Sweetpotato Storage Roots Research Articles

Molecular Genetic Characterization of Sweet potato virus G (SPVG) Isolates from Areas of the Pacific Ocean and Southern Africa.

Sweet potato virus G (SPVG, genus Potyvirus, family Potyviridae) was detected in sweetpotato (Ipomoea batatas) storage roots sold in the local markets and storage roots or cuttings sampled directly from farmers' fields. Using serological and molecular methods, the virus was detected for the first time in Java, New Zealand, Hawaii, Tahiti, Tubuai, Easter Island, Zimbabwe, and South Africa, and also in an imported storage root under post-entry quarantine conditions in Western Australia. In some specimens, SPVG was detected in mixed infection with Sweet potato feathery mottle virus (genus Potyvirus). The coat protein (CP) encoding sequences of SPVG were analyzed for 11 plants from each of the aforementioned locations and compared with the CP sequences of 12 previously characterized isolates from China, Egypt, Ethiopia, Spain, Peru, and the continental United States. The nucleotide sequence identities of all SPVG isolates ranged from 79 to 100%, and amino acid identities ranged from 89 to 100%. Isolates of the same strain of SPVG had nucleotide and amino acid sequence identities from 97 to 100% and 96 to 100%, respectively, and were found in sweetpotatoes from all countries sampled except Peru. Furthermore, a plant from Zimbabwe was co-infected with two clearly different SPVG isolates of this strain. In contrast, three previously characterized isolates from China and Peru were phylogenetically distinct and exhibited <90% nucleotide identity with any other isolate. So far, the highest genetic diversity of SPVG seems to occur among isolates in China. Distribution of SPVG within many sweetpotato growing areas of the world emphasizes the need to determine the economic importance of SPVG.

Antimicrobial, Dehydroascorbate Reductase, and Monodehydroascorbate Reductase Activities of Defensin from Sweet Potato [Ipomoea batatas (L.) Lam. ‘Tainong 57’] Storage Roots

A cDNA encoding a small cysteine-rich protein designated defensin (SPD1) was isolated from sweet potato storage roots. On the basis of the amino acid sequence similarity and conserved residues, it is suggested that SPD1 is a member of the plant defensin family. Recombinant SPD1 protein overproduced in Escherichia coli was purified by Ni (2+)-chelated affinity chromatography. A recombinant protein from the storage root cDNA clone effectively inhibited the trypsin activity in a dose-dependent manner. Both the corresponding mRNA and protein level were found to be highest in the storage roots, followed by sprout. SPD1 reduced dehydroascorbate (DHA) in the presence of glutathione to regenerate l-ascorbic acid (AsA). However, without glutathione, SPD1 has very low DHA reductase activity, and AsA was oxidized by AsA oxidase to generate monodehydroascorbate (MDA) free radical. MDA was also reduced by SPD1 to AsA in the presence of NADH, mimicking the MDA reductase catalyzed reaction. These data suggest that SPD1 has both DHA reductase and MDA reductase activities. SPD1 was also shown to inhibit the growth of both fungi and bacteria. SPD1 is apparently the first reported plant defensin exhibiting DHA and MDA activities in vitro.

Suppression of root-knot nematode damage to succeeding sweet potato by summer-sown cultivation of an oat variety, "Tachiibuki"

Reproduction of four populations of Meloidogyne incognita on ten oat varieties was examined in a greenhouse. Eggmass numbers produced on oat roots inoculated with 500 J2 were counted. Eggmasses of all nematode populations were present on all oat varieties but“Tachiibuki”had the lowest number (1.8 - 11.8 eggmasses / root system). Summersown cultivation of four early forage oat varieties sown in September and a fallow treatment were examined in a field infested with M. incognita and M. arenaria. The final / initial population density of J2 (Pf / Pi) in December for varieties “Haeibuki”,“Super Hayate Hayabusa”, “Tachiakane”,“Tachiibuki”and the fallow were 36.5, 34.7, 23.9, 1.9 and 0.2, respectively. Yield of succeeding sweet potato planted in May of the next year and harvested in September was highest in the plot that was previously cropped with the variety “Tachiibuki”, and in the “Tachiakane” plot which also received a nematicide treatment (1.5% a.i. fosthiazate, 20 kg / 10 a) before planting. Sweet potato storage roots from the “Haeibuki”, “Super Hayate Hayabusa” and fallow plots were significantly damaged by root-knot nematode with similar low yields. Damage to storage roots caused by the nematode was significantly reduced by the preceding “Tachiibuki” cropping to an extent similar to the nematicide treatment.

Piecemeal versus one-time harvesting of sweet potato in north-eastern Uganda with special reference to pest damage

In north-eastern Uganda, the sweet potato crop of small subsistence farmers is severely affected by many pests, including (rough) sweet potato weevils, nematodes and millipedes. Field experiments with sweet potato ( Ipomoea batatas (L.) Lam.) were conducted at Arapai Station in Soroti District, northeastern Uganda in three consecutive seasons to study the differences between the indigenous practice of harvesting piecemeal in combination with storage ‘in-ground on plants’ and one-time harvesting after crop senescence, with special reference to damage caused by sweet potato weevils ( Cylas spp.), rough sweet potato weevils ( Blosyrus spp.), millipedes (Diplopoda) and nematodes. The area has two rainy seasons per calendar year, the first one with long, reliable rains and the second one with short, unreliable rains. Severe sweet potato weevil damage in the vines was responsible for the mortality of 46% of the plants in Experiment 1, which was carried out during the first rainy season. Starting 3 months after planting (MAP), sizable storage roots could be harvested, although their number and weight declined after 4 MAP with piecemeal harvesting. The highest storage-root yield (17.8 Mg ha −1) was found in Experiment 2 (second rainy season) at the final harvest. The yield of storage roots stored ‘in-ground on plants’ during the prolonged dry season (Experiment 3) was very low compared with the yields of Experiment 1 (first rainy season) and Experiment 2 (second rainy season). Sweet potato weevil damage of the storage roots was significantly less with piecemeal harvesting than with onetime harvesting, and piecemeal harvesting also increased the quality of the storage roots for human consumption and commercial purposes. However, with piecemeal harvesting the rough sweet potato weevil ( Blosyrus spp.) caused more storage root damage than with one-time harvesting. No statistically significant differences between the two types of harvesting were found for damage caused by nematodes or millipedes. It was concluded that piecemeal harvesting of sweet potato storage roots contributes to the control of sweet potato weevil in both vines and storage roots and hence improves the quality of the harvested roots. As rainfall distribution affects the population dynamics of this weevil this method can only be used during a limited period of the year.

Inhibition of Reactive Nitrogen Species in Vitro and ex Vivo by Trypsin Inhibitor from Sweet Potato ‘Tainong 57' Storage Roots

Peroxynitrite (ONOO-), formed from a reaction of superoxide and nitric oxide, is one of the most potent cytotoxic species known to oxidize cellular constituents including essential proteins, lipids, and DNA. ONOO- induces cellular and tissue injury, resulting in several human diseases such as Alzheimer's disease, atherosclerosis, and stroke. Due to the lack of endogenous enzymes responsible for ONOO- scavenging activity, finding a specific ONOO- scavenger is of considerable importance. In this study, the ability of trypsin inhibitor (TI), isolated from sweet potato storage roots (SPTI), to scavenge *ON and ONOO- was investigated. The data obtained show that TI generated a dose-dependent inhibition on production of nitrite and superoxide radicals. The IC50 value of TI on superoxide radical was 143.2 +/- 4.29 microg/mL. SOD activity staining was used to confirm SOD activity of SPTI. SPTI also caused a dose-dependent inhibition of the oxidation of dihydrorhodamine 123 (DHR) by peroxynitrite. A calculated IC50 value of 809.1 +/- 32.36 microg/mL was obtained on the inhibition of peroxynitrite radical. Spectrophotometric analyses revealed that TI suppressed the formation of ONOO--mediated tyrosine nitration through an electron donation mechanism. In further studies, TI also showed a significant ability to inhibit nitration of bovine serum albumin (BSA) in a dose-dependent manner. In vivo TI inhibited lipopolysaccharide-induced nitrite production in macrophages in a concentration-dependent manner with an IC50 value of 932.8 +/- 29.85 microg/mL. The present study suggested that TI had an efficient reactive nitrogen species scavenging ability. TI might be a potential effective NO and ONOO- scavenger useful for the prevention of NO- and ONOO--involved diseases.

Feeding activity of the East African millipede Omopyge sudanica Kraus on different crop products in laboratory experiments

Millipedes can cause considerable damage in the production of sweet potato and some other crops in East Africa. Quantitative information on intake of crop diets by and body weight gain of millipedes was collected in short-term no-choice feeding activity laboratory experiments conducted in north-eastern Uganda using female millipedes of the species Omopyge sudanica. Diets consisted of sweet potato and cassava storage root material, groundnut seeds, or maize grains. Differences in intake and body weight gain between diets were not statistically different. The consumption index, i.e., the ratio between intake and body weight gain, was significantly higher for sweet potato than for most other diets. The efficiency of conversion of ingested food, i.e., 100 × the ratio between body weight gain and intake, was significantly lower for the root crops — especially sweet potato — than for the grain crops. The research showed how difficult it is to obtain reliable, quantitative data on the feeding habits of millipedes, but also illustrated that O. sudanica can cause harm to crops in north-eastern Uganda and elsewhere in East Africa.

Growth Inhibition and Induction of Apoptosis in NB4 Promyelocytic Leukemia Cells by Trypsin Inhibitor from Sweet Potato Storage Roots

The objective of this study was to investigate the antiproliferative effect and the mechanism of trypsin inhibitor (TI) from sweet potato [Ipomoea batatas (L.) Lam. 'Tainong 57'] storage roots on NB4 promyelocytic leukemia cells. The results showed that TI inhibited cellular growth of NB4 promyelocytic leukemia cells in a time-dependent and dose-dependent manner, and treatment for 72 h induced a marked inhibition of cellular growth, showing an IC50 of 57.1 +/- 8.26 microg/mL. TI caused cell cycle arrest at the G1 phase as determined by flow cytometric analysis and apoptosis as shown by DNA laddering. TI-induced cell apoptosis involved p53, Bcl-2, Bax, and cytochrome c protein in NB4 cells. P53 and Bax proteins were accumulated, and antiapoptotic molecule Bcl-2 was decreased in the tested cells in a time-dependent manner during TI treatment. TI also induced a substantial release of cytochrome c from the mitochondria into the cytosol. Hence, TI induced apoptosis in NB4 cells through a mitochondria-dependent pathway, which was associated with the activation of caspase-3 and -8. These results demonstrated that TI induces NB4 cell apoptosis through the inhibition of cell growth and the activation of the pathway of caspase-3 and -8 cascades.

Extraction of RNA from fresh, frozen, and lyophilized tuber and root tissues.

A method for isolating transcriptionally competent RNA from fresh, frozen, and lyophilized plant storage tissues containing high levels of starch and phenolics is described. The protocol avoids the use of guanidium salts, which often lead to the formation of a viscous gel during extraction of high starch-containing tissues, and instead uses a borate-Tris buffer in combination with high concentrations of NaCl, Na2SO3, and sodium dodecyl sulfate in the extraction medium. RNA was extracted from fresh, frozen, and lyophilized tissues of potato tubers, storage roots of sweet potato, radish, and turnip, and rhizomes of ginger. The yield of RNA from potato tubers averaged 281 microg g fresh weight(-1) and 1584 microg g dry weight(-1) from frozen and lyophilized samples, respectively. A260/A230 ratios of potato RNA extracts were 2.2 or greater, indicating minimal contamination by polyphenols and carbohydrates. Similarly, A260/A280 ratios exceeded 1.9, demonstrating minimal contamination of the RNA by tuber protein. While A260/A280 ratios of extracts from the other plant species were somewhat lower than those for potato (average = 1.56 and 1.80 for fresh and lyophilized samples, respectively), A260/A230 ratios averaged more than 2.0, and the RNA extracted from fresh and lyophilized samples of all species was intact, as demonstrated by denaturing agarose-formaldehyde gel electrophoresis. The protocol yielded RNA suitable for downstream molecular applications involving reverse transcription-polymerase chain reaction from all five species. Transcriptionally competent RNA was also recovered from lyophilized potato tuber tissue stored for 6 years (ambient temperature) by a simple modification to the protocol involving extraction in cold acetone. Lyophilization can thus be used to preserve RNA in high starch- and phenolic-containing plant tissues for studies on gene expression.

TRANSGENIC SWEETPOTATO WITH AMYLOSE-FREE STARCH

In the storage roots of sweetpotato (Ipomoea batatas (L.) Lam. cv. 'Kokei 14'), the starch consists of 18 to 20% of amylose and the other major component is amylopectin. Granule-bound starch synthase I (GBSSI) is one of the key enzymes to catalyze the formation of amylose. Amylose-free transgenic sweetpotato plants were successfully obtained by inhibition of the sweetpotato GBSSI gene expression through RNA interference. The gene construct consisting of an inverted repeat of the first exon separated by the first intron of GBSSI and driven by the CaMV 35S promoter was integrated into the sweetpotato genome by Agrobacterium tumefaciens-mediated transformation. About 73% of transgenic plants were inactivated by the expression of GBSSI, resulting in the storage roots containing only amylopectin but no amylose. The results clearly demonstrate that the amylose synthesis is completely inhibited in roots of sweetpotato plants which constitutively synthesized double stranded RNA of GBSSI. The RNA interference is very effective in inhibiting the gene expression in the starch metabolic pathway in sweetpotato.

Increase of amylose content of sweetpotato starch by RNA interference of the starch branching enzyme II gene (IbSBEII)

In the storage roots of sweetpotato (Ipomoea batatas (L.) Lam. cv. Kokei 14), 10 to 20% of the starch is essentially unbranched linear amylose and the other major component is branched amylopectin. The starch branching enzymes, which are responsible for production of amylopectin to form α-1,6-linkages in the glucan can be divided into two classes, class A (e.g. potato and maize SBEII, pea SBEI) and class B (e.g. potato and maize SBEI, pea SBEII). On the bases of the registered cDNA of sweetpotato SBEII (IbSBEII) encoding class A branching enzyme, we constructed double-stranded RNA (dsRNA) interference vectors and introduced them into sweetpotato genome via Agrobacterium-mediated gene transformation. We obtained eight independent transgenic plants by using two kinds of RNA interference (RNAi) constructs, encoding GBSSI 1st intron-spliced RNA or a GUS fragment-spliced RNA, respectively. All transgenic plants were confirmed not to express IbSBEII by RT-PCR and to have the starch with a higher amylose content than the non-transgenic control (up to 25% compared to 10% in the control). Both constructs induced the same level of silencing of IbSBEII in all transgenic plants. The morphological characters showed no significant differences between the transgenic and control plants. Starch yield of transgenic tubers was slightly lower than that of non-transgenic tubers. The starch granules of the transgenic plants were similar to those of typical sweetpotato starchs in shape and the distribution in granule size, but slightly different in grain structure.

安価な原料用サツマイモを用いたアリモドキゾウムシの大量増殖

We compared three sweet potato cultivars used mainly for starch and alcohol production, (‘Shirosatsuma’, ‘Shiroyutaka’ and ‘Koganesengan’) with another used for cooking (‘Tosabeni’) to study the feasibility of those three cultivars as an inexpensive diet material for the mass-production of adult sweet potato weevils to be sterilized for insect release. About 1,500 adult weevils (sex ratio≒1:1) were reared on sweet potato storage roots for 2 wk to allow oviposition. Four roots (ca. 800 g) were set out at a time and were replaced with new ones at intervals of 3–4 d. The emergence time of new adults from the roots of Shiroyutaka tended to be a little earlier, and those of Koganesengan a little later than those of Tosabeni. The number of adult weevils available for sterile insect release was no more than 2.7% less when weevils were reared on Koganesengan than when reared on Tosabeni. There was no significant difference in the number of adult weevils produced per gram of sweet potato root between the three cultivars and Tosabeni. Importantly, the percentage of males among emerged adults (sex ratio) was significantly higher in the three cultivars than in Tosabeni. The weevils in a root of Shiroyutaka tended to reach the stage suitable for irradiation 1–2 d earlier than those in Tosabeni. Based on these results, it was concluded that the three cultivars 'Shirosatsuma, Shiroyutaka and Koganesengan' were suitable as diet materials for the mass-production of weevils.

Two sweetpotato ADP-glucose pyrophosphorylase isoforms are regulated antagonistically in response to sucrose content in storage roots

The transcriptional regulation of ADP-glucose pyrophosphorylase (AGPase) genes in detached leaves in response to exogenous sucrose has been investigated earlier; however the effects of endogenous sucrose on AGPase gene transcription in leaves or starch-accumulating tissues have not yet been determined. We therefore have investigated the relationship between endogenous sucrose content in the storage tissues of sweetpotato ( Ipomoea batatas cv. Yulmi) and the rate of transcription of the two sweetpotato AGPase isoforms, ibAGP1 and ibAGP2, by means of transient expression analysis of their promoters. Sequence analysis of the two promoters identified putative sucrose-responsive elements on the ibAGP1 promoter and, conversely, putative sucrose-starvation elements on the ibAGP2 promoter. Transient expression analyses on transverse storage root sections revealed that the ibAGP1 and ibAGP2 promoters directed strong expression in the sweetpotato storage roots (diameter: 1.5 cm). Sucrose contents of the sweetpotato storage roots were positively correlated with growth of the storage root. In the storage roots, ibAGP1 promoter activity became stronger with increasing endogenous sucrose levels, while ibAGP2 promoter activity became markedly weaker. Consequently, ibAGP2 was expressed primarily during the early stages of storage root development, whereas ibAGP1 was abundantly expressed in the later stages, during which a profound level of starch accumulation occurs. The antagonistic regulation of the two promoters in response to endogenous sucrose levels was also confirmed in carrot ( Daucus carota L. cv. Hapa-ochon) taproots.

Post Harvest Spoilage of Sweetpotato in Tropics and Control Measures

Sweetpotato storage roots are subjected to several forms of post harvest spoilage in the tropical climate during transportation from farmers' field to market and in storage. These are due to mechanical injury, weight loss, sprouting, and pests and diseases. Sweetpotato weevil is the single most important storage pest in tropical regions for which no control measures or resistant variety are yet available. Several microorganisms (mostly fungi) have been found to induce spoilage in stored sweetpotatoes. The most important among them are Botryodiplodia theobromae, Ceratocystis fimbriata, Fusarium spp., and Rhizopus oryzae. The other less frequently occurring spoilage microorganisms include Cochliobolus lunatus (Curvularia lunata), Macrophomina phaseolina, Sclerotium rolfsii, Rhizoctonia solani, Plenodomus destruens. Microbial spoilage of sweetpotato is found associated with decrease in starch, total sugar, organic acid (ascorbic acid and oxalic acid) contents with concomitant increase in polyphenols, ethylene, and in some instances phytoalexins. Several methods are used to control microbial spoilage. Curing to promote wound healing is found as the most suitable method to control microbial spoilage. Curing naturally occurs in tropical climates where mean day temperature during sweetpotato harvesting season (February–April) invariably remains at 32–35°C and relative humidity at 80–95%. Sweetpotato varieties varied in their root dry matter content, and low root dry matter content attributed for their high curing efficiency. Curing efficiency of varieties also differed in response to curing periods. Fungicide treatment, bio-control, gamma irradiation, hydro warming, and storage in sand and saw dust were found to have intermediate impacts in controlling spoilage and enhancing shelf life of sweetpotato roots. Breeding program has to be chalked out to develop new varieties suitable to curing under tropical conditions in addition to developing varieties having multi-spectrum resistance to major post harvest rot pathogens and sweet potato weevils.

Sweet potato ( Ipomoea batatas [L.] Lam ‘Tainong 57’) storage root mucilage with antioxidant activities in vitro

Sweet potato storage root mucilage was extracted and purified by SDS and heating treatments. Total antioxidant activity, DPPH (1,1-diphenyl-2-picrylhydrazyl) staining, reducing power method, metal ion-dependent hydroxyl radical, FTC (ferric thiocyanate) method, and protection of calf thymus DNA against hydroxyl radical-induced damage were studied. Half-inhibition concentrations, IC 50, were 0.08 mg/ml and IC 50 > 0.1 mg/ml, respectively, for the crude and purified mucilage in the total antioxidant activity test. In the DPPH staining, the crude and purified mucilage appeared as white spots when they were diluted to 50 and 100 μg per application, respectively. Like total antioxidant activity, reducing power, scavenging capacity against hydroxyl radical, FTC activity and protection of calf thymus DNA against hydroxyl radical-induced damage were found in the mucilage. It is suggested that the mucilage might contribute its antioxidant activities against both hydroxyl and peroxyl radicals.

Regulating the composition of anthocyanins and phenolic acids in a sweetpotato cell culture towards production of polyphenolic complex with enhanced physiological activity

Recent confirmation in the scientific literature of the health-promoting qualities of natural food colorants prompted their increased application in food products. Anthocyanins, a large group of natural pigments, include compounds with diverse molecular structures and different physiological activities. Therefore, selection of specific anthocyanins with enhanced bioactivity for application in functional foods needs to be addressed. Biotechnology offers an opportunity for ongoing production of selected phytochemicals for application in pharmaceutical, cosmetic or food industries. However, application of plant cell culture for commercial production of natural food colorants is still not an achieved goal due to lack of economical viability. One of the ways of improving the efficiency of the system is the production of high-value compounds superior to those accumulated in field-grown plant. This paper presents a review of our earlier works aiming to establish a plant cell culture-based system for the production of anthocyanin–phenolic acid complex with enhanced stability and physiological activity from a high-anthocyanin accumulating cell line generated from the storage root of sweetpotato ( Ipomoea batatas L.), cv. Ayamurasaki. Modifications of the physical and chemical environment of culture growth have been employed to direct the in vitro production of anthocyanins towards the generation of components with enhanced stability and radical scavenging ability. Under the same conditions we have enhanced the accumulation of caffeic acid and chlorogenic (caffeoylquinic) acid and induced accumulation of derivatives: 4,5-dicaffeoylquinic acid, 3,5-dicaffeoylquinic acid, 3,4-dicaffeoylquinic acid and 3,4,5-tricaffeoylquinic acid. In vitro generation of polyphenolic complex consisting of selected anthocyanins and phenolic acids with enhanced nutraceutical value has been achieved.

Probing Anthocyanin Profiles in Purple Sweet Potato Cell Line (Ipomoea batatas L. Cv. Ayamurasaki) by High-Performance Liquid Chromatography and Electrospray Ionization Tandem Mass Spectrometry

A purple line cell line (PL) generated from the storage root of purple-fleshed sweet potato (Ipomoea batatas L.) cv. Ayamurasaki produces a complex mixture of anthocyanins, and seven major anthocyanins have been isolated and identified to date. All these anthocyanins are exclusively cyanidin or peonidin 3-sophoroside-5-glucosides and their acylated derivatives. High-performance liquid chromatography (HPLC) coupled to photodiode array (PDA) detection and electrospray ionization tandem mass spectrometry (ESI-MS/MS) on a triple quadrupole instrument was employed to further investigate the anthocyanin composition of the PL extract. Precursor-ion analysis, product-ion analysis, and selected reaction monitoring (SRM) MS/MS experiments were conducted sequentially to screen and characterize anthocyanins in the aqueous extract of the PL cell line. Precursor-ion analysis specifically detected the molecular cations of each category of anthocyanins by scanning the precursors of anthocyanidins (cyanidin, peonidin, and pelargonidin). The detected molecular cation of each anthocyanin was fragmented using product-ion analysis by collisionally activated dissociation (CAD). MS/MS using SRM detection was conducted to further confirm the fragmentation observed during product-ion analysis. In comparison to the commonly used product-ion analysis technique, the combined use of precursor-ion analysis, product-ion analysis, and SRM is particularly useful for positive identification of anthocyanins in complex matrixes and provides important information to confirm the proposed structures. Twenty-six anthocyanins were detected and characterized in the aqueous extract of the PL cell line. Several anthocyanins, including two pelargonidin derivatives, were tentatively identified for the first time in these cells.

(361) Public Domain Computer Programs for Quantifying Size and Shape in Horticultural Research

Shape measurements in horticultural research have generally been expressed as ratios or indexes. Computer-based image analysis enables the objective quantification and statistical analysis of two-dimensional sample shape variability. In addition, the availability of public domain software facilitates the inexpensive but accurate quantification of object shape in horticultural research. We describe the procedures for measuring sample shape using the following publicly available software: ImageJ, ImageTool, and SHAPE. Using U.S. #1 sweetpotato storage root samples from plots subjected to various weed control treatments, we detected significant differences in elongation, compactness, as well as shape attributes. We also measured size and shape variability from representative fruit, leaf, and floral organ samples. The results demonstrate that, where possible, measurement of two-dimensional samples can be undertaken inexpensively and accurately using public domain software applications.

Isolation and expression of protein disulfide isomerase cDNA from sweet potato ( Ipomoea batatas [L.] Lam ‘Tainong 57’) storage roots

A protein disulfide isomerase (PDI) coding sequence was cloned by differential display from sweet potato ( Ipomoea batatas [L.] Lam ‘Tainong 57’) storage roots. The cDNA contains 1869 bp in length and encodes a protein of 503 amino acids. Primary structure analysis of the deduced protein revealed two thioredoxin-like active sites (CGHC), and an endoplasmic reticulum-retention signal at its C-terminus (KDEL), which is also found in PDIs of plants and animals. Although there is only about 65% amino acid identity between SPPDI1 and other plant PDIs, the active site regions are almost identical. A recombinant protein expressed from the storage root cDNA clone effectively catalyzed glutathione–insulin transhydrogenation. SPPDI1 reduced dehydroascorbate (DHA) in the presence of glutathione to regenerate l-ascorbic acid (AsA). However, without glutathione, SPPDI1 has very low DHA reductase activity. And AsA was oxidized by AsA oxidase to generate monodehydroascorbate (MDA) free radical. MDA was also reduced by SPPDI1 to AsA in the presence of NADH mimicking the MDA reductase catalyzed reaction. These data suggest that SPPDI1 have both DHA reductase and MDA reductase activities. The corresponding mRNA level was found the highest in the storage roots, followed by sprouts and full-expanded green leaves; while was the lowest in sprouted roots and vein. In Western blot analysis, SPPDI1 level was the highest in the storage roots, followed by sprouts, full-expanded green leaves and vein and no signal at all in sprouted root. These results suggested that the protein coded for by the sweet potato gene is a novel member of the PDI family in plants. SPPDI genes of sweet potato storage roots display differential gene expression patterns, which may be associated with the antioxidant functions they play in plant physiology in order to cope with particular developmental cue.

Expression and function of a cysteine proteinase cDNA from sweet potato ( Ipomoea batatas [L.] Lam ‘Tainong 57’) storage roots

Cysteine proteinase (CPR) cDNA clone (SPCPRPP) of sweet potato ( Ipomoea batatas [L.] Lam ‘Tainong 57’) storage roots were isolated by differential display. The open reading frame in this cDNA encodes a pre-proprotein of 371 amino acids with conserved catalytic amino acids of papain. Examination of the expression patterns in sweet potato by Northern blot analyses revealed that the transcripts of SPCPRPP were specifically induced in the storage roots. Recombinant SPCPRPP protein overproduced in Escherichia coli (M15) was purified by Ni 2+-chelated affinity chromatography. Active recombinant SPCPRPP protein was able to digest the 22 kDa sweet potato trypsin inhibitor (TI) protein when the latter was reduced by DTT (dithiothreitol) or NTS (NADPH/thioredoxin system). A smaller peptide (14 kDa) was obtained as a digestion product. These results suggest that CPR is responsible for initiation of degradation and re-mobilization of stored 22 kDa TI during sprouting of SP storage roots after the reduction of 22 kDa TI by the NTS.

Variance component estimations and allocation of resources for breeding sweetpotato under East African conditions

AbstractIn Africa, average sweetpotato storage root yields are low and breeding is considered to be an important factor in increasing production. The objectives of this study were to obtain variance component estimations for sweetpotato in this region of the world and then use these to determine the efficiency of variety trials and breeding systems. From an incomplete series of variety trials in Kenya and Uganda (comprising 15 genotypes, three locations, two crop durations and three seasons) variance components were estimated ‐ using the REML method ‐ for the following traits: storage root yield, biomass production, harvest index, storage root dry matter and the Elston index which was used to aggregate all four traits. The storage root yield of clones across all 12 environments ranged from 15.2 to 33.0 t/ha. The variance components were significant for all traits, except the genotype by season interactions for storage root dry matter. The efficiency of selection systems was determined for total test capacities of 450 and 900 plots and using not more than five locations. Two‐stage selection was 17‐81% more efficient than one‐stage selection after two seasons of testing. Two‐stage selection was optimized under the restriction of using at least two locations at step 1. Trials with two locations and one replication at step 1 and five locations and two replications at step 2 were appropriate both for selecting for storage root yield and for simultaneously selecting for storage root yield, biomass production, harvest index and storage root dry matter content by using the Elston index. There are indications that such an allocation of resources for breeding sweetpotato is also appropriate for other regions in Sub‐Saharan Africa.