Inhibition of autophagy by hydroxychloroquine enhances antioxidant nutrients and delays postharvest fruit senescence of Ziziphus jujuba

TOR and SnRK1 signaling pathways manipulation for improving postharvest fruits and vegetables marketability

During postharvest life, intracellular sugar insufficiency accompanied by insufficient intracellular ATP and NADPH supply, intracellular ROS overaccumulation along with intracellular ABA accumulation arising from water shortage could be responsible for accelerating fruits and vegetables deterioration through promoting SnRK1 and SnRK2 signaling pathways while preventing TOR signaling pathway. By TOR and SnRK1 signaling pathways manipulation, sufficient intracellular ATP and NADPH providing, supporting phenols, flavonoids and anthocyanins accumulation accompanied by improving DPPH, FRAP, and ABTS scavenging capacity by enhancing phenylpropanoid pathway activity, stimulating endogenous salicylic acid accumulation and NPR1-TGA-PRs signaling pathway, enhancing fatty acids biosynthesis, elongation and unsaturation, suppressing intracellular ROS overaccumulation, and promoting endogenous sucrose accumulation could be responsible for chilling injury palliating, fungal decay alleviating, senescence delaying and sensory and nutritional quality preservation in fruits and vegetables. Therefore, TOR and SnRK1 signaling pathways manipulation during postharvest shelf life by employing eco-friendly approaches such as exogenous trehalose and ATP application or engaging biotechnological approaches such as genome editing CRISPR-Cas9 or sprayable double-stranded RNA-based RNA interference would be applicable for improving fruits and vegetables marketability.

Transient autophagy inhibition strengthened postharvest tomato (Solanum lycopersicum) resistance against Botrytis cinerea through curtailing ROS-induced programmed cell death

Autophagy (AU) and programmed cell death (PCD) are dynamically regulated during tomato fruit defense against Botrytis cinerea, which are also manipulated by pathogenic effectors to promote colonization. Present study demonstrated that the enhanced defense induced by transient inhibition on AU by hydroxychloroquine (HCQ) facilitated the restriction of B. cinerea lesion on postharvest tomato. Pre-treatment of 2 mM (16.08 ± 3.42 cm at 7 d) and 6 mM (7.80 ± 2.39 cm at 7 d) HCQ inhibited the lesion development of B. cinerea compared with Mock treatment (50.02 ± 7.69 cm at 7 d). Transient inhibition of AU induced expression of fungal defense and transcriptional regulation related genes, but attenuated reactive oxygen species (ROS) burst gene expression. The ROS-induced PCD was compromised by HCQ with promoted ROS scavenging. The transient pre-treatment of HCQ slightly inhibited AU which triggered the feedback loop that enhanced the autophagic activity defensing against B. cinerea infection.

Interaction of methionine sulfoxide reductase B5 with SlMYC2 stimulates the transcription of MeJA-mediated autophagy-related genes in tomato fruit

Methyl jasmonate (MeJA) has been shown to induce autophagy in various plant stress responses and metabolic pathways. MYC2 is involved in MeJA-mediated postharvest fruit biological metabolism, but it is unclear how it affects MeJA-induced fruit autophagy. In this study, we noticed that silencing SlMYC2 significantly reduced the increase in autophagy-related genes (SlATGs) expression induced by MeJA. SlMYC2 could also bind to the promoters of several SlATGs, including SlATG13a, SlATG13b, SlATG18a, and SlATG18h, and activate their transcript levels. Moreover, SlMsrB5, a methionine sulfoxide reductase, could interact with SlMYC2. Methionine oxidation in SlMYC2 and mimicking sulfoxidation in SlMYC2 by mutation of methionine-542 to glutamine reduced the DNA-binding ability and transcriptional activity of SlMYC2, respectively. SlMsrB5 partially repaired oxidized SlMYC2 and restored its DNA-binding ability. On the other hand, silencing SlMsrB5 inhibited the transcript levels of SlMYC2-targeted genes (SlATG13a, SlATG13b, SlATG18a, and SlATG18h). Similarly, dual-luciferase reporter (DLR) analysis revealed that SlMsrB5-SlMYC2 interaction significantly increased the ability of SlMYC2-mediated transcriptional activation of SlATG13a, SlATG13b, SlATG18a, and SlATG18h. These findings demonstrate that SlMsrB5-mediated cyclic oxidation/reduction of methionine in SlMYC2 influences SlATGs expression. Collectively, these findings reveal the mechanism of SlMYC2 in SlATGs transcriptional regulation, providing insight into the mechanism of MeJA-mediated postharvest fruit quality regulation.

Effects of cold plasma, high hydrostatic pressure, ultrasound, and high-pressure carbon dioxide pretreatments on the quality characteristics of vacuum freeze-dried jujube slices

Pretreatment combined with vacuum freeze-drying is an effective technique to extend the storage period of jujube fruits and reduce energy consumption and cost; however, the effects of pretreatment on the quality characteristics of jujube during vacuum freeze-drying remain unknown. In this study, the effects of cold plasma (CP), high hydrostatic pressure (HHP), ultrasound (US), high-pressure carbon dioxide (HPCD), and conventional blanching (BC) as pretreatments on the performance of vacuum freeze-dried jujube slices were investigated. The results indicated that the application of different pretreatments decreased the water activity and increased the rehydration capacity, owing to the pretreatment etching larger and more porous holes in the microstructure. Freeze-dried jujube slices pretreated with HPCD retained most of their quality characteristics (color, hardness, and volatile compounds), followed by the HHP- and US-pretreated samples, whereas samples pretreated with BC showed the greatest deterioration in quality characteristics, and hence, BC is not recommended as a pretreatment for freeze-dried jujube slices. Sensory evaluation based on hedonic analysis showed that jujube slices pretreated with HPCD and US were close to the control sample and scored highest. Compared to other pretreated samples and the control, freeze-dried jujube slices pretreated with HPCD showed the least degradation (4.93%) of cyclic adenosine monophosphate (cAMP), the highest contents of total phenol, total flavonoid, and l-ascorbic acid, and the highest antioxidant capacity. Partial least squares-discriminant analysis (PLS-DA) was performed to screen all the quality characteristic data of different pretreated samples, and 12 volatile compounds, including ethyl hexanoate and (E)-2-hexenal, along with color, l-ascorbic acid content, and cAMP content were found suitable to be used as discriminators for pretreated freeze-dried jujube slices. Therefore, non-thermal pretreatments, including HPCD, US, and HHP pretreatments, are promising techniques for the vacuum freeze-drying of jujube products.

Applying Cold Atmospheric Plasma to Preserve the Postharvest Qualities of Winter Jujube (Ziziphus jujuba Mill. cv. Dongzao) During Cold Storage

Winter jujube (Ziziphus jujuba Mill. cv. Dongzao) is a very popular horticultural fruit worldwide, which contains a high number of bioactive compounds. Nevertheless, jujube is perishable by microbial contamination and has a short shelf life under non-controlled conditions. Cold atmospheric plasma (CAP) presents a great potential for food sterilization, maintain postharvest quality, and prolonged storage time. Herein, this study investigated the potential effect of CAP with different exposure times (0, 5, 10, and 20 min) on the physicochemical and biochemical changes in jujube during 15-day storage at 4°C and 90% relative humidity (RH). The results showed that CAP treatment could obviously delay ripening, but displayed no effects on the speed of weight loss and moisture content. Meanwhile, the total native aerobic bacterial count in each jujube group was restrained during whole storage. However, CAP treatment showed a time-dependent manner to improve gene expression (PAL, 4CL, DFR, ANS, LAR, and ANR) related to phenolic biosynthesis. As compared to other groups, 20-min CAP treatment can keep or increase total phenolic content (TPC), maintain antioxidant activity, and reduce oxidative damage. Furthermore, the hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) content in jujube during middle storage were visibly reduced by 20-min CAP treatment. All in all, our findings concluded that appropriate CAP exposure time can be a promising candidate for the postharvest preservation of jujube.

Green alternative methods for pretreatment of whole jujube before the drying process

BACKGROUND

Jujube contains a waxy cuticle that acts as a barrier against fungal pathogens, prevents nutrition damage and leakage due to mechanical damage, and maintains water content. Chemical treatment before drying is the most commonly used method for whole jujube. Although chemical pretreatment can effectively enhance drying kinetics, it can lead to the loss of soluble nutrients and cause food safety issues due to chemical residues. Therefore, this study aimed to explore the effect of various pretreatments (cold plasma, cold plasma activated water, ultrasonics, thermosonication, and blanching) on the drying process and quality properties of whole jujube so as to find effective green alternatives to chemical pretreatment.

RESULTS

The application of chemical, cold plasma, and thermosonication significantly altered the surface morphology of jujube by etching larger cracks and holes, which can facilitate the transfer of moisture, thereby improving the drying rate and the effective diffusivity. Chemical, cold plasma, and thermosonication pretreatment reduced drying time by 18%, 12%, and 7% respectively, thereby increasing the content of total phenolics by 13%, 12%, and 6% respectively, and enhancing antioxidant capacity (ferric reducing antioxidant power) by 13%, 11%, and 3% respectively. In addition, chemical and cold plasma pretreatment reduced the generation of 5-hydroxymethylfurfural by 25% and 15% respectively.

CONCLUSION

Cold plasma is a promising green alternative method to chemical pretreatment for drying processes of whole jujube. © 2021 Society of Chemical Industry.

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.

Hepatic interferon regulatory factor 8 expression mediates liver ischemia/reperfusion injury in mice

Hepatic ischemia/reperfusion (I/R) injury is an inevitable complication of hepatic surgery occasioned by liver transplantation and resection. The progression from liver ischemia to reperfusion injury is accompanied by abnormal metabolism, Kupffer cell activation, neutrophil recruitment and the release of cytokines. Activation of several interferon regulatory factors (IRFs) has been reported to either enhance or restrict I/R progression, but the role of IRF8 in the regulation of I/R injury progression is still unknown. In this study, we explore the IRF8 function in the I/R-mediated liver injury using overexpressed hepatic IRF8 and knockout mice. According to our results, IRF8 knockout mice had significantly lower inflammatory cells infiltration, inflammatory cytokines release and serum aspartate aminotransferase/alanine aminotransferase levels that improved the necrotic injury after I/R, unlike the control mice. Conversely, the overexpression of IRF8 in WT mice markedly aggravated the liver structure damage and its abnormal function. We further showed that IRF8-mediated inflammatory cells infiltration were partly dependent on early autophagy and NF-κΒ signal pathway during I/R. AAV8-IRF8-I/R mice pretreated with autophagy inhibitor hydroxychloroquine and NF-κΒ signal pathway inhibitor secukinumab could drastically reverse the IRF8-mediated increase of neutrophil infiltration and chemokine release at different degrees. This work uncovered a critical role of IRF8 in the modulation of the hepatic microenvironment and as a potential target in the initial treatment of I/R injury.

Metabolic and transcriptomic analyses reveal different metabolite biosynthesis profiles between leaf buds and mature leaves in Ziziphus jujuba mill

Jujube leaf is well known for its high nutritional value and medicinal benefits. However, a thorough and dynamic assessment of the metabolites present in jujube leaves is lacking. Here, the primary and secondary metabolites from purple leaf buds and green mature leaves were investigated using ultra-high-performance liquid chromatography/tandem mass spectrometry. A total of 778 metabolites were characterized and more than 700 compounds were reported for the first time. Analysis of differentially accumulated metabolites showed that the flavonoids were the major differential metabolites and determined the leaf coloration. The transcriptome data indicated that 20 flavonoid structural genes and three main types of flavonoid regulatory genes were significantly differentially expressed. Moreover, light had a significant influence on flavonoid accumulation. These results improve our understanding of metabolite accumulation and the molecular mechanisms of flavonoid biosynthesis in jujube leaf.

ZnCl2 treatment improves nutrient quality and Zn accumulation in peanut seeds and sprouts

Peanut is a popular food due to its high nutrient content. The effects of ZnCl₂ on peanut seed germination, fatty acid and sugar contents, vitamin biosynthesis, antioxidant content, and Zn assimilation were evaluated in this study. Treatment with ZnCl₂ significantly improved the germination rate, enhanced reactive oxygen species production and reduced the content of total fatty acids in peanut seed and sprout. However, ZnCl₂ treatment did not reduce total sugar or total protein relative to the control. Germination promoted the biosynthesis of phenolics and resveratrol and increased the antioxidant capacity, as evaluated by Fe³⁺ reducing power and 2,2-diphenyl-1-picrylhydrazyl radical scavenging ability, especially under Zn stress conditions. The vitamin content decreased in the following order among treatments: germinated seeds with ZnCl₂ treatment > germinated seeds without ZnCl₂ treatment > dormant seeds. Interestingly, Zn content was approximately five times higher in the germinated ZnCl₂-treated seeds compared to in the untreated germinated seeds and the dormant seeds. The results of this study provide a new method for producing healthy foods with enhanced vitamin content and antioxidant capacity.

Molecular Mechanisms of Autophagy Regulation in Plants and Their Applications in Agriculture

Autophagy is a highly conserved cellular process for the degradation and recycling of unnecessary cytoplasmic components in eukaryotes. Various studies have shown that autophagy plays a crucial role in plant growth, productivity, and survival. The extensive functions of plant autophagy have been revealed in numerous frontier studies, particularly those regarding growth adjustment, stress tolerance, the identification of related genes, and the involvement of metabolic pathways. However, elucidation of the molecular regulation of plant autophagy, particularly the upstream signaling elements, is still lagging. In this review, we summarize recent progress in research on the molecular mechanisms of autophagy regulation, including the roles of protein kinases, phytohormones, second messengers, and transcriptional and epigenetic control, as well as the relationship between autophagy and the 26S proteasome in model plants and crop species. We also discuss future research directions for the potential application of autophagy in agriculture.

Zinc thiazole enhances defense enzyme activities and increases pathogen resistance to Ralstonia solanacearum in peanut (Arachis hypogaea) under salt stress

Crop plants always encounter multiple stresses in the natural environment. Here, the effects of the fungicide zinc thiazole (ZT) on propagation of Ralstonia solanacearum, a bacterial pathogen, were investigated in peanut seedlings under salt stress. Compared with water control, salt stress markedly reduced pathogen resistance in peanut seedlings. However, impaired pathogen resistance was alleviated by treatment with dimethylthiourea, a specific ROS scavenger, or ZT. Subsequently, salt stress or combined salt and pathogen treatment resulted in inhibition of photosynthesis, loss of chlorophyll and accumulation of thiobarbituric acid reactive substances, which could be reversed by ZT. In addition, ZT treatment suppressed the salt stress up-regulated Na⁺ content and Na⁺/K⁺ ratios in peanut roots. Furthermore, salt stress or combined salt and pathogen treatment impaired the activities of antioxidant (e.g. superoxide dismutase/SOD and catalase/CAT), and defense-related (e.g. phenylalanine ammonia lyase /PAL and polyphenol oxidase/PPO) enzymes, which could be rescued by addition of ZT. In contrast, only slight changes of SOD and CAT activities were observed in pathogen-infected seedlings. Similarly, activities of PAL and PPO were slightly modified by salt stress in peanut seedlings. These results suggest that the ZT-enhanced pathogen resistance can be partly attributed to the improvement of photosynthetic capacity and defense enzyme activities, and also the inhibition of Na⁺/K⁺ ratios, in this salt-stressed crop plant.