These results indicate that NO and MAP treatments are effective at suppressing the quality deterioration of water bamboo shoots, MAP improves the effect of NO in extending postharvest life, and NO may be the main effective factor in the combination of NO and MAP.

Effects of nitric oxide treatment on lignin biosynthesis and texture properties at wound sites of muskmelons

Lignin is an important component of the healing tissue in fruits. In this study, we treated muskmelon (Cucumis melo L. cv. "Manao") fruit with exogenous nitric oxide (NO) donor sodium nitroprusside (SNP) to observe and analyze its effect on lignin synthesis and accumulation during healing. Results showed that SNP treatment enhanced the contents of endogenous NO and H₂O₂, increased the activities of phenylalanine ammonia lyase, cinnamate 4 hydroxylase, cinnamyl alcohol dehydrogenase, and peroxidase, and raised the contents of sinapyl alcohol, coniferyl alcohol, coumaryl alcohol, and lignin. SNP augmented the hardness of the healing tissue and decreased its resilience, springiness, and cohesiveness. In addition, SNP treatment effectively reduced the weight loss and disease index of wounded muskmelons. All these results suggest that lignin metabolism mediated by NO play a crucial role in wound healing of muskmelons.

Suppression on postharvest juice sac granulation and cell wall modification by chitosan treatment in harvested pummelo (Citrus grandis L. Osbeck) stored at room temperature

Deposition of both lignin and cellulose accompanied by juice sac granulation is widespread in harvested citrus fruit. Hence, measures to suppress postharvest granulation of 'Majiayou' pummelo is of great importance. The fruit was treated with 1.5% chitosan and then stored at room temperature (20 ± 2 °C) for 150 d. As compared to the control fruits, chitosan coating significantly suppressed granulation index and maintained good quality. Chitosan coating inhibited lignification by suppressing the activities and expression levels of lignin synthesis-related enzymes (PAL, CAD and POD). By contrast, chitosan treatment enhanced the activities and expression levels of cell wall degrading enzymes, including PME, PG, Cx, XTH and β-Gal, which might contribute to the decrease in cellulose. In a nutshell, chitosan coating can effectively suppress juice sac granulation and fruit senescence of pummelo fruits, and play a crucial role in maintaining the cell wall modification.

Nitric oxide alleviates lignification and softening of water bamboo (Zizania latifolia) shoots during postharvest storage

Water bamboo shoots quickly deteriorate after harvest as a result of rapid lignification and softening. Nitric oxide (NO) has been used to extend the postharvest life of several other vegetables. Here, we examined the effect of NO on the storage of water bamboo shoots at 4℃ for 28 days. Without NO, fresh weight and firmness decreased quickly, while the cellulose and lignin contents increased sharply during storage. NO treatment delayed softening by maintaining the integrity of the cell wall and inhibiting the degradation of protopectin and the expressions of pectin methylesterase and polygalacturonase. NO treatment also delayed cellulose synthesis by increasing cellulase activity. NO treatment decreased the synthesis of lignin by inhibiting the activities of phenylalanine ammonia-lyase, cinnamyl alcohol dehydrogenase, laccase and peroxidase. These results indicate that NO treatment is effective at suppressing the softening and lignification of water bamboo shoots during postharvest storage.

Complete chloroplast genome sequence of the rose apple, Syzygium jambos (Myrtaceae)

Plants in the genus Syzygium have been widely used as traditional medicine, fruit crops, and ornamental trees. In this study, we reported the complete chloroplast genome of Syzygium jambos (L.) Alston which was known as rose apple. The chloroplast genome of this species is 158541 bp in length, including a pair of inverted repeat regions (IRs) (26076 bp) that is divided by a large single copy area (LSC) (88036 bp) and a small single copy area (SSC) (18353 bp). The circular chloroplast genome of S. jambos contains 132 unique genes, composing of 85 protein-coding genes, 39 tRNA genes and 8 rRNA genes. Phylogenetic analysis indicates that S. jambos is clustered with species in genus Syzygium. This complete chloroplast genome of S. jambos will provide a powerful tool to accelerate breeding, biotechnological and phylogenetic study.

Lignin Accumulation in Three Pumelo Cultivars in Association with Sucrose and Energy Depletion

Lignification, which occurs in many horticultural fruit and vegetables, brings about undesirable texture and unfavorable consumer preference. However, this problem has rarely been studied. In this work, three pumelo cultivars cvs "Hongroumiyou" (HR), "Bairoumiyou" (BR), and "Huangroumiyou" (HuR) were stored at 25 °C for 90 days, and juice sacs were sampled to explore the lignin accumulation and its relationship to sucrose and energy depletion were investigated. The results displayed that HuR contained lower sucrose content, lower ATP level, but higher lignin content compared to BR and HR during postharvest storage, indicating that the sequence according to storage resistance on the basis of lignin content is as follows: HuR < BR < HR. Furthermore, sucrose degradation attributed to enhanced activities of neutral invertase (NI), soluble acid invertase (S-AI), cell wall-bound invertase (B-AI), and energy deficit on account of declined ATP level, showed significantly negative correlation with lignin accumulation, suggesting that lignin accumulation occurrence could induce sucrose degradation and energy deficit during postharvest storage. Additionally, higher activities of phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), peroxidase (POD) could accelerate lignin synthesis and resulted in lignin accumulation during postharvest pumelo storage.

Evaluation of the volatile profile of wax apple (Syzygium samarangense) wines fermented with different commercial Saccharomyces cerevisiae strains

The effect of four commercial Saccharomyces cerevisiae strains (D254, VIC, BV818, and RV100) on the volatile profile of wax apple (Syzygium samarangense) wine was investigated in this study. Alcohols and esters were the most two abundant groups of identified volatiles in wax apple wines. However, different S. cerevisiae strains possess various capacities in releasing/synthesizing volatiles with varied mRNA levels of genes involved in volatiles metabolism during wax apple wine fermentation. VIC, which yielded the highest total concentration of volatiles and largest number of volatiles with odor activity value (OAV) > 1, could be used as a starter culture to produce wax apple wine characterized with intense aroma. D254 and RV100, which produced the greatest variety of volatiles and scored the highest in global aroma, respectively, could be used to enhance the wine complexity. Four wax apple wines could be differentiated by their main volatile compounds.

Melatonin Inhibits Ethylene Synthesis via Nitric Oxide Regulation To Delay Postharvest Senescence in Pears

Understanding ripening and senescence processes in postharvest stored fruit is key to the identification and implementation of effective treatment methods. Here, we explored the effects of exogenous applications of melatonin (MT) and nitric oxide (NO) on ripening and softening processes in three cultivars of European pear ( Pyrus communis L.). The results showed that MT and NO played important roles in the two processes: they decreased the rate of upregulation of PcCel and PcPG, inhibited expression of ethylene synthetase genes ( PcACS and PcACO), and reduced rates of respiration and ethylene production. MT increased activity of NO synthase through upregulation of expression of PcNOS that subsequently led to an increase in NO content. However, when NO synthesis was inhibited, the delaying effect of MT on fruit senescence was almost eliminated. These findings indicate that MT acted on the upstream process of NO synthesis that then delayed senescence in pear fruit.

Efficacy of ABA-Mimicking Ligands in Controlling Water Loss and Maintaining Antioxidative Capacity of Spinacia oleracea

Abscisic acid (ABA) is a central regulator for various developmental processes and responses to abiotic stresses in plants. However, its practical application in controlling water loss of postharvest produces is largely restrained. Herein, the present study reported that two ABA-mimicking ligands, AM1 and AMF4, markedly reduced water loss by promoting stomatal closure and effectively alleviated weight loss in spinach. AM1 and AMF4 also alleviated chlorophyll and vitamin C degradation and simultaneously reduced hydrogen peroxide and malondialdehyde (MDA) production; moreover, both enzymatic and nonenzymatic systems involved in antioxidative capacity were activated. The expression levels of SoOST1, SoSLAC1, SoRCAR3, SoPYL5, SoNCED3, and SoAREB1 were also up-regulated. These findings indicate that AM1 and AMF4 are promising as novel means for reducing water loss, maintaining visual quality, delaying senescence, and extending shelf life in leafy vegetables.

Influence of postmortem treatment with nitric oxide on the muscle color and color stability of tilapia (Oreochromis niloticus) fillets

BACKGROUND

Nitric oxide (NO) has been recognized as pivotal for color and color stability of meat products and has an evident effect on inhibiting microbial growth in processed meat. The use of indirect NO (nitrate/nitrite) in industrial meat curing has potential deleterious effects and great concerns have been expressed over residual nitrite in meat after curing. To find a succedaneum, we have demonstrated the influence of direct NO (saturated NO solution) through euthanasia before slaughter on the fillets color of tilapia and the results suggested that direct NO treatment prior to slaughter is a good procedure to improve the color of tilapia fillets.

OBJECTIVE

To further investigate the effect of direct NO on the muscle color and shelf-life of fillets from tilapia, this study was conducted to investigate the muscle color and color stability of tilapia fillets postmortem treated with saturated NO solution and their shelf-life during refrigerated storage.

METHODS

Tilapia fillets were immersed in a saturated NO solution for 13 min, vacuum-packed and stored at refrigerated temperature for 15 days. Visual observations, color values and absorption maxima were used to evaluate the muscle color and color stability of tilapia fillets. Total volatile basic nitrogen (TVB-N) values were used to evaluate the shelf-life of tilapia fillets during refrigerated storage.

RESULTS

By visual observation, NO treated tilapia fillets showed a brighter red color as compered to control samples after NO-treatment and during the whole storage. The redness (a*) values of NO treated tilapia fillets were significantly increased (P < 0.05) after NO-treatment, continuously increased (P < 0.05) during the earlier 9 days of the storage and remained roughly unchanged during the rest days of the storage. While the a* values of control samples decreased progressively during the storage. NO-treatment effectively improved the muscle color and color stability of tilapia fillets. The peak wavelengths of extract from the muscles of NO treated tilapia fillets increased from 418 nm to 421 nm at 15 d of the storage, while that of control decreased from 418 nm to 410 nm, indicated that color improvement in NO-treated tilapia fillets is mainly due to the formation of MbNO. Moreover, NO-treatment resulted in less TVB-N values than control (16.06 and 21.93 mg of N/100 g at the end of the storage, respectively), prolonging the shelf-life of tilapia fillets.

CONCLUSION

The results suggested that postmortem treatment with NO is a good procedure not only for improving the muscle color and color stability but also for prolonging the shelf-life of tilapia fillets during the storage, which is valuable for industrial manufacturing of tilapia and possibly for other fish species.