Transcriptomic and metabolomic analyses of Tartary buckwheat roots during cadmium stress

Cadmium (Cd) can adversely damage plant growth. Therefore, understanding the control molecular mechanisms of Cd accumulation will benefit the development of strategies to reduce Cd accumulation in plants. This study performed transcriptomic and metabolomic analyses on the roots of a Cd-tolerant Tartary buckwheat cultivar following 0 h (CK), 6 h (T1), and 48 h (T2) of Cd treatment. The fresh weight and root length were not significantly inhibited under the T1 treatment but they were in the T2 treatment. The root's ultrastructure was seriously damaged in T2 but not in T1 treatment. This was evidenced by deformed cell walls, altered shape and number of organelles. A total of 449, 999 differentially expressed genes (DEGs) and eight, 37 differentially expressed metabolites (DEMs) were identified in the CK versus T1 and CK versus T2 comparison, respectively. DEGs analysis found that the expression of genes related to cell wall function, glutathione (GSH) metabolism, and phenylpropanoid biosynthesis changed significantly during Cd stress. Several WRKY, MYB, ERF, and bHLH transcription factors and transporters also responded to Cd treatment. Our results indicate that Cd stress affects cell wall function and GSH metabolism and that changes in these pathways might contribute to mechanisms of Cd tolerance in Tartary buckwheat.

Increasing Antioxidant Activity in Food Waste Extracts by β-Glucosidase

Research background

Food by-products such as onion peels and olive leaves are rich in bioactive compounds applicable as natural and low-cost sources of antioxidants. Still, these compounds mainly exist in glycosylated form. Often, hydrolysis of glycoside compounds increases their antioxidant activity and health benefits. However, not many studies have been done concerning the β-glucosidase effect, specifically from Aspergillus niger, on glycosylated compounds within these by-products. Also, changes in the antioxidant activity of the mentioned by-products under the effect of β-glucosidase have not been reported yet. Therefore, this study considers the effect of A. niger β-glucosidase on glucoside compounds and the antioxidant activity of onion peel and olive leaf extracts.

Experimental approach

The antioxidant activity of the extracts was determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays. Also, glucose, total phenolic and flavonoid contents were measured. Moreover, TLC and HPLC analyses were performed before and after the enzymatic hydrolysis.

Results and conclusions

The obtained results showed an increase in the extract antioxidant activity after treatment. Also, β-glucosidase increased the glucose content of the extracts. The thin layer chromatography (TLC) and high-performance liquid chromatography (HPLC) results showed the β-glucosidase efficacy to hydrolyze quercetin glucosides in onion peel extract, and the quercetin concentration increased from (0.48±0.04) mg/mL in the untreated extract to (1.26±0.03) mg/mL in the treated extract (0.5% m/V) after 3 h of enzymatic hydrolysis at 45 °C. Also, the content of quercetin-3-O-glucoside increased considerably from (1.8±0.1) to (54±9) µg/mL following the enzyme treatment. Moreover, oleuropein in olive leaf extract (1% m/V) was hydrolyzed completely from (0.382±0.016) to 0 mg/mL by β-glucosidase for 24 h at 50 °C.

Novelty and scientific contribution

This study showed that A. niger β-glucosidase, as a stable enzyme, hydrolyzed quercetin and oleuropein glycosides in onion peel and olive leaf extracts. Thus, A. niger β-glucosidase is a good candidate for processing the food waste and extracting valuable bioactive compounds. Also, the treated extracts with higher antioxidant and biological activity, and without bitter taste can be applicable as potent, natural and cost-effective antioxidants in the food industry.

Breeding of Buckwheat for Usage of Sprout and Pre-Harvest Sprouting Resistance

Buckwheat is recognized as an important traditional crop and supports local economies in several regions around the world. Buckwheat is used, for example, as a cereal grain, noodle and bread. In addition, buckwheat is also used as a sprout or a young seedling. For these foods, sprouting is an important characteristic that affects food quality. For foods made from buckwheat flour, pre-harvest sprouting may decrease yield, which also leads to the deterioration of noodle quality. Breeding buckwheat that is resistant to pre-harvest sprouting is therefore required. Germination and subsequent growth are also important characteristics of the quality of sprouts. Although buckwheat sprouts are the focus because they contain many functional compounds, such as rutin, several problems have been noted, such as thin hypocotyls and husks remaining on sprouts. To date, several new varieties have been developed to resolve these quality issues. In this review, we summarize and introduce research on the breeding of buckwheat related to quality, sprouting and subsequent sprout growth.

Elevated Ozone Levels Affect Metabolites and Related Biosynthetic Genes in Tartary Buckwheat

Global climate change and the industrial revolution have increased the concentration of tropospheric ozone, a photochemical air pollutant that can negatively affect plant growth and crop production. In the present study, we investigated the effects of O₃ on the metabolites and transcripts of tartary buckwheat. A total of 36 metabolites were identified by gas chromatography coupled with time-of-flight mass spectrometry, and principal component analysis was performed to verify the metabolic differences between nontreated and O₃-treated tartary buckwheat. The content of threonic acid increased after 2 days of the O₃ treatment, whereas it decreased after 4 days of exposure, after which it gradually increased until the eighth day of exposure. In addition, the levels of most metabolites decreased significantly after the O₃ treatment. On the contrary, the levels of two anthocyanins, cyanidin-3-O-glucoside and cyanidin-3-O-rutinoside, increased more than 11.36- and 11.43-fold, respectively, after the O₃ treatment. To assess the effect of O₃ on the genomic level, we analyzed the expression of anthocyanin biosynthesis pathway genes in O₃-treated and nontreated buckwheat using quantitative real-time reverse transcription polymerase chain reaction (PCR). We found that the expression of all anthocyanin pathway genes increased significantly in the O₃-treated buckwheat compared to that in the nontreated buckwheat. Altogether, our results suggested that O₃ affected the transcripts and metabolites of tartary buckwheat, which would eventually cause phenotypic changes in plants.

Laser light as a promising approach to improve the nutritional value, antioxidant capacity and anti-inflammatory activity of flavonoid-rich buckwheat sprouts

Buckwheat sprouts are rich in several nutrients such as antioxidant flavonoids that have a positive impact on human health. Although there are several studies reported the positive impact of laser light on crop plants, no studies have applied laser light to enhance the nutritive values of buckwheat sprouts. Herein, the contents of health-promoting minerals, metabolites and enzymes as well as the antioxidant and anti-inflammatory activities were determined in laser-treated (He-Ne laser, 632 nm, 5 mW) common buckwheat (CBW) and tartarybuckwheat (TBW) sprouts. Out of 49 targeted minerals, vitamins, pigments and antioxidants, more than 35 parameters were significantly increased in CBW and/or TBW sprouts by laser light treatment. Also, laser light boosted the antioxidant capacity and anti-inflammatory activities through inhibiting cyclooxygenase-2 and lipoxygenase activities, particularly in TBW sprouts. Accordingly, laser light could be recommended as a promising method to improve the nutritional and health-promoting values of buckwheat sprouts.

Sprouted Grains: A Comprehensive Review

In the last decade, there has been an increase in the use of sprouted grains in human diet and a parallel increase in the scientific literature dealing with their nutritional traits and phytochemical contents. This review examines the physiological and biochemical changes during the germination process, and the effects on final sprout composition in terms of macro- and micro-nutrients and bioactive compounds. The main factors affecting sprout composition are taken into consideration: genotype, environmental conditions experimented by the mother plant, germination conditions. In particular, the review deepens the recent knowledge on the possible elicitation factors useful for increasing the phytochemical contents. Microbiological risks and post-harvest technologies are also evaluated, and a brief summary is given of some important in vivo studies matching with the use of grain sprouts in the diet. All the species belonging to Poaceae (Gramineae) family as well as pseudocereals species are included.

Accumulation of phenylpropanoids and correlated gene expression during the development of tartary buckwheat sprouts

Buckwheat sprouts are considered an excellent dietary source of phenolic compounds. The time duration and amount of light for sprouting strongly affect the nutritional quality of sprouts. In this study, these two factors were investigated in two cultivars of tartary buckwheat sprouts: Hokkai T8 and T10. The transcriptional levels of flavonoid biosynthetic genes were investigated in light/dark- and dark-treated sprouts. Among the main flavonoid biosynthesis structural genes, FtPAL, Ft4CL, FtF3H, FtDFR, and FtANS exhibited higher transcriptional levels than others as compared to that of a housekeeping gene (histone H3) during sprouting; FtF3'H1, FtF3'H2, FtFLS2, and FtANS were substantially upregulated at 2, 4, and 6 days in light/dark-treated T10 sprouts than in dark-treated ones. However, FtDFR was downregulated in 8 and 10 day old light/dark-treated sprouts of both cultivars. High-performance liquid chromatography (HPLC) analysis revealed that increasing the culture time did not affect the accumulation of flavonoids or anthocyanins. However, light contributed the production of anthocyanins in Hokkai T10 sprouts. The anthocyanins included cyanidin 3-O-glucoside, cyanidin 3-O-rutinoside, and delphinidin-3-O-coumarylglucoside, which were identified by HPLC and electrospray ionization-tandem mass spectrometry. Instead of anthocyanins, Hokkai T8 sprouts produced large amounts of 4 flavonoid C-glycosylflavone compounds in both light/dark and dark conditions: orientin, isoorientin, vitexin, and isovitexin. These results indicate that these two types of tartary buckwheat sprouts have different mechanisms for flavonoid and anthocyanin biosynthesis that also vary in light/dark and dark conditions.

AFLP fingerprinting of tartary buckwheat accessions (Fagopyrum tataricum) displaying rutin content variation

In light of the economic importance of buckwheat as well as existence of enormous accessions of Fagopyrum species in the Himalayan regions of India, the characterization of tartary buckwheat for rutin content variation vis-à-vis DNA fingerprinting was undertaken so as to identify fingerprint profiles unique to high rutin content accessions. Rutin content analysis in mature seeds of 195 accessions of Fagopyrum tataricum showed a wide range of variation (6 μg/mg to 30 μg/mg D.W.) with most of the accessions (81%) containing 10-16 μg/mg of rutin followed by 14% accessions with significantly higher rutin content (17 μg/mg to 30 μg/mg) and 5% accessions with low rutin content (≤10 μg/mg). AFLP fingerprinting of 18 accessions having high (≥17 μg/mg) and low rutin content (≤10 μg/mg) with 19 EcoRI/MseI primer combinations yielded 136 polymorphic fragments out of total 907. The hierarchical and model-based cluster analyses of AFLP data strongly suggested that the 18 populations of F. tataricum were clustered into two separate groups. The high and low rutin content accessions were clustered into two separate groups based on AFLP fingerprinting. The AFLP fingerprints associated with high rutin content accessions of F. tataricum are expected to be useful for evaluation, conservation and genetic improvement of buckwheat.

Time-course study and effects of drying method on concentrations of gamma-aminobutyric acid, flavonoids, anthocyanin, and 2''-hydroxynicotianamine in leaves of buckwheats

Concentrations of gamma-aminobutyric acid (GABA), rutin, minor flavonoids (such as orientin), anthocyanin, and 2''-hydroxynicotianamine (2HN) were quantified in the leaves of common and tartary buckwheat (Fagopyrum esculentum Moench and Fagopyrum tataricum Gaertn., respectively), at 14, 28, and 42 days after sowing (DAS). GABA and rutin concentrations peaked at 42 DAS, whereas anthocyain, 2HN, and minor flavonoid concentrations declined with the age of the plants. However, at 42 DAS, anthocyanin concentrations in the leaves of tartary buckwheat Hokkai T10 leaves were at least 10-fold greater than in the other buckwheats tested. In addition, the effects on target compound concentrations and 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity of three different drying methods (20 h at 40 degrees C, 7 h at 70 degrees C, or lyophilization) were investigated. In general, the drying method had no significant effect on the parameters tested. These results indicate that, in terms of GABA, rutin, and anthocyanin concentrations, leaf powder from 42 day old Hokkai T10 has the potential to be a useful food ingredient, such as Ao-jiru juice.

Comparison of phenolic compositions between common and tartary buckwheat (Fagopyrum) sprouts

The phenolic compositions of non-germinated/germinated seeds and seed sprouts (at 6-10 day-old) of common (Fagopyrum esculentum Möench) and tartary (Fagopyrum tataricum Gaertn.) buckwheats were investigated. Phenolic compounds, including chlorogenic acid, four C-glycosylflavones (orientin, isoorientin vitexin, isovitexin), rutin and quercetin, were determined in the seed sprouts by high-performance liquid chromatography (HPLC). In the edible parts of common buckwheat sprouts, individual phenolics significantly increased during sprout growth from 6 to 10 days after sowing (DAS), whereas in tartary buckwheat sprouts they did not. While the sum contents of phenolic compounds in the edible part (mean 24.4mg/g DW at 6-10 DAS) of tartary buckwheat sprouts were similar to those of common buckwheat sprouts, rutin contents in the non-germinated/germinated seeds (mean 14.7mg/g DW) and edible parts (mean 21.8mg/g DW) of tartary buckwheat were 49- and 5-fold, respectively, higher than those of common buckwheat. Extracts of the edible parts of both species showed very similar free radical-scavenging activities (mean 1.7μmol trolox eq/g DW), suggesting that the overall antioxidative activity might be affected by the combination of identified phenolics and unidentified (minor) components. Therefore, buckwheat seed sprouts are recommended for their high antioxidative activity, as well as being an excellent dietary source of phenolic compounds, particularly tartary buckwheat sprouts, being rich in rutin.