Postharvest Treatment of ‘Florida Prince’ Peaches with a Calcium Nanoparticle–Ascorbic Acid Mixture during Cold Storage and Its Effect on Antioxidant Enzyme Activities

Chilling injury (CI) is a physiological disorder resulting from low storage temperatures that affects the fruit quality and marketing of the ‘Florida Prince’ peach. In this study, the exogenous application of a mixture of calcium nanoparticles (CaNPs) and ascorbic acid was found to significantly alleviate the symptoms of CI in peaches during cold storage. Fruits were treated with CaNPs plus different concentrations of ascorbic acid (AA; 0, 3, 6, and 9 mM). Peaches were immersed in CaNP–AA for 15 min before being stored at 4 ± 1 °C and 95 ± 1% RH for 30 days. We observed that the 9 mM CaNP–AA treatment lowered the values for the CI index, ion leakage, and malondialdehyde (MDA) content and increased antioxidant enzyme activities (AEAs), such as for ascorbate oxidase (APX), catalase (CAT), superoxide dismutase (SOD), and glutathione reductase (GR). Furthermore, the treatment reduced the accumulation of both H2O2 and O2•− and increased the level of DPPH reduction throughout the duration of cold storage. Our results suggest that 9 mM CaNP–AA treatment suppresses the incidence of CI in peach fruit throughout cold storage, possibly because 9 mM CaNP–AA is at least partly involved in enhancing the antioxidant system via its effect on antioxidant substances. The results indicate that applying the 9 mM CaNP–AA treatment afforded peaches with enhanced tolerance against cold storage stress.

Metabolite Diversity and Metabolic Genome-Wide Marker Association Studies (Mgwas) for Health Benefiting Nutritional Traits in Pearl Millet Grains

As efforts are made to increase food security, millets are gaining increasing importance due to their excellent nutritional credentials. Among the millets, pearl millet is the predominant species possessing several health benefiting nutritional traits in its grain that are helpful in mitigating chronic illnesses such as type−2 diabetes and obesity. In this paper, we conducted metabolomic fingerprinting of 197 pearl millet inbred lines drawn randomly from within the world collection of pearl millet germplasm and report the extent of genetic variation for health benefitting metabolites in these genotypes. Metabolites were extracted from seeds and assessed using flow infusion high-resolution mass spectrometry (FIE-HRMS). Metabolite features (m/z), whose levels significantly differed among the germplasm inbred lines, were identified by ANOVA corrected for FDR and subjected to functional pathway analysis. A number of health-benefiting metabolites linked to dietary starch, antioxidants, vitamins, and lipid metabolism-related compounds were identified. Metabolic genome-wide association analysis (mGWAS) performed using the 396 m/z as phenotypic traits and the 76 K SNP as genotypic variants identified a total of 897 SNPs associated with health benefiting nutritional metabolite at the -log p-value ≤ 4.0. From these associations, 738 probable candidate genes were predicted to have an important role in starch, antioxidants, vitamins, and lipid metabolism. The mGWAS analysis focused on genes involved in starch branching (α-amylase, β-amylase), vitamin-K reductase, UDP-glucuronosyl, and UDP-glucosyl transferase (UGTs), L-ascorbate oxidase, and isoflavone 2′-monooxygenase genes, which are known to be linked to increases in human health benefiting metabolites. We demonstrate how metabolomic, genomic, and statistical approaches can be utilized to pinpoint genetic variations and their functions linked to key nutritional properties in pearl millet, which in turn can be bred into millets and other cereals crops using plant breeding methods.

Role of Ascorbic Acid in the Extraction and Quantification of Potato Polyphenol Oxidase Activity

The ability to accurately measure the activity of polyphenol oxidase (PPO) in complex matrices is essential. A problem encountered when using spectrophotometric methods is interference due to ascorbic acid (AA), often used as an enzyme “protecting agent” during PPO extraction. This study focuses on the nature of AA’s effect on spectrophotometric determinations of PPO activity as well as enzyme extraction. Potato extracts and semi-purified PPO were used as enzyme sources. The inactivation of PPO attributed to AA is substrate-mediated. The extent of AA-dependent inactivation of PPO in model systems varied between substrates. AA only slows mechanism-based inactivation of PPO induced by catechol, possibly owing to the prevention of quinone formation. AA minimally protects PPO activity during enzyme extraction. The problem associated with AA in PPO assay could be circumvented by using ascorbate oxidase to remove AA when catechol is the primary substrate or by using chlorogenic acid as the primary substrate.

An Ascorbate Bluetooth© Analyzer for Quality Control of Fresh-Cut Parsley Supply Chain

This work provides companies in the fresh-cut produce sector with an Ascorbate Bluetooth© Analyzer (ABA), a screen-printed sensor-based device for ascorbic acid (AA) detection, for quality control all along the supply chain. The amperometric detection of AA on fresh and fresh-cut parsley, under correct and incorrect storage temperature, allowed us to investigate the kinetics of AA decay in response to oxidative stress. The role of ascorbate oxidase (AOx) and ascorbate peroxidase (APx) was studied. ABA was used in situ by unskilled personnel. Treatments influenced AA decay kinetics, which were linear in fresh parsley, and non-linear in fresh-cut. Two hours at 28 °C immediately after chopping, the resilience of the fresh-cut parsley was reduced, even though the cold chain was restored. Two hours at −2 °C caused a rapid loss of AA until its complete decay after 72 h. Significant differences between treatments were observed in both the expression and activity of AOx and APx. ABA registered sudden changes of parsley AA following unpredicted variations of temperature during processing or transport. It was useful to remedy the effects of unexpected flaws in the cold chain, which can be proposed for quality preservation of different fresh-cut produce.

Induced Resistance by Ascorbate Oxidation Involves Potentiating of the Phenylpropanoid Pathway and Improved Rice Tolerance to Parasitic Nematodes

Anticipating an increased ecological awareness, scientists have been exploring new strategies to reduce the use of chemical pesticides to control pests and diseases. Triggering the intrinsic plant defense system is one of the promising strategies to reduce yield loss by pathogenic organisms, such as nematodes. Ascorbate oxidase (AO) enzyme plays an important role in plant defense by regulating the apoplastic ascorbate/dehydroascorbate (DHA) ratio via the ascorbate oxidation process. Ascorbate oxidation is known to induce systemic resistance in rice against parasitic root-knot nematodes (RKN). Here, we sought to evaluate if AO- or DHA-induced resistance (IR) against RKN M. graminicola involves activation of the phenylpropanoid pathway and whether this IR phenotype has potential effects on growth of rice seedlings under stressed and unstressed conditions. Our results show that AO/DHA-IR against these parasitic nematodes is dependent on activation of phenylalanine ammonia lyase (PAL). However, application of reduced ascorbic acid (AA) did not induce this response. Gene expression analysis via qRT-PCR showed that OsPAL2 and OsPAL4 are highly expressed in AO/DHA-sprayed nematode-infected roots and PAL-activity measurements confirmed that AO/DHA spraying triggers the plants for primed activation of this enzyme upon nematode infection. AO/DHA-IR is not effective in plants sprayed with a chemical PAL inhibitor confirming that AO/DHA-induced resistance is dependent on PAL activity. Improved plant growth and low nematode infection in AO/DHA-sprayed plants was found to be correlated with an increase in shoot chlorophyll fluorescence (Fv/Fm), chlorophyll index (ChlIdx), and modified anthocyanin reflection index which were proven to be good above-ground parameters for nematode infestation. A detailed growth analysis confirmed the improved growth of AO/DHA-treated plants under nematode-infected conditions. Taken together, our results indicate that ascorbate oxidation enhances the phenylpropanoid-based response to nematode infection and leads to a tolerance phenotype in treated rice plants.

RNA-Seq based exploration of differentially expressed genes (DEGs) in cotton(Gossypium hirsutum. L) upon infection with Aspergillus tubingensis

Differentially expressed genes help in exploring plant defense mechanism under variable stress conditions. In current investigation, RNA sequencing was executed to explore the differential gene expression in resistant and susceptible varieties of Cotton (Gossypium hirsutum), upon infection with Aspergillus tubingensis. Comparative RNA-Seq of control and infected plants was performed using Illumina HiSeq 2,500. Overall 79.84 G clean data was generated and 6,558 DEGs were identified in both varieties, in response to pathogen inoculation. Differentially expressed genes were found to be involved in defense, antifungal response, signaling pathways, oxidative burst and transcription. Genes involved in defense responses, MAPK signaling, cell wall fortification and signal transduction were highly induced in resistant variety. Real time PCR also revealed the up regulation of MAPKKK YODA like, L-ascorbate oxidase, late embryogenesis abundant protein (At1g64065) and flavonoid 3',5'-hydroxylase-like, in resistant variety. Elevated accumulation of such DEGs in resistant variety could function as the source for identifying biomarkers for breeding and these can be used as potential candidate genes for transgenic manipulation. Their study also helped in understanding complex plant-fungal interaction and advanced the understanding of plant-microbe interaction. Inclusively, our findings provide an indispensable foundation for advanced understanding of the plant resistance mechanisms of cotton.

Integrative analysis of transcriptome and proteome revealed nectary and nectar traits in the plant-pollinator interaction of Nitraria tangutorum Bobrov

Background Nitraria tangutorum is an important desert shrub that shows resistance to drought, salt and wind erosion stresses. It is a central ecological species in its area. Here, we have studied how N. tangutorum has adapted to achieve a successful reproduction strategy. Results We found that N. tangutorum is mainly pollinated by insects of the Hymenoptera, Diptera and Coleoptera orders. Nitraria tangutorum has very small flowers, with the nectary composed of secretive epidermal cells from which nectar is secreted, located within the inner petals. In addition, analyzing the transcriptome of four successive flower developmental stages revealed that mainly differentially expressed genes associated with flower and nectary development, nectar biosynthesis and secretion, flavonoid biosynthesis, plant hormone signal transduction and plant-pathogen interaction show dynamic expression. From the nectar, we could identify seven important proteins, of which the L-ascorbate oxidase protein was first found in plant nectar. Based on the physiological functions of these proteins, we predict that floral nectar proteins of N. tangutorum play an important role in defending against microbial infestation and scavenging active oxygen. Conclusions This study revealed that N. tangutorum is an insect-pollinated plant and its nectary is composed of secretive epidermal cells that specialized into secretive trichomes. We identified a large number of differentially expressed genes controlling flower and nectary development, nectar biosynthesis and secretion, flavonoid biosynthesis, plant hormone signal transduction and plant-pathogen interaction. We suggest that proteins present in N. tangutorum nectar may have both an antibacterial and oxygen scavenging effect. These results provide a scientific basis for exploring how the reproductive system of N. tangutorum and other arid-desert plants functions.

Synthesis and Evaluation of Structural and Functional Biomimetic Models of Oxidase-Type Metalloenzymes Based on Polynuclear Compounds with Copper (II) and Manganese (II) Ions

Biomimetic compounds are an alternative for to the limited action and fragile nature of enzymes. This work deals with the synthesis, characterization and evaluation of catalytic activity of two new biomimetic models for the active centers of ascorbate oxidase and catalase. [Cu3(S,S(+)cpse)3(H2O)3][Cu3(R,R(-)cpse)3(H2O)3]·17H2O (model for ascorbate oxidase, 1), and [Mn2(S,S(+)Hcpse)4(NaClO4)2(NaOH)(CH4O)]n·[(C2H6O)2]n·[(CH4O)2]n (model for catalase, 2) were prepared through the synchronic method (yields > 78%). The compound 1 has electronic and optical characteristics for racemic compound. The magnetic properties and electrochemical behavior evidence electronic transfer between metal centers. Meanwhile, the compound 2 showed polymeric properties in solid state and dimeric behavior in solution. Compound 1 was able to effectively catalyze the oxidation of ascorbic acid to dehydroascorbic acid (65.6% and 78.24% for racemic and enantiomeric pure compounds) showing structural and functional similarity to the natural enzyme. Besides, Compound 2 catalyzed the decomposition of hydrogen peroxide toward oxygen and water molecules (45%), evidencing that the prepared complex mimics the action of catalases. These two biomimetic models are relationship between them for the structural ligands, the coordination form to metal center and the catalytic activity as oxidase. This research shows the relationship with the design, evaluation, and comprehension of fundamentals aspects for the biomimetic models of active center of metalloenzymes that have importance for biological and industrial processes.

Validation and demonstration of a pericarp disc system for studying blossom-end rot of tomatoes

Background Blossom-end rot in tomatoes is often used as a model system to study fruit calcium deficiency. The study of blossom-end rot development in tomatoes has been greatly impeded by the difficulty of directly studying and applying treatments to the affected cells. This manuscript presents a novel method for studying blossom-end rot development after harvest in immature whole fruit and in pericarp discs. Results Pericarp discs removed from the bottom pericarp of immature healthy fruit developed blossom-end rot like symptoms, corresponding to a decrease in L* value and an increase in a* value. Symptoms also developed in columella tissue, but not in stem-end pericarp tissue, similar to patterns observed during blossom-end rot development on the plant. Ascorbate oxidase and peroxidase activity, which are elevated in blossom-end rot affected fruit compared to healthy fruit, were both correlated with colorimetric measures of tissue darkening in discs. Respiration rate was higher in discs that later developed blossom-end rot symptoms, with increased respiration in asymptomatic discs on day 1 of storage being associated with symptom development on day 2. Calcium chloride and ascorbic acid treatments inhibited symptom development, demonstrating the potential of this method to provide causal evidence. Conclusions Results indicate that symptom development in this system is consistent with blossom-end rot development with regards to location, color change, and the activity of key enzymes. This system has the potential to be used to elucidate the cause of fruit calcium deficiency and improve knowledge of the biological basis for calcium’s diverse effects on fruit.