Starch Granule Morphology Research Articles

Ultrasound assisted extraction of cadmium for decontamination of rice and its influence on structure/texture of cooked rice

Cadmium (Cd) is a nonessential heavy metal and ranks seventh on the list of World Health Organization Agency's Toxic Substances. In this study, ultrasound assisted extraction (UAE) was used for Cd decontamination of rice grains and rice flour. Extraction conditions were developed [particle size, ultrasound (US) power, treatment time, temperature, pH, extraction solution volumes and treatment cycles] and applied for both low and high Cd contaminated rice. Under selected UAE conditions, 83% and 66% of total Cd were removed in just one cycle UAE treatment while over 93% Cd were removed after two and three-cycles for rice flour and rice grain, respectively. The total protein, total starch, pasting properties, thermal stability, morphology structure and textural properties of rice were evaluated after UAE treatment. Although a considerable amount of starch was lost during the UAE treatment (common to such treatments), UAE-treated cooking rice maintained good structural and textural quality. The pasting temperature was decreased with low damage to the morphology of starch granule. With several advantages like short treatment (20–30 min), rice good texture quality retention, simple and easy operation, low cost and applicability to rice grain and rice flour, the UAE process provides a very useful method for Cd removal contaminated rice.

Ruminal and post‐ruminal barley grain digestion and starch granule morphology under three heat methods

AbstractThis study was designed to investigate the effect of three heating methods on the ruminal and post‐ruminal nutrient degradability and starch granule morphology of barley grain (BG ‐ Hordeum vulgare). Treatments were Control (CG): without processing; Roasted (RG): roasted BG for 300 s at 130°C; Microwaved (MG): irradiated BG for 120 s at 1200 W; and Steam flaked (SG): BG misted for 30 min under steam flow of boiling water and flaked. Gas production and in situ techniques were used to evaluate the ruminal degradability of treatments, and a modified three‐step method was utilised to estimate the total‐tract digestibility. Morphological changes of starch granules were determined by field emission scanning electron microscopy (FESEM). Ruminal gas production and dry matter disappearance were increased (p < .05) in SG vs. CG. Heat processing had different effects on starch and crude protein degradability; however, starch degradability increased (p < .05) from CG to SG. Post‐ruminal disappearance of dry matter in CG was greater (p < .05) than other treatments. These results validated by FESEM images that explained high barley grain degradability in relation to the number of holes on the surface of starch granules. Heat processing can enhance ruminal and post‐ruminal utilisation efficiency of barley grain, resulting in improvement of total‐tract digestibility.

Effects of endogenous proteins on rice digestion during small intestine (in vitro) digestion

Rices with higher protein contents are nutritionally desirable. This study investigates the effects of endosperm proteins on starch in vitro digestibility in cooked and uncooked rice, and the mechanisms underlying any changes. The composition of rice endosperm proteins and the morphologies of proteins and starch granules were determined by SDS-PAGE and confocal microscopy. Starch molecular fine structure was examined using size-exclusion chromatography. In vitro digestion showed that the digestion rate coefficients (k) of cooked rice flour were significantly lower than those of isolated starch or of a starch-protein mixture. (e.g for samples from SWR4, k is 9.6, 12.9 and 11.6 × 10-2 min−1 for cooked rice flour, isolated starch and starch-protein mixture, respectively). For uncooked samples, digestion rate coefficients were 1.4, 1.5 and 1.8 × 10-2 min−1 for flour, starch-protein mixture and starch, respectively. The digestion rates in cooked samples were higher than those in uncooked samples. This suggests that, in cooked samples, starch digestion rates are more affected by the protein physical barrier than by some chemical effect (e.g. hydrogen bonding between protein and starch), while in uncooked samples, a chemical effect from protein is more pronounced than a physical barrier from protein.

Genetic loci determining potato starch yield and granule morphology revealed by genome-wide association study (GWAS).

BackgroundIt is well-documented that (bio)chemical reaction capacity of raw potato starch depends on crystallinity, morphology and other chemical and physical properties of starch granules, and these properties are closely related to gene functions. Preparative yield, amylose/amylopectin content, and phosphorylation of potato tuber starch are starch-related traits studied at the genetic level. In this paper, we perform a genome-wide association study using a 22K SNP potato array to identify for the first time genomic regions associated with starch granule morphology and to increase number of known genome loci associated with potato starch yield.MethodsA set of 90 potato (Solanum tuberosum L.) varieties from the ICG “GenAgro” collection (Novosibirsk, Russia) was harvested, 90 samples of raw tuber starch were obtained, and DNA samples were isolated from the skin of the tubers. Morphology of potato tuber starch granules was evaluated by optical microscopy and subsequent computer image analysis. A set of 15,214 scorable SNPs was used for the genome-wide analysis. In total, 53 SNPs were found to be significantly associated with potato starch morphology traits (aspect ratio, roundness, circularity, and the first bicomponent) and starch yield-related traits.ResultsA total of 53 novel SNPs was identified on potato chromosomes 1, 2, 4, 5, 6, 7, 9, 11 and 12; these SNPs are associated with tuber starch preparative yield and granule morphology. Eight SNPs are situated close to each other on the chromosome 1 and 19 SNPs—on the chromosome 2, forming two DNA regions—potential QTLs, regulating aspect ratio and roundness of the starch granules. Thirty-seven of 53 SNPs are located in protein-coding regions. There are indications that granule shape may depend on starch phosphorylation processes. The GWD gene, which is known to regulate starch phosphorylation—dephosphorylation, participates in the regulation of a number of morphological traits, rather than one specific trait. Some significant SNPs are associated with membrane and plastid proteins, as well as DNA transcription and binding regulators. Other SNPs are related to low-molecular-weight metabolite synthesis, and may be associated with flavonoid biosynthesis and circadian rhythm-related metabolic processes. The preparative yield of tuber starch is a polygenic trait that is associated with a number of SNPs from various regions and chromosomes in the potato genome.

How do elevated atmosphere CO2 and temperature alter the physiochemical properties of starch granules and rice taste?

Elevated atmospheric CO2 (EC) and temperature (ET) strongly affect agricultural production, but the mechanism through which EC and/or ET influence starch granules and their relationship to cooked rice taste remain largely unknown. Therefore, a field experiment using a popular japonica cultivar grown in a temperature/free-air CO2 enrichment environment was conducted to investigate the responses of volume and fine structure of starch granules and their formation physiology to EC (+200 ppm) and/or ET (+1 °C) in 2015–2016. EC markedly enhanced the activity of soluble-starch synthase and granule-bound starch synthase by 28.0% and 27.9% respectively, thereby increasing the long chains and the volume of starch granules. However, EC decreased the activity of starch-branch enzyme by 7.5% possibly via the pathway of ethylene signalling (EC prominently decreased the ethylene evolution rate of rice grains by 28.8%), resulting in a remarkable decrease in α-1′6 glucosidic bonds and significant increase in the iodine-binding capacity and double helix in starch molecules. These EC-induced changes in morphology and fine structure of starch granules synergistically altered the thermal properties of rice flour and eventually improved the cohesiveness and taste of cooked rice, as suggested by the significant relationships between them. ET partially offset the beneficial EC effects in most cases. However, few remarkable CO2 × temperature or CO2 × year effects were detected, indicating that the effects of EC on starch granules and rice taste less varied with meteorological conditions. These findings have important implications on rice palatability and for the development of adaptive strategies in the starch industry in future environment.

Analyses of phylogenetics, starch granule morphology and consumer preference of Canna indica L. grown in Sri Lanka

Canna indica is a tuber crop which has many medicinal values. In Sri Lanka, C. indica tubers are consumed in rural areas and mainly available in street-markets of Nuwara-Eliya and Kandy Districts. In the present study, we assessed the phylogenetics of C. indica, starch granule morphology and consumer preference of C. indica tubers in comparison to the popular tuber crops. The phylogenetic analysis was conducted based on the sequence polymorphism at rbcL, atpB gene, trnL-trnF and trnH-psbA marker-loci with respect to the ornamental Canna spp. in Sri Lanka and the previously published sequences of Canna spp. The starch granules were isolated and observed under optical and scanning electron microscopes. The diameter and the surface area of the starch granules were measured under the optical microscope and subjected to analysis of variance. As C. indica tubers are consumed as boiled tuber pieces in Sri Lanka, the consumer preference analysis was conducted using the boiled tuber pieces C. indica, Xanthosoma sagittifolium, Manihot esculenta, Solanum tuberosum, and Ipomoea batatas. The phylogenetic tree based on rbcL marker revealed that C. indica in Sri Lanka is slightly divergent from the other Canna spp. Only the polymorphism of the atpB gene can be used to differentiate C. indica from the ornamental Canna sp. in Sri Lanka. The morphological analysis of starch granules revealed that C. indica has the biggest scallop-seashell shaped starch granules compared to other tuber species. The boiled C. indica tubers were accepted better than that of X. sagittifolium, rated equally to the tubers of S. tuberosum and M. esculenta, and rated less than I. batatas. The hardy and fibrous nature of C. indica tubers must be the major limiting factors for achieving the highest consumer preference highlighting the need of breeding for better texture in tubers

Effects of elevated atmosphere CO2 and temperature on the morphology, structure and thermal properties of starch granules and their relationship to cooked rice quality

The rapidly increasing atmospheric CO2 is accompanied by global warming. However, the effects of the elevated CO2 concentration (EC) and/or air temperature (ET) on starch morphology, structure and thermal properties which considerably contribute to the taste of cooked rice have not been reported to date. Therefore, a field experiment using a temperature/free-air CO2 enrichment facility was conducted with EC (+200 ppm) and/or ET (+1 °C) treatments from 2014 to 2016. The surface area of starch granules and proportion of large starch granules were significantly increased by EC and ET, but the most significant increases of 3.4% and 5.9%, respectively, were induced by the combined treatment. EC did not change the crystalline type but altered the order structure of starch molecules: EC averagely decreased the ratios of 1045/1022 and 1022/995 cm−1 by 2.6% and 3.3% respectively, however, significantly increased the crystallinity by 4%. For most cases, EC significantly increased the gelatinization temperature and pasting viscosity of starch, decreased setback, enthalpy and protein content and eventually improved rice taste. Results of correlation analysis suggested that EC affected the thermal properties of starch and the taste of cooked rice mainly by improving the size and molecule order structure of starch granules. Small and few significant ET and EC × ET effects were detected, indicating that the EC influence will be predominant in future climate. These findings will help in improving rice palatability and developing the starch industry.

Potentially lactic acid bacteria as an EPS producing starter from yellow sweet potato fermentation


 Potentially lactic acid bacteria as a starter for EPS production from yellow sweet potato fermentation were determined. The fermentation profile and partial characteristics of isolated lactic acid bacteria were used as considerations. The fermentation of yellow sweet potato was performed in the back-slopping and spontaneous procedure and was paid attention to the hours of 0, 24, 48, and 72. The results showed that the 72 hours of fermentation was found to have the highest EPS metabolites, the number of a LAB, the total lactic acid, and the lowest pH. The 72 hours of fermentation also seemed to cause a significant change in the sweet potato starch granules morphology. The potential starter, therefore, can be taken from the yellow sweet potato fermentation either spontaneously or by a back-slopping method, at 72 hours. From the sixty selected LAB, the 34 strains showed an ability to produce EPS. Among these, eight strains exhibited the potential high production of EPS. They were capable of growth on 28-45C and exhibited tolerance to 3-4% NaCl. The favorable carbon sources for the growth and production of EPS were isolated dependent.

The impact of the indica rice SSIIa allele on the apparent high amylose starch from rice grain with downregulated japonica SBEIIb.

Catalytically active indica SSIIa allele in high amylose rice with down-regulated japonica SBEIIb can increase starch content and modify the starch structure and properties without changing its amylose content. Rice (Oryza sativa) genotypes with inactive starch synthase IIa (SSIIa) with recessive variants of starch branching enzyme IIb (SBEIIb) exhibit a range of alterations in grain phenotype, starch granule morphology, starch granule bound proteins, starch structure, and functional properties. However, the interactions between the two enzymes have not been thoroughly investigated yet. We analysed recombinant rice lines having down-regulated SBEIIb expression (SBEIIbDR) with either indica or japonica type SSIIa (SSIIaind or SSIIajap). In SBEIIbDR rice starch granules, the increased abundance of two protein bands (SSI and SSIIa) was found with eight additional protein bands not generally associated with starch granules. The amount of SSIIa was higher in SSIIaindSBEIIbDR than SSIIajapSBEIIbDR, which indicated that indica type SSIIa, possibly in the monomer form, was extensively involved in starch biosynthesis in the SBEIIbDR endosperm. Furthermore, SSIIaindSBEIIbDR grains had higher total starch content and higher starch swelling power than SSIIajapSBEIIbDR lines, but the amylopectin gelatinization temperatures and enthalpy and the apparent amylose content remained similar. In summary, this work suggests that SSIIaind can partly compensate for the alteration of starch synthesis resulting from the SBEIIb down-regulation in japonica background without reducing its amylose content. The study provides insight into the starch structural and textural improvements of high amylose starch.

Pre-harvest glyphosate application and effects on wheat starch chemistry: Analysis from application to harvest.

The objective of this study was to determine if the pre-harvest glyphosate application time affects the chemistry of wheat starch. Glyphosate was sprayed at the ripe stage (recommended) and the soft dough stage (early application) of hard red spring wheat. Wheat kernel samples were collected before application and every 3days until harvest, after which different starch characteristics were analyzed. The results indicate that glyphosate timing does not impact the spatial distribution or morphology of starch granules, as well as the percentage or molecular weight of amylose and amylopectin. However, thermal characteristics of wheat starch, especially when glyphosate was applied at the soft dough stage, showed significant differences. A decrease in the average amylopectin chain length and differences in the proportion of short-, medium-, and long-chain amylopectin was also observed. Overall, this study shows that the pre-harvest application of glyphosate can affect wheat starch chemistry, especially if applied earlier than recommended. PRACTICAL APPLICATIONS: Glyphosate is the most commonly used herbicide in the world, and it is sometimes used pre-harvest during wheat cultivation. The recommended time of application is 7days prior to harvest when the crops are in the ripe stage of physiological maturity. However, some crops may not be at this stage during application due to non-uniform maturation in the field. The goal of this work was to determine the effect of glyphosate application time (recommended/ripe stage vs. early/soft dough stage) on wheat starch chemistry. The results show that the starch chain length characteristics and thermal behavior are impacted, especially if applied early. Thus, this study shows the importance of timely application to avoid effects on starch chemical properties, which in return could impact starch functionality in food systems. This information is critical in the field of agriculture and to our knowledge this study is one of the first in this area.

The study on starch granules by using darkfield and polarized light microscopy

A deep understanding of starch granule properties is important for its food and non-food industrial applications. On the other hand, the advance of optical microscopy has been ongoing. In this study, optical microscopies including transmission light microscopy, darkfield microscopy (DFM), differential interference contrast microscopy and polarized light microscopy (PLM) are compared for studying starch granules. It was found that detailed morphology and size of native starch granules could be precisely obtained by DFM, while crystalline is reflected by the Maltese cross under PLM. Optical images showed that native starch granules from rice and maize are polygonal, while starch granules of sweet potato are oval-shaped. Starch granules from sweet potato have the largest size of 15.2 ± 3.8 μm. After gelatinization, starches aggregated and chunks were formed under DFM, accompanied by the vanishing of crystalline (Maltese cross) under PLM. More importantly, the technique can visualize gelatinization progress of single rice starch granules in situ with a time scale of 100 ms at 1 mol/L NaOH. Due to gelatinization, micelle structures of granules with a decreasing size were determined by DFM, while the branched structure with an increased size was observed through PLM. The gelatinization at different subregions of starch granules was heterogeneous; structural changes at specific subregions are relatively faster. The combination of PLM and TLM may become an important technique for studying starch properties, especially obtaining detailed dynamic changes.

Morphology and Physicochemical Properties of Starch from Waxy and Non‐Waxy Barley

AbstractBarley flour is widely utilized in food and nonfood industries. Morphological, structural, and functional properties of starches extracted from waxy and non‐waxy barley are investigated and compared in this work. The morphology of starch granules in waxy and non‐waxy barley is similar while waxy barley has a higher proportion of A‐type starch granules and a lower proportion of B‐type starch granules than those of non‐waxy barley. Compared with non‐waxy barley starch, waxy barley starch shows higher amylopectin content with higher levels of amylopectin short and long branch‐chains; better ordered structures with higher relative crystallinity, IR ratio of 1045/1022 cm−1, and a double helical component, a lower amorphous and V‐type single helix components. The gelatinization temperature and enthalpy of waxy barley starch are higher than those of non‐waxy barley starch. Meanwhile, waxy barley starch presents higher swelling power, solubility, pasting viscosities, breakdown value, and lower setback value than those of non‐waxy barley starch. Furthermore, waxy barley starch is more susceptible to acid and enzymatic hydrolysis than non‐waxy barley starch. Results indicate that waxy and non‐waxy barley starches differ in physicochemical properties, and waxy barley may have a better mouthfeel and edible quality.

In vitro examination of starch digestibility of Saba banana [Musa \u2018saba\u2019(Musa acuminata\u2009\xd7\u2009Musa balbisiana)]: impact of maturity and physical properties of digesta

The digestibility of starch in Saba banana as affected by maturity and physical properties of digesta was investigated. Five maturity stages were identified based on peel color index which also showed significant differences in physicochemical properties and starch granule morphology. The effect of physical properties of digesta was evaluated by monitoring the viscosity throughout the simulated digestion process and comparing two different physical structures of banana: (1) unhomogenized cut samples which have intact tissue structure and (2) homogenized slurry representing disrupted cellular structure. During ripening process, a decrease in starch content was noted with a concomitant formation of sugars and increasing concentration of acids. Green unripe stages showed the highest rate of starch hydrolysis in both physical structures and a decreasing trend was observed as ripening proceeded. The high digesta viscosity values of ripe stages was found to have an inhibitory effect on starch hydrolysis. Similarly, the differences in physical structure of food affected the digestive enzymes efficiency in breaking down starch. These results suggested that the physicochemical changes accompanying maturation and the physical properties (i.e. high viscosity and presence of intact cell structure) of food could significantly impact the rate of starch digestion.

Ultrasound-assisted preparation of octenyl succinic anhydride modified starch and its influence mechanism on the quality

The purpose of this study was to reveal the influence mechanism of preparing high quality modified starch by ultrasonic-assisted treatment. In this paper, ultrasonic modified starch and octenyl succinic anhydride (OSA) modified starch were prepared under ultrasonic conditions. The effect of ultrasound on the structure and properties of native starch were studied to see whether ultrasound could produce mechanochemical effect on starch granules. Then the mechanism of ultrasonic effect on the quality of OSA-modified starch was revealed by mechanochemical effect. The results showed that the morphology and crystalline regions of starch granules were destroyed after ultrasonic treatment, and the structure and properties of starch granules changed in different stages. These changes showed that ultrasonic treatment produced significant mechanochemical effect on starch granules. Thus the quality of OSA-modified starch prepared by ultrasonic-assisted treatment was improved significantly, and its influence mechanism was analyzed using the theory of mechanochemistry.

Effect of soaking and sprouting treatment on germination rate of paddy

The aim of this study was to determine the effect of germination process (i.e., soaking time and temperature, germination time, and ultrasound treatment) on the germination rate of germinated paddy. In addition, gamma-aminobutyric acid (GABA) content, and morphology of starch granule of dehulled germinated paddy (germinated brown rice, GB) were characterized. The results showed that extended soaking time from 4 h to 24 h insignificantly increased the germination rate, and increased soaking temperature from 30°C to 40°C had no effect on germination rate (p>0.05). However, extended germination time from 14 h to 48 h significantly improved the germination rate, given soaking time and temperature of 2-8 h at 30°C (p<0.05). Ultrasound treatment for 15 min after 8 h soaking significantly increased the germination rate of 24 h germination, compared with non-ultrasound and ultrasound treatment for 15 min before 8 h soaking. Meanwhile, extended germination time to 48 h, the ultrasound treatment had no effect on the germination rate (p>0.05). The germination process did not affect the morphology of the GB starch granule, compared with brown rice (BR). However, GaBa content of GB (11.67 mg/l00g) was significantly higher than that of BR (1.08 mg/100g) (p<0.05).

Extraction and characterization of native starch obtained from the inhambu tuber.

Starch is the main carbohydrate consumed by humans, obtained from many vegetable sources and known for its non-toxicity, applications and low cost. The aim of this work was the extraction and study of characteristics of non-conventional starch arising from inhambu (Dioscorea trifida L.). Chemical, physicochemical, thermal, morphological, structural and technological properties were evaluated. The starch yield percentage obtained from the extraction, starch and amylose contents of inhambu starch were considerably high, 22.76%, 84.56% and 36.82% respectively. Native starch presented high purity due the low ash, protein and fat content. The thermogravimetric analysis shown 69% weight loss in a 293.12-476.59°C temperature range and the endothermic peak was at 100.0°C. The starch granule morphology shown spherical shapes and smooth surfaces and size ranging from 5.06 to 14.59µm. Considering the unique starch characteristics, its application in different industrial sectors can be foreseen.

Understanding the impact of Pulsed Electric Fields treatment on the thermal and pasting properties of raw and thermally processed oat flours.

The aim of this research was to investigate the effect of Pulsed Electric Fields (PEF) treatments (electric field strengths 2 and 4.4kV/cm combined with specific energy inputs between 48 and 484kJ/kg) on the thermal and pasting properties of oat flours. Colour, β-glucan content, particle size distribution, morphological characteristics, starch short-range molecular order, protein secondary structure, thermal, and pasting properties of raw (dehulled and milled) and thermally processed (kilned at 115°C for 30min and steamed at 100-104°C for 18min under industrial process condition) oat flours under the influence of PEF treatment were evaluated. Results showed that PEF treatment, applied at any intensity, led to considerable changes in the structural properties especially when applied on raw oat flour. Both types of oat flour experienced an increase in particle size (up to four-fold), damage of starch granule morphology, and modifications in starch short-range molecular order and protein secondary structures as a result of PEF treatment. These physical changes observed after PEF treatment, particularly at increasing specific energy input, coincided with the thermal and pasting behaviour of PEF-treated oat flours, which include a decrease in gelatinisation enthalpy (up to 80%), increase in thermal transition temperatures (at least 3°C), decrease in overall viscosity profile, and reduction in pasting temperature (up to 12°C). Overall results suggested that PEF treatment improved majorly on starch-related functionality of oat, such as increased the pasting stability of raw and thermally processed oat flours and at the same time enhanced the retrogradation property (reduced syneresis and hardness) of raw oat flour, under lower temperature requirement without affecting pasting time. This research demonstrated the potential of PEF treatment in modifying the thermal and pasting properties of oat flour, thereby offering opportunities for novel products for food industry.

Introducing Daluga (Cyrtosperma merkusii) starch from corms collected in Siau Island, North Sulawesi

Daluga (Cyrtosperma merkusii) found naturally growing at some sites inside Siau Island, North Sulawesi, Indonesia. This plant is an aroid, known as giant swamp taro, and its corm is edible. Very little information known about the plant and corm, and none for its starch. The tendency surfaced is that the plant has been abandoned despite of the corm potency may serve as food source. The same practices also happened around the islands on the same region: even the statistics shown that daluga is excluded from both food expenditure and food crops consideration (BPS 2013). For that reason, this research mainly focus on the study of daluga corm starch that has never been studied or reported before. The major findings are starch yield, chemical composition, and granules morphology studied from scanning electron microscopy (SEM) images. The data shows that daluga starch is unimodal with average size of 12.50 μm and crystalline type A. The average starch yield is 14.70%, and has medium to low amylose content that shall give good mouthfeel taste. These findings shall possibly support more research and utilization of daluga starch, improving people’s knowledge about it, thus it will benefit researchers or islands communities in the future, as it is a natural resource of food found on these islands of Indonesia.

Physicochemical, morphological and antioxidant properties of spray-dried mango kernel starch

Abstract Recovery of starch from mango processing wastes is an excellent alternative for byproducts production. Starch is a polysaccharide that finds use on several applications, so its final properties are critical for performance. Therefore, the objective of our work was to study the properties of starch extracted from mango kernel wastes after spray drying. An experimental design comprising 11 experiments were used with variations on inlet drying temperature, feed flow rate, and atomization pressure. Starch physicochemical, morphological, and antioxidant properties were assessed. Results revealed that drying below 6% of relative humidity increased process yield and could induce the formation of amylose-lipids complexes. From FTIR, it was found a high content of amylopectin short-chains, which could have lowered the gelatinization temperature. A-type, B-type, and V-type starches were found, revealing the presence of the amylose-lipid complex. The first two types of starch granules morphology were also identified by SEM. Spray-dried mango kernel starch revealed antioxidant and lipid oxidation properties, which started at concentrations of 0.5 mg/mL and 0.05 mg/mL, respectively.

Upregulated Lipid Biosynthesis at the Expense of Starch Production in Potato (Solanum tuberosum) Vegetative Tissues via Simultaneous Downregulation of ADP-Glucose Pyrophosphorylase and Sugar Dependent1 Expressions.

Triacylglycerol is a major component of vegetable oil in seeds and fruits of many plants, but its production in vegetative tissues is rather limited. It would be intriguing and important to explore any possibility to expand current oil production platforms, for example from the plant vegetative tissues. By expressing a suite of transgenes involved in the triacylglycerol biosynthesis, we have previously observed substantial accumulation of triacylglycerol in tobacco (Nicotiana tabacum) leaf and potato (Solanum tuberosum) tuber. In this study, simultaneous RNA interference (RNAi) downregulation of ADP-glucose pyrophosphorylase (AGPase) and Sugar-dependent1 (SDP1), was able to increase the accumulation of triacylglycerol and other lipids in both wild type potato and the previously generated high oil potato line 69. Particularly, a 16-fold enhancement of triacylglycerol production was observed in the mature transgenic tubers derived from the wild type potato, and a two-fold increase in triacylglycerol was observed in the high oil potato line 69, accounting for about 7% of tuber dry weight, which is the highest triacylglycerol accumulation ever reported in potato. In addition to the alterations of lipid content and fatty acid composition, sugar accumulation, starch content of the RNAi potato lines in both tuber and leaf tissues were also substantially changed, as well as the tuber starch properties. Microscopic analysis further revealed variation of lipid droplet distribution and starch granule morphology in the mature transgenic tubers compared to their parent lines. This study reflects that the carbon partitioning between lipid and starch in both leaves and non-photosynthetic tuber tissues, respectively, are highly orchestrated in potato, and it is promising to convert low-energy starch to storage lipids via genetic manipulation of the carbon metabolism pathways.