Genotype influences sulfur metabolism in broccoli (Brassica oleracea L.) under elevated CO2 and NaCl stress

RNA sequencing-based exploration of the effects of far-red light on microRNAs involved in the shade-avoidance response of D. officinale

Dendrobium officinale (D. officinale) has remarkable medicinal functions and high economic value. The shade-avoidance response to far-red light importantly affects the D. officinale productivity. However, the regulatory mechanism of miRNAs involved in the far-red light-avoidance response is unknown. Previous studies have found that, in D. officinale, 730 nm (far-red) light can promote the accumulation of plant metabolites, increase leaf area, and accelerate stem elongation. Here, the effects of far-red light on D. officinale were analysed via RNA-seq. KEGG analysis of miRNA target genes revealed various far-red light response pathways, among which the following played central roles: the one-carbon pool by folate; ascorbate and aldarate; cutin, suberine and wax biosynthesis; and sulfur metabolism. Cytoscape analysis of DE miRNA targets showed that novel_miR_484 and novel_miR_36 were most likely involved in the effects of far-red light on the D. officinale shade avoidance. Content verification revealed that far-red light promotes the accumulation of one-carbon compounds and ascorbic acid. Combined with qPCR validation results, the results showed that miR395b, novel_miR_36, novel_miR_159, novel_miR_178, novel_miR_405, and novel_miR_435 may participate in the far-red light signalling network through target genes, regulating the D. officinale shade avoidance. These findings provide new ideas for the efficient production of D. officinale.

Enriched-biochar application increases broccoli nutritional and phytochemical content without detrimental effect on yield

BACKGROUND

Soil fertility is a major concern during vegetable production. Conventional versus organic fertilization has been studied in order to conserve soil properties. While some reports point out an increase in food nutritional properties, the loss of crop yield under organic conditions continues to be a problem. Thus, an experiment with broccoli in the field was carried out, comparing crop management under conventional fertilization (CF) and two soil amendment treatments: manure pellet (M) and an enriched-biochar (EB) supplemented by an organic fertilizer (AND) applied alone (M + CF; EB+AND) or in combination (M + EB + AND). Crop yield and the nutritional properties in the flowering heads (mineral content, phenolic compounds and glucosinolates (GSLs)), were determined.

RESULTS

Enriched-biochar and manure as a standalone amendment resulted in higher crop yield regarding CF, but not when they were applied in combination. The number of flowering heads with no-commercial characteristics was lower after enriched-biochar soil application. Finally, enriched-biochar treatment enhanced NO₃ ^- , PO₄ ^3- and SO₄ ^2- levels in the flowering heads, and some of the ion contents can be associated with mineral changes in the soil after the biochar amendment. Also, the contents of phenolic compounds and indole GSLs were higher after enriched-biochar application compared with the other treatments, GSL increase being due to the higher percentage of sulfur in the plant rather that an adequate N/S ratio.

CONCLUSION

Application of enriched-biochar amendment in the cultivation of broccoli is appropriate, since there are no losses of yield and an increase in nutritional compounds in the flowering heads. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Effects of Plant Hormones, Metal Ions, Salinity, Sugar, and Chemicals Pollution on Glucosinolate Biosynthesis in Cruciferous Plant

Cruciferous vegetable crops are grown widely around the world, which supply a multitude of health-related micronutrients, phytochemicals, and antioxidant compounds. Glucosinolates (GSLs) are specialized metabolites found widely in cruciferous vegetables, which are not only related to flavor formation but also have anti-cancer, disease-resistance, and insect-resistance properties. The content and components of GSLs in the Cruciferae are not only related to genotypes and environmental factors but also are influenced by hormones, plant growth regulators, and mineral elements. This review discusses the effects of different exogenous substances on the GSL content and composition, and analyzes the molecular mechanism by which these substances regulate the biosynthesis of GSLs. Based on the current research status, future research directions are also proposed.

Influence of Cabbage (Brassica oleracea) Accession and Growing Conditions on Myrosinase Activity, Glucosinolates and Their Hydrolysis Products

Glucosinolates are secondary plant metabolites present in Brassica vegetables. The endogenous enzyme myrosinase is responsible for the hydrolysis of glucosinolates, yielding a variety of compounds, including health-promoting isothiocyanates. The influence of cabbage accession and growing conditions on myrosinase activity, glucosinolates (GSL) and their hydrolysis products (GHPs) of 18 gene-bank cabbage accessions was studied. Growing conditions, cabbage morphotype and accession all significantly affected myrosinase activity and concentration of glucosinolates and their hydrolysis products. In general, cabbages grown in the field with lower growth temperatures had significantly higher myrosinase activity than glasshouse samples. Profile and concentration of glucosinolates and their hydrolysis products differed across the accessions studied. Aliphatic glucosinolates accounted for more than 60 % of total glucosinolates in most of the samples assessed. Nitriles and epithionitriles were the most abundant hydrolysis products formed. The results obtained showed that consumption of raw cabbages might reduce the amount of beneficial hydrolysis products available to the consumer, as more nitriles were produced from hydrolysis compared to beneficial isothiocyanates. However, red and white cabbages contained high concentrations of glucoraphanin and its isothiocyanate, sulforaphane. This implies that careful selection of accessions with ample concentrations of certain glucosinolates can improve the health benefits derived from raw cabbage consumption.

Exposure to Salinity and Light Spectra Regulates Glucosinolates, Phenolics, and Antioxidant Capacity of Brassica carinata L. Microgreens

The effect of salt treatment on Brassica carinata (BC) microgreens grown under different light wavelengths on glucosinolates (GLs) and phenolic compounds were evaluated. Quantifiable GLs were identified using ultra-high performance-quadrupole time of flight mass spectrometry. Extracts' ability to activate antioxidant enzymes (superoxide dismutase (SOD) and catalase (CAT)) was evaluated on human colorectal carcinoma cells (HCT116). Furthermore, BC compounds' ability to activate expression of nuclear transcription factor-erythroid 2 related factor (Nrf2) and heme-oxygenase-1 (HO-1) proteins was examined using specific antibodies on HCT116 cells. Sinigrin (SIN) was the abundant GLs of the six compounds identified and its content together with total aliphatic GLs increased in saline conditions. Fluorescent (FL) and blue plus red (B1R1) lights were identified as stable cultivation conditions for microgreens, promoting biomass and glucobrassicin contents, whereas other identified individual and total indole GLs behaved differently in saline and non-saline environments. Blue light-emitting diodes and FL light in saline treatments mostly enhanced SIN, phenolics and antioxidant activities. The increased SOD and CAT activities render the BC microgreens suitable for lowering oxidative stress. Additionally, activation of Nrf2, and HO-1 protein expression by the GLs rich extracts, demonstrate their potential to treat and prevent oxidative stress and inflammatory disorders. Therefore, effective salt treatments and light exposure to BC microgreens present an opportunity for targeted regulation of growth and accumulation of bioactive metabolites.

Environmental Conditions and Agronomical Factors Influencing the Levels of Phytochemicals in Brassica Vegetables Responsible for Nutritional and Sensorial Properties

Recently, the consumption of healthy foods has been related to the prevention of cardiovascular, degenerative diseases and different forms of cancers, underlying the importance of the diet for the consumer’s health. Fruits and vegetables contain phytochemicals that act as protective factors for the human body, through different mechanisms of action. Among vegetables, Brassica received a lot of attention in the last years for the phytochemical compounds content and antioxidant capacity that confer nutraceutical value to the product. The amount of healthy bioactive compounds present in the Brassica defines the nutritional quality. These molecules could belong to the class of antioxidant compounds (e.g., phenols, vitamin C, etc.), or to non-antioxidant compounds (e.g., minerals, glucosinolates, etc.). The amount of these compounds in Brassica vegetables could be influenced by several factors, depending on the genotypes, the environmental conditions and the cultivation techniques adopted. The aim of this study is to highlight the main phytochemical compounds present in brassicas used as a food vegetable that confer nutritional and sensorial quality to the final product, and to investigate the main factors that affect the phytochemical concentration and the overall quality of Brassica vegetables.

Human, Animal and Plant Health Benefits of Glucosinolates and Strategies for Enhanced Bioactivity: A Systematic Review

Glucosinolates (GSs) are common anionic plant secondary metabolites in the order Brassicales. Together with glucosinolate hydrolysis products (GSHPs), they have recently gained much attention due to their biological activities and mechanisms of action. We review herein the health benefits of GSs/GSHPs, approaches to improve the plant contents, their bioavailability and bioactivity. In this review, only literature published between 2010 and March 2020 was retrieved from various scientific databases. Findings indicate that these compounds (natural, pure, synthetic, and derivatives) play an important role in human/animal health (disease therapy and prevention), plant health (defense chemicals, biofumigants/biocides), and food industries (preservatives). Overall, much interest is focused on in vitro studies as anti-cancer and antimicrobial agents. GS/GSHP levels improvement in plants utilizes mostly biotic/abiotic stresses and short periods of phytohormone application. Their availability and bioactivity are directly proportional to their contents at the source, which is affected by methods of food preparation, processing, and extraction. This review concludes that, to a greater extent, there is a need to explore and improve GS-rich sources, which should be emphasized to obtain natural bioactive compounds/active ingredients that can be included among synthetic and commercial products for use in maintaining and promoting health. Furthermore, the development of advanced research on compounds pharmacokinetics, their molecular mode of action, genetics based on biosynthesis, their uses in promoting the health of living organisms is highlighted.

Myrosinase: insights on structural, catalytic, regulatory, and environmental interactions

Glucosinolate-myrosinase is a substrate-enzyme defense mechanism present in Brassica crops. This binary system provides the plant with an efficient system against herbivores and pathogens. For humans, it is well known for its anti-carcinogenic, anti-inflammatory, immunomodulatory, anti-bacterial, cardio-protective, and central nervous system protective activities. Glucosinolate and myrosinase are spatially present in different cells that upon tissue disruption come together and result in the formation of a variety of hydrolysis products with diverse physicochemical and biological properties. The myrosinase-catalyzed reaction starts with cleavage of the thioglucosidic linkage resulting in release of a D-glucose and an unstable thiohydroximate-O-sulfate. The outcome of this thiohydroximate-O-sulfate has been shown to depend on the structure of the glucosinolate side chain, the presence of supplementary proteins known as specifier proteins and/or on the physiochemical condition. Myrosinase was first reported in mustard seed during 1939 as a protein responsible for release of essential oil. Until this date, myrosinases have been characterized from more than 20 species of Brassica, cabbage aphid, and many bacteria residing in the human intestine. All the plant myrosinases are reported to be activated by ascorbic acid while aphid and bacterial myrosinases are found to be either neutral or inhibited. Myrosinase catalyzes hydrolysis of the S-glycosyl bond, O-β glycosyl bond, and O-glycosyl bond. This review summarizes information on myrosinase, an essential component of this binary system, including its structural and molecular properties, mechanism of action, and its regulation and will be beneficial for the research going on the understanding and betterment of the glucosinolate-myrosinase system from an ecological and nutraceutical perspective.

Exposure of kale root to NaCl and Na2SeO3 increases isothiocyanate levels and Nrf2 signalling without reducing plant root growth

A plant factory is a closed cultivation system that provides a consistent and modified environment for plant growth. We speculated that treatment of kale (Brassica oleracea) grown in a plant factory with NaCl, Na₂SeO₃, or both would increase the bioactive phytochemical levels including glucosinolates (GLSs) and isothiocyanates (ITCs), the key molecules in cancer prevention. The kale was harvested and analysed after treatment with NaCl and Na₂SeO₃ alone or in combination for 1 or 2 weeks. Exposure to NaCl alone but not Na₂SeO₃ increased plant root growth. Levels of sinigrin were increased by a 2-week exposure to Na₂SeO₃ alone or in combination with NaCl, whereas no changes were observed in glucoraphanin and gluconasturtiin gluconasturtiin levels. Importantly, the ITC concentration was affected by 2-week treatment with both compounds. To evaluate the bioactivity of kale, HepG2 human hepatoma cells were treated with plant extract for 6 h. Only the extract of kale roots exposed to a combination NaCl and Na₂SeO₃ for 2 weeks showed an increased expression of nuclear factor erythroid 2-related factor (Nrf2), which regulates genes encoding antioxidant proteins. These data suggest that co-treatment with NaCl and Na₂SeO₃ increased the ITC content and chemopreventive effects of kale root.

Metabolic Profiling in Chinese Cabbage (Brassica rapa L. subsp. pekinensis) Cultivars Reveals that Glucosinolate Content Is Correlated with Carotenoid Content

A total of 38 bioactive compounds, including glucosinolates, carotenoids, tocopherols, sterols, and policosanols, were characterized from nine varieties of Chinese cabbage (Brassica rapa L. subsp. pekinensis) to determine their phytochemical diversity and analyze their abundance relationships. The metabolite profiles were evaluated with principal component analysis (PCA), Pearson correlation analysis, and hierarchical clustering analysis (HCA). PCA and HCA identified two distinct varieties of Chinese cabbage (Cheonsangcheonha and Waldongcheonha) with higher levels of glucosinolates and carotenoids. Pairwise comparisons of the 38 metabolites were calculated using Pearson correlation coefficients. The HCA, which used the correlation coefficients, clustered metabolites that are derived from closely related biochemical pathways. Significant correlations were discovered between chlorophyll and carotenoids. Additionally, aliphatic glucosinolate and carotenoid levels were positively correlated. The Cheonsangcheonha and Waldongcheonha varieties appear to be good candidates for breeding because they have high glucosinolate and carotenoid levels.

Characterization of the Chloride Channel-Like, AtCLCg, Involved in Chloride Tolerance in Arabidopsis thaliana

In plant cells, anion channels and transporters are essential for key functions such as nutrition, ion homeostasis and resistance to biotic or abiotic stresses. We characterized AtCLCg, a member of the chloride channel (CLC) family in Arabidopsis localized in the vacuolar membrane. When grown on NaCl or KCl, atclcg knock-out mutants showed a decrease in biomass. In the presence of NaCl, these mutants overaccumulate chloride in shoots. No difference in growth was detected in response to osmotic stress by mannitol. These results suggest a physiological function of AtCLCg in the chloride homeostasis during NaCl stress. AtCLCg shares a high degree of identity (62%) with AtCLCc, another vacuolar CLC essential for NaCl tolerance. However, the atclcc atclccg double mutant is not more sensitive to NaCl than single mutants. As the effects of both mutations are not additive, gene expression analyses were performed and revealed that: (i)AtCLCg is expressed in mesophyll cells, hydathodes and phloem while AtCLCc is expressed in stomata; and (ii)AtCLCg is repressed in the atclcc mutant background, and vice versa. Altogether these results demonstrate that both AtCLCc and AtCLCg are important for tolerance to excess chloride but not redundant, and form part of a regulatory network controlling chloride sensitivity.

Physiological and Transcriptome Responses to Combinations of Elevated CO2 and Magnesium in Arabidopsis thaliana

The unprecedented rise in atmospheric CO2 concentration and injudicious fertilization or heterogeneous distribution of Mg in the soil warrant further research to understand the synergistic and holistic mechanisms involved in the plant growth regulation. This study investigated the influence of elevated CO2 (800 μL L(-1)) on physiological and transcriptomic profiles in Arabidopsis cultured in hydroponic media treated with 1 μM (low), 1000 μM (normal) and 10,000 μM (high) Mg2+. Following 7-d treatment, elevated CO2 increased the shoot growth and chlorophyll content under both low and normal Mg supply, whereas root growth was improved exclusively under normal Mg nutrition. Notably, the effect of elevated CO2 on mineral homeostasis in both shoots and roots was less than that of Mg supply. Irrespective of CO2 treatment, high Mg increased number of young leaf but decreased root growth and absorption of P, K, Ca, Fe and Mn whereas low Mg increased the concentration of P, K, Ca and Fe in leaves. Transcriptomics results showed that elevated CO2 decreased the expression of genes related to cell redox homeostasis, cadmium response, and lipid localization, but enhanced signal transduction, protein phosphorylation, NBS-LRR disease resistance proteins and subsequently programmed cell death in low-Mg shoots. By comparison, elevated CO2 enhanced the response of lipid localization (mainly LTP transfer protein/protease inhibitor), endomembrane system, heme binding and cell wall modification in high-Mg roots. Some of these transcriptomic results are substantially in accordance with our physiological and/or biochemical analysis. The present findings broaden our current understanding on the interactive effect of elevated CO2 and Mg levels in the Arabidopsis, which may help to design the novel metabolic engineering strategies to cope with Mg deficiency/excess in crops under elevated CO2.

Health-promoting compounds of broccoli (Brassica oleracea L. var. italica) plants as affected by nitrogen fertilisation in projected future climatic change environments

BACKGROUND

The complex interactions between CO2 increase and salinity were investigated in relation to decreased N supply, in order to determine the nutritional quality of broccoli (Brassica oleracea L. var. italica) plants under these conditions. Three different decreased N fertilisation regimes (NO3(-)/NH4(+) ratios of 100:0, 50:50 and 0:100 respectively) were combined with ambient (380 ppm) and elevated (800 ppm) [CO2 ] under non-saline (0 mmol L(-1) NaCl) and saline (80 mmol L(-1) NaCl) conditions. Nutrients (minerals, soluble protein and total amino acids) and natural antioxidants (glucosinolates, phenolic acids, flavonoids and vitamin C) were determined.

RESULTS

In NH4(+) -fed broccoli plants, a marked growth reduction was shown and a redistribution of amino acids to cope with NH4(+) toxicity resulted in higher levels of indolic glucosinolate and total phenolic compounds. However, the positive effect of the higher [CO2] - ameliorating adverse effects of salinity--was only observed when N was supplied as NO3(-). Under reduced N fertilisation, the total glucosinolates were increased by a decreased NO3(-)/NH4 (+) ratio and elevated [CO2] but were unaffected by salinity.

CONCLUSION

Under future climatic challenges, such as increased salinity and elevated [CO2], a clear genotypic dependence of S metabolism was observed in broccoli plants. In addition, an influence of the form in which N was supplied on plant nutritional quality was observed; a combined NO3(-)/NH4(+) (50:50) supply allowed broccoli plants not only to deal with NH4(+) toxicity but also to modify their glucosinolate content and profile. Thus, for different modes of N fertilisation, the interaction with climatic factors must be considered in the search for an optimal balance between yield and nutritional quality.

The role of promoter cis-element, mRNA capping, and ROS in the repression and salt-inducible expression of AtSOT12 in Arabidopsis

Inducible gene expression is a gene regulatory mechanism central to plant response to environmental cues. The inducible genes are often repressed under normal growth conditions while their expression levels are significantly elevated by conditions such as abiotic stresses. Induction of gene expression requires both cis-acting DNA elements and trans-acting proteins that are modulated through signal transduction pathways. Here we report several molecular events that affect salt induced expression of the Arabidopsis AtSOT12 gene. Promoter deletion analysis revealed that DNA elements residing in the 5' UTR are required for the salt induced expression of AtSOT12. Cytosine methylation in the promoter was low and salt stress slightly increased the DNA methylation level, suggesting that DNA methylation may not contribute to AtSOT12 gene repression. Co-transcriptional processing of AtSOT12 mRNA including capping and polyadenylation site selection was also affected by salt stress. The percentage of capped mRNA increased by salt treatment, and the polyadenylation sites were significantly different before and after exposure to salt stress. The expression level of AtSOT12 under normal growth conditions was markedly higher in the oxi1 mutant defective of reactive oxygen species (ROS) signaling than in the wild type. Moreover, AtSOT12 transcript level was elevated by treatments with DPI and DMTU, two chemicals preventing ROS accumulation. These results suggest that repression of AtSOT12 expression may require physiological level of ROS and ROS signaling.