Photosynthesis product allocation and yield in sweet potato with spraying exogenous hormones under drought stress.

This study investigated the alleviation effects of spraying phytohormones on the physiological characteristics and yield of sweet potato under drought stress during the early vine development and storage root bulking stage, respectively. The endogenous hormone contents, photosynthetic fluorescence indexes, photosynthetic products transfer allocation (based on 13C labeling method), and yield of sweet potato were studied by spraying water, 6-benzylaminopurine (6-BA), abscisic acid (ABA), and combined with the two exogenous hormones under artificial dry shed and dry pond. Results indicated that the yield was increased by spraying 6-BA or ABA separately in comparison with the control treatment under drought stress, and the alleviation effects of spraying 6-BA at the early stage were better than at the storage root bulking stage, while spraying ABA at the storage root bulking stage was better than at the early stage. The sweet potato yield increased when sprayed with 6-BA, especially at the early vine development stage, and sweet potato yield was further enhanced by the addition of ABA. When sprayed together, exogenous 6-BA and ABA increased plant shoot and storage root biomass, as well as leaf area and yield, at both stages. The combination of exogenous 6-BA and ABA also increased shoot 13C accumulation at the early vine development stage and storage root 13C accumulation at the storage root bulking stage, in comparison with 6-BA or ABA alone under drought stress. Spraying exogenous hormones under drought stress increased the endogenous hormone contents, enhanced carbon metabolism enzyme activities, improved the photosynthetic fluorescence characteristics of leaves, and regulated the source-sink balance, all of which alleviated the yield reduction caused by drought stress. Application of the combination of 6-AB and ABA yielded better results than that of the 6-BA or ABA alone.

Novel antifungal mechanism of oligochitosan by triggering apoptosis through a metacaspase-dependent mitochondrial pathway in Ceratocystis fimbriata.

The antifungal effects of oligochitosan (OCS) against Ceratocystis fimbriata that causes black rot disease in sweet potato and its apoptosis mechanism were evaluated. OCS restrained the mycelial growth and spores germination of C. fimbriata, and decreased the ergosterol content of cell membrane. Transmission electron microscopy observation and flow cytometry analysis revealed that OCS induced morphology changes with smaller size and increased granularity of C. fimbriata, which was the typical feature of apoptosis. To clarify the apoptosis mechanism induced by OCS, a series of apoptosis-related parameters were analyzed. Results showed that OCS induced reactive oxygen species accumulation, Ca2+ homeostasis dysregulation, mitochondrial dysfunction and metacaspase activation, coupled with hallmarks of apoptosis including phosphatidylserine externalization, DNA fragmentation, and nuclear condensation. In summary, OCS triggered apoptosis through a metacaspase-dependent mitochondrial pathway in C. fimbriata. These findings have important implications for the application of OCS to control pathogens in food and agriculture.

Effect of copper oxide nanoparticles on two varieties of sweetpotato plants.

Little information is available on the interaction of CuO nanoparticles (nCuO) with tuberous roots. In this study, Beauregard-14 (B-14, low lignin) and Covington (COV, high lignin) sweetpotato varieties were cultivated until maturity in soil amended with nCuO, bulk copper oxide (bCuO) and CuCl2 at 25-125 mg/kg. The Cu treatments had no significant influence on chlorophyll content. Gas exchange parameters were not affected in B-14. In COV, however, at 125 mg/kg treatments, bCuO reduced the intercellular CO2 (11%), while CuCl2 increased it by 7%, compared with control (p ≤ 0.035). At 25 mg/kg nCuO increased the length of COV roots (20.7 ± 2.0 cm vs. 14.6 ± 0.8 cm, p ≤ 0.05). In periderm of B-14, nCuO, at 125 mg/kg, increased Mg by 232%, while the equivalent concentration of CuCl2 reduced P by 410%, compared with control (p ≤ 0.05). The data suggest the potential application of nCuO as nanofertilizer for sweetpotato storage root production.

Split application enhances sweetpotato starch production by regulating the conversion of sucrose to starch under reduced nitrogen supply.

Split application could improve nitrogen (N) uptake and increase sweetpotato yields under reduced N supply; however, little is known about how it affects the process of starch production in storage roots. An experiment was conducted to determine the effects of three N management strategies [conventional basal N management; 80% of the conventional N rate applied as a basal fertilizer; 80% of the conventional N rate equally split at transplanting and 35 days after transplanting] on starch accumulation, enzyme activity and genes expression in the conversion of sucrose to starch and the relationships among them. The results showed that, compared with conventional basal N management, split application decreased sucrose accumulation by 11.78%, but increased starch accumulation by 11.12% through improving the starch accumulation rate under reduced N supply. The ratio of sucrose synthetase to sucrose phosphate synthase, the enzymatic activity of ADP-glucose pyrophosphorylase (AGPP), starch synthase, and the expression of their corresponding genes were promoted by split application under reduced N supply and were positively correlated with starch accumulation rate. AGPP is the rate-limiting enzyme in starch synthesis in storage roots under different N management strategies. These results indicate that starch accumulation was enhanced by split application through regulating the activity and gene expression of key enzymes involved in the conversion of sucrose to starch under reduced N supply.

Postharvest benzothiazole treatment enhances healing in mechanically damaged sweet potato by activating the phenylpropanoid metabolism.

BACKGROUND: Sweet potato often suffers mechanical damage during harvest, handling, and transportation. Infections, water loss, and quality changes of sweet potato caused by mechanical damage pose great financial losses. Wound healing is an effective method to alleviate such problems. In this study, the effects of postharvest treatment with benzothiazole (BTH) on wound healing of sweet potato was investigated. RESULTS: Postharvest BTH treatment of sweet potatoes promoted lignin accumulation in wounded tissues, and 100 mg L-1 BTH exhibited better effects than 50 mg L-1 or 150 mg L-1 BTH. The biosynthesis of lignin in wounded tissues significantly decreased the weight loss of sweet potatoes. An increase in respiration intensity after BTH treatment was observed. The total phenolic and flavonoid contents and the activity of phenylalanine ammonia-lyase, peroxidase, and polyphenol oxidase were increased in BTH-treated sweet potatoes. This suggests that BTH increases phenylpropanoid metabolism. CONCLUSION: Postharvest 100 mg L-1 BTH treatment could promote wound healing in mechanically damaged sweet potatoes. The activation of the phenylpropanoid metabolism might be the mechanism of action of BTH in wound healing. © 2020 Society of Chemical Industry.

Foliar application of glycinebetaine regulates soluble sugars and modulates physiological adaptations in sweet potato (Ipomoea batatas) under water deficit.

Drought tolerance in higher plants can result in enhanced productivity, especially in case of carbohydrate storage root crop. Sweet potato has been reported as a drought-tolerant crop, while it is very sensitive to water shortage in the root initiation of cutting propagation and tuber initiation stages. In the present study, we aimed to alleviate the drought-tolerant abilities in sweet potato cv. Tainung 57 (drought-sensitive cultivar) using foliar glycine betaine (GlyBet) application as compared with drought-tolerant cultivar (cv. Japanese Yellow). Leaf osmotic potential in GlyBet applied plants under mild- (25.5% soil water content; SWC) and severe-water deficit (15.5% SWC) stresses was maintained through the accumulation of total soluble sugars as a major osmotic adjustment, thus stabilizing the photosynthetic pigments, chlorophyll fluorescence, net photosynthetic rate, and retaining the overall growth performances, i.e., shoot height, number, and length of leaves. In the harvesting process, storage root weight in water deficit stressed sweet potato cv. Tainung 57 (11.75 g plant-1) with 50 mM GlyBet application was retained in a similar pattern to cv. Japanese Yellow (12.25 g plant-1). In the present investigation, exogenous foliar GlyBet application strongly alleviated water deficit stress via sugar enrichment to control cellular osmotic potential, retain high photosynthetic abilities and maintain the yield of storage root yield. In summary, the regulation on total soluble sugar enrichment in water deficit-stressed sweet potato using GlyBet foliar application may play an important role in maintaining the controlled osmotic potential of leaves, thereby retaining the photosynthetic abilities, overall growth characters and increasing the yield of storage roots.

Transgenic sweetpotato plants overexpressing tocopherol cyclase display enhanced α-tocopherol content and abiotic stress tolerance.

Oxidative stress caused by reactive oxygen species (ROS) under various environmental stresses significantly reduces plant productivity. Tocopherols (collectively known as vitamin E) are a group of lipophilic antioxidants that protect cellular components against oxidative stress. Previously, we isolated five tocopherol biosynthesis genes from sweetpotato (Ipomoea batatas [L.] Lam) plants, including tocopherol cyclase (IbTC). In this study, we generated transgenic sweetpotato plants overexpressing IbTC under the control of cauliflower mosaic virus (CaMV) 35S promoter (referred to as TC plants) via Agrobacterium-mediated transformation to understand the function of IbTC in sweetpotato. Three transgenic lines (TC2, TC9, and TC11) with high transcript levels of IbTC were selected for further characterization. High performance liquid chromatography (HPLC) analysis revealed that α-tocopherol was the most predominant form of tocopherol in sweetpotato tissues. The content of α-tocopherol was 1.6-3.3-fold higher in TC leaves than in non-transgenic (NT) leaves. No significant difference was observed in the tocopherol content of storage roots between TC and NT plants. Additionally, compared with NT plants, TC plants showed enhanced tolerance to multiple environmental stresses, including salt, drought, and oxidative stresses, and showed consistently higher levels of photosystem II activity and chlorophyll content, indicating abiotic stress tolerance. These results suggest IbTC as a strong candidate gene for the development of sweetpotato cultivars with increased α-tocopherol levels and enhanced abiotic stress tolerance.

Impacts of nitrogen fertilization rate on the root yield, starch yield and starch physicochemical properties of the sweet potato cultivar Jishu 25.

In recent years, the sweet potato cultivar Jishu 25 has exhibited good characteristics for starch processing in northern China. The storage root dry matter yields of this cultivar can exceed one ton per mu (1/15 of a hectare) at nitrogen (N) rates of 60-90 kg ha-1 based on soil nutrient content. However, the effect of N fertilizer on the physicochemical properties of starches isolated from this cultivar has not been reported. In order to evaluate these effects, three different N rates, 0 (control, N0), 75 (N1), and 150 kg ha-1 (N2), were selected for a field experiment in 2017. The results showed that N1 exhibited the highest storage root yield and starch yield. Compared to the control group, N fertilizer significantly increased the total starch content while no significant difference was found in these between the N1 and N2 groups. The amylose (AM) content was highest in the N2 group and lowest in the N0 group. In addition, N fertilizer exhibited no significant effects on the values of [D(v, 0.9)], D [4, 3] and D [3, 2]. Compared to the control group, N1 demonstrated significantly higher setback viscosity (SV), while N2 showed significantly higher peak viscosity (PV), cold paste viscosity (CPV) and SV. However, there were no significant differences in the hot paste viscosity (HPV), peak time and pasting temperature between the N1 and N2 groups. For the thermal properties of starch, there were no significant differences in peak temperature (Tp), conclusion temperature (Tc) or gelatinization enthalpy (ΔH) between the N1 and N2 groups. Overall, for the starch samples of cultivar Jishu 25, N fertilizer exerts significant effects on the starch content, AM content and viscosity properties but little effect on the particle size distribution and ΔH. 75 kg N ha-1 can easily lead to substantial planting benefits from the high storage root yield, dry matter yield and total starch content of this cultivar.

Spectral insight into thiosulfate-induced mercury speciation transformation in a historically polluted soil.

We studied the effect of different doses (0.5%, 2% and 5% (w/w)) of ammonium thiosulfate on mercury (Hg) speciation fractionation following its addition to the soil, as well as its accumulation by oilseed rape (Brassica napus L.), corn (Zea mays L.), and sweet potato (Ipomoea batatas L.), and compared them to a non-treated control in a historically polluted soil. The oilseed rape, corn, and sweet potato were planted consecutively in the same soils on days 30, 191, and 276, respectively after the addition of thiosulfate to the soil. The key results showed that bioavailable Hg contents in the rhizosphere soils ranged from 0.18 to 2.54 µg kg-1, 0.28 to 2.77 µg kg-1, and 0.24 to 2.22 µg kg-1, respectively, for the 0.5%, 2% and 5% thiosulfate treatments, which were close to the control soil (0.25 to 1.98 µg kg-1). The Hg L3-edge X-ray absorption near edge structure (XANES) results showed a tendency of the Hg speciation to transform from the Hg(SR)2 (initial soil, 56%; day-191 soil, 43%; day-276 soil, 46%, and day-356 soil, 16%) to nano particulated HgS (initial soil, 26%; day-191 soil, 42%; day-276 soil, 42%, and day-356 soil, 73%) with time in the soil treated with a 5% dose of thiosulfate. The Hg contents in the tissues of the crops, except for oilseed rape, were slightly affected by the addition of thiosulfate to the soil at all dosages, compared to the control. The addition of thiosulfate did not induce the movement of bioavailable Hg to the lower layer of the soil profile. We conclude a promotion of Hg immobilization by thiosulfate in the soil for over one year, offering a promising method for in-situ Hg remediation at Hg mining regions in China.

1-Methylcyclopropene (1-MCP) effects on natural disease resistance in stored sweet potato.

BACKGROUND: The potential of 1-methylcyclopropene (1-MCP) to maintain postharvest storage of sweet potato was studied. In two separate experiments, the orange-fleshed sweet potato cv. Covington was treated with 1-MCP (1.0 µL L-1 , 24 h) and roots stored at 15 °C. During storage, samples were evaluated for the respiration rate, sprout growth, weight loss, incidence of decay and changes in dry matter. The roots were further assayed for the temporal changes in individual non-structural carbohydrates and phenolic compounds in the skin and flesh tissues of the proximal (stem end), middle and distal (root end) regions. RESULTS: 1-MCP treatment reduced root weight loss and decay but respiration rate and non-structural carbohydrates were not affected. No sprouting was recorded irrespective of the treatment. 1-MCP transiently suppressed the accumulation of individual phenolic compounds, especially in the middle and distal segments. This accentuated the proximal dominance of phenolic compounds. Isochlorogenic acid A and chlorogenic acid were the dominant phenolics in the skin and flesh tissues, respectively. CONCLUSION: 1-MCP treatment may have an anti-decay effect and reduce weight loss. Therefore, storage trials that involve the use of continuous ethylene supplementation to inhibit sprout growth may be combined with 1-MCP to alleviate ethylene-induced weight loss and decay in sweet potato. © 2018 Society of Chemical Industry.

Differences between nitrogen-tolerant and nitrogen-susceptible sweetpotato cultivars in photosynthate distribution and transport under different nitrogen conditions.

To characterize the differences in photosynthate distribution and transport between nitrogen(N)-tolerant and N-susceptible sweetpotato cultivars under different N conditions, three N levels, including 0 (N0), 120 (N120), and 240 kg ha-1 (N240), were used in field experiments with the Jishu26 (J26) and Xushu32 (X32) cultivars in 2015 and 2016. The results from both years revealed that high N application reduced the tuberous root yield, the tuber/vine rate of carbon-13 (13C), and top-to-base (three equal segments of stem divided from the fifth opened leaf of the shoot tip to the main stem, defined as the top, middle, and base parts, respectively) gradients such as sucrose, ammonia N and potassium along the stem. 'J26' showed a higher yield than 'X32' under N0 but lower yield than 'X32' under N120 and N240. It also exhibited a higher 13C distribution to tuberous roots compared with that of 'X32' under N0, and the opposite trend was observed under N120 and N240. Under N0, 'J26' showed a steep top-to-base amino acid gradient and a significantly lower top-to-base sucrose increase along the stem in the late growth stage. Under N120 and N240, 'X32' exhibited a greater top-to-base decrease in the ammonia N along the stem during the main growth stages, a steep top-to-base sucrose gradient along the stem in the early growth stage, and a lower top-to-base sucrose increase along the stem in the middle and late growth stages. The formation of a reasonable photosynthate distribution structure attributed to high yield was related to a desirable sucrose, ammonia N or K+ gradient downward along the stem. These results might help provide farmers with sweetpotato cultivars using less or no N fertilizer in soils of different fertility and enhance the knowledge of yield-related physiology.

Xerophyta viscosa Aldose Reductase, XvAld1, Enhances Drought Tolerance in Transgenic Sweetpotato.

Sweetpotato is a significant crop which is widely cultivated particularly in the developing countries with high and stable yield. However, drought stress is a major limiting factor that antagonistically influences the crop's productivity. Dehydration stress caused by drought causes aggregation of reactive oxygen species (ROS) in plants, and aldose reductases are first-line safeguards against ROS caused by oxidative stress. In the present study, we generated transgenic sweetpotato plants expressing aldose reductase, XvAld1 isolated from Xerophyta viscosa under the control of a stress-inducible promoter via Agrobacterium-mediated transformation. Our results demonstrated that the transgenic sweetpotato lines displayed significant enhanced tolerance to simulated drought stress and enhanced recuperation after rehydration contrasted with wild-type plants. In addition, the transgenic plants exhibited improved photosynthetic efficiency, higher water content and more proline accumulation under dehydration stress conditions compared with wild-type plants. These results demonstrate that exploiting the XvAld1 gene is not only a compelling and attainable way to improve sweetpotato tolerance to drought stresses without causing any phenotypic imperfections but also a promising gene candidate for more extensive crop improvement.

A ζ-carotene desaturase gene, IbZDS, increases ß-carotene and lutein contents and enhances salt tolerance in transgenic sweetpotato.

ζ-Carotene desaturase (ZDS) is one of the key enzymes in carotenoid biosynthesis pathway. However, the ZDS gene has not been applied to carotenoid improvement of plants. Its roles in tolerance to abiotic stresses have not been reported. In this study, the IbZDS gene was isolated from storage roots of sweetpotato (Ipomoea batatas (L.) Lam.) cv. Nongdafu 14. Its overexpression significantly increased ß-carotene and lutein contents and enhanced salt tolerance in transgenic sweetpotato (cv. Kokei No. 14) plants. Significant up-regulation of lycopene ß-cyclase (ß-LCY) and ß-carotene hydroxylase (ß-CHY) genes and significant down-regulation of lycopene ε-cyclase (ε-LCY) and ε-carotene hydroxylase (ε-CHY) genes were found in the transgenic plants. Abscisic acid (ABA) and proline contents and superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities were significantly increased, whereas malonaldehyde (MDA) content was significantly decreased in the transgenic plants under salt stress. The salt stress-responsive genes encoding pyrroline-5-carboxylate reductase (P5CR), SOD, CAT, ascorbate peroxidase (APX) and POD were found to be significantly up-regulated in the transgenic plants under salt stress. This study indicates that the IbZDS gene has the potential to be applied for improving ß-carotene and lutein contents and salt tolerance in sweetpotato and other plants.

Suppression of the ß-carotene hydroxylase gene increases ß-carotene content and tolerance to abiotic stress in transgenic sweetpotato plants.

ß-carotene, a carotenoid that plays a key photo-protective role in plants is converted into zeaxanthin by ß-carotene hydroxylase (CHY-ß). Previous work showed that down-regulation of IbCHY-ß by RNA interference (RNAi) results in higher levels of ß-carotene and total carotenoids, as well as salt stress tolerance, in cultured transgenic sweetpotato cells. In this study, we introduced the RNAi-IbCHY-ß construct into a white-fleshed sweetpotato cultivar (cv. Yulmi) by Agrobacterium-mediated transformation. Among the 13 resultant transgenic sweetpotato plants (referred to as RC plants), three lines were selected for further characterization on the basis of IbCHY-ß transcript levels. The RC plants had orange flesh, total carotenoid and ß-carotene contents in storage roots were 2-fold and 16-fold higher, respectively, than those of non-transgenic (NT) plants. Unlike storage roots, total carotenoid and ß-carotene levels in the leaves of RC plants were slightly increased compared to NT plants. The leaves of RC plants also exhibited tolerance to methyl viologen (MV)-mediated oxidative stress, which was associated with higher 2,2-diphenyl-1- picrylhydrazyl (DPPH) radical-scavenging activity. In addition, RC plants maintained higher levels of chlorophyll and higher photosystem II efficiency than NT plants after 250 mM NaCl stress. Yield of storage roots did not differ significantly between RC and NT plants. These observations suggest that RC plants might be useful as a nutritious and environmental stress-tolerant crop on marginal lands around the world.

Zinc, copper, or cerium accumulation from metal oxide nanoparticles or ions in sweet potato: Yield effects and projected dietary intake from consumption.

The potential release of metal oxide engineered nanoparticles (ENP) into agricultural systems has created the need to evaluate the impact of these materials on crop yield and food safety. The study here grew sweet potato (Ipomoea batatas) to maturity in field microcosms using substrate amended with three concentrations (100, 500 or 1000 mg kg DW-1) of either nZnO, nCuO, or nCeO2 or equivalent amounts of Zn2+, Cu2+, or Ce4+. Adverse effects on tuber biomass were observed only for the highest concentration of Zn or Cu applied. Exposure to both forms of Ce had no adverse effect on yield and a slight positive benefit at higher concentrations on tuber diameter. The three metals accumulated in both the peel and flesh of the sweet potato tubers, with concentrations higher in the peel than the flesh for each element. For Zn, >70% of the metal was in the flesh and for Cu >50%. The peels retained 75-95% of Ce in the tubers. The projected dietary intake of each metal by seven age-mass classes from child to adult only exceeded the oral reference dose for chronic toxicity in a scenario where children consumed tubers grown at the highest metal concentration. The results throughout were generally not different between the ENP- and ionic-treatments, suggesting that the added ENPs underwent dissolution to release their component ions prior to accumulation. The results offer insight into the fate and impact of these ENPs in soils.

Essential Oil from Sweet Potato Vines, a Potential New Natural Preservative, and an Antioxidant on Sweet Potato Tubers: Assessment of the Activity and the Constitution.

Pathogenic fungi and oxidation are the major factors that cause the deterioration of sweet potatoes and also cause the loss of quality that makes consumption unsafe. In the present study, the in vitro results demonstrate that the essential oil from sweet potato vines exhibits significantly enhanced activity compared to that of the control. Furthermore, the essential oil can actively inhibit the growth of some common microorganisms inducing pathogenic bacteria and fungi (inhibition rates above 50% at low concentrations). A total of 31 constituents were identified using GC-MS and confirmed that linalool and p-hydroxybenzoic acid are the major active ingredients. The experiment involving actual tubers showed that the essential oil could retains its quality and effectiveness again the fungus disease. This suggests that it could be used in the food industry to increase the shelf life of stored produce (tubers) to ensure food safety without the use of additives or preservatives.

Molecular characterization of tocopherol biosynthetic genes in sweetpotato that respond to stress and activate the tocopherol production in tobacco.

Tocopherol (vitamin E) is a chloroplast lipid that is presumed to be involved in the plant response to oxidative stress. In this study, we isolated and characterized five tocopherol biosynthetic genes from sweetpotato (Ipomoea batatas [L.] Lam) plants, including genes encoding 4-hydroxyphenylpyruvate dioxygenase (IbHPPD), homogentisate phytyltransferase (IbHPT), 2-methyl-6-phytylbenzoquinol methyltransferase (IbMPBQ MT), tocopherol cyclase (IbTC) and γ-tocopherol methyltransferase (IbTMT). Fluorescence microscope analysis indicated that four proteins localized into the chloroplast, whereas IbHPPD observed in the nuclear. Quantitative RT-PCR analysis revealed that the expression patterns of the five tocopherol biosynthetic genes varied in different plant tissues and under different stress conditions. All five genes were highly expressed in leaf tissues, whereas IbHPPD and IbHPT were highly expressed in the thick roots. The expression patterns of these five genes significantly differed in response to PEG, NaCl and H2O2-mediated oxidative stress. IbHPPD was strongly induced following PEG and H2O2 treatment and IbHPT was strongly induced following PEG treatment, whereas IbMPBQ MT and IbTC were highly expressed following NaCl treatment. Upon infection of the bacterial pathogen Pectobacterium chrysanthemi, the expression of IbHPPD increased sharply in sweetpotato leaves, whereas the expression of the other genes was reduced or unchanged. Additionally, transient expression of the five tocopherol biosynthetic genes in tobacco (Nicotiana bentamiana) leaves resulted in increased transcript levels of the transgenes expressions and tocopherol production. Therefore, our results suggested that the five tocopherol biosynthetic genes of sweetpotato play roles in the stress defense response as transcriptional regulators of the tocopherol production.

Plant-growth regulators alter phytochemical constituents and pharmaceutical quality in Sweet potato (Ipomoea batatas L.).

BACKGROUND: Sweet potato (Ipomoea batatas L.) is one of the most important consumed crops in many parts of the world because of its economic importance and content of health-promoting phytochemicals. METHODS: With the sweet potato (Ipomoea batatas L.) as our model, we investigated the exogenous effects of three plant-growth regulators methyl jasmonate (MeJA), salicylic acid (SA), and abscisic acid (ABA) on major phytochemicals in relation to phenylalanine ammonia lyase (PAL) activity. Specifically, we investigated the total phenolic content (TPC), total flavonoid content (TFC), total anthocyanin content (TAC), and total ß-carotene content (TCC). Individual phenolic and flavonoid compounds were identified using ultra-high performance liquid chromatography (UHPLC). Antioxidant activities of treated plants were evaluated using a 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay and a ß-carotene bleaching assay. Anticancer activity of extracts was evaluated against breast cancer cell lines (MCF-7 and MDA-MB-231) using MTT assay. RESULTS: TPC, TFC, TAC, and TCC and antioxidant activities were substantially increased in MeJA-, SA-, and ABA-treated plants. Among the secondary metabolites identified in this study, MeJA application significantly induced production of quercetin, kaempferol, myricetin, gallic acid, chlorogenic acid, 3,5-dicaffeoylquinic acid, and 4,5-dicaffeoylquinic acid. Luteolin synthesis was significantly induced by SA application. Compared with control plants, MeJA-treated sweet potato exhibited the highest PAL activity, followed by SA and ABA treatment. The high DPPH activity was observed in MeJA followed by SA and ABA, with half-maximal inhibitory concentration (IC50) values of 2.40, 3.0, and 3.40 mg/mL compared with α-tocopherol (1.1 mg/mL). Additionally, MeJA-treated sweet potato showed the highest ß-carotene bleaching activity, with an IC50 value of 2.90 mg/mL, followed by SA (3.30 mg/mL), ABA (3.70 mg/mL), and control plants (4.5 mg/mL). Extracts of sweet potato root treated with MeJA exhibited potent anticancer activity with IC50 of 0.66 and 0.62 mg/mL against MDA-MB-231 and MCF-7 cell lines respectively, compared to that of extracts of sweet potato treated with SA (MDA-MB-231 = 0.78 mg/mL; MCF-7 = 0.90 mg/mL) and ABA (MDA-MB-231 = 0.94 mg/mL; MCF-7 = 1.40 mg/mL). The results of correlation analysis showed that anthocyanins and flavooids are corresponding compounds in sweet potato root extracts for anticancer activity against breast cancer cell lines. CONCLUSIONS: MeJA has great potential to enhance the production of important health-promoting phytochemicals in sweet potato.

Phyotoxicity of diesel soil contamination on the germination of Lactuca sativa and Ipomoea batatas.

Phytotoxic effect of diesel contaminated soil on germination rate of Lactuca sativa and Ipomoea batatas, at two concentrations ranges (0-6ml and 0-30ml), were investigated and compared. Diesel soil contamination was simulated and soil samples were taken from contaminated soil at 1, 5,10, 15, 25, 50, 75 and 100 days should be after planting. The result showed that in both plant species, diesel inhibited germination in a concentration dependent manner, Also, the influence of diesel contamination diminished with increased time duration; suggesting possible reduction in diesel toxicity over time. However, germination of lettuce was significant and negatively correlated (r2 = -0.941) with diesel contamination as compared to sweet potato (r2 = -0.638).Critical concentration of diesel in relation to seed germination of L. sativa was lower than vegetative germination of I. batatas, indicating that germination of I. batatas was less sensitive to diesel contamination as compared to L. sativa.

CRYOPRESERVATION OF SWEET POTATO SHOOT TIPS USING A DROPLET-VITRIFICATION PROCEDURE.

BACKGROUND: Sweet potato is a staple food worldwide, but a problematic species in terms of long term storage, as it is not suitable for germplasm conservation. OBJECTIVE: This study aimed to develop cryopreservation protocols for sweet potato shoot tips based on a droplet-vitrification procedure. METHODS: As a standard procedure, sweet potato shoot tips were precultured in a liquid MS medium supplemented with 10% sucrose (S-10%) and 17.5% sucrose (S-17.5%) for 31 and 17 h, respectively. They were then osmoprotected with C4-35% (17.5% glycerol + 17.5% sucrose) for 50 min and cryoprotected with PVS3 (50% glycerol + 50% sucrose) for 60 min. A set of experiments was designed to investigate critical factors, i.e. stepwise sucrose preculture, osmoprotection, cryoprotection with PVS2- and PVS3-based vitrification solutions, and their combinational effect, as well as temperature alteration through placement in a cooling/rewarming container. RESULTS: Sucrose preculture was determined to be necessary for the adaptation of sweet potato shoot tips to cryoprotection with PVS3, and the highest post-thaw (LN) regeneration rate was observed in a preculture with S-10% for 31 h → S-17.5% for 17 h (19.0%). The effect of one-step or two-step osmoprotection was not significant on survival or regeneration of either the cryoprotected-control (LNC) or LN shoot tips. Responses of sweet potato shoot tips to osmoprotection and cryoprotection were linked to the level of sucrose preculture. The use of alumimium foil strips (droplet-vitrification) resulted in significantly higher LN survival (89.8%) and regeneration (19.0%), compared to those using cryovials (vitrification, 67.2% and 0%, respectively). LN regeneration increased by 67.5% when cryopreserved shoot tips were transferred to a new postculture medium. CONCLUSIONS: This study demonstrates that the combination of stepwise sucrose preculture with a higher final concentration (up to 17.5%), cryoprotection with PVS3 and cooling with foil strip is crucial to the regeneration of LN sweet potato shoot tips.