Difference between light- and wound-induced biosynthesis of α-solanine and α-chaconine in potato tubers

Potato tuber tissues can incorporate mevalonic acid-2-14C into glycoalkaloids, namely α-chaconine and α-solanine. The percent incorporation of this labeled precursor into α-chaconine in light exposed tubers is more than that of mechanically injured tubers.     

The sesquiterpene α-copaene is induced in tomato leaves infected by Botrytis cinerea

Abstract

Explorative experiments were done to investigate the possibility that tomato plants infected by Botrytis cinerea have a different emission of volatile organic compounds (VOC) than healthy plants. This was done by headspace analysis of volatiles emitted by detached leaves of infected and healthy plants. Principal component analysis (PCA) of GC-FID chromatograms revealed clearly separated clusters between infected and control leaves and identification of an interesting compound. In further analysis by GC-MS, the significantly distinctive component (p≤0.05) was identified as the sesquiterpene α-copaene. In previous work on herbivore damage, α-copaene was not distinctive, which may suggest that α-copaene may be specifically associated to fungal infections in tomato.     

The contribution of adenosine 5′-diphosphoglucose pyrophosphorylase to the control of starch synthesis in potato tubers

The aim of this work was to investigate the extent to which starch synthesis in potato (Solanum tuberosum L.) tubers is controlled by the activity of ADPglucose pyrophosphorylase (EC 2.7.7.27; AGPase). In order to do this, fluxes of carbohydrate metabolism were measured in tubers that had reduced AGPase activity as a result of the expression of a cDNA encoding the B subunit in the antisense orientation. Reduction in AGPase activity led to a reduction in starch accumulation, and an increase in sucrose accumulation. The control coefficient of AGPase on starch accumulation in intact plants was estimated to be around 0.3. The fluxes of carbohydrate metabolism were measured in tuber discs from wild-type and transgenic plants by investigating the metabolism of [U-¹⁴C]glucose. In tuber discs, the control coefficient of AGPase over starch synthesis was estimated as 0.55, while the control coefficient of the enzyme over sucrose synthesis was −0.47. The values obtained suggest that AGPase activity exerts appreciable control over tuber metabolism in potato. Received: 24 February 1999 / Accepted: 8 April 1999     

Osmotic regulation of starch synthesis in potato tubers?

Using potato (Solanum tuberosum L.) tuber discs incubated in a range of mannitol concentrations it has been demonstrated that both sucrose uptake and the conversion of sucrose to starch are sensitive to the osmotic environment of the storage cells. Starch synthesis was optimised at 300 mM but declined sharply at both lower and higher osmotic concentrations. The decline in starch synthesis on either side of optimum was not proportional to the change in mannitol concentration, indicating different inhibitory mechanisms under low and high osmotica. The fraction of the total sucrose converted to starch i.e. the partitioning between sucrose and starch, was also influenced by osmotic environment. The amount of soluble material taken up by the storage cells, but not converted to starch, was maintained under mannitol concentrations (300–400 mM) which inhibited starch synthesis, indicating that sucrose uptake continued during declining starch synthesis. At mannitol concentrations above 400 mM, sucrose uptake was greatly enhanced but no significant change in starch synthesis occurred.     

Enhanced operation of 4-aminobutyrate shunt in γ-irradiated potato tubers

γ-Radiation at a sprout inhibiting dose of 100 Gy enhanced the operation of the 4-aminobutyrate shunt by about 3-fold 48 hr after irradiation, but there was no accumulation of the amino acid in irradiated potatoes during storage up to 6 months. γ-Radiation increased the activity of the first enzyme of the 4-aminobutyrate shunt, glutamate decarboxylase and the maximum increase of 2.6-fold was found on the fourth day after irradiation. γ-Radiation had no pronounced effect on the activity of the other two enzymes of the pathway, 4-aminobutyrate transaminase and succinate semialdehyde dehydrogenase. Based on the results obtained, a possible role for the 4-aminobutyrate shunt in potato tuber physiology was suggested.     

Contribution of adenosine 5′-diphosphoglucose pyrophosphorylase to the control of starch synthesis is decreased by water stress in growing potato tubers

Water stress stimulates sucrose synthesis and inhibits starch and cell-wall synthesis in tissue slices of growing potato (Solanum tuberosum L. cv. Desirée) tubers. Based on the analysis of fluxes and metabolites, Geigenberger et al. (1997, Planta 201: 502–518) proposed that water deficits up to −0.72 MPa stimulate sucrose synthesis, leading to decreased starch synthesis as a result of the resulting decline of phosphorylated metabolite levels, whereas more-severe water deficits directly inhibit the use of ADP-glucose. Potato plants with decreased expression of adenosine 5′-diphosphoglucose pyrophosphorylase (AGPase) have been used to test the prediction that the contribution of AGPase to the control of starch synthesis should decrease in severely water-stressed tuber material. Freshly cut slices from wild-type and antisense tubers were incubated at a range of mannitol concentrations (20, 300 and 500 mM) and the metabolism of [¹⁴C]glucose was analysed. A 86–97% reduction of AGPase activity led to a major but non-stoichiometric inhibition of starch accumulation in intact growing tubers attached to the plant (40–85%), and an inhibition of starch synthesis in non-stressed tuber slices incubated in 20 mM mannitol (60–80%). The inhibition of starch synthesis was accompanied by a 2- to 8-fold increase in the levels of sugars in intact tubers and a 2- to 3-fold stimulation of sucrose synthesis in tuber slices, whereas respiration and cell-wall synthesis were not significantly affected. The strong impact of AGPase on carbon partitioning in non-stressed tubers and tuber slices was retained in slices subjected to moderate water deficit (300 mM mannitol, corresponding to −0.72 MPa). In discs incubated in 500 mM mannitol (corresponding to −1.2 MPa) this response was modified. A 80–97% reduction of AGPase resulted in only a 0–40% inhibition of starch synthesis. Further, the water stress-induced stimulation of sucrose synthesis was abolished in the transformants. The results provide direct evidence that the contribution of AGPase to the control of starch synthesis can be modified by environmental factors, leading to a lower degree of control during severe water deficits. There was also a dramatic decrease in the labelling of cell-wall components in wild-type tuber slices incubated with 300 or 500 mM mannitol. The water stress-induced inhibition of cell-wall synthesis occurred independently of AGPase expression and the accompanying changes in starch and sucrose metabolism, indicating a direct inhibition of cell-wall synthesis in response to water stress. Received: 24 February 1999 / Accepted: 28 May 1999     

Synergistic interaction between the potato glycoalkaloids α-solanine and α-chaconine in relation to lysis of phospholipid/sterol liposomes

At pH 7.2, the steroidal glycoalkaloid α-chaconine disrupted phosphatidylcholine/cholesterol liposomes whereas α-solanine was virtually without effect. A glycoalkaloid mixture extracted from potato sprouts and comprising approximately equal amounts of solanine and chaconine had, at 150 μM, a lytic effect the same as a 150 μM solution of chaconine only. The apparent synergistic interaction between the two compounds was confirmed using 1:1 mixtures of authentic solanine and chaconine from different sources and of different batches. Combinations (1:1) of solanine or chaconine and tomatine or digitonin (both of which lysed liposomes) or β₂-chaconine (which is non-lytic) did not produce synergistic effects. The synergism between solanine and chaconine was observed only when the two compounds were present together, although the order of addition into the test system did not appear crucial. Pretreatment of liposomes with one glycoalkaloid and its subsequent removal did not permanently sensitize the membranes to the second glycoalkaloid. The magnitude of the synergism was dependent on the relative amounts of solanine and chaconine with maximal effects where chaconine comprised 40% or more of the mixture.     

Monte Carlo simulation of the α-amylolysis of amylopectin potato starch

The branched structure of potato amylopectin (degree of polymerization ~200,000) was modeled in a computer matrix. The chain-length distribution and the length and width of a cluster of the amylopectin molecule were used as input variables in the model. Independent literature values related to the structure of amylopectin (percentage #-hydrolysis and ratio of A- to B-chains) were used for evaluation of the branching characteristics (length of branch area and chance of branching) of the modeled amylopectin. The structural parameters predicted by the model agreed very well with data from the literature. The chain-length distribution and values for the percentage of #-hydrolysis were the two most important parameters required to model the structure of amylopectin. This computer-generated model of potato amylopectin in solution can be used to simulate various enzymatic (i.e., !-amylase, #-amylase, glucoamylase, pullunanase) or chemical reactions (i.e., acid hydrolysis, hypochlorite oxidation). The modeling approach described in this paper is also suitable for starches from other botanical sources (i.e., corn, wheat, tapioca).     

Obese state leads to elevated levels of TGF-β and COX isoforms in platelets of Zucker rats

Platelets are rich sources of growth factors and enzymes that are implicated in a number of diseases including obesity, atherosclerosis, heart disease, syndrome X, liver and kidney diseases and certain types of cancers. In this research we investigated, if platelets in Zucker obese rats differ from their lean counterparts with respect to the levels of TGF-β and COX isoforms, implicated in the pathogenesis of chronic diseases. In addition, we investigated if energy intake of the animals affects the platelet physiology. Platelets were isolated from obese and lean rats bearing preneoplastic lesions in their colon. Prior to platelet isolation these rats were fed either ad libitum (Ob or Ln) or energy restricted (Ob-ER or Ln-ER) diets for 8 weeks (n = 8/group). The levels of TGF-β1/-β2 and COX-1/-2 proteins in platelets were analyzed by Western blot. The platelets of the Ob rats had significantly higher levels of TGF-β1, COX-1/-2 (p < 0.001) than did the platelets of the Ln rats and were not affected by moderate energy restriction. There were no significant differences in the protein expression of platelet TGF-β2 among any of the groups. These results demonstrate that cytokines and candidates playing a role in the pathogenesis of chronic diseases, such as TGF-β1 and COX-1/-2, are over-expressed in platelets of Zucker obese rats by comparison to their lean counterparts. These findings also demonstrate that the genotype of the animals exerts a significant effect on the biochemical composition of the platelets and could contribute to the pathogenesis of colon cancer and other metabolic abnormalities associated with obesity.     

Translational arrest in hypoxic potato tubers is correlated with the aberrant association of elongation factor EF-1α with polysomes

Translation elongation factor EF-1 became stably associated with potato tuber polysomes at the onset of hypoxia, coincident with a sharp rise in lactate and decrease in tissue pH. This aberrant association of EF-1 with polysomes also occurred when aerobic tuber extracts were acidified in vitro. Upon resumption of protein synthesis, an increase in the steady-state levels of EF-1, and expression of an EF-1/GUS transgene was observed. These results indicate that translational arrest results from to the failure of EF-1 to dissociate from ribosomes during the elongation cycle, and that restoration of protein synthesis is coordinated with expression of EF-1.     

Are the effects of α-glucosidase inhibitors on cardiovascular events related to elevated levels of hydrogen gas in the gastrointestinal tract?

The major side-effect of treatment with α-glucosidase inhibitors, flatulence, occurs when undigested carbohydrates are fermented by colonic bacteria, resulting in gas formation. We propose that the cardiovascular benefits of α-glucosidase inhibitors are partly attributable to their ability to neutralise oxidative stress via increased production of H₂ in the gastrointestinal tract. Acarbose, which is an α-glucosidase inhibitor, markedly increased H₂ production, with a weaker effect on methane production. Our hypothesis is based on our recent discovery that H₂ acts as a unique antioxidant, and that when inhaled or taken orally as H₂-dissolved water it ameliorates ischaemia-reperfusion injury and atherosclerosis development.     

Feeding experiment using uniformly 13C-labeled α-linolenic acid supports the involvement of the decarboxylation mechanism to produce cis-jasmone in Lasiodiplodia theobromae

ABSTRACT

In our previous report, it was found that Lasiodiplodia theobromae produced cis-jasmone via partially utilizing the biosynthetic pathway of JA. A feeding experiment using uniformly ¹³C-labeled α-linolenic acid, which was added to the culture media of the fungus, strongly supported that the fungus produced CJ via the decarboxylation step of the biosynthetic pathway.     

Monte Carlo simulation of the α-amylolysis of amylopectin potato starch. 2. α-amylolysis of amylopectin

A model is presented that describes all the saccharides that are produced during the hydrolysis of starch by an -amylase. Potato amylopectin, the substrate of the hydrolysis reaction, was modeled in a computer matrix. The four different subsite maps presented in literature for -amylase originating from Bacillus amyloliquefaciens were used to describe the hydrolysis reaction in a Monte Carlo simulation. The saccharide composition predicted by the model was evaluated with experimental values. Overall, the model predictions were acceptable, but no single subsite map gave the best predictions for all saccharides produced. The influence of an (16) linkage on the rate of hydrolysis of nearby (14) linkages by the -amylase was evaluated using various inhibition constants. For all the subsites considered the use of inhibition constants led to an improvement in the predictions (a decrease of residual sum of squares), indicating the validity of inhibition constants as such. As without inhibition constants, no single subsite map gave the best fit for all saccharides. The possibility of generating a hypothetical subsite map by fitting was therefore investigated. With a genetic algorithm it was possible to construct hypothetical subsite maps (with inhibition constants) that gave further improvements in the average prediction for all saccharides. The advantage of this type of modeling over a regular fit is the additional information about all the saccharides produced during hydrolysis, including the ones that are difficult to measure experimentally.     

Molecular dynamics simulations to the bidirectional adhesion signaling pathway of integrin αVβ3

The bidirectional force transmission process of integrin through the cell membrane is still not well understood. Several possible mechanisms have been discussed in literature on the basis of experimental data, and in this study, we investigate these mechanisms by free and steered molecular dynamics simulations. For the first time, constant velocity pulling on the complete integrin molecule inside a dipalmitoyl-phosphatidylcholine membrane is conducted. From the results, the most likely mechanism for inside-out and outside-in signaling is the switchblade model with further separation of the transmembrane helices.     

Disruption of β-oxidation pathway in Pseudomonas putida KT2442 to produce new functionalized PHAs with thioester groups

This work describes the generation of novel PHAs (named PHACOS) with a new monomer composition containing thioester groups in the side chain, which confers new properties and made them suitable for chemical modifications after their biosynthesis. We have analyzed the PHACOS production abilities of the wild-type strain Pseudomonas putida KT2442 vs. its derived strain P. putida KT42FadB, mutated in the fadB gene from the central metabolic β-oxidation pathway involved in the synthesis of medium-chain-length PHA (mcl-PHA). Different fermentation strategies based on one- or two-stage cultures have been tested resulting in PHACOS with different monomer composition. Using decanoic acid as inducer of the growth and polymer synthesis and 6-acetylthiohexanoic acid as PHA precursor in a two-stage strategy, the maximum yield was obtained by culturing the strain KT42FadB. Nuclear magnetic resonance and gas chromatography coupled to mass spectrometry showed that polymers obtained from the wild-type and KT42FadB strains, included 6-acetylthio-3-hydroxyhexanoic acid (OH-6ATH) and the shorter derivative 4-acetylthio-3-hydroxybutanoic acid (OH-4ATB) in their composition, although in different ratios. While the polymer obtained from KT42FadB strain contained mainly OH-6ATH monomer units, mcl-PHA produced by the wild-type strain contained OH-6ATH and OH-4ATB. Furthermore, polyesters showed differences in the OH-alkyl derivates moiety. The strain KT42FadB overproduced PHACOS when compared to the production rate of the control strain in one- and two-stage cultures. Thermal properties obtained by differential scanning calorimetry indicated that both polymers have different glass transition temperatures related to their composition.     

Effects of single and mixed inoculation with two arbuscular mycorrhizal fungi in two different levels of phosphorus supply on β-carotene concentrations in sweet potato (Ipomoea batatas L.) tubers

Aims

This study aimed to determine the effect of arbuscular mycorrhizal (AM) fungi and phosphorus (P) supply levels on β-carotene concentrations in sweet potato (Ipomoea batatas L.) tubers.

Methods

Two commercial AM fungal isolates of Glomus intraradices (IFP Glintra) and Glomus mosseae (IFP Glm) which differ in their life cycles were used. Sweet potato plants were grown in a horizontal split-root system that consisted of two root compartments. A root-free fungal compartment that allowed the quantification of mycelial development was inserted into each root compartment. The two root compartments were inoculated either with the same or with different AM isolates, or remained free of mycorrhizal propagules. Each fungal treatment was carried out in two P supply levels.

Results

In the low P supply level, mycorrhizal colonization significantly increased β-carotene concentrations in sweet potato tubers compared with the non-mycorrhizal plants. Glomus intraradices appeared to be more efficient in increasing β-carotene concentrations than G. mosseae. Dual inoculation of the root system with the two mycorrhizal fungi did not result in a higher increase in tuber β-carotene concentrations than inoculation with the single isolates. Improved P nutrition led to higher plant tuber biomass but was not associated with increased β-carotene concentrations.

Conclusions

The results indicate a remarkable potential of mycorrhizal fungi to improve β-carotene concentrations in sweet potato tubers in low P fertilized soils. These results also suggest that β-carotene metabolism in sweet potato tubers might be specifically activated by root mycorrhizal colonization.     

Cerebrospinal fluid α-synuclein levels are elevated in multiple sclerosis and neuromyelitis optica patients during replase

The concept that the immune system plays a central role in the pathogenesis of multiple sclerosis (MS) and neuromyelitis optica (NMO) was indisputable. However, neurodegenerative pathological features including loss of axons and neurons were also found in the lesions of these diseases. α-Synuclein is one of the most abundant proteins in pre-synaptic terminals. Recently, many research show α-synuclein level in CSF may reflect the progression of synaptic dysfunction and neuronal apoptosis. Whether the levels of CSF α-synuclein are changed in MS and NMO patients remain unknown. In this study, CSF α-synuclein was measured by an enzyme-linked immunosorbent assay (ELISA) in MS (n = 18) patients, NMO (n = 22) patients, Parkinson's disease patients (n = 9), and the controls (n = 11). We found concentration of α-synuclein in MS and NMO patients were significantly higher than Parkinson's disease subgroup and the controls. Both MS and NMO revealed an increased disease disability with increased CSF α-synuclein. Thus, CSF α-synuclein may be reflect injure axons and neurons in inflammatory demyelinating diseases.