Antioxidants in Potatoes: A Functional View on One of the Major Food Crops Worldwide.

With a growing world population, accelerating climate changes, and limited arable land, it is critical to focus on plant-based resources for sustainable food production. In addition, plants are a cornucopia for secondary metabolites, of which many have robust antioxidative capacities and are beneficial for human health. Potato is one of the major food crops worldwide, and is recognized by the United Nations as an excellent food source for an increasing world population. Potato tubers are rich in a plethora of antioxidants with an array of health-promoting effects. This review article provides a detailed overview about the biosynthesis, chemical and health-promoting properties of the most abundant antioxidants in potato tubers, including several vitamins, carotenoids and phenylpropanoids. The dietary contribution of diverse commercial and primitive cultivars are detailed and document that potato contributes much more than just complex carbohydrates to the diet. Finally, the review provides insights into the current and future potential of potato-based systems as tools and resources for healthy and sustainable food production.

Altering potato isoprenoid metabolism increases biomass and induces early flowering.

Isoprenoids constitute the largest class of plant natural products and have diverse biological functions including in plant growth and development. In potato (Solanum tuberosum), the regulatory mechanism underlying the biosynthesis of isoprenoids through the mevalonate pathway is unclear. We assessed the role of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) homologs in potato development and in the metabolic regulation of isoprenoid biosynthesis by generating transgenic lines with down-regulated expression (RNAi-hmgr) or overexpression (OE) of one (StHMGR1 or StHMGR3) or two genes, HMGR and farnesyl diphosphate synthase (FPS; StHMGR1/StFPS1 or StHMGR3/StFPS1). Levels of sterols, steroidal glycoalkaloids (SGAs), and plastidial isoprenoids were elevated in the OE-HMGR1, OE-HMGR1/FPS1, and OE-HMGR3/FPS1 lines, and these plants exhibited early flowering, increased stem height, increased biomass, and increased total tuber weight. However, OE-HMGR3 lines showed dwarfism and had the highest sterol amounts, but without an increase in SGA levels, supporting a rate-limiting role for HMGR3 in the accumulation of sterols. Potato RNAi-hmgr lines showed inhibited growth and reduced cytosolic isoprenoid levels. We also determined the relative importance of transcriptional control at regulatory points of isoprenoid precursor biosynthesis by assessing gene-metabolite correlations. These findings provide novel insights into specific end-products of the sterol pathway and could be important for crop yield and bioenergy crops.

Synthesis and regulation of chlorogenic acid in potato: Rerouting phenylpropanoid flux in HQT-silenced lines.

Chlorogenic acid (CGA) is the major phenolic sink in potato tubers and can constitute over 90% of total phenylpropanoids. The regulation of CGA biosynthesis in potato and the role of the CGA biosynthetic gene hydroxycinnamoyl CoA:quinate hydroxycinnamoyl transferase (HQT) was characterized. A sucrose induced accumulation of CGA correlated with the increased expression of phenylalanine ammonia-lyase (PAL) rather than HQT. Transient expression of the potato MYB transcription factor StAN1 (anthocyanin 1) in tobacco increased CGA. RNAi suppression of HQT resulted in over a 90% reduction in CGA and resulted in early flowering. The reduction in total phenolics and antioxidant capacity was less than the reduction in CGA, suggesting flux was rerouted into other phenylpropanoids. Network analysis showed distinct patterns in different organs, with anthocyanins and phenolic acids showing negative correlations in leaves and flowers and positive in tubers. Some flavonols increased in flowers, but not in leaves or tubers. Anthocyanins increased in flowers and showed a trend to increase in leaves, but not tubers. HQT suppression increased biosynthesis of caffeoyl polyamines, some of which are not previously reported in potato. Decreased PAL expression and enzyme activity was observed in HQT suppressed lines, suggesting the existence of a regulatory loop between CGA and PAL. Electrophysiology detected no effect of CGA suppression on potato psyllid feeding. Collectively, this research showed that CGA in potatoes is synthesized through HQT and HQT suppression altered phenotype and redirected phenylpropanoid flux.

Loss of function of FATTY ACID DESATURASE7 in tomato enhances basal aphid resistance in a salicylate-dependent manner.

We report here that disruption of function of the ω-3 FATTY ACID DESATURASE7 (FAD7) enhances plant defenses against aphids. The suppressor of prosystemin-mediated responses2 (spr2) mutation in tomato (Solanum lycopersicum), which eliminates the function of FAD7, reduces the settling behavior, survival, and fecundity of the potato aphid (Macrosiphum euphorbiae). Likewise, the antisense suppression of LeFAD7 expression in wild-type tomato plants reduces aphid infestations. Aphid resistance in the spr2 mutant is associated with enhanced levels of salicylic acid (SA) and mRNA encoding the pathogenesis-related protein P4. Introduction of the Naphthalene/salicylate hydroxylase transgene, which suppresses SA accumulation, restores wild-type levels of aphid susceptibility to spr2. Resistance in spr2 is also lost when we utilize virus-induced gene silencing to suppress the expression of NONEXPRESSOR OF PATHOGENESIS-RELATED PROTEINS1 (NPR1), a positive regulator of many SA-dependent defenses. These results indicate that FAD7 suppresses defenses against aphids that are mediated through SA and NPR1. Although loss of function of FAD7 also inhibits the synthesis of jasmonate (JA), the effects of this desaturase on aphid resistance are not dependent on JA; other mutants impaired in JA synthesis (acx1) or perception (jai1-1) show wild-type levels of aphid susceptibility, and spr2 retains aphid resistance when treated with methyl jasmonate. Thus, FAD7 may influence JA-dependent defenses against chewing insects and SA-dependent defenses against aphids through independent effects on JA synthesis and SA signaling. The Arabidopsis (Arabidopsis thaliana) mutants Atfad7-2 and Atfad7-1fad8 also show enhanced resistance to the green peach aphid (Myzus persicae) compared with wild-type controls, indicating that FAD7 influences plant-aphid interactions in at least two plant families.

Transcription factors, sucrose, and sucrose metabolic genes interact to regulate potato phenylpropanoid metabolism.

Much remains unknown about how transcription factors and sugars regulate phenylpropanoid metabolism in tuber crops like potato (Solanum tuberosum). Based on phylogeny and protein similarity to known regulators of phenylpropanoid metabolism, 15 transcription factors were selected and their expression was compared in white, yellow, red, and purple genotypes with contrasting phenolic and anthocyanin profiles. Red and purple genotypes had increased phenylalanine ammonia lyase (PAL) enzyme activity, markedly higher levels of phenylpropanoids, and elevated expression of most phenylpropanoid structural genes, including a novel anthocyanin O-methyltransferase. The transcription factors Anthocyanin1 (StAN1), basic Helix Loop Helix1 (StbHLH1), and StWD40 were more strongly expressed in red and purple potatoes. Expression of 12 other transcription factors was not associated with phenylpropanoid content, except for StMYB12B, which showed a negative relationship. Increased expression of AN1, bHLH1, and WD40 was also associated with environmentally mediated increases in tuber phenylpropanoids. Treatment of potato plantlets with sucrose induced hydroxycinnamic acids, flavonols, anthocyanins, structural genes, AN1, bHLH1, WD40, and genes encoding the sucrose-hydrolysing enzymes SUSY1, SUSY4, and INV2. Transient expression of StAN1 in tobacco leaves induced bHLH1, structural genes, SUSY1, SUSY4, and INV1, and increased phenylpropanoid amounts. StAN1 infiltration into tobacco leaves decreased sucrose and glucose concentrations. In silico promoter analysis revealed the presence of MYB and bHLH regulatory elements on sucrolytic gene promoters and sucrose-responsive elements on the AN1 promoter. These findings reveal an interesting dynamic between AN1, sucrose, and sucrose metabolic genes in modulating potato phenylpropanoids.

Differential effects of environment on potato phenylpropanoid and carotenoid expression.

BACKGROUND: Plant secondary metabolites, including phenylpropanoids and carotenoids, are stress inducible, have important roles in potato physiology and influence the nutritional value of potatoes. The type and magnitude of environmental effects on tuber phytonutrients is unclear, especially under modern agricultural management that minimizes stress. Understanding factors that influence tuber secondary metabolism could facilitate production of more nutritious crops. Metabolite pools of over forty tuber phenylpropanoids and carotenoids, along with the expression of twenty structural genes, were measured in high-phenylpropanoid purple potatoes grown in environmentally diverse locations in North America (Alaska, Texas and Florida). RESULTS: Phenylpropanoids, including chlorogenic acid (CGA), were higher in samples from the northern latitudes, as was the expression of phenylpropanoid genes including phenylalanine ammonia lyase (PAL), which had over a ten-fold difference in relative abundance. Phenylpropanoid gene expression appeared coordinately regulated and was well correlated with metabolite pools, except for hydroxycinnamoyl-CoA:quinatehydroxcinnamoyl transferase (HQT; r = -0.24). In silico promoter analysis identified two cis-acting elements in the HQT promoter not found in the other phenylpropanoid genes. Anthocyanins were more abundant in Alaskan samples and correlated with flavonoid genes including DFR (r = 0.91), UFGT (r = 0.94) and F3H (r = 0.77). The most abundant anthocyanin was petunidin-3-coum-rutinoside-5-glu, which ranged from 4.7 mg g-1 in Alaska to 2.3 mg g-1 in Texas. Positive correlations between tuber sucrose and anthocyanins (r = 0.85), suggested a stimulatory effect of sucrose. Smaller variation was observed in total carotenoids, but marked differences occurred in individual carotenoids, which had over a ten-fold range. Violaxanthin, lutein or zeaxanthin were the predominant carotenoids in tubers from Alaska, Texas and Florida respectively. Unlike in the phenylpropanoid pathway, poor correlations occurred between carotenoid transcripts and metabolites. CONCLUSION: Analysis of tuber secondary metabolism showed interesting relationships among different metabolites in response to collective environmental influences, even under conditions that minimize stress. The variation in metabolites shows the considerable phenotypical plasticity possible with tuber secondary metabolism and raises questions about to what extent these pathways can be stimulated by environmental cues in a manner that optimizes tuber phytonutrient content while protecting yields. The differences in secondary metabolites may be sufficient to affect nutritional quality.

Pigmented potato consumption alters oxidative stress and inflammatory damage in men.

Pigmented potatoes contain high concentrations of antioxidants, including phenolic acids, anthocyanins, and carotenoids. These bioactive compounds have been implicated in the inhibition or prevention of cellular oxidative damage and chronic disease susceptibility. We assessed the effects of pigmented potato consumption on oxidative stress and inflammation biomarkers in adult males. Free-living healthy men (18-40 y; n = 12/group) consumed 150 g of cooked white- (WP), yellow- (YP), or purple-flesh potatoes (PP) once per day for 6 wk in a randomized study. Blood was collected at baseline and wk 6 to analyze total antioxidant capacity (TAC), DNA damage as assessed by plasma 8-hydroxydeoxyguanosine (8-OHdG), protein oxidation, lipid peroxidation, C-reactive protein (CRP), inflammatory cytokines, lymphoproliferation, NK cytotoxicity, and phenotypes. Potatoes were analyzed for TAC, phenolic acids, anthocyanins, and carotenoids. Compared with the WP group, the YP group had higher concentrations of phenolic acids (P < 0.002) and carotenoids (P < 0.001), whereas the PP group had higher concentrations of phenolic acids (P < 0.002) and anthocyanins (P < 0.001). Men who consumed YP and PP tended to have lower (P < 0.08) plasma IL-6 compared with those consuming WP. The PP group tended to have a lower plasma CRP concentration than the WP group (P = 0.07). The 8-OHdG concentration was lower in men who consumed either YP or PP compared with WP. Pigmented potato consumption reduced inflammation and DNA damage in healthy adult males. This offers consumers an improved nutritional choice in potato consumption.

R2R3-MYB transcription factors, StmiR858 and sucrose mediate potato flavonol biosynthesis.

Flavonols and other phenylpropanoids protect plants from biotic and abiotic stress and are dietarily desirable because of their health-promoting properties. The ability to develop new potatoes (Solanum tuberosum) with optimal types and amounts of phenylpropanoids is limited by lack of knowledge about the regulatory mechanisms. Exogenous sucrose increased flavonols, whereas overexpression of the MYB StAN1 induced sucrolytic gene expression. Heterologous StAN1 protein bound promoter fragments from sucrolytic genes (SUSY1 and INV1). Two additional MYBs and one microRNA were identified that regulated potato flavonols. Overexpression analysis showed MYB12A and C increased amounts of flavonols and other phenylpropanoids. Endogenous flavonol amounts in light-exposed organs were much higher those in the dark. Expression levels of StMYB12A and C were high in flowers but low in tubers. Transient overexpression of miR858 altered potato flavonol metabolism. Endogenous StmiR858 expression was much lower in flowers than leaves and correlated with flavonol amounts in these organs. Collectively, these findings support the hypothesis that sucrose, MYBs, and miRNA control potato phenylpropanoid metabolism in a finely tuned manner that includes a feedback loop between sucrose and StAN1. These findings will aid in the development of potatoes with phenylpropanoid profiles optimized for crop performance and human health.

Effect of Cooking Methods on Bioactivity of Polyphenols in Purple Potatoes.

Purple-fleshed potato (Solanum tuberosum L.) is a good dietary source of anthocyanins, flavonols, and polyphenolic acids, mostly chlorogenic acid. The objective of this study was to examine the impacts of cooking methods including boiling, steaming, and the newly developed vacuum-sealed boiling (VSBoil) on extractability and bioactivity of polyphenolic compounds in a purple potato (PP) cultivar, Purple Pelisse. Data showed that boiling and steaming reduced the total polyphenolic content in PP. High-performance liquid chromatography analysis showed that steaming slightly reduced the extractable chlorogenic acid content, while VSBoil increased it. For DPPH free radical scavenging activities, VSBoil and steaming effectively preserved the antioxidant activity of a polyphenol-rich extract of PP, while boiling resulted in a significant reduction compared to raw potato extract. All extracts effectively suppressed bursts of intracellular reactive oxygen species in human colonic epithelial cells upon hydrogen peroxide induction, of which the extract from the VSBoil group showed the highest antioxidant potential. In addition, all extracts showed anti-inflammatory effects in Caco-2 cells induced with tumor necrosis factor-α. In conclusion, the content and bioactivity of extractable polyphenols were largely retained in PP subjected to different cooking processes. VSBoil resulted in the highest content of extractable polyphenolic compounds and bioactivity among tested cooking methods.

Tomato susceptibility to root-knot nematodes requires an intact jasmonic acid signaling pathway.

Responses of resistant (Mi-1/Mi-1) and susceptible (mi-1/ mi-1) tomato (Solanum lycopersicum) to root-knot nematodes (RKNs; Meloidogyne spp.) infection were monitored using cDNA microarrays, and the roles of salicylic acid (SA) and jasmonic acid (JA) defense signaling were evaluated in these interactions. Array analysis was used to compare transcript profiles in incompatible and compatible interactions of tomato roots 24 h after RKN infestation. The jai1 and def1 tomato mutant, altered in JA signaling, and tomato transgenic line NahG, altered in SA signaling, in the presence or absence of the RKN resistance gene Mi-1, were evaluated. The array analysis identified 1,497 and 750 genes differentially regulated in the incompatible and compatible interactions, respectively. Of the differentially regulated genes, 37% were specific to the incompatible interactions. NahG affected neither Mi-1 resistance nor basal defenses to RKNs. However, jai1 reduced tomato susceptibility to RKNs while not affecting Mi-1 resistance. In contrast, the def1 mutant did not affect RKN susceptibility. These results indicate that JA-dependent signaling does not play a role in Mi-1-mediated defense; however, an intact JA signaling pathway is required for tomato susceptibility to RKNs. In addition, low levels of SA might be sufficient for basal and Mi-1 resistance to RKNs.

Purple Potato Extract Promotes Intestinal Epithelial Differentiation and Barrier Function by Activating AMP-Activated Protein Kinase.

SCOPE: Perturbation of gut epithelial barrier function induces inflammation and other health problems that originate from the gut. Purple potato contains a high content of beneficial polyphenolic compounds. The objective of this study is to evaluate the effect of purple potato extract (PPE) on intestinal differentiation and barrier function, and explore its underlying mechanism using Caco-2 cells and ex vivo cultured gut tissues. METHODS AND RESULTS: PPE increases transepithelial electrical resistance and decreases FITC-dextran paracellular flux in Caco-2 cells, which are associated with strengthened intestinal epithelial differentiation in both Caco-2 cells and ex vivo guts. Furthermore, PPE treatment enhances AMP-activated protein kinase (AMPK) activity, concomitant with the increased expression of CDX2, a key transcriptional factor regulating intestinal epithelial differentiation. Knocking out AMPK using CRISPR/Cas9 system abolishes the positive effects of PPE on intestinal epithelial differentiation and barrier function, in junction with the reduced expression of CDX2. CONCLUSION: PPE improves gut epithelial differentiation and barrier function via activating AMPK, indicating that PPE, as well as associated purple potato consumption, could be used as a supportive dietary therapeutic strategy for improving gut epithelial health.

Determination of folate concentrations in diverse potato germplasm using a trienzyme extraction and a microbiological assay.

Folate deficiency is a leading cause of birth defects and is implicated in several other diseases. We are interested in how much folate concentrations vary among potato germplasm. We determined total folate concentrations of potato tubers from 67 cultivars, advanced breeding lines, or wild species. Folates were extracted by a tri-enzyme treatment and analyzed by using a Lactobacillus rhamnosus microbiological assay. Folate concentrations varied from 521 +/- 96 to 1373 +/- 230 ng/g dry weight and were genotype and location dependent. The highest folate concentrations were mostly found in color-fleshed potatoes. Variations of folate concentrations within either color- or white-fleshed tubers were similar ( approximately 2-fold). Skin contained approximately 30% higher folate concentrations than flesh. Storage of tubers for 7 months generally led to an increase in folate contents. Semiquantitative RT-PCR analyses showed that higher folate contents were correlated with lower mRNA expression of some folate genes.

Mi-1-Mediated aphid resistance involves salicylic acid and mitogen-activated protein kinase signaling cascades.

The tomato Mi-1 gene confers resistance to root-knot nematodes (Meloidogyne spp.), potato aphids (Macrosiphum eluphorbiae), and whiteflies (Bemisia tabaci and B. tabaci biotype B). Resistance to potato aphid is developmentally regulated and is not associated with induction of a hypersensitive response. The NahG transgene that eliminates endogenous salicylic acid (SA) was used to test the role of the SA signaling pathway in the resistance mediated by Mi-1 to potato aphids. Aphids survived longer on NahG tomato plants than on wild type. However, aphid reproduction was not affected on NahG tomato. Aphid resistance in Mi-1 NahG plants was completely abolished and the phenotype was successfully rescued by application of BTH (benzo(1,2,3)-thiaiazole-7-carbothioic acid S-methyl ester), indicating that the SA signaling pathway is an important component of Mi-1-mediated aphid resistance. Using virus-induced gene silencing, one or more mitogen-activated protein kinase (MAPK) cascades required for Mi-1-mediated aphid resistance were identified. Silencing plants for MAPK kinase (LeMKK2) and MAPKs (LeMPK2 and LeMPK1, or LeMPK3) resulted in attenuation of Mi-1-mediated aphid resistance. These results further demonstrate that resistance gene-mediated signaling events against piercing-sucking insects are similar to those against other plant pathogens.

Rapid screening of ascorbic acid, glycoalkaloids, and phenolics in potato using high-performance liquid chromatography.

Evaluation of phenolic metabolism in potato tubers (Solanum tuberosum) would be facilitated by faster analytical methods. A high-throughput HPLC method was developed for the qualitative and quantitative determination in potato of numerous phenolic compounds, the sum of the glycoalkaloids chaconine and solanine, plus ascorbic acid. Following a fast extraction, HPLC run times of 12 min were achieved with the use of a monolithic RP C18 column. UV and MS analyses were used to characterize the phenolic complement in extracts from two white-fleshed varieties. Over 30 compounds were identified, some of which are thought to possess either nutritional value or are involved in plant disease resistance. This method is expected to be useful for germplasm mining and for varietal development programs in which large numbers of lines are generated.

Overexpression of a rice NPR1 homolog leads to constitutive activation of defense response and hypersensitivity to light.

Arabidopsis NPR1/NIM1 is a key regulator of systemic acquired resistance (SAR), which confers lasting broad-spectrum resistance. Previous reports indicate that rice has a disease-resistance pathway similar to the Arabidopsis SAR pathway. Here we report the isolation and characterization of a rice NPR1 homologue (NH1). Transgenic rice plants overexpressing NH1 (NH1ox) acquire high levels of resistance to Xanthomonas oryzae pv. oryzae. The resistance phenotype is heritable and correlates with the presence of the transgene and reduced bacterial growth. Northern analysis shows that NH1ox rice spontaneously activates defense genes, contrasting with NPR1-overexpressing Arabidopsis, where defense genes are not activated until induction. Wild-type NH1, but not a point mutant corresponding to npr1-1, interacts strongly with the rice transcription factor rTGA2.2 in yeast two-hybrid. Greenhouse-grown NH1ox plants develop lesion-mimic spots on leaves at preflowering stage although no other developmental effects are observed. However, when grown in growth chambers (GCs) under low light, NH1ox plants are dwarfed, indicating elevated sensitivity to light. The GC-grown NH1ox plants show much higher salicylic acid (SA) levels than the wild type, whereas greenhouse-grown NH1ox plants contain lower SA. These results indicate that NH1 may be involved in the regulation of SA in response to environmental changes.

Salicylic acid is part of the Mi-1-mediated defense response to root-knot nematode in tomato.

The Mi-1 gene of tomato confers resistance against three species of root-knot nematode in tomato (Lycopersicon esculentum). Transformation of tomato carrying Mi-1 with a construct expressing NahG, which encodes salicylate hydroxylase, a bacterial enzyme that degrades salicylic acid (SA) to catechol, results in partial loss of resistance to root-knot nematodes. Exogenous SA was toxic to roots expressing NahG but not to control roots. This toxicity is most likely due to the production of catechol from SA, and we report here that 100 microM catechol is toxic to tomato roots. Benzothiadiazole, a SA analog, completely restores nematode resistance in Mi-1 roots transformed with NahG but does not confer resistance to susceptible tomato roots. The localized cell death produced by transient expression in Nicotiana benthamiana of Mi-DS4, a constitutively lethal chimera of Mi-1 with one of its homologs, was prevented by coexpression of NahG. These results indicate that SA is an important component of the signaling that leads to nematode resistance and the associated hypersensitive response.

Developmental effects on phenolic, flavonol, anthocyanin, and carotenoid metabolites and gene expression in potatoes.

Potato phytonutrients include phenolic acids, flavonols, anthocyanins, and carotenoids. Developmental effects on phytonutrient concentrations and gene expression were studied in white, yellow, and purple potatoes. Purple potatoes contained the most total phenolics, which decreased during development (from 14 to 10 mg g(-1)), as did the activity of phenylalanine ammonia-lyase. The major phenolic, 5-chlorogenic acid (5CGA), decreased during development in all cultivars. Products of later branches of the phenylpropanoid pathway also decreased, including quercetin 3-O rutinoside, kaempferol 3-O-rutinoside, and petunidin 3-O-(p-coumaroyl)rutinoside-3-glucoside (from 6.4 to 4.0 mg g(-1)). Violaxanthin and lutein were the two most abundant carotenoids and decreased 30-70% in the yellow and white potatoes. Sucrose, which can regulate phenylpropanoid metabolism, decreased with development in all cultivars and was highest in purple potatoes. Total protein decreased by 15-30% in two cultivars. Expression of most phenylpropanoid and carotenoid structural genes decreased during development. Immature potatoes like those used in this study are marketed as "baby potatoes", and the greater amounts of these dietarily desirable compounds may appeal to health-conscious consumers.

Changes in potato phenylpropanoid metabolism during tuber development.

Phenylpropanoid metabolite and transcript expression during different developmental stages were examined in field grown potatoes. Carbohydrate and shikimic acid metabolism was assessed to determine how tuber primary metabolism influences phenylpropanoid metabolism. Phenylpropanoid concentrations were highest in immature tubers, as were some transcript levels and enzyme activities including phenylalanine ammonia lyase (PAL). Phenylpropanoid concentration differences between mature and immature tubers varied by genotype, but in some cases were approximately three-fold. The most abundant phenylpropanoid was chlorogenic acid (5CGA), which decreased during tuber maturation. Hydroxycinnamoyl-CoA:quinate hydroxycinnamoyl transferase (HQT) transcripts were highly expressed relative to other phenylpropanoid genes, but were not well correlated with 5CGA concentrations (r = -0.16), whereas HQT enzyme activity was. In contrast to 5CGA, less abundant chlorogenic isomers increased during development. Concentrations of hydroxycinnamic acid amides were higher in immature tubers, as was expression of arginine- and ornithine decarboxylases. Expression of several genes involved in carbohydrate or shikimate metabolism, including sucrose synthase and DAHP, showed similar developmental patterns to phenylpropanoid pools, as did shikimate dehydrogenase enzyme activity. Sucrose, glucose and fructose concentrations were highest in immature tubers. Exogenous treatment of potatoes with sugars stimulated phenylpropanoid biosynthesis, suggesting sugars contribute to the higher phenylpropanoid concentrations in immature tubers. These changes in phenylpropanoid expression suggest the nutritional value of potatoes varies during development.

High-antioxidant potatoes: acute in vivo antioxidant source and hypotensive agent in humans after supplementation to hypertensive subjects.

Potatoes have the highest daily per capita consumption of all vegetables in the U.S. diet. Pigmented potatoes contain high concentrations of antioxidants, including phenolic acids, anthocyanins, and carotenoids. In a single-dose study six to eight microwaved potatoes with skins or a comparable amount of refined starch as cooked biscuits was given to eight normal fasting subjects; repeated samples of blood were taken over an 8 h period. Plasma antioxidant capacity was measured by ferric reducing antioxidant power (FRAP). A 24 h urine was taken before and after each regimen. Urine antioxidant capacity due to polyphenol was measured by Folin reagent after correction for nonphenolic interferences with a solid phase (Polyclar) procedure. Potato caused an increase in plasma and urine antioxidant capacity, whereas refined potato starch caused a decrease in both; that is, it acted as a pro-oxidant. In a crossover study 18 hypertensive subjects with an average BMI of 29 were given either six to eight small microwaved purple potatoes twice daily or no potatoes for 4 weeks and then given the other regimen for another 4 weeks. There was no significant effect of potato on fasting plasma glucose, lipids, or HbA1c. There was no significant body weight increase. Diastolic blood pressure significantly decreased 4.3%, a 4 mm reduction. Systolic blood pressure decreased 3.5%, a 5 mm reduction. This blood pressure drop occurred despite the fact that 14 of 18 subjects were taking antihypertensive drugs. This is the first study to investigate the effect of potatoes on blood pressure. Thus, purple potatoes are an effective hypotensive agent and lower the risk of heart disease and stroke in hypertensive subjects without weight gain.

LC-MS analysis of solanidane glycoalkaloid diversity among tubers of four wild potato species and three cultivars (Solanum tuberosum).

Secondary metabolites in potato tubers include both phytonutrients and plant defense compounds. The extent these small molecules vary among different potato genotypes is not well characterized. LC-MS analysis of tuber extracts from seven potato genotypes showed that one large source of small molecule variation is the glycoalkaloids. Glycoalkaloids are involved in the resistance of potatoes to pathogens and pests, but they also have implications for human health and nutrition. This study focused on glycoalkaloids with solanidane or solanidane-like aglycones, of which over 50 were tentatively identified, many of which appeared to be novel glycoalkaloids. Results suggested the variety of glycoalkaloids in potatoes is considerably greater than previously thought. Dissecting the role of these many glycoalkaloids in human health or pest and pathogen resistance will be a formidable undertaking.