Molasses-based waste water irrigation: a friend or foe for carrot (Daucus carota L.) growth, yield and nutritional quality.

Management of molasses-based wastewater generated in yeast and sugar industries is a major environmental concern due to its high chemical oxygen demand and other recalcitrant substances. Several strategies have been used to reduce the inland discharge of wastewater but the results are not satisfactory due to high operating cost. However, reuse of molasses-based wastewater irrigation in agriculture has been a major interest nowadays to reduce the freshwater consumption. Thus, it is crucial to monitor the impacts of molasses-based waste water irrigation on growth, metabolism, yield and nutritional quality of crops for safer consumer's health. In present study, carrot seeds of a local cultivar (T-29) were germinated on filter paper in Petri dishes under controlled conditions. The germinated seeds were then transplanted into pots and irrigated with three different treatments normal water (T0), diluted molasses-based wastewater (T1), and untreated molasses-based wastewater (T2), in six replicates. Results revealed that carrot irrigated with untreated molasses-based waste water had exhibited significant reductions in growth, yield, physiology, metabolism, and nutritional contents. Additionally, accumulation of Cd and Pb contents in carrot roots irrigated with untreated molasses-based waste water exceed the permissible limits suggested by WHO and their consumption may cause health risks. While, diluted molasses-based waste water irrigation positively enhanced the growth, yield of carrot plants without affecting the nutritional quality. This strategy is cost effective, appeared as most appropriate alternative mean to reduce the freshwater consumption in water deficit regions of the world.

Seed priming with potassium nitrate alleviates the high temperature stress by modulating growth and antioxidant potential in carrot seeds and seedlings.

Early season carrot (Daucus carota) production is being practiced in Punjab, Pakistan to meet the market demand but high temperature hampers the seed germination and seedling establishment which cause marked yield reduction. Seed priming with potassium nitrate breaks the seed dormancy and improves the seed germination and seedling growth potential but effects vary among the species and ecological conditions. The mechanism of KNO3 priming in high temperature stress tolerance is poorly understood yet. Thus, present study aimed to evaluate high temperature stress tolerance potential of carrot seeds primed with potassium nitrate and impacts on growth, physiological, and antioxidant defense systems. Carrot seeds of a local cultivar (T-29) were primed with various concentration of KNO3 (T0: unprimed (negative control), T1: hydroprimed (positive control), T2: 50 mM, T3:100mM, T4: 150 mM, T5: 200 mM, T6: 250 mM and T7: 300 mM) for 12 h each in darkness at 20 ± 2℃. Seed priming with 50 mM of KNO3 significantly enhanced the seed germination (36%), seedling growth (28%) with maximum seedling vigor (55%) and also exhibited 16.75% more carrot root biomass under high temperature stress as compared to respective control. Moreover, enzymatic activities including peroxidase, catalase, superoxidase dismutase, total phenolic contents, total antioxidants contents and physiological responses of plants were also improved in response to seed priming under high temperature stress. By increasing the level of KNO3, seed germination, growth and root biomass were reduced. These findings suggest that seed priming with 50 mM of KNO3 can be an effective strategy to improve germination, growth and yield of carrot cultivar (T-29) under high temperature stress in early cropping. This study also proposes that KNO3 may induces the stress memory by heritable modulations in chromosomal structure and methylation and acetylation of histones that may upregulate the hormonal and antioxidant activities to enhance the stress tolerance in plants.

The influence of the Or and Carotene Hydroxylase genes on carotenoid accumulation in orange carrots [Daucus carota (L.)].

KEY MESSAGE: The Or and CH genes are necessary for the accumulation of high amounts of ß-carotene and other carotenoid pigments in carrot roots, in addition to the Y and Y2 genes. Carrot taproot color results from the accumulation of various carotenoid and anthocyanin pigments. Recently, the Or gene was identified as a candidate gene associated with the accumulation of ß-carotene and other provitamin A carotenoids in roots. The specific molecular mechanisms involved with this process, as well as the interactions between Or and the other genes involved in this process are not well understood. In order to better characterize the effect that Or alleles have on conditioning the accumulation of carotenoids in roots, we analyzed an F3 family fixed homozygous recessive for y and y2, derived from a cross between an orange carrot and a white wild carrot, segregating for the two known Or alleles, which we name Orc and Orw. QTL mapping across three different environments revealed that the accumulation of several carotenoids was associated with the Orc allele, with consistent patterns across environments. A second QTL on chromosome 7, harboring a carotene hydroxylase gene homologous to Lut5 in Arabidopsis, was also associated with the accumulation of several carotenoids. Two alleles for this gene, which we name CHc and CHw, were discovered to be segregating in this population. Our study provides further evidence that Or and CH are likely involved with controlling the accumulation of ß-carotene and may be involved with modulating carotenoid flux in carrot, demonstrating that both were important domestication genes in carrot.

Effects of silicon dioxide, zinc oxide and titanium dioxide nanoparticles on Meloidogyne incognita, Alternaria dauci and Rhizoctonia solani disease complex of carrot.

Foliar spray of silicon dioxide (SiO2 NPs), zinc oxide (ZnO NPs) and titanium dioxide (TiO2 NPs) nanoparticles were used for the management of Meloidogyne incognita, Alternaria dauci and Rhizoctonia solani disease complex of carrot. Foliar spray of SiO2 NPs/ZnO NPs or TiO2 NPs increased plant growth attributes, chlorophyll and carotenoid of carrot. Foliar spray of 0.10 mg ml-1 SiO2 NPs caused the highest increase in plant growth, chlorophyll and carotenoid content of leaves followed by spray of 0.10 mg ml-1 ZnO NPs, 0.05 mg ml-1 SiO2 NPs, 0.05 mg ml-1 ZnO NPs, 0.10 mg ml-1 TiO2 NPs and 0.05 mg ml-1 TiO2 NPs. Use of SiO2 NPs caused a higher reduction in root galling, nematode multiplication and disease indices followed by ZnO NPs and TiO2 NPs. Two principal components analysis showed a total of 97.84% overall data variance in plants inoculated with single pathogen and 97.20% in plants inoculated with two or more pathogens. Therefore, foliar spray of SiO2 NPs appears interesting for the management of disease complex of carrot.

Multiplex Site-Directed Gene Editing Using Polyethylene Glycol-Mediated Delivery of CRISPR gRNA:Cas9 Ribonucleoprotein (RNP) Complexes to Carrot Protoplasts.

The aim of this work was to show an efficient, recombinant DNA-free, multiplex gene-editing method using gRNA:Cas9 ribonucleoprotein (RNP) complexes delivered directly to plant protoplasts. For this purpose, three RNPs were formed in the tube, their activity was confirmed by DNA cleavage in vitro, and then they were delivered to carrot protoplasts incubated with polyethylene glycol (PEG). After 48 h of incubation, single nucleotide deletions and insertions and small deletions at target DNA sites were identified by using fluorescent-PCR capillary electrophoresis and sequencing. When two or three RNPs were delivered simultaneously, long deletions of 33-152 nt between the gRNA target sites were generated. Such mutations occurred with an efficiency of up to 12%, while the overall editing effectiveness was very high, reaching 71%. This highly efficient multiplex gene-editing method, without the need for recombinant DNA technology, can be adapted to other plants for which protoplast culture methods have been established.

A de novo transcriptome analysis revealed that photomorphogenic genes are required for carotenoid synthesis in the dark-grown carrot taproot.

Carotenoids are terpenoid pigments synthesized by all photosynthetic and some non-photosynthetic organisms. In plants, these lipophilic compounds are involved in photosynthesis, photoprotection, and phytohormone synthesis. In plants, carotenoid biosynthesis is induced by several environmental factors such as light including photoreceptors, such as phytochromes (PHYs) and negatively regulated by phytochrome interacting factors (PIFs). Daucus carota (carrot) is one of the few plant species that synthesize and accumulate carotenoids in the storage root that grows in darkness. Contrary to other plants, light inhibits secondary root growth and carotenoid accumulation suggesting the existence of new mechanisms repressed by light that regulate both processes. To identify genes induced by dark and repressed by light that regulate carotenoid synthesis and carrot root development, in this work an RNA-Seq analysis was performed from dark- and light-grown carrot roots. Using this high-throughput sequencing methodology, a de novo transcriptome model with 63,164 contigs was obtained, from which 18,488 were differentially expressed (DEG) between the two experimental conditions. Interestingly, light-regulated genes are preferably expressed in dark-grown roots. Enrichment analysis of GO terms with DEGs genes, validation of the transcriptome model and DEG analysis through qPCR allow us to hypothesize that genes involved in photomorphogenesis and light perception such as PHYA, PHYB, PIF3, PAR1, CRY2, FYH3, FAR1 and COP1 participate in the synthesis of carotenoids and carrot storage root development.

Mining for Candidate Genes Controlling Secondary Growth of the Carrot Storage Root.

BACKGROUND: Diverse groups of carrot cultivars have been developed to meet consumer demands and industry needs. Varietal groups of the cultivated carrot are defined based on the shape of roots. However, little is known about the genetic basis of root shape determination. METHODS: Here, we used 307 carrot plants from 103 open-pollinated cultivars for a genome wide association study to identify genomic regions associated with the storage root morphology. RESULTS: A 180 kb-long region on carrot chromosome 1 explained 10% of the total observed phenotypic variance in the shoulder diameter. Within that region, DcDCAF1 and DcBTAF1 genes were proposed as candidates controlling secondary growth of the carrot storage root. Their expression profiles differed between the cultivated and the wild carrots, likely indicating that their elevated expression was required for the development of edible roots. They also showed higher expression at the secondary root growth stage in cultivars producing thick roots, as compared to those developing thin roots. CONCLUSIONS: We provided evidence for a likely involvement of DcDCAF1 and/or DcBTAF1 in the development of the carrot storage root and developed a genotyping assay facilitating the identification of variants in the region on carrot chromosome 1 associated with secondary growth of the carrot root.

Impact of biochar on plant growth and uptake of ciprofloxacin, triclocarban and triclosan from biosolids.

Application of municipal biosolids in agriculture present a concern with potential uptake and bioaccumulation of pharmaceutical compounds from biosolids into agronomic plants. We evaluated the efficacy of biochar as a soil amendment to minimize uptake of antimicrobial agents (ciprofloxacin, triclocarban, and triclosan) in lettuce (Lactuca sativa) and carrot (Daucus carota) plants. Biochar reduced the concentration of ciprofloxacin and triclocarban in lettuce leaves and resulted in a 67% reduction of triclosan in carrot roots. There was no substantial difference in pharmaceutical concentrations in carrot and lettuce plant matter at low (2.0 g kg-1 soil) and high (20.4 g kg-1 soil) rates of applied biochar. The co-amendment of biochar and biosolids increased soil pH and nutrient content which were positively correlated with an increase in lettuce shoot biomass. Our results demonstrate the potential efficacy of using walnut shell biochar as a sorbent for pharmaceutical contaminants in soil without negatively affecting plant growth.

Dissecting the genetic control of root and leaf tissue-specific anthocyanin pigmentation in carrot (Daucus carota L.).

KEY MESSAGE: Inheritance, QTL mapping, phylogenetic, and transcriptome (RNA-Seq) analyses provide insight into the genetic control underlying carrot root and leaf tissue-specific anthocyanin pigmentation and identify candidate genes for root phloem pigmentation. Purple carrots can accumulate large quantities of anthocyanins in their root tissues, as well as in other plant parts. This work investigated the genetic control underlying tissue-specific anthocyanin pigmentation in the carrot root phloem and xylem, and in leaf petioles. Inheritance of anthocyanin pigmentation in these three tissues was first studied in segregating F2 and F4 populations, followed by QTL mapping of phloem and xylem anthocyanin pigments (independently) onto two genotyping by sequencing-based linkage maps, to reveal two regions in chromosome 3, namely P1 and P3, controlling pigmentation in these three tissues. Both P1 and P3 condition pigmentation in the phloem, with P3 also conditioning pigmentation in the xylem and petioles. By means of linkage mapping, phylogenetic analysis, and comparative transcriptome (RNA-Seq) analysis among carrot roots with differing purple pigmentation phenotypes, we identified candidate genes conditioning pigmentation in the phloem, the main tissue influencing total anthocyanin levels in the root. Among them, a MYB transcription factor, DcMYB7, and two cytochrome CYP450 genes with putative flavone synthase activity were identified as candidates regulating both the presence/absence of pigmentation and the concentration of anthocyanins in the root phloem. Concomitant expression patterns of DcMYB7 and eight anthocyanin structural genes were found, suggesting that DcMYB7 regulates transcription levels in the latter. Another MYB, DcMYB6, was upregulated in specific purple-rooted samples, suggesting a genotype-specific regulatory activity for this gene. These data contribute to the understanding of anthocyanin regulation in the carrot root at a tissue-specific level and maybe instrumental for improving carrot nutritional value.

Identification of transcription factor genes involved in anthocyanin biosynthesis in carrot (Daucus carota L.) using RNA-Seq.

BACKGROUND: Anthocyanins are water-soluble colored flavonoids present in multiple organs of various plant species including flowers, fruits, leaves, stems and roots. DNA-binding R2R3-MYB transcription factors, basic helix-loop-helix (bHLH) transcription factors, and WD40 repeat proteins are known to form MYB-bHLH-WD repeat (MBW) complexes, which activates the transcription of structural genes in the anthocyanin pathway. Although black cultivars of carrots (Daucus carota L.) can accumulate large quantities of anthocyanin in their storage roots, the regulatory genes responsible for their biosynthesis are not well characterized. The current study aimed to analyze global transcription profiles based on RNA sequencing (RNA-Seq), and mine MYB, bHLH and WD40 genes that may function as positive or negative regulators in the carrot anthocyanin biosynthesis pathways. RESULTS: RNA was isolated from differently colored calli, as well as tissue samples from taproots of various black carrot cultivars across the course of development, and gene expression levels of colored and non-colored tissue and callus samples were compared. The expression of 32 MYB, bHLH and WD40 genes were significantly correlated with anthocyanin content in black carrot taproot. Of those, 11 genes were consistently up- or downregulated in a purple color-specific manner across various calli and cultivar comparisons. The expression of 10 out of these 11 genes was validated using real-time quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). CONCLUSIONS: The results of this study provide insights into regulatory genes that may be responsible for carrot anthocyanin biosynthesis, and suggest that future focus on them may help improve our overall understanding of the anthocyanin synthesis pathway.

Genome-wide identification, expansion, and evolution analysis of homeobox genes and their expression profiles during root development in carrot.

The homeobox gene family, a large family represented by transcription factors, has been implicated in secondary growth, early embryo patterning, and hormone response pathways in plants. However, reports about the information and evolutionary history of the homeobox gene family in carrot are limited. In the present study, a total of 130 homeobox family genes were identified in the carrot genome. Specific codomain and phylogenetic analyses revealed that the genes were classified into 14 subgroups. Whole genome and proximal duplication participated in the homeobox gene family expansion in carrot. Purifying selection also contributed to the evolution of carrot homeobox genes. In Gene Ontology (GO) analysis, most members of the HD-ZIP III and IV subfamilies were found to have a lipid binding (GO:0008289) term. Most HD-ZIP III and IV genes also harbored a steroidogenic acute regulatory protein-related lipid transfer (START) domain. These results suggested that the HD-ZIP III and IV subfamilies might be related to lipid transfer. Transcriptome and quantitative real-time PCR (RT-qPCR) data indicated that members of the WOX and KNOX subfamilies were likely implicated in carrot root development. Our study provided a useful basis for further studies on the complexity and function of the homeobox gene family in carrot.

Hypoxia enhances lignification and affects the anatomical structure in hydroponic cultivation of carrot taproot.

KEY MESSAGE: Hypoxia enhances lignification of carrot root. Hypoxia stress was thought to be one of the major abiotic stresses that inhibiting the growth and development of higher plants. The genes encoding the plant alcohol dehydrogenase (ADH-P) were induced when suffering hypoxia. To investigate the impact of hypoxia on the carrot root growth, carrot plants were cultivated in the hydroponics with or without aeration. Morphological characteristics, anatomical structure, lignin content, and the expression profiles of DcADH-P genes and lignin biosynthesis-related genes were measured. Six DcADH-P genes were identified from the carrot genome. The expression profiles of only three (DcADH-P1, DcADH-P2, and DcADH-P3) genes could be detected and the other three (DcADH-P4, DcADH-P5, and DcADH-P6) could not be detected when carrot cultivated in the solution without aeration. In addition, carrot roots had more lignin content, aerenchyma and less fresh weight when cultivated in the solution without aeration. These results suggested that hypoxia could enhance the lignification and affect anatomical structure of the carrot root. However, the expression levels of the genes related to lignin biosynthesis were down-regulated under the hypoxia. The enhancement of lignification may be the consequence of the structure changes in the carrot root. Our work was potentially helpful for studying the effect of hypoxia on carrot growth and may provide useful information for carrot hydroponics.

Effects of cadmium and copper mixtures to carrot and pakchoi under greenhouse cultivation condition.

A pot experiment was undertaken to investigate the effects of Cd and Cu mixtures to growth and nutrients (sugar, carotene or vitamin C) of carrot and pakchoi under greenhouse cultivation condition. The study included: (a) physical-chemical properties of soil and soil animals in response to Cd and Cu stress; (b) bioaccumulation of heavy metals, length, biomass, contents of sugar and carotene (vitamin C) of carrot and pakchoi; (c) estimation the effects of Cd and Cu mixtures by multivariate regression analysis. The results implied that heavy metals impacted negative influence on soil animals' abundance. The metals contents in plants increased obviously with Cd and Cu contamination in soil. The biomass production and nutrients declined with Cd and Cu contents increasing. Cd (20 mg kg-1) treatment caused maximum reduction of sugar content (45.29%) in carrot root; maximum reduction in carotene content (75.73%) in carrot, 75.1% sugar content reduction and 70.58% vitamin C content reduction in pakchoi shoots were observed with addition of Cd (20 mg kg-1) and Cu (400 mg kg-1) mixture. The results of multivariate regression analysis indicated that combination of Cd and Cu exerts negative effects to both carrot and pakchoi, and both growth and nutrients were negatively correlated with metals concentrations. It is concluded that the Cd and Cu mixtures caused toxic damage to vegetable plants as Cd and Cu gradient concentrations increased.

Optimum plot size of planting and bio-agroeconomic revenues from arugula-carrot intercropping systems in a semi-arid region.

The production of vegetable crops has been characterized as a highly intensive activity in the use of soil, water, inputs and labor in semi-arid regions, being practiced mostly by small family farmers as a way of subsistence, or in the small-scale commercialization of surplus production. Among the agricultural practices that have been successfully used by vegetable producers are intercrop systems that, when implemented with adequate management, present gains in productivity, nutritional, economic, and environmental value. The aim of this study was to estimate the optimal plot sizes of plantings of carrot (Daucus carota L.) intercropped with arugula (Eruca sativa L.) in bi-cultivation in three spatial arrangements, as well as to determine bio-agroeconomic revenues from associations between these vegetable crops in a semi-arid region. Estimates of optimal sizes of experimental plots in intercropping systems, provided by the methods of bootstrap resampling and of sampling intensity (10%), were four, four and three basic units, respectively, for the spatial arrangements 2R:2C, 3R:3C, and 4R: 4C, between rows of arugula (R) intercropped with carrot (C), and by the Hatheway method, all spatial arrangements were of four basic units. The best bio-agroeconomic performance of carrot intercropped with arugula in bi-cultivation was obtained in the spatial arrangement 2R:2C.

Maturation-related changes of carrot lignins.

BACKGROUND: Lignified cell walls are important factors for textural and physiological properties of plant-based foods. However, carrot lignins and their modifications during maturation are poorly described. The objective of this study was to describe carrot lignins in detail and to study lignin structural alterations at later stages of maturity. RESULTS: Klason and acetyl bromide soluble lignin contents of insoluble fibers of carrots harvested at different times (26, 29 and 35 weeks after seeding) ranged between 46.38 and 62.68 g kg-1 and between 19.79 and 28.08 g kg-1 , respectively. As determined by both 2D-nuclear magnetic resonance and the derivatization followed by reductive cleavage method, coniferyl alcohol heavily dominated the traditional monolignol composition in carrot lignins, independently of harvest times. By using 2D-nuclear magnetic resonance experiments on isolated lignins, p-hydroxybenzoate was identified as a less common lignin constituent, attached to lignin γ-hydroxyl groups and being increasingly incorporated with maturation. ß-Aryl ethers, phenylcoumaran, resinol and dibenzodioxocin structures were identified as lignin interunit linkages, largely independent of harvest times and with ß-aryl ethers being expectedly dominant. CONCLUSION: Carrots contain guaiacyl-rich lignins that incorporate increasing amounts of p-hydroxybenzoate with maturation. All other lignin characteristics appear to be widely independent of harvest times. © 2017 Society of Chemical Industry.

Carotenoid gene expression explains the difference of carotenoid accumulation in carrot root tissues.

Main conclusion Variations in gene expression can partially explain the difference of carotenoid accumulation in secondary phloem and xylem of fleshy carrot roots. The carrot root is well divided into two different tissues separated by vascular cambium: the secondary phloem and xylem. The equilibrium between these two tissues represents an important issue for carrot quality, but the knowledge about the respective carotenoid accumulation is sparse. The aim of this work was (i) to investigate if variation in carotenoid biosynthesis gene expression could explain differences in carotenoid content in phloem and xylem tissues and (ii) to investigate if this regulation is differentially modulated in the respective tissues by water-restricted growing conditions. In this work, five carrot genotypes contrasting by their root color were studied in control and water-restricted conditions. Carotenoid content and the relative expression of 13 genes along the carotenoid biosynthesis pathway were measured in the respective tissues. Results showed that in orange genotypes and the purple one, carotenoid content was higher in phloem compared to xylem. For the red one, no differences were observed. Moreover, in control condition, variations in gene expression explained the different carotenoid accumulations in both tissues, while in water-restricted condition, no clear association between gene expression pattern and variations in carotenoid content could be detected except in orange-rooted genotypes. This work shows that the structural aspect of carrot root is more important for carotenoid accumulation in relation with gene expression levels than the consequences of expression changes upon water restriction.

Carotenoid Biosynthesis in Daucus carota.

Carrot (Daucus carota) is one of the most important vegetable cultivated worldwide and the main source of dietary provitamin A. Contrary to other plants, almost all carrot varieties accumulate massive amounts of carotenoids in the root, resulting in a wide variety of colors, including those with purple, yellow, white, red and orange roots. During the first weeks of development the root, grown in darkness, is thin and pale and devoid of carotenoids. At the second month, the thickening of the root and the accumulation of carotenoids begins, and it reaches its highest level at 3 months of development. This normal root thickening and carotenoid accumulation can be completely altered when roots are grown in light, in which chromoplasts differentiation is redirected to chloroplasts development in accordance with an altered carotenoid profile. Here we discuss the current evidence on the biosynthesis of carotenoid in carrot roots in response to environmental cues that has contributed to our understanding of the mechanism that regulates the accumulation of carotenoids, as well as the carotenogenic gene expression and root development in D. carota.

Evaluation of vegetable-faba bean (Vicia faba L.) intercropping under Latvian agro-ecological conditions.

BACKGROUND: Monoculture is used mostly in conventional agriculture, where a single crop is cultivated on the same land for a period of at least 12 months. In an organic and integrated growing approach, more attention is paid to plant-environment interactions and, as a result, diverse growing systems applying intercropping, catch crops, and green manure are being implemented. Thus, field experiments for evaluation of vegetable/faba bean full intercropping efficiency, in terms of vegetable and faba bean yield and protein content, were set up during two consecutive growing seasons (2014 and 2015). RESULTS: Data obtained showed that the most efficient intercropping variants were cabbage/faba bean (cabbage yield 1.27-2.91 kg m-2 , immature faba bean pods 0.20-0.43 kg m-2 ) and carrot/faba bean (carrot yield 1.67-2.28 kg m-2 , immature faba bean pods 0.10-0.52 kg m-2 ), whilst onion and faba bean intercrop is not recommended for vegetable growing since it induces a very low onion yield (0.66-1.09 kg m-2 ), although the highest immature faba bean pod yield was found in the onion/faba bean intercropping scheme (up to 0.56 kg m-2 ). CONCLUSION: Vegetable/faba bean intercropping can be used in practical horticulture for carrot and cabbage growing in order to ensure sustainable farming and environmentally friendly horticultural production. © 2017 Society of Chemical Industry.

Identification of ROS Produced by Nanobubbles and Their Positive and Negative Effects on Vegetable Seed Germination.

Exogenous reactive oxygen species (ROS) produced by nanobubble (NB) water offer a reasonable explanation for NBs' physiological promotion and oxidation effects. To develop and exploit the NB technology, we have performed further research to identify the specific ROS produced by NBs. Using a fluorescent reagent APF, a Fenton reaction, a dismutation reaction of superoxide dismutase and DMSO, we distinguished four types of ROS (superoxide anion radical (O2·-), hydrogen peroxide (H2O2), hydroxyl radical (·OH), and singlet oxygen (1O2)). ·OH was confirmed to be the specific ROS produced by NB water. The role of ·OH produced by NB water in physiological processes depends on its concentration. The amount of exogenous ·OH has a positive correlation with the NB number density in the water. Here, spinach and carrot seed germination tests were repeatedly performed with three seed groups submerged in distilled water, high-number density NB water, and low-number density NB water under similar dissolved oxygen concentrations. The final germination rates of spinach seeds in distilled water, low-number density NB water, and high-number density NB water were 54%, 65%, and 69%, respectively. NBs can also promote sprout growth. The sprout lengths of spinach seeds dipped in NB water were longer than those in the distilled water. For carrot seeds, the amount of exogenous ·OH in high-number density NB water was beyond their toxic threshold, and negative effects were shown on hypocotyl elongation and chlorophyll formation. The presented results allow us to obtain a deeper understanding of the physiological promotion effects of NBs.

Transcriptome-based identification of genes revealed differential expression profiles and lignin accumulation during root development in cultivated and wild carrots.

KEY MESSAGE: Carrot root development associates lignin deposition and regulation. Carrot is consumed worldwide and is a good source of nutrients. However, excess lignin deposition may reduce the taste and quality of carrot root. Molecular mechanisms underlying lignin accumulation in carrot are still lacking. To address this problem, we collected taproots of wild and cultivated carrots at five developmental stages and analyzed the lignin content and characterized the lignin distribution using histochemical staining and autofluorescence microscopy. Genes involved in lignin biosynthesis were identified, and their expression profiles were determined. Results showed that lignin was mostly deposited in xylem vessels of carrot root. In addition, lignin content continuously decreased during root development, which was achieved possibly by reducing the expression of the genes involved in lignin biosynthesis. Carrot root may also prevent cell lignification to meet the demands of taproot growth. Our results will serve as reference for lignin biosynthesis in carrot and may also assist biologists to improve carrot quality.