Natural variation of folate content and composition in spinach (Spinacia oleracea) germplasm

Reduced γ-glutamyl hydrolase activity likely contributes to high folate levels in Periyakulam-1 tomato

Tomato cultivars show wide variation in nutraceutical folate in ripe fruits, yet the loci regulating folate levels in fruits remain unexplored. To decipher regulatory points, we compared two contrasting tomato cultivars: Periyakulam-1 (PKM-1) with high folate and Arka Vikas (AV) with low folate. The progression of ripening in PKM-1 was nearly similar to AV but had substantially lower ethylene emission. In parallel, the levels of phytohormones salicylic acid, ABA, and jasmonic acid were substantially lower than AV. The fruits of PKM-1 were metabolically distinct from AV, with upregulation of several amino acids. Consistent with higher °Brix, the red ripe fruits also showed upregulation of sugars and sugar-derived metabolites. In parallel with higher folate, PKM-1 fruits also had higher carotenoid levels, especially lycopene and β-carotene. The proteome analysis showed upregulation of carotenoid sequestration and folate metabolism-related proteins in PKM-1. The deglutamylation pathway mediated by γ-glutamyl hydrolase (GGH) was substantially reduced in PKM-1 at the red-ripe stage. The red-ripe fruits had reduced transcript levels of GGHs and lower GGH activity than AV. Conversely, the percent polyglutamylation of folate was much higher in PKM-1. Our analysis indicates the regulation of GGH activity as a potential target to elevate folate levels in tomato fruits.

B vitamin supply in plants and humans: the importance of vitamer homeostasis

B vitamins are a group of water-soluble micronutrients that are required in all life forms. With the lack of biosynthetic pathways, humans depend on dietary uptake of these compounds, either directly or indirectly, from plant sources. B vitamins are frequently given little consideration beyond their role as enzyme accessory factors and are assumed not to limit metabolism. However, it should be recognized that each individual B vitamin is a family of compounds (vitamers), the regulation of which has dedicated pathways. Moreover, it is becoming increasingly evident that individual family members have physiological relevance and should not be sidelined. Here, we elaborate on the known forms of vitamins B₁ , B₆ and B₉ , their distinct functions and importance to metabolism, in both human and plant health, and highlight the relevance of vitamer homeostasis. Research on B vitamin metabolism over the past several years indicates that not only the total level of vitamins but also the oft-neglected homeostasis of the various vitamers of each B vitamin is essential to human and plant health. We briefly discuss the potential of plant biology studies in supporting human health regarding these B vitamins as essential micronutrients. Based on the findings of the past few years we conclude that research should focus on the significance of vitamer homeostasis - at the organ, tissue and subcellular levels - which could improve the health of not only humans but also plants, benefiting from cross-disciplinary approaches and novel technologies.

Variability in somatic embryo-forming capacity of spinach

High variability in somatic embryo (SE)-forming capacity has previously been observed in several spinach cultivars. Such variability frequently accounted for more variation in embryogenic response of the explants than the factor being investigated. Hence, the variability in embryogenic capacity was examined in the present study at both the population and the single-seedling level, using seeds of spinach cultivar Matador obtained from nine European seed companies. Seed population obtained from Slovenia (Sl) was superior to others, with the highest regeneration frequency (100%) and the highest mean SE number (14.4). A total of 82% of these seedlings had 80–100% of regenerating explants, while in populations with intermediate embryogenic capacity approximately 40% of seedlings had 20–60% of regenerating explants. The explants from the majority of seedlings (52–100%) in the least responsive populations were irresponsive. Furthermore, the explants from Sl seedlings regenerated from 10–20 (43.5%) up to > 20 (27.6%) SEs on average, while the explants from the majority of seedlings belonging to other populations regenerated 1–10 SEs. The present study strongly indicates that the variability of plant material must not be overlooked, because choosing more responsive individuals for one treatment and less responsive ones for another may lead to misinterpretation of the data.

Effect of folic acid on the postharvest physiology of broccoli during storage

The objective of the present study was to explore the effect of folic acid on the postharvest physiology of broccoli placed in storage. Broccoli heads were immersed in 5 mg L^-1 folic acid for 10 min, then stored at 20 ± 1 °C for 4 days. Results indicated that the postharvest treatment of broccoli with folic acid decreased the rate of flower opening and yellowing, inhibited weight loss, reduced the level of respiration, as well as ethylene generation. Folic acid-treated broccoli maintained their level of chlorophyll, total soluble solids, vitamin C, total phenolics, flavonoids, glucosinolate, and folic acid. Treated broccoli also exhibited reduced accumulation of malondialdehyde (MDA) and reactive oxygen species (ROS). Concomitantly, antioxidant enzyme activity and corresponding gene expression were also enhanced. In contrast, chlorophyll-degrading enzyme gene expression was suppressed. These results indicated that folic acid treatment of broccoli could be used to prolong shelf-life.

Genetic and physiological regulation of folate in pak choi (Brassica rapa subsp. Chinensis) germplasm

Folates are one of the essential micronutrients for all living organisms. Due to inadequate dietary intake, folate deficiency remains prevalent in humans. Genetically diverse germplasms can potentially be used as parents in breeding programs and also for understanding the folate regulatory network. Therefore, we investigated the natural genetic diversity of folates and their physiological regulation in pak choi (Brassica rapa subsp. Chinensis) germplasm. The total folate concentration ranged from 52.7 μg 100 gFW-1 to 166.9 μg 100 gFW-1, with 3.2-fold variation. The main folate vitamer was represented by 5-CH3-H4folate, with 4.5-fold variation. The activities of GTP cyclohydrolase I and aminodeoxy chorismate synthase, the first step of folate synthesis, were high in high folate accessions and low in low folate accessions. Analysis of the transcription levels of 11 genes associated with folate metabolism demonstrated that the difference in folate concentrations may be primarily controlled at the post-transcriptional level. A general correlation between total folate and their precursors was observed. Folate diversity and chlorophyll content were tightly regulated through the methyl cycle. The diverse genetic variation in pak choi germplasm indicated the great genetic potential to integrate breeding programs for folate biofortification and unravel the physiological basis of folate homeostasis in planta.

Folate content analysis of wheat cultivars developed in the North China Plain

Folates are essential micronutrients in the human diet. Germplasm rich in folates can be used as genetic resource for diet and breeding to produce new varieties with enhanced folates. To investigate the natural variation of folates among wheat cultivars and identify high folate materials for breeding, we studied the grain folate contents of 360 wheat samples consisting of 315 wheat genotypes grown in North China using the high performance liquid chromatography coupled with mass spectrometry (HPLC-MS/MS) method. The total folate content among wheat genotypes ranged from 10.15 ± 2.86 to 91.44 ± 5.64 µg per 100 g grains, thus showing a remarked variation. Fifty-two wheat cultivars, such as Henong58-3, were identified as good sources of folates. 5-Formyltetrahydrate and 5-methyltetrahydrate were found to be the two major folate derivatives in wheat germplasm. In addition, we found that environment factor also had significant effect on folate production. This investigation can help wheat breeders for folate improvement.

Toward Eradication of B-Vitamin Deficiencies: Considerations for Crop Biofortification

'Hidden hunger' involves insufficient intake of micronutrients and is estimated to affect over two billion people on a global scale. Malnutrition of vitamins and minerals is known to cause an alarming number of casualties, even in the developed world. Many staple crops, although serving as the main dietary component for large population groups, deliver inadequate amounts of micronutrients. Biofortification, the augmentation of natural micronutrient levels in crop products through breeding or genetic engineering, is a pivotal tool in the fight against micronutrient malnutrition (MNM). Although these approaches have shown to be successful in several species, a more extensive knowledge of plant metabolism and function of these micronutrients is required to refine and improve biofortification strategies. This review focuses on the relevant B-vitamins (B1, B6, and B9). First, the role of these vitamins in plant physiology is elaborated, as well their biosynthesis. Second, the rationale behind vitamin biofortification is illustrated in view of pathophysiology and epidemiology of the deficiency. Furthermore, advances in biofortification, via metabolic engineering or breeding, are presented. Finally, considerations on B-vitamin multi-biofortified crops are raised, comprising the possible interplay of these vitamins in planta.

Guava (Psidium guajava L. cv. Red Suprema) Crude Extract Protect Human Dermal Fibroblasts against Cytotoxic Damage Mediated by Oxidative Stress

We analyzed guava fruits (Psidium guajava L. cv. Red Suprema) from Cuba to determine their chemical composition, total antioxidant capacity, as well as their protective effect against oxidative damage using an in vitro model of human dermal fibroblasts. The guava fruit is a natural source of bioactive compounds, such as polyphenols, vitamin C, folates and beta carotenes with proven health benefits. Human dermal fibroblasts were pre-incubated with different concentrations of guava crude extract and then subjected to oxidative stress using the AAPH stressor. The number of apoptotic and dead cells, as well as the markers of oxidative damage such as lipid and protein oxidation significantly decreased when cells were pre-incubated with guava crude extract and then exposed to the stressor. The activity of antioxidant enzymes also improved when cells were pre-incubated with guava crude extract in comparison to cells subjected to stress without prior pre-incubation with the guava extract. The results obtained in this study highlight the health benefits of guava regarding oxidative stress, proving it to be an important source of bioactive compounds associated with important biological properties.

The protective effect of acerola (Malpighia emarginata) against oxidative damage in human dermal fibroblasts through the improvement of antioxidant enzyme activity and mitochondrial functionality

Acerola fruits (Malpighia emarginata DC.) from the central region of Cuba were analyzed to determine their chemical composition and protective capacity against oxidative damage using an in vitro human dermal fibroblast (HDFa) model. The chemical composition analyses showed a high content of vitamin C, total polyphenols, β-carotene and folates in the acerola fruit. From the HPLC-DAD/ESI-MSⁿ analyses, two anthocyanins (cyanidin 3-O-rhamnoside and pelargonidin 3-O-rhamnoside), three hydroxycinnamoyl derivatives (caffeoyl hexoside, dihydrocaffeoylquinic acid and coumaroyl hexoside) and fifteen flavonols (mostly glycosylated forms of quercetin and kaempferol) were detected. HDFa were pre-incubated with an acerola crude extract (ACExt) and subsequently subjected to oxidative stress induced by AAPH. Apoptosis, intracellular ROS and the biomarkers of lipid and protein oxidation significantly increased after inducing stress, while the activities of the antioxidant enzyme catalase and superoxide dismutase and mitochondrial functionality were markedly affected. However, ACExt was able to protect against oxidative damage through decreasing apoptosis, intracellular ROS levels and lipid and protein damage, besides improving antioxidant enzyme activities and mitochondrial functionality. The obtained results support acerola fruits as relevant sources of functional compounds with promising effects on human health.

Lactic acid fermentation as a tool for increasing the folate content of foods

Folate is an essential micronutrient involved in numerous vital biological reactions. The dietary consumption of naturally occurring vitamin B9 is often inadequate in many countries, and supplementation or fortification programs (using synthetic folic acid) are implemented to alleviate folate deficiency. Other food-based alternatives are possible, such as the use of lactic acid bacteria (LAB) to synthesize folate during fermentation. Many studies have been conducted on this topic, and promising results were reported for some fermented dairy products. However, in other studies, folate consumption by LAB or rather low folate production were observed, resulting in fermented foods that may not significantly contribute to the recommended B9 intake. In addition, the optimum conditions for folate biosynthesis by LAB are still not clear. The aim of this review was thus to (i) clarify the ability of LAB to produce folate in food products, (ii) check if the production of folate by LAB in various fermented foods is sufficient to meet human vitamin B9 requirements and (iii) suggest ways to optimize folate production by LAB in fermented food products.

Draft genome of spinach and transcriptome diversity of 120 Spinacia accessions

Spinach is an important leafy vegetable enriched with multiple necessary nutrients. Here we report the draft genome sequence of spinach (Spinacia oleracea, 2n=12), which contains 25,495 protein-coding genes. The spinach genome is highly repetitive with 74.4% of its content in the form of transposable elements. No recent whole genome duplication events are observed in spinach. Genome syntenic analysis between spinach and sugar beet suggests substantial inter- and intra-chromosome rearrangements during the Caryophyllales genome evolution. Transcriptome sequencing of 120 cultivated and wild spinach accessions reveals more than 420 K variants. Our data suggests that S. turkestanica is likely the direct progenitor of cultivated spinach and spinach domestication has a weak bottleneck. We identify 93 domestication sweeps in the spinach genome, some of which are associated with important agronomic traits including bolting, flowering and leaf numbers. This study offers insights into spinach evolution and domestication and provides resources for spinach research and improvement.

Spinach is an economically important vegetable crop but previous genomic resources were of limited use for comparative and functional analyses. Here, Xu et al. present a high quality draft spinach genome and transcriptome data for multiple Spinacia accessions providing insight into Caryophyllales genome evolution.

A rapid method for sensitive profiling of folates from plant leaf by ultra-performance liquid chromatography coupled to tandem quadrupole mass spectrometer

Previous published methods for the analysis of folates are time consuming because of lengthy sample extraction, clean-up and total running time. This study details the development and validation of a rapid, sensitive and robust method that combines a simple extraction step with ultra-performance liquid chromatography coupled to tandem quadrupole mass spectrometry. Here, we reported application of a tandem quadrupole mass spectrometer to analyze maximum seven vitamers of folate from plant origin. The analytical performance was evaluated by linearity, sensitivity, precision, recovery test and analysis of certified reference materials. The limit of detection and limit of quantification ranged between 0.003 and 0.021μg/100g FW and between 0.011 and 0.041μg/100g FW, respectively; the recovery and precession ranged from 71.27 to 99. 01% and from 1.7 to 7.8% RSD, respectively, depending upon folate vitamers. This newly developed and validated method is rapid (a chromatographic run time of 5min), easy to be performed (no laborious and time consuming clean-up) and can be used to simultaneously analyze seven vitamers of folate from plant sources.

Natural variation in folate levels among tomato (Solanum lycopersicum) accessions

Folate content was estimated in tomato (Solanum lycopersicum) accessions using microbiological assay (MA) and by LC-MS. The MA revealed that in red-ripe fruits folate levels ranged from 4 to 60μg/100g fresh weight. The LC-MS estimation of red-ripe fruits detected three folate forms, 5-CH3-THF, 5-CHO-THF, 5,10-CH(+)THF and folate levels ranged from 14 to 46μg/100g fresh weight. In mature green and red ripe fruit, 5-CH3-THF was the most abundant folate form. Comparison of LC-MS with MA revealed that MA inaccurately estimates folate levels. The accumulation of folate forms and their distribution varied among accessions. The single nucleotide polymorphism was examined in the key genes of the folate pathway to understand its linkage with folate levels. Despite the significant variation in folate levels among tomato accessions, little polymorphism was found in folate biosynthesis genes. Our results indicate that variation in folate level is governed by a more complex regulation at cellular homeostasis level.

Folates: Chemistry, analysis, occurrence, biofortification and bioavailability

Folates (Vitamin B₉) include both naturally occurring folates and synthetic folic acid used in fortified foods and dietary supplements. Folate deficiency causes severe abnormalities in one-carbon metabolism can result chronic diseases and developmental disorders, including neural tube defects. Mammalian cells cannot synthesize folates de novo; therefore, diet and dietary supplements are the only way to attain daily folate requirements. In the last decade, significant advancements have been made to enhance the folate content of rice, tomato, common bean and lettuce by using genetic engineering approaches. Strategies have been developed to improve the stability of folate pool in plants. Folate deglutamylation through food processing and thermal treatment has the potential to enhance the bioavailability of folate. This review highlights the recent developments in biosynthesis, composition, bioavailability, enhanced production by elicitation and metabolic engineering, and methods of analysis of folate in food. Additionally, future perspectives in this context are identified. Detailed knowledge of folate biosynthesis, degradation and salvage are the prime requirements to efficiently engineer the plants for the enhancement of overall folate content. Similarly, consumption of a folate-rich diet with enhanced bioavailability is the best way to maintain optimum folate levels in the body.

Review of Neuro-nutrition Used as Anti-Alzheimer Plant, Spinach, Spinacia oleracea

Neuro-nutrition is the nutrition needed to achieve health brain and neurocognitive function. Diets rich in antioxidants, vitamins, flavonoids, and polyphenolic compounds will help suppress the onset of Alzheimer's disease. Spinacia oleracea (Family: Amaranthaceae) commonly known as spinach or Buai Leng (in Thai), one of the traditional medicinal plants with high in those mention nutrients. The micronutrients in spinach include a range of vitamins and minerals, which can prevent deficiency diseases and are essential for normal physiological function. Its phytochemicals are carotenoids, flavonoids, and phenolic compounds, which can prevent chronic health problems, as well as other diseases associated with aging. The objective of this article was to conduct a review on various ethnomedicinal uses of the spinach and its influences on the pathophysiology of Alzheimer's disease based on a literature review.

Relative bioavailability of folate from the traditional food plant Moringa oleifera L. as evaluated in a rat model

Moringa oleifera is an affordable and rich source of dietary folate. Quantification of folate by HPLC showed that 5-formyl-5,6,7,8-tetrahydrofolic acid (502.1 μg/100 g DW) and 5,6,7,8-tetrahydrofolic acid (223.9 μg/100 g DW) as the most dominant forms of folate in M. oleifera leaves. The bioavailability of folate and the effects of folate depletion and repletion on biochemical and molecular markers of folate status were investigated in Wistar rats. Folate deficiency was induced by keeping the animals on a folate deficient diet with 1 % succinyl sulfathiazole (w/w). After the depletion period, animals were repleted with different levels of folic acid and M. oleifera leaves as a source of folate. Feeding the animals on a folate deficient diet for 7 weeks caused a significant (3.4-fold) decrease in serum folate content, compared to non-depleted control animals. Relative bioavailability of folate from dehydrated leaves of M. oleifera was 81.9 %. During folate depletion and repletion, no significant changes in liver glycine N-methyl transferase and 5-methyltetrahydrofolate-homocysteine methyltransferase expression were recorded. In RDA calculations, only 50 % of natural folate is assumed to be bioavailable. Therefore, the bioavailability of folate from Moringa is much higher, suggesting that M. oleifera based food can be used as a significant source of folate.

High performance liquid chromatography coupled to mass spectrometry for profiling and quantitative analysis of folate monoglutamates in tomato

Folates are essential micronutrients for animals as they play a major role in one carbon metabolism. Animals are unable to synthesize folates and obtain them from plant derived food. In the present study, a high performance liquid chromatography coupled to mass spectrometric (HPLC-MS/MS) method was developed for the high throughput screening and quantitative analysis of folate monoglutamates in tomato fruits. For folate extraction, several parameters were optimized including extraction conditions, pH range, amount of tri-enzyme and boiling time. After processing the extract was purified using ultra-filtration with 10 kDa membrane filter. The ultra-filtered extract was chromatographed on a RP Luna C18 column using gradient elution program. The method was validated by determining linearity, sensitivity and recovery. This method was successfully applied to folate estimation in spinach, capsicum, and garden pea and demonstrated that this method offers a versatile approach for accurate and fast determination of different folate monoglutamates in vegetables.

Occurrence, stability, and determination of formyl folates in foods

The B-vitamin folate has specific tasks as a one-carbon (C1) group supplier in the building and repair of DNA and RNA as well as in the methylation of homocysteine to methionine. Folate occurs in all living cells as a dynamic pool of several interconvertible forms carrying different C1 groups. Along the food chain, this dynamic pool of folates constantly changes due to either enzymatic or chemical interconversions during food processing and storage. These interconversions make it difficult to determine individual folate forms in foods. The formyl folates, the second most predominant forms of food folates, after 5-methyltetrahydrofolate, are particularly prone to interconvert at low pH. Today, this knowledge is often neglected, leading to risks for analytical underestimation of formyl folates. The purpose of the review is to explore the stability and interconversions of formyl folates in foods as well as to analyze the pitfalls in the determination of formyl folates.

Changes of folate and other potential health-promoting phytochemicals in legume seeds as affected by germination

Folate deficiency associated with low dietary intake is a well-documented public health problem, resulting in serious health and socioeconomic burdens. Therefore, optimization of the germination process of different cultivars of legume seeds in relation to the content and composition of folate, vitamin C, and total phenolics and total antioxidant capacity was carried out to maximize the health-promoting properties. The content and composition of folate, vitamin C, and total phenolic and total antioxidant capacities varied between species, among cultivars, and with germination time. During germination, total folate content was maximum at 815.2 μg/100 g fresh weight in soybean sprout and at 675.4 μg/100 g fresh weight in mungbean sprout on the fourth day, which were equivalent to, respectively, 3.5- and 3.9-fold increases in the seed's content, and total folate content strongly decreased thereafter. 5-CH(3)-H(4)folate was the most abundant folate species in legume sprouts and reached a maximum on the fourth day. Vitamin C was not detected in raw seeds, and its content increased sharply in soybean and mungbean sprouts and reached a maximum at the fourth day of germination (29 and 27.7 mg/100 g fresh weight, respectively). Germination of soybean and mungbean for 4 days provided the largest amount of total folate as well as the more stable species 5-CH(3)-H(4)folate and also brought about large amounts of vitamin C and total phenolics and substantial antioxidant capacities.