Sweet Tubers Research Articles

Development of homozygous tetraploid potato and whole genome doubling-induced the enrichment of H3K27ac and potentially enhanced resistance to cold-induced sweetening in tubers.

Polyploid plants typically display advantages on some agronomically important traits over their diploid counterparts. Extensive studies have shown genetic, transcriptomic, and epigenetic dynamics upon polyploidization in multiple plant species. However, few studies have unveiled those alternations imposed only by ploidy level, without any interference from heterozygosity. Cultivated potato is highly heterozygous. Thus, in this study, we developed two homozygous autotetraploid lines and one homozygous diploid line in parallel from a homozygous diploid potato. We confirmed their ploidy levels using chloroplast counting and karyotyping. Oligo-FISH and genome re-sequencing validated that these potato lines are nearly homozygous. We investigated variations in phenotypes, transcription, and histone modifications between two ploidies. Both autotetraploid lines produced larger but fewer tubers than the diploid line. Interestingly, each autotetraploid line displayed ploidy-related differential expression for various genes. We also discovered a genome-wide enrichment of H3K27ac in genic regions upon whole-genome doubling (WGD). However, such enrichment was not associated with the differential gene expression between two ploidies. The tetraploid lines may exhibit better resistance to cold-induced sweetening (CIS) than the diploid line in tubers, potentially regulated through the expression of CIS-related key genes, which seems to be associated with the levels of H3K4me3 in cold-stored tubers. These findings will help to understand the impacts of autotetraploidization on dynamics of phenotypes, transcription, and histone modifications, as well as on CIS-related genes in response to cold storage.

Prebiotic Profiling of Indigenous Selected Dioscorea Spp. Using In-vitro Techniques

The current study used an in-vitro technique to evaluate the functional potential of Dioscorea alata L. and D. bulbifera L. extracts as prebiotics. Prebiotics are nondigestible carbohydrates that undergo a selective fermentation process in the gut to benefit the host, according to Gibson and Roberfroid in 1995. Many wild edible plants are high in carbohydrates and are utilised as both a staple food and medicine for a variety of stomach-related disorders. This study employed sweet tuber (ST), bitter tuber (BT), sweet bulbils (SB), and bitter bulbils (BB) from D. bulbifera, as well as tuber (AT) from D. alata and extracted prebiotics using standard method.The AT plant sample seemed to have the least reducing sugars, with a concentration of 2.83 mg/mL. The prebiotic activity of ST, BT, SB, BB, and AT samples was examined as the sole carbon source for microorganisms; among these, AT exhibited a considerable increase in the growth of recognised probiotics Lactobacillus plantarum, Saccharomyces cerevisiae, S. boulardii, and Pichia spp. in-vitro when compared to fructooligosaccharides (FOS). This preliminary investigation indicates that AT has the potential to be used as a promising prebiotic.

Fuel Grade Bioetanol Production from Suweg Starch Through Distilation-Adsorption Process Using Natural Zeolite

Suweg (Amorphophallus campanulatus B) is a sweet tuber which has starch content around 77%, it is suitable as raw material for fuel grade bioethanol production. Bioethanol is ethanol derived from biomass. Fuel grade bioethanol must have a minimum concentration 99.5%. This research will study the effect of zeolite adsorbent concentration on the ethanol purification. The manufacture of fuel grade bioethanol through hydrolysis, fermentation, and purification via distillation and adsorption. Hydrolysis and fermentation (SSF) were carried out on Suweg starch at concentration of 250 g/L using StargenTM 002 at a concentration of 1.5% (w/w) and a concentration of 5 g/L Saccharomyces cerevisiae for 78 hours, producing maximum crude ethanol at a concentration of 14.09% for 54 hours. Furthermore, this crude ethanol is purified using two-stage distillation for 105 minutes and adsorption using natural zeolite with various concentration of 30-90% (w/v) for 120 minutes. The best results of distillation purification produce ethanol concentration of 94.78% (v/v) for 90 minutes, while the adsorption process stage produces 99.62% bioethanol using 90% (w/v) zeolite for 90 minutes.

Repression of Sex4 and Like Sex Four2 Orthologs in Potato Increases Tuber Starch Bound Phosphate With Concomitant Alterations in Starch Physical Properties.

To examine the roles of starch phosphatases in potatoes, transgenic lines were produced where orthologs of SEX4 and LIKE SEX FOUR2 (LSF2) were repressed using RNAi constructs. Although repression of either SEX4 or LSF2 inhibited leaf starch degradation, it had no effect on cold-induced sweetening in tubers. Starch amounts were unchanged in the tubers, but the amount of phosphate bound to the starch was significantly increased in all the lines, with phosphate bound at the C6 position of the glucosyl units increased in lines repressed in StSEX4 and in the C3 position in lines repressed in StLSF2 expression. This was accompanied by a reduction in starch granule size and an alteration in the constituent glucan chain lengths within the starch molecule, although no obvious alteration in granule morphology was observed. Starch from the transgenic lines contained fewer chains with a degree of polymerization (DP) of less than 17 and more with a DP between 17 and 38. There were also changes in the physical properties of the starches. Rapid viscoanalysis demonstrated that both the holding strength and the final viscosity of the high phosphate starches were increased indicating that the starches have increased swelling power due to an enhanced capacity for hydration.

Comparative proteomic analysis of cold-induced sweetening in potato (Solanum tuberosum L.) tuber

Cold-induced sweetening is one of the major factors limiting the quality of fried potato products. To understand the mechanisms of protein regulation for cold-induced sweetening in potato tubers, a comparative proteomic approach was used to analyse the differentially expressed proteins both during control (25 °C, 30 days) and cold treatment (4 °C, 30 days) using two-dimensional gel electrophoresis. Quantitative image analyses indicated that there were 25 protein spots with their intensities significantly altered more than twofold. Of these proteins, 9 were up-regulated, 13 were down-regulated, 2 were absent, and 1 was induced in the cold-stored tubers. The MALDI-TOF/TOF MS analyses led to the identification of differentially expressed proteins that are involved in several processes and might work cooperatively to maintain metabolic homeostasis in tubers during low-temperature storage. The preponderance of metabolic proteins reflects the inhibition of starch re-synthesis and the accumulation of sugars in carbon fluxes, linking starch–sugar conversion. The respiration-related proteins suggest the transfer of respiratory activity from aerobic respiration to anaerobic respiration in the cold-stored tubers. The proteins associated with defence appear to protect the tuber cells from low-temperature stress. Some heat shock proteins that act as chaperones also displayed a differential expression pattern, suggesting a potentially important role in cold-stored tubers, although their exact contribution remains to be investigated. The proposed hypothetical model might explain the interaction of these differentially expressed proteins that are associated with cold-induced sweetening in tubers.

A proposed role for the anaerobic pathway during low‐temperature sweetening in tubers of Solanum tuberosum

Following exposure to low temperatures (i.e. < 9–10°C), tubers of potato (Solanum tuberosum) undergo a phenomenon known as low‐temperature sweetening (LTS), which results in the conversion of starch to sugars. LTS in stored potato tubers was evaluated by monitoring glycolysis, the oxidative pentose phosphate pathway, anaerobic respiration and mitochondrial respiration, in order to obtain an overview of the regulation of sugar metabolism during LTS. Carbohydrate metabolism during 4°C storage was evaluated in four different storage seasons, comparing tubers of cold‐tolerant (low sugar‐accumulating) clones (ND 860‐2, V 0056‐1 and Wis 1355‐1) and cold‐sensitive (high sugar‐accumulating) cultivars (Novachip and Monona). Parameters measured included whole tuber respiration, concentrations of sucrose, reducing sugars, ATP, NADH, NADPH, lactate and ethanol, as well as tissue pH. In three of the four seasons of study, the cold‐tolerant tubers maintained lower levels of reducing sugars, and higher levels of lactate and ethanol, relative to cold‐sensitive tubers. A higher anaerobic flux in tubers of cold‐tolerant genotypes may be partially responsible for a lower accumulation of reducing sugars relative to cold‐sensitive tubers. This study represents the first known report on the role of the anaerobic pathway during LTS in potato tubers.

Membrane lipid dynamics and lipid peroxidation in the early stages of low‐temperature sweetening in tubers of Solanum tuberosum

Sugar accumulation and membrane lipid parameters associated with membrane permeability in chilling injury and senescence were followed in the early stages of low‐temperature sweetening in Solanum tuberosum tubers to monitor their dynamics. Norchip, a low‐temperature sweetening‐susceptible potato cultivar, and North Dakota 860‐2, a low‐temperature sweetening‐tolerant selection, were stored for 55 days at 4 and 12°C. Sugar accumulations were not linear and were characterized by fluctuations or cycles over storage time. Sucrose cycling and accumulation were greatest for Norchip tubers stored at 4°C as compared to the other treatments. Increases in membrane permeability were not detected by increases in electrolyte leakage. No significant changes in the phospholipid, galactolipid, free sterol levels or phospholipid to free sterol ratio were observed. The double bond index obtained from the fatty acid profiles of the total lipid fraction decreased significantly (decreased unsaturation) for Norchip tubers at 4°C over time. Free fatty acid and diene conjugation values fluctuated and increased over time for all treatments with greater amplitude of fluctuations observed for Norchip tubers stored at 4°C. These latter effects may be due to the high levels of lipid acyl hydrolase and lipoxygenase found in potato tubers. When free fatty acid and diene conjugation values were plotted with glucose accumulation over time, a possible relationship among the variables was revealed. The observed peroxidation products could relate low‐temperature stress and the resultant low‐temperature sweetening to chilling injury and drought stress. The anti‐oxidative potential of potato tubers should be considered for future cultivar development as a mechanism to lessen the severity or rate of low‐temperature sweetening development.

Hydrocyanic acid levels in fermented cassava

SummaryThe extent of loss of hydrocyanic acid during the fermentation of cassava tubers selected from both sweet and bitter varieties in the traditional method (whole unpeeled tubers) compared with the fermentation of peeled tubers and crushed pulps with or without the addition of water. Although the traditional fermentation is terminated after 3–4 days, in this study the fermentation was allowed to proceed for 8 days. Loss of cyanide from the whole tubers was 8047% after 8 days and was only 51–53% after 4 days. Loss of cyanide from the whole sweet tuber was not significant after 5 days. The loss of cyanide from the peeled tubers was comparable to the whole tubers after 8 days of fermentation. However, there was a marked decrease in free cyanide in the 1st day of fermentation of the peeled tubers compared to whole tubers. The loss in cyanide in the crushed pulp, which occurred primarily in the 1st day, appears to be due to the action of endogenous linamarase rather than hydrolysis by fermentation. When water is added to the crushed pulp the reduction in cyanide was 83–91% with marked decrease in bound cyanide in the 1st day of fermentation. It seems that autohydrolysis is enhanced by addition of water to the crushed pulp.