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.

Phosphatidylinositol-specific phospholipase C-associated phospholipid metabolism mediates DcGLRs channel to promote calcium influx under CaCl2 treatment in shredded carrots during storage.

The rapid activation of phosphatidylinositol-specific phospholipase C (PI-PLC) occurs early after the stimulation of biotic and abiotic stress in plants, which directly associated with the calcium channel-induced calcium ion (Ca2+) influx. Exogenous calcium chloride (CaCl2) mediates the calcium signaling transduction to promote the γ-aminobutyric acid accumulation and nutritional quality in shredded carrots whereas the generation mechanism remains uncertain. Therefore, the involvement of PI-PLC-associated phospholipid metabolism was investigated in present study. Our result revealed that CaCl2 treatment promoted the expression and activity of PI-PLC and increased the inositol 1,4,5-trisphosphate and hexakisphosphate content in shredded carrots. The transcripts of multi-glutamate receptor-like channels (DcGLRs), the glutamate and γ-aminobutyric acid (GABA) content, and Ca2+ influx were induced by CaCl2 treatment in shredded carrots during storage. However, PI-PLC inhibitor (U73122) treatment inhibited the activation of PI-PLC, the increase of many DcGLRs family genes expression levels, and Ca2+ influx. Moreover, the identification of DcPI-PLC4/6 and DcGLRs proteins, along with the analysis of characteristic domains such as PLCXc, PLCYc, C2 domain, transmembranous regions, and ligand binding domain, suggests their involvement in phospholipid catalysis and calcium transport in carrots. Furthermore, DcPI-PLC4/6 overexpression in tobacco leaves induced the Ca2+ influx by activating the expressions of NtGLRs and the accumulation of glutamate and GABA. These findings collectively indicate that CaCl2 treatment-induced PI-PLC activation influences DcGLRs expression levels to mediate cytosolic Ca2+ influx, thus, highlighting the "PI-PLC-GLRs-Ca2+" pathway in calcium signaling generation and GABA biosynthesis in shredded carrots.

Effect of ozone, lactic acid and combination treatments on the control of microbial and pesticide contaminants of fresh vegetables.

BACKGROUND: Fruit and vegetable consumption has increased due to their tremendous health benefits. However, recent studies have shown that contaminated products may serve as vehicles for foodborne pathogens and harmful chemicals. Therefore, fresh vegetables must be decontaminated before consumption to ensure food safety. RESULTS: In this study, the combined decontamination treatment of lactic acid (2.5 mL L-1 ) and ozone (9 mg L-1 ) for 10 min showed better efficacy in the removal of contaminants from fresh vegetables as compared to individual treatments. The combined treatment resulted in a reduction of 1.5-3.5 log CFU of native mesophilic bacteria per gram and 1.6-2.9 log CFU of artificially inoculated Escherichia coli per gram from tomato, cucumber, carrot and lettuce. The combined treatment also removed spiked pesticides, which represent artificial chemical contamination (28-97% chlorpyrifos and 62-100% λ-cyhalothrin residues), from fresh vegetables. No significant difference (P > 0.05) in various sensory attributes of vegetables was observed between untreated and treated (lactic acid and ozone) vegetables. CONCLUSIONS: The combination treatment provides a novel approach to target two groups of contaminants using a single procedure. The combination treatment can be used as an alternative to currently used decontamination techniques for the supply of safe vegetables to consumers. © 2020 Society of Chemical Industry.

Sequential Application of High-Voltage Electric Field Cold Plasma Treatment and Acid Blanching Improves the Quality of Fresh Carrot Juice (Daucus carota L.).

The study was aimed to investigate the combined effect of acid blanching (AB) and high-voltage electric field cold plasma (HVCP) on carrot juice quality. Before juice extraction, carrots were separated into three parts: control, blanched (100 °C for 5 min) with non-acidified water, and blanched with acidified water (35 g/L citric acid at pH 1.34). Carrot juice was then subjected to dielectric barrier discharge at 80 kV for 4 min. Results indicated that AB treatment significantly influenced the efficiency of HVCP. AB-HVCP resulted in antimicrobial synergism, which is an outcome of acidified NO2-, H2O2, O-, and peroxynitrites (ONOO-) or its precursor OH/NO2, along with other species. In addition, plasma treatment also promotes the accumulation of coloring compounds, chlorogenic acid, and sugar contents by surface erosion of the epidermal layer, cis isomerization, rupturing of phenol-sugar and phenolic-cell matrix bonds, and depolymerized long-chain polysaccharides by cleavage of the glycoside bond. Therefore, AB-HVCP is a potential emerging hurdle strategy for fresh produce.

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.

Physiological and genetic effects of cadmium and copper mixtures on carrot under greenhouse cultivation.

The exposure to combinations of heavy metals can affect the genes of vegetables and heavy metals would accumulate in vegetables and thereby indirectly affecting human health. Exploring the links between genetic changes and phenotypic changes of carrot under the combined pollution of Cd and Cu is of great significance for studying the mechanism of heavy metal pollution. Therefore, this study examined the effects of mixtures of cadmium (Cd) and copper (Cu) on physiological measures (malondialdehyde (MDA), proline, and antioxidant enzyme) and expression of growth-related genes (gibberellin gene, carotene gene, and glycogene) in carrot under greenhouse cultivation. The results showed in the additions with mixtures of Cd and Cu at higher concentration, the MDA content increased significantly (p < 0.05), whereas the proline content was not significantly different from those in the control. In the mixed treatments with high Cd concentrations, the activity of superoxide dismutase (SOD) was significantly lower than that in the control (p < 0.05); whereas the activity of peroxidase (POD) increased to different degrees compared to the control. In the additions with mixtures of Cd and Cu, compared with the control, the expression of the gibberellin gene was downregulated from 1.97 to 20.35 times (not including the 0.2 mg kg-1 Cd and 20 mg kg-1 Cu mixture, the expression of gibberellin gene in this treatment was upregulated 1.29 times), which lead to decreases in the length and dry weight of carrots. The expression of the carotene gene in mixed treatments downregulated more than that in single treatments, which could reduce the ability of carrots to resist oxidative damage, as suggested by the significant increase in the MDA content. In the addition with mixtures of Cd and Cu, compared with the control, the expression of the glycogene was downregulated by 1.42-59.40 times, which can cause a significant reduction in the sugar content in carrots and possibly further reduce their ability to resist heavy metal damage. A cluster analysis showed that in the additions with mixtures of Cd and Cu, the plant phenotype was affected first, and then with increases in the added concentration, the expression of genes was also affected. In summary, in the additions with mixtures of Cd and Cu, plants were damaged as Cd and Cu concentrations increased.

Sanitizing after fresh-cutting carrots reduces the wound-induced accumulation of phenolic antioxidants compared to sanitizing before fresh-cutting.

BACKGROUND: During the production of fresh-cut products, crops are exposed to wounding stress, and as a stress response, phenolic antioxidants are synthesized. This stress response is elicited by extracellular adenosine triphosphate, released from wounded cells and recognized by receptors of unwounded cells. The phenolic antioxidants produced as a stress response are beneficial for human health. However, a common practice in the fresh-cut industry is the application of washing/sanitizing procedures after cutting. These procedures could be highly detrimental, since they partially remove the wound signal that elicits the biosynthesis of phenolics in plants. In this study, the impact of different washing/sanitizing treatments post-shredding on the wound-induced accumulation of chlorogenic acid (CHA) in carrot was evaluated. Peeled carrots were shredded and dipped in aqueous solutions containing chlorine (100 ppm, 2 min), hydrogen peroxide (1.5%, 2 min) or water (2 min). The content of CHA in treated carrots was evaluated before and after 48 h of storage (19 ± 2 °C). RESULTS: The control carrots sanitized only before peeling and shredding showed 4000% higher content of CHA as compared with time 0 h samples. However, carrots treated with washing/sanitizing procedures post-shredding including water, chlorine and hydrogen peroxide showed a decrease in the accumulation of CHA by 46.9%, 53.6% and 89.9%, respectively. CONCLUSIONS: The results demonstrated that washing/sanitizing procedures applied after fresh-cutting are potentially detrimental to the wound-induced accumulation of health-promoting compounds during storage of fresh produce. Thus, the fresh-cut industry could consider avoiding washing procedures after cutting and implement alternative sanitizing procedures that avoid the partial removal of the wound signal, such as sanitizing only before cutting. © 2020 Society of Chemical Industry.

NAC Family Transcription Factors in Carrot: Genomic and Transcriptomic Analysis and Responses to Abiotic Stresses.

Carrot is an annual or biennial herbaceous plant of the Apiaceae family. Carrot is an important vegetable, and its fresh taproot, which contains rich nutrients, is the main edible part. In the life cycle of carrot, NAC family transcription factors (TFs) are involved in almost all physiological processes. The function of NAC TFs in carrot remains unclear. In this study, 73 NAC family TF members in carrot were identified and characterized using transcriptome and genome databases. These members were divided into 14 subfamilies. Multiple sequence alignment was performed, and the conserved domains, common motifs, phylogenetic tree, and interaction network of DcNAC proteins were predicted and analyzed. Results showed that the same group of NAC proteins of carrot had high similarity. Eight DcNAC genes were selected to detect their expression profiles under abiotic stress treatments. The expression levels of the selected DcNAC genes significantly increased under treatments with low temperature, high temperature, drought, and salt stress. Results provide potentially useful information for further analysis of the roles of DcNAC transcription factors in carrot.

Ultrasonication assisted salt-spices impregnation in black carrots to attain anthocyanins stability, quality retention and antimicrobial efficacy on hot-air convective drying.

The present study aims at optimisation of enhanced solute impregnation through ultrasonication (US) at 37 kHz using central composite design of response surface methodology (RSM). Black carrots were blanched at 98 °C/3 min followed by immersion in salt-spices based solutions for 8 h, treated with bath sonication at specific intervals (2, 4 & 6 h) for 5, 10 and 15 min. Responses for optimum water loss (WL), solute gain (SG), anthocyanins retention, texture and highest antioxidant activity were optimized in effect of NaCl%, spices mix% and US time. The suggested models were of good fit while lack of fit as non-significant (p < 0.0500). Best combination was compared for anthocyanins retention on pressure-cooking (120 °C/15 psi) with fresh, blanched, salt-spiced without US subjected to hot-air convective drying (55 °C/5 h). Ultrasonication-assisted salt-spiced convective dried (USPCD) carrots retained highest anthocyanin content (41%) post cooking which correlated with increased glass transition (Tg) and antimicrobial efficacy (as zone of inhibition) in comparison to fresh, blanched convective dried (BCD) and salt-spiced convective dried (SPCD) carrots. FTIR spectra suggested the correlation of textural effects with pectin degradation and solute impregnation. XRD spectra revealed changes in pectin (2θ = 22.06°) and NaCl crystallinity peaks at 2θ = 27.49, 31.86, 45.62, 56.68, 66.45 and 75.43°, owing to the processing of black carrots. The spectra also confirmed higher solute impregnation in USPCD than SPCD carrots. Scanning electron micrographs of USPCD also indicated higher impregnation through smallest pores visible in longitudinal section of carrot tissue structure, which also appeared to be polymeric network filled with higher solutes than SPCD. Taken together, US assisted solute impregnation might have provided protection to the anthocyanins degradation as well as retention of other quality parameters on processing.

Combined biofortification of carrot with iodine and selenium.

The aim of a three-year study was to assess the effect of combined biofortification with I and Se in carrot. Four cultivars ('Askona' F1, 'Samba' F1, 'Kazan' F1 and 'White Satin') were grown in soil fertilized with KI (4 kg I ha-1) and Na2SeO4 (0.25 kg Se ha-1). The I + Se fertilization did not affect yield but the plants of all cultivars accumulated both elements in leaves and roots. On average, the I and Se contents in roots increased 7.7-times for I and 4.9-times for Se as well as the average I:Se molar ratio was 0.28:1. The contents of both elements in roots remained well below the hazard threshold thus the intake of 100 g of biofortified carrot would substantially cover the RDA for I and Se. The changes in chemical composition of roots (nitrates, phenolic compounds, sugars, carotenoids, macro-, microelements and cadmium) were rather year-dependent than affected by the applied I + Se fertilization.

Composting of municipal solid waste by different methods improved the growth of vegetables and reduced the health risks of cadmium and lead.

Reutilization of putrescible municipal solid wastes (MSW) in agriculture can provide valuable plant nutrients. However, it may pose serious noncarcinogenic health risks for a human when contaminants, especially the heavy metals in MSW, end up in plants through the waste-soil-plant continuum. This study examined the effects of composting methods viz. aerobically (AC), anaerobically (ANC), and aerobic-anaerobically (AANC) composted MSW material on (i) fertilizer value: vegetable yield, nitrogen (N) mineralization, and apparent N recovery (ANR); and (ii) associated health risks: selected heavy metal concentration, daily intake of metals (DIM), health risk index (HRI), hazard index (HI), and target hazard quotient (THQ) when applied to a loamy soil. All the aforementioned compost materials were incorporated into the sandy loam soil filled in pots and carrot and spinach were cultivated for 85 and 90 days, respectively. After soil application, between 51 and 56% of the applied organic N was mineralized from ANC material, while the values in case of AC and AANC were 26-31% and 34-40%, respectively. Consequently, dry matter yield and vegetable N uptake from composts were in the order ANC > AANC > AC (P < 0.05). Further, vegetable ANR was the highest from ANC (56 and 56%) than AANC (42 and 45%), and AC (30 and 33%) for spinach and carrot, respectively (P < 0.05). Interestingly, plant uptake of lead and cadmium was lowest from ANC as compared to AC or AANC (P < 0.05), irrespective of the vegetable type. Consequently, DIM, HRI, and THQ for these metals were substantially lower in the former as compared to the latter compost materials. Further, HI from ANC material was 50% lower over the unfertilized control indicating the absence of noncarcinogenic human health risks via vegetable intake. This all indicates that from viewpoint of sustainable waste recycling in agriculture, anaerobic composting is superior to the other composting methods.

Effect of diflufenican on total carotenoid and phytoene production in carrot suspension-cultured cells.

MAIN CONCLUSION: Diflufenican increased 493-fold the level of phytoene. Diflufenican-induced inhibition of phytoene desaturase gene expression in carrot cells resulted in an increased production of phytoene. This work analyzes the effect of diflufenican, an inhibitor of phytoene desaturase, on the gene expression profiles of the biosynthetic pathway of carotenoids related with the production of these compounds in carrot cell cultures. The results showed that the presence of 10 µM diflufenican in the culture medium increased phytoene levels, which was 493-fold higher than in control cells after 7 days of treatment but did not alter cell growth in carrot cell cultures. The maximal production of phytoene was reached with 10 µM diflufenican after 7 days of incubation in the presence of light and with 30 g/L sucrose in the culture medium. Moreover, diflufenican decreased the expression of phytoene synthase and phytoene desaturase genes at all the times studied. This diflufenican-induced inhibition of phytoene desaturase gene expression in carrot cell cultures resulted in an increased production of phytoene. Our results provide new insights into the action of diflufenican in carrot cell cultures, which could represent an alternative more sustainable and environmentally friendly system to produce phytoene than those currently used.

Exogenous brassinosteroids altered cell length, gibberellin content, and cellulose deposition in promoting carrot petiole elongation.

Brassinosteroid (BR) is a predominant plant hormone in regulating cell elongation and cell size. BR-deficient mutants display reduced plant growth and dwarfism in Arabidopsis and rice. In carrot, BRs promote petiole elongation, but its underlying mechanism involving exogenous BR remains unknown. Here, weighted gene co-expression network analysis and promoter region analysis were adopted to identify the potential genes that interacted with DcBZR1/BES1. Bioactive gibberellin (GA) level and cellulose deposition were also determined in the control and treated plants. Quantitative real-time PCR was performed to detect the expression profiles of GA biosynthesis-related genes, GA signaling genes, and cellulose synthase genes. Bioactive GA level and cellulose deposition were upregulated after the petioles were treated with 24-epibrassinolide (24-EBL). The most putative DcBZR1/BES1 genes were clustered in yellow module. The expression level of DCAR_009411 (a GA5-like gene) was significantly induced after 3 h of treatment. The expression levels of DCAR_019754 and DCAR_013973 (CESA-like genes) were also significantly induced after 3 h of 24-EBL treatment. Our results suggested that the effect of BR on carrot petiole growth was quick. These results also provided potential insights into the mechanism by which BRs modulate GA and cellulose synthesis to promote cell elongation in carrot petioles.

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.

Effect of terbinafine on the biosynthetic pathway of isoprenoid compounds in carrot suspension cultured cells.

KEY MESSAGE: Terbinafine induced a significant increase of squalene production. Terbinafine increased the expression levels of squalene synthase. Cyclodextrins did not work as elicitors due to the gene expression levels obtained. Plant sterols are essential components of membrane lipids, which contributing to their fluidity and permeability. Besides their cholesterol-lowering properties, they also have anti-inflammatory, antidiabetic and anticancer activities. Squalene, which is phytosterol precursor, is widely used in medicine, foods and cosmetics due to its anti-tumor, antioxidant and anti-aging activities. Nowadays, vegetable oils constitute the main sources of phytosterols and squalene, but their isolation and purification involve complex extraction protocols and high costs. In this work, Daucus carota cell cultures were used to evaluate the effect of cyclodextrins and terbinafine on the production and accumulation of squalene and phytosterols as well as the expression levels of squalene synthase and cycloartenol synthase genes. D. carota cell cultures were able to produce high levels of extracellular being phytosterols in the presence of cyclodextrins (12 mg/L), these compounds able to increase both the secretion and accumulation of phytosterols in the culture medium. Moreover, terbinafine induced a significant increase in intracellular squalene production, as seen after 168 h of treatment (497.0 ± 23.5 µg g dry weight-1) while its extracellular production only increased in the presence of cyclodextrins.The analysis of sqs and cas gene expression revealed that cyclodextrins did not induce genes encoding enzymes involved in the phytosterol biosynthetic pathway since the expression levels of sqs and cas genes in cyclodextrin-treated cells were lower than in control cells. The results, therefore, suggest that cyclodextrins were only able to release phytosterols from the cells to the extracellular medium, thus contributing to their acumulation. To sum up, D. carota cell cultures treated with cyclodextrins or terbinafine were able to produce high levels of phytosterols and squalene, respectively, and, therefore, these suspension-cultured cells of carrot constitute an alternative biotechnological system, which is at the same time more sustainable, economic and ecological for the production of these bioactive compounds.

Effects of hydrogen sulfide on the surface whitening and physiological responses of fresh-cut carrots.

BACKGROUND: The effect of hydrogen sulfide (H2 S) on the inhibition of the surface whitening of fresh-cut carrots was investigated. Whitening index; H2 O2 and malondialdehyde (MDA) contents; activities of catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POD); and antioxidant capacities were evaluated. RESULTS: H2 S treatment significantly inhibited the surface whitening of fresh-cut carrots (P < 0.05), reduced the accumulation of H2 O2 and MDA, and enhanced antioxidant enzymes (CAT, APX and GR) activities and antioxidant capacities (P < 0.05). The PAL, PPO and POD activities of fresh-cut carrots were inhibited by treatment with H2 S (P < 0.05). Furthermore, correlation analysis revealed that whitening index was significantly positively correlated with H2 O2 content, lipid peroxidation, PPO and POD activities. CONCLUSION: H2 S inhibited the surface whitening of fresh-cut carrots by reducing H2 O2 accumulation and lipid peroxidation, and also inhibited PPO and POD activities. © 2018 Society of Chemical Industry.

Ozone treatment for pesticide removal from carrots: Optimization by response surface methodology.

The present study aimed to optimize ozone (O3) treatments, as gas and dissolved in water, to remove difenoconazole and linuron in carrots. We employed a central composite design to study three variables governing the efficacy of treatments: O3 concentration, temperature and treatment time. The temperature did not influence the efficacy of treatments. The removal percentage of pesticides increases with increases in ozone concentration and the time of treatment. O3 application promoted the removal of more than 80% of pesticides when the roots were exposed for approximately 120min at 5 and 10mgL-1, respectively, in treatments with O3 as gas and dissolved in water. After storage, pesticide removal was higher than 98% for difenoconazole and 95% for linuron. The degradation products from the pesticides resulting from treatment were monitored, but none were found. This is the first report demonstrating the removal of difenoconazole and linuron from carrots by ozone.

Foliar-applied ethephon enhances the content of anthocyanin of black carrot roots (Daucus carota ssp. sativus var. atrorubens Alef.).

BACKGROUND: Black carrots (Daucus carota ssp. sativus var. atrorubens Alef.) constitute a valuable source of anthocyanins, which are used as natural red, blue and purple food colourants. Anthocyanins and phenolic compounds are specialised metabolites, accumulation of which often requires elicitors, which act as molecular signals in plant stress responses. In the present study, ethephon, an ethylene-generating compound was explored as enhancer of anthocyanin and phenolic contents during growth of 'Deep Purple' black carrots. The effects of ethephon on several parameters were investigated, and the expression of biosynthetic anthocyanin genes was studied during growth and anthocyanin accumulation. RESULTS: Roots of ethephon-treated carrot plants exhibited an increase in anthocyanin content of approximately 25%, with values ranging from 2.25 to 3.10 mg g-1 fresh weight, compared with values ranging from 1.50 to 1.90 mg g-1 fresh weight in untreated roots. The most rapid accumulation rate for anthocyanins, phenolic compounds, soluble solids and dry matter was observed between 10 and 13 weeks after sowing in both untreated and ethephon-treated carrots. The differences in anthocyanin contents between untreated and treated carrots increased for several weeks after the ethephon treatment was terminated. Five cyanidin-based anthocyanin forms were identified, with variable relative abundance values detected during root growth. Overall, the expression of the anthocyanin biosynthetic genes analysed (PAL1, PAL3, F3H1, DFR1, LDOX2) increased in response to ethephon treatment, as did the expression of the MYB1 transcription factor, which is associated with activation of the phenylpropanoid pathway under stress conditions. In addition, a correlation was proposed between ethylene and sugar contents and the induction of anthocyanin synthesis. CONCLUSIONS: This study presents a novel method for enhancing anthocyanin content in black carrots. This finding is of economic importance as increased pigment concentration per unit of biomass implies improved profitability parameters in food colour production. We provide new insight into the accumulation patterns of the different cyanidin-based anthocyanins and phenolic compounds during root growth. Moreover, we show that enhanced anthocyanin content in ethephon-treated carrots is accompanied by increased expression of anthocyanin biosynthetic genes.

Exogenous gibberellin enhances secondary xylem development and lignification in carrot taproot.

Gibberellins (GAs) are important growth regulators involved in plant development processes. However, limited information is known about the relationship between GA and xylogenesis in carrots. In this study, carrot roots were treated with GA3. The effects of applied GA3 on root growth, xylem development, and lignin accumulation were then investigated. Results indicated that GA treatment dose-dependently inhibited carrot root growth. The cell wall significantly thickened in the xylem parenchyma. Autofluorescence analysis with ultraviolet (UV) excitation indicated that these cells became lignified because of long-term GA3 treatment. Moreover, lignin content increased in the roots, and the transcripts of lignin biosynthesis genes were altered in response to applied GA3. Our data indicate that GA may play important roles in xylem growth and lignification in carrot roots. Further studies shall focus on regulating plant lignification, which may be achieved by modifying GA levels within plant tissues.

Analysis of the use of microcystin-contaminated water in the growth and nutritional quality of the root-vegetable, Daucus carota.

Toxic cyanobacterial blooms are often observed in freshwaters and may reflect the increased eutrophication of these environments and alterations in climate. Cyanotoxins, such as microcystins (MCs), are an effective threat to many life forms, ranging from plants to humans. Despite the research conducted to date on cyanotoxins, the risks associated to the use of contaminated water in agriculture require further elucidation. To tackle this aim, a research was conducted with the root-vegetable Daucus carota. The specific aims of this work were the following: (i) to evaluate the effects of MC-LR on the plant growth and photosynthesis; (ii) to evaluate the nutritional quality of carrot roots; and (iii) to measure bioaccumulation. To this purpose, young carrots were grown in soil during 1 month in natural conditions and exposed to Mycrocystis aeruginosa aqueous extracts containing environmentally realistic concentrations of MC-LR (10 and 50 MC-LR µg/L). The results showed that MC-LR may decrease root growth after 28 days of exposure to 50 µg/L and increase photosynthetic efficiency. We also observed changes in mineral and vitamin content in carrots as a result of the exposure to contaminated water. Moreover, MC-LR was detected in carrot roots by ELISA at very low concentration 5.23 ± 0.47 ng MC eq./g FW. The soil retained 52.7 % of the toxin potentially available for plants. This result could be attributed to MC-LR adsorption by soil particles or due to microbial degradation of the toxin. We conclude that the prolonged use of MC-LR-contaminated water may affect crop growth, alter the nutritional value of vegetable products, and potentiate contamination.