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In recent studies we have reported on the near-UV light-induced degradation of iron complexes of various pharmaceutical excipients, such as Fe(III)-citrate and Fe(III)-amino acid complexes. Mechanistic studies revealed a common photo-degradation pattern, i.e. the formation of carbon dioxide radical anion, a potent reducing agent, via an alkoxyl/amino radical intermediate generated by light-induced ligand-to-metal charge transfer (LMCT) involving α-hydroxycarboxylates or amino acids. Herein, we confirm the proposed general photo-degradation pathways through the study of the iron complexes of other α-hydroxycarboxylates that may be present in protein formulations, such as lactate and glycolate. The results indicate that lactate generates even higher yields of •CO 2 − as compared to citrate, suggesting a significant potential of lactate for the promotion of photo-degradation in pharmaceutical formulations. [Display omitted] [ABSTRACT FROM AUTHOR]

Malic acid is the predominant organic acid in grape berries, and its content is affected by abiotic factors such as temperature (fruit zone microclimate) and water (vine water status). The objectives of this study were to explore the potential mechanisms behind the effects of vine water status on the biosynthesis and degradation of berry malic acid and the potential downstream effects on berry metabolism. This study was conducted over two growing seasons in 2021 and 2022, comprising three watering regimes: no water stress (CK), light water stress (LWS), and moderate water stress (MWS). Compared to CK, a significantly higher level of malic acid was found in berries from the MWS treatment when the berry was still hard and green (E-L 33) in both years. However, water stress reduced the malic acid content at the ripe berry harvest (E-L 38) stage. The activities of NAD-malate dehydrogenase (NAD-MDH) and pyruvate kinase (PK) were enhanced by water stress. Except for the E-L 33 stage, the activity of phosphoenolpyruvate carboxylase (PEPC) was reduced by water stress. The highest phosphoenolpyruvate carboxykinase (PEPCK) activity was observed at the berry veraison (E-L 35) stage and coincided with the onset of a decrease in the malate content. Meanwhile, the expression of VvPEPCK was consistent with its enzyme activity. This study showed that water stress changed the content of some free amino acids (GABA, proline, leucine, aspartate, and glutamate), two of which (glutamate and GABA) are primary metabolites of the GABA pathway. [ABSTRACT FROM AUTHOR]

The response of wheat (Triticum aestivum L.) plants to the soil drought at the metabolome level is still not fully explained. In addition, research focuses mainly on single periods of drought, and there is still a lack of data on the response of plants to short-term cyclical periods of drought. The key to this research was to find out whether wheat shoots are able to resume metabolism after the stress subsides and if the reaction to subsequent stress is the same. Gas chromatography coupled with mass spectrometry (GC-MS) is one of the most valuable and fast methods to discover changes in the primary metabolism of plants. The targeted GC-MS analyses of whole shoots of wheat plants exposed (at the juvenile stage of development) to short-term (five days) mild soil drought/rewatering cycles (until the start of shoot wilting) enabled us to identify 32 polar metabolites. The obtained results revealed an accumulation of sugars (sucrose, fructose, glucose, and 1-kestose), proline, and malic acid. During five days of recovery, shoots regained full turgor and continued to grow, and the levels of accumulated metabolites decreased. Similar changes in metabolic profiles were found during the second drought/rewatering cycle. However, the concentrations of glucose, proline, and malic acid were higher after the second drought than after the first one. Additionally, the concentration of total polar metabolites after each plant rewatering was elevated compared to control samples. Although our results confirm the participation of proline in wheat responses to drought, they also highlight the responsiveness of soluble carbohydrate metabolism to stress/recovery. [ABSTRACT FROM AUTHOR]

Background: Malic acid, a dicarboxylic acid mainly used in the food industry, is currently produced from fossil resources. The utilization of low-cost substrates derived from biomass could render microbial processes economic. Such feedstocks, like lignocellulosic hydrolysates or condensates of fast pyrolysis, can contain high concentrations of acetic acid. Acetate is a suitable substrate for l-malic acid production with the filamentous fungus Aspergillus oryzae DSM 1863, but concentrations obtained so far are low. An advantage of this carbon source is that it can be used for pH control and simultaneous substrate supply in the form of acetic acid. In this study, we therefore aimed to enhance l-malate production from acetate with A. oryzae by applying a pH-coupled feeding strategy. Results: In 2.5-L bioreactor fermentations, several feeding strategies were evaluated. Using a pH-coupled feed consisting of 10 M acetic acid, the malic acid concentration was increased about 5.3-fold compared to the batch process without pH control, resulting in a maximum titer of 29.53 ± 1.82 g/L after 264 h. However, it was not possible to keep both the pH and the substrate concentration constant during this fermentation. By using 10 M acetic acid set to a pH of 4.5, or with the repeated addition of NaOH, the substrate concentration could be maintained within a constant range, but these strategies did not prove beneficial as lower maximum titers and yields were obtained. Since cessation of malic acid production was observed in later fermentation stages despite carbon availability, a possible product inhibition was evaluated in shake flask cultivations. In these experiments, malate and succinate, which is a major by-product during malic acid production, were added at concentrations of up to 50 g/L, and it was found that A. oryzae is capable of organic acid production even at high product concentrations. Conclusions: This study demonstrates that a suitable feeding strategy is necessary for efficient malic acid production from acetate. It illustrates the potential of acetate as carbon source for microbial production of the organic acid and provides useful insights which can serve as basis for further optimization. [ABSTRACT FROM AUTHOR]

Summary: There is currently considerable interest in the prospects for bioengineering crassulacean acid metabolism (CAM) photosynthesis – or key elements associated with it, such as increased water‐use efficiency – into C3 plants. Resolving how CAM photosynthesis evolved from the ancestral C3 pathway could provide valuable insights into the targets for such bioengineering efforts. It has been proposed that the ability to accumulate organic acids at night may be common among C3 plants, and that the transition to CAM might simply require enhancement of pre‐existing fluxes, without the need for changes in circadian or diurnal regulation. We show, in a survey encompassing 40 families of vascular plants, that nocturnal acidification is a feature entirely restricted to CAM species. Although many C3 species can synthesize malate during the light period, we argue that the switch to night‐time malic acid accumulation requires a fundamental metabolic reprogramming that couples glycolytic breakdown of storage carbohydrate to the process of net dark CO2 fixation. This central element of the CAM pathway, even when expressed at a low level, represents a biochemical capability not seen in C3 plants, and so is better regarded as a discrete evolutionary innovation than as part of a metabolic continuum between C3 and CAM. [ABSTRACT FROM AUTHOR]

Whole-cell immobilization by entrapment in natural polymers can be a tool for morphological control and facilitate biomass retention. In this study, the possibility of immobilizing the filamentous fungus Aspergillus oryzae for l-malic acid production was evaluated with the two carbon sources acetate and glucose. A. oryzae conidia were entrapped in alginate, agar, and κ-carrageenan and production was monitored in batch processes in shake flasks and 2.5-L bioreactors. With glucose, the malic acid concentration after 144 h of cultivation using immobilized particles was mostly similar to the control with free biomass. In acetate medium, production with immobilized conidia of A. oryzae in shake flasks was delayed and titers were generally lower compared to cultures with free mycelium. While all immobilization matrices were stable in glucose medium, disintegration of bead material and biomass detachment in acetate medium was observed in later stages of the fermentation. Still, immobilization proved advantageous in bioreactor cultivations with acetate and resulted in increased malic acid titers. This study is the first to evaluate immobilization of A. oryzae for malic acid production and describes the potential but also challenges regarding the application of different matrices in glucose and acetate media. [ABSTRACT FROM AUTHOR]

Background: Microbial malic acid production is currently not able to compete economically with well-established chemical processes using fossil resources. The utilization of inexpensive biomass-based substrates containing acetate could decrease production costs and promote the development of microbial processes. Acetate is a by-product in lignocellulosic hydrolysates and fast pyrolysis products or can be synthesized by acetogens during syngas fermentation. For the fermentation of these substrates, a robust microorganism with a high tolerance for biomass-derived inhibitors is required. Aspergillus oryzae is a suitable candidate due to its high tolerance and broad substrate spectrum. To pave the path towards microbial malic acid production, the potential of acetate as a carbon source for A. oryzae is evaluated in this study. Results: A broad acetate concentration range was tested both for growth and malic acid production with A. oryzae. Dry biomass concentration was highest for acetic acid concentrations of 40–55 g/L reaching values of about 1.1 g/L within 48 h. Morphological changes were observed depending on the acetate concentration, yielding a pellet-like morphology with low and a filamentous structure with high substrate concentrations. For malic acid production, 45 g/L acetic acid was ideal, resulting in a product concentration of 8.44 ± 0.42 g/L after 192 h. The addition of 5–15 g/L glucose to acetate medium proved beneficial by lowering the time point of maximum productivity and increasing malic acid yield. The side product spectrum of cultures with acetate, glucose, and cultures containing both substrates was compared, showing differences especially in the amount of oxalic, succinic, and citric acid produced. Furthermore, the presence of CaCO3, a pH regulator used for malate production with glucose, was found to be crucial also for malic acid production with acetate. Conclusions: This study evaluates relevant aspects of malic acid production with A. oryzae using acetate as carbon source and demonstrates that it is a suitable substrate for biomass formation and acid synthesis. The insights provided here will be useful to further microbial malic acid production using renewable substrates. [ABSTRACT FROM AUTHOR]

• Sugar and acid ratio mainly determine quality of the fruit. • Malic acid is predominant organic acid in Chinese plum. • Transcriptome analysis was done to identify malic acid metabolism-related genes. • 11 enzyme coding, 21 transporter and 5 MYB TF genes were identified. Chinese plum (Prunus salicina Lindl.) is an important commercially produced stone fruit that accumulates high amounts of organic acids with numerous health benefits. Organic acids are key components to determine the flavor of any fruit. Here, to identify the potential genes involved in organic acids accumulation in plum, the metabolomic and transcriptomic analysis of plum fruits were performed at four developmental stages (i.e., fruitlet, green, veraison, and mature). The results suggest that malic acid was predominant among the eight organic acids analyzed. RNA-Seq analysis revealed a total of 26,547 unigenes, of which 7,584 representing 28.56% differentially expressed genes (DEGs) were identified. In addition, 11 enzyme coding genes, 21 transporter genes and 5 MYB transcription factor genes involved in malic acid accumulation were identified. Our combined transcriptomic and targeted metabolomic analyses provides new comprehensive insights into understanding the genetic control of fruit acidity in plum which will be useful for future breeding. [ABSTRACT FROM AUTHOR]

Abstract Background The organic acid producer Aspergillus oryzae and Rhizopus delemar are able to convert several alternative carbon sources to malic and fumaric acid. Thus, carbohydrate hydrolysates from lignocellulose separation are likely suitable as substrate for organic acid production with these fungi. Results Before lignocellulose hydrolysate fractions were tested as substrates, experiments with several mono- and disaccharides, possibly present in pretreated biomass, were conducted for their suitability for malic acid production with A. oryzae. This includes levoglucosan, glucose, galactose, mannose, arabinose, xylose, ribose, and cellobiose as well as cheap and easy available sugars, e.g., fructose and maltose. A. oryzae is able to convert every sugar investigated to malate, albeit with different yields. Based on the promising results from the pure sugar conversion experiments, fractions of the organosolv process from beechwood (Fagus sylvatica) and Miscanthus giganteus were further analyzed as carbon source for cultivation and fermentation with A. oryzae for malic acid and R. delemar for fumaric acid production. The highest malic acid concentration of 37.9 ± 2.6 g/L could be reached using beechwood cellulose fraction as carbon source in bioreactor fermentation with A. oryzae and 16.2 ± 0.2 g/L fumaric acid with R. delemar. Conclusions We showed in this study that the range of convertible sugars for A. oryzae is even higher than known before. We approved the suitability of fiber/cellulose hydrolysate obtained from the organosolv process as carbon source for A. oryzae in shake flasks as well as in a small-scale bioreactor. The more challenging hemicellulose fraction of F. sylvatica was also positively evaluated for malic acid production with A. oryzae.

Highlights • We comprehensively review the importance of NADP-ME under different stress conditions. • We focus in particular on the responses of NADP-ME to stress at the levels of activity and gene expression. • We discuss the importance of NADPH in apoplastic oxidative burst, ascorbate-glutathione pathway and flavonoid synthesis. • CRISPR technology would be a potential approach for analyzing redundancy between NADP-ME isoforms or between NADP-ME and other dehydrogenases. • Our review also places emphasis on the reversibility of the NADP-ME reaction. Abstract Under natural conditions, plants constantly encounter various fluctuating environmental stresses, which potentially restrict plant growth, plant development and even limit crop productivity. In addition to carbon fixation activity in C4 photosynthesis, NADP-dependent malic enzyme (NADP-ME) has been suggested to play important roles in diverse stress responses in plants. NADP-ME is one of the essential enzymes metabolizing malate, which is important for stabilizing cytoplasmic pH, controlling stomatal aperture, increasing resistance to aluminum excess and pathogen. Pyruvate, another product of NADP-ME reaction, participates in the synthesis of defense compounds such as flavonoids and lignin, which are involved in stresses tolerance such as mechanical wounding and pathogen invasion. Moreover, NADP-ME provides essential reductive coenzyme NADPH in the biosynthesis of flavonoids and lignin. On the other hand, NADPH is crucial for reactive active species (ROS) metabolizing systems such as the ascorbate-glutathione pathway and NADPH-dependent thioredoxin reductase, and is also required by apoplastic oxidative burst in most plant-pathogen interactions. This mini-review is largely focus on the characteristics of gene expression and activity of NADP-ME, as well as its interaction with ROS signaling under a variety of biotic and abiotic stress responses, which will provide a theoretical foundation for breeding of stress resistant crops. [ABSTRACT FROM AUTHOR]

The effects of sodium and calcium salts of malic acid on growth performance, rumen pH, protozoa number, NH3- N level and volatile fatty acid (VFA) ratio and carcass yield in Akkaraman lambs fed alfalfa hay either restricted or ad-libitum were investigated. In a completely randomized design experiment, treatments were arranged at 2x2 factorial fashion: two forage levels (100 g/d or ad-libitum) and two malate levels (0 or 5 g/d), which were tested in 32 male lambs (3-4 months of age, 23.28±1.27 kg BW). Adaptation to feeding lasted 10 days; while sampling period lasted for 60 days. Growth performance, feed intake, slaughter and carcass weight were not affected by the treatments. A significant change was found in ruminal pH by forage feding level over time. At the beginning of the experiment the amount of acetic acid was increased by ad-libitum alfalfa hay consumption and malate addition but this effect was disappeared end of the trial. Rumen propionic acid, NH3-N concentration and protozoa number were not affected by the treatments but they changed by the sampling time. There was alfalfa hay level x malate supplementation x sampling time interaction effect on butyric acid concentration. In conclusion, malate addition did not improve growth rate and carcass yield of lambs but it affected ruminal acetic acid and butyric acid concentrations in lambs fed alfalfa ad-libitum. [ABSTRACT FROM AUTHOR]

Phosphoenolpyruvate carboxylase (PEPC) is an important regulatory enzyme situated at a key branch point of central plant metabolism. Plant genomes encode several plant-type PEPC (PTPC) isozymes, along with a distantly related bacterial-type PEPC (BTPC). BTPC is expressed at high levels in developing castor oil seeds where it tightly interacts with co-expressed PTPC polypeptides to form unusual hetero-octameric Class-2 PEPC complexes that are desensitized to allosteric inhibition by L-malate. Analysis of RNA-Seq and microarray transcriptome datasets revealed two distinct patterns of tissue-specific BTPC expression in vascular plants. Species such as Arabidopsis thaliana, strawberry, rice, maize, and poplar mainly exhibited pollen- or floral-specific BTPC expression. By contrast, BTPC transcripts were relatively abundant in developing castor, cotton, and soybean seeds, cassava tubers, as well as immature tomato, cucumber, grape, and avocado fruit. Immunoreactive 118 kDa BTPC polypeptides were detected on immunoblots of cucumber and tomato fruit extracts. Co-immunoprecipitation established that as in castor, BTPCs physically interact with endogenous PTPCs to form Class-2 PEPC complexes in tomato and cucumber fruit. We hypothesize that Class-2 PEPCs simultaneously maintain rapid anaplerotic PEP carboxylation and respiratory CO2 refixation in diverse, biosynthetically active sinks that accumulate high malate levels. [ABSTRACT FROM AUTHOR]

Background: The organic acid producer Aspergillus oryzae and Rhizopus delemar are able to convert several alternative carbon sources to malic and fumaric acid. Thus, carbohydrate hydrolysates from lignocellulose separation are likely suitable as substrate for organic acid production with these fungi. Results: Before lignocellulose hydrolysate fractions were tested as substrates, experiments with several mono- and disaccharides, possibly present in pretreated biomass, were conducted for their suitability for malic acid production with A. oryzae. This includes levoglucosan, glucose, galactose, mannose, arabinose, xylose, ribose, and cellobiose as well as cheap and easy available sugars, e.g., fructose and maltose. A. oryzae is able to convert every sugar investigated to malate, albeit with different yields. Based on the promising results from the pure sugar conversion experiments, fractions of the organosolv process from beechwood (Fagus sylvatica) and Miscanthus giganteus were further analyzed as carbon source for cultivation and fermentation with A. oryzae for malic acid and R. delemar for fumaric acid production. The highest malic acid concentration of 37.9 ± 2.6 g/L could be reached using beechwood cellulose fraction as carbon source in bioreactor fermentation with A. oryzae and 16.2 ± 0.2 g/L fumaric acid with R. delemar. Conclusions: We showed in this study that the range of convertible sugars for A. oryzae is even higher than known before. We approved the suitability of fiber/cellulose hydrolysate obtained from the organosolv process as carbon source for A. oryzae in shake flasks as well as in a small-scale bioreactor. The more challenging hemicellulose fraction of F. sylvatica was also positively evaluated for malic acid production with A. oryzae. [ABSTRACT FROM AUTHOR]

Batch cultures of rumen microorganisms were used to compare the fermentation of sunflower seed (SS) and meal (SM) treated with malic acid and heat (MAH; 150 °C for 1 h) to protect the protein from ruminal degradation with that of the untreated samples supplemented the same amount of malate (as additive), either as free acid (MA) or disodium malate (DSM). As previous studies have shown the influence of donors’ diet on in vitro fermentation, cultures were inoculated with ruminal fluid from four sheep fed a medium-concentrate diet (MC; 50:50 hay:concentrate) or a high-concentrate diet (HC; 15:85 barley straw:concentrate) in a cross-over experimental design. Cultures were sampled at 6 and 16.5 h of fermentation. In 16.5 h incubations, MAH treatment reduced ( P < 0.001) CH 4 production and ammonia-N concentrations for both substrates (by 60.3 and 45.3% for SS and by 23.7 and 17.2% for SM substrate, respectively). Whereas the MAH treatment reduced total volatile fatty (VFA) production by 16.5% for SS substrate, no effects were observed for SM substrate ( P = 0.441). For both substrates, adding the same amount of MA to untreated samples (as a feed additive) resulted in greater CH 4 production and ammonia-N concentrations compared with the MAH treatment. A positive relationship ( P < 0.001) was observed between the concentrations of NH 3 N and CH 4 production at both incubation times for both substrates. Compared with the untreated feeds, MA and DSM did not affect ( P > 0.05) CH 4 production for either substrate, but reduced ammonia-N concentrations (13.8%; P = 0.004) for SM substrate. Compared with DSM, MA treatment resulted in greater ( P < 0.05) production of gas, butyrate, isovalerate and valerate and tended ( P < 0.10) to greater total VFA, and propionate production for SS substrate at 6 h incubation, but most differences disappeared after 16.5 h incubation. For some fermentation parameters, the response to MAH treatment was more pronounced by using fluid from sheep fed the HC diet than that from MC-fed sheep. In conclusion, the MAH treatment was more effective at reducing CH 4 emissions and NH 3 N concentrations than the supplementation of malic acid or disodium malate as a feed additive. [ABSTRACT FROM AUTHOR]

Background and aims: Long distance signals in xylem from roots to leaves are important in plant response to drought stress. Abscisic acid (ABA) plays a key role in drought signaling in plants but apoplastic pH may modulate its effect by distributing ABA into various compartments in leaves. We aimed to reveal the dynamics of changes in sap pH and its relationships with the transport of inorganic and organic ions in eight herbaceous plant species under continuously declining soil water content. We tested several hypotheses related to the mechanism of pH changes in xylem. Methods: We used a pressure chamber to collect xylem sap and to measure of leaf/stem water potential at various stages of soil drying. We measured pH and concentrations of the most abundant inorganic (NO , SO , PO and Cl) and organic (malate and citrate) anions in xylem sap. Results: Species differed considerably in the dynamics of pH changes in xylem in drying soil. Changes in xylem sap pH during drying did not relate to the nitrogen assimilation strategy but may be affected by sap flow rate. Simultaneous changes in the concentrations of inorganic and organic anions were highly species-specific. Conclusions: High variability among species in the observed relationships in response to drought indicates that comparisons among different studies and the generalization of results should be made with caution. [ABSTRACT FROM AUTHOR]

Citrate, malate and histidine have been involved in many processes including metal tolerance and accumulation in plants. These molecules have been frequently reported to be the potential nickel chelators, which most likely facilitate metal transport through xylem. In this context, we assess here, the relationship between organics acids and histidine content and nickel accumulation in Mesembryanthemum crystallinum and Brassica juncea grown in hydroponic media added with 25, 50 and 100 µM NiCl 2 . Results showed that M. crystallinum is relatively more tolerant to Ni toxicity than B. juncea. For both species, xylem transport rate of Ni increased with increasing Ni supply. A positive correlation was established between nickel and citrate concentrations in the xylem sap. In the shoot of B. juncea , citric and malic acids concentrations were significantly higher than in the shoot of M. crystallinum. Also , the shoots and roots of B. juncea accumulated much more histidine. In contrast, a higher root citrate concentration was observed in M. crystallinum . These findings suggest a specific involvement of malic and citric acid in Ni translocation and accumulation in M. crystallinum and B. juncea. The high citrate and histidine accumulation especially at 100 µM NiCl 2 , in the roots of M. crystallinum might be among the important factors associated with the tolerance of this halophyte to toxic Ni levels. [ABSTRACT FROM AUTHOR]

Background: The large surplus of crude glycerol, as main low-value waste stream in biodiesel production, has led to the investigation of new possibilities for the production of value-added chemicals from this feedstock. New and efficient (bio-) catalysts are needed that are able to convert glycerol to versatile chemical building blocks. This would contribute to further develop away from a mainly petroleum based, to a sustainable, bio-based industry. One promising group of discussed building block chemicals are dicarbonic acids. Results: Here, we report the efficient synthesis of malate from glycerol using Ustilago trichophora RK089, which was identified in a screening of 74 Ustilaginaceae. For economically feasible production that can compete with existing processes, a high productivity is required. By adaptive laboratory evolution, the growth and production rate were increased by 2.5- and 6.6-fold, respectively. Further medium optimization increased the final titer, yield, and overall production rate to 196 g L-1, 0.82 gmal g-1 gly, and 0.39 g L-1 h-1, respectively. Conclusions: This titer is the highest reported for microbial malate production, making U. trichophora TZ1 a promising microbial production host for malate from crude glycerol, especially since it is not genetically engineered. Since this production process starts from an industrial waste stream as substrate and yields an interesting platform chemical, which can be used to replace petro-chemicals, it greatly contributes to a sustainable bio-economy. [ABSTRACT FROM AUTHOR]

Malic acid is a C dicarboxylic acid that is currently mainly used in the food and beverages industry as an acidulant. Because of the versatility of the group of C dicarboxylic acids, the chemical industry has a growing interest in this chemical compound. As malic acid will be considered as a bulk chemical, microbial production requires organisms that sustain high rates, yields, and titers. Aspergillus oryzae is mainly known as an industrial enzyme producer, but it was also shown that it has a very competitive natural production capacity for malic acid. Recently, an engineered A. oryzae strain, 2103a-68, was presented which overexpressed pyruvate carboxylase, malate dehydrogenase, and a malic acid transporter. In this work, we report a detailed characterization of this strain including detailed rates and yields under malic acid production conditions. Furthermore, transcript levels of the genes of interest and corresponding enzyme activities were measured. On glucose as carbon source, 2103a-68 was able to secrete malic acid at a maximum specific production rate during stationary phase of 1.87 mmol (g dry weight (DW)) h and with a yield of 1.49 mol mol. Intracellular fluxes were obtained using C flux analysis during exponential growth, supporting the success of the metabolic engineering strategy of increasing flux through the reductive cytosolic tricarboxylic acid (rTCA) branch. Additional cultivations using xylose and a glucose/xylose mixture demonstrated that A. oryzae is able to efficiently metabolize pentoses and hexoses to produce malic acid at high titers, rates, and yields. [ABSTRACT FROM AUTHOR]

Summary: Self-rooted, 10-month-old, uniform tea [Camellia sinensis (L.) O. Kuntze cv. Huangguanyin] plants were supplied for 17 weeks with 0, 40, 80, 160, 400, or 1000μM phosphorus (P) to investigate the effects of P supply on root citrate and malate release, the concentrations of malate and citrate and the activities of acid-metabolizing enzymes in leaves and roots. Root malate release and accumulation was induced by both 0 and 40μM P, while root citrate release and accumulation was induced only by 0μM P. Phosphorus-deficiency-induced malate and citrate release coincided with higher concentrations of root malate and citrate. The higher concentrations of malate and citrate were accompanied by increased activities of phosphoenolpyruvate carboxylase (PEPC), phosphoenolpyruvate phosphatase (PEPP), citrate synthase (CS) and NAD-malic enzyme (NAD-ME) and decreased activities of pyruvate kinase (PK), NADP-ME and NADP-isocitrate dehydrogenase (NADP-IDH) in roots. In contrast to roots, malate accumulated in the leaves only in response to 0μM P, and no change was observed in citrate levels. The P-deficiency-induced leaf malate accumulation coincided with increased activities of NADP-ME, NAD-ME and PK. Overall, the P-deficiency-induced changes in organic acid (OA) metabolism differed between roots and leaves. The high tolerance of tea plants to P-deficiency might be involved in two major processes: (a) increasing the availability of P by inducing root release of OA anions; and (b) improving the ability to use P efficiently by inducing bypass enzymes involved in tissue P economy. [ABSTRACT FROM AUTHOR]

Background and Aims: Rootstocks influence the inorganic ion and organic acid composition of grapes of the scion variety. The aim was to investigate the impact of rootstocks on the inter-relationship of inorganic ions and organic acid anions in the skin and pulp of grapes and in resultant wine. Methods and Results: Vines were irrigated with water having electrical conductivities in the range 1.6–2.1 dS/m. Chloride, sodium, potassium, malic and tartaric acid concentrations were higher in almost all cases in skin than in pulp. Significant positive correlations existed between chloride and sodium concentrations in both pulp and skin. A significant negative linear regression existed between malic acid and both chloride and sodium concentrations in skin of Chardonnay berries. There were positive linear regressions in chloride concentration between berry (pulp and skin) and resultant wine chloride in both Chardonnay and Shiraz. Conclusion: The higher malic acid and lower chloride concentrations in skin of most grafted Chardonnay and Shiraz vines, and vice versa for own rooted vines, may indicate competition for similar transporter proteins involved in loading into skins. Alternatively, higher salt concentrations in skins may be associated with accelerated malic acid catabolism. Significance of the Study: Chloride-excluding rootstocks demonstrated advantages through reduced chloride (but not sodium) in pulp and skin of grape berries and in resultant wines. Where rootstocks reduced chloride concentrations in skin of grape berries, there is potential for higher malic acid in skin and in the resultant red wines. [ABSTRACT FROM AUTHOR]

Abstract: The effects of fermentation and digestion characteristics of lambs fed high grain finishing diets with two ionophores (monensin and lasalocid) were compared, and the additive response of malate in rations containing ionophores were evaluated. Twenty 4-month-old Pelibuey lambs, weighing approximately 16kg, were assigned to a completely randomize designed experiment with a 2×2 factorial arrangement of treatments (two ionophores with or without malate). The four treatment groups (diets) were: (1) diet with 30 parts per million (ppm) lasalocid, (2) diet with 30ppm lasalocid and 0.3% malate, (3) diet with 30ppm monensin, and (4) diet with 30ppm monensin and 0.3% malate. Animals were confined to individual metabolic cages. Body weight during the sampling phase averaged 20.6kg. Lambs fed diets with monensin had a 10.9% lower (P <0.05) dry matter (DM) intake (g/kg0.75) than those fed lasalocid. Malate had no effect (P >0.05) on DM intake. Lambs fed monensin had lower (P <0.01) NDF intake (37.8%) than those fed lasalocid. When malate was included in the diet, NDF intake was also reduced (P <0.05) by about 25%. However, no difference (P >0.05) in NDF or NFC digestibilities was observed between ionophores or by the addition of malate. Although time spent ruminating was 33% lower (P <0.05) for lambs fed monensin diets, time dedicated to eating was not different (P >0.05) between ionophores. Ruminal pH was similar (P >0.05) for all treatments (5.8). Type of ionophore had no effect (P >0.05) on concentration or molar percent of VFA, whereas the inclusion of malate increased (P <0.05) acetic acid concentration in rumen fluid (60.5mM vs. 48.2mM). Nitrogen balance was greater for lambs fed lasalocid diets, which had a higher crude protein intake, than lambs fed diets with monensin. Lambs fed diets with monensin or malate consumed less NDF, and dedicated less time to ruminate than those fed lasalocid. Lambs on the lasalocid diets consumed more fiber, which might be attributed to a greater selection of fibrous components of the diet. [Copyright &y& Elsevier]

Abstract: Rhodobacter sphaeroides O.U.001 is one of the candidates for photobiological hydrogen production among purple non-sulfur bacteria. Hydrogen is produced by Mo-nitrogenase from organic acids such as malate or lactate. A hupSL in frame deletion mutant strain was constructed without using any antibiotic resistance gene. The hydrogen production potential of the R. sphaeroides O.U.001 and its newly constructed hupSL deleted mutant strain in acetate media was evaluated and compared with malate containing media. The hupSL − R. sphaeroides produced 2.42l H2/l culture and 0.25l H2/l culture in 15mM malate and 30mM acetate containing media, respectively, as compared to the wild type cells which evolved 1.97l H2/l culture and 0.21l H2/l culture in malate and acetate containing media, correspondingly. According to the results, hupSL − R. sphaeroides is a better hydrogen producer but acetate alone does not seem to be an efficient carbon source for photoheterotrophic H2 production by R. sphaeroides. [Copyright &y& Elsevier]

The contribution of the seed and pericarp to the content of malic, quinic, citric and fumaric acids, and sucrose, fructose and glucose was determined during development and ripening of damson plum fruits. In whole fruit, (i) malic and quinic acids were the principal organic acids (OA) and their levels varied significantly, the highest being found at the beginning of the late-green stage; and (ii) the content of citric and fumaric acids was scarce but fluctuated remarkably towards development and ripening. In the seed, the levels of malic, quinic and fumaric acid were lower in ripening than at the beginning of maturation, and a notable synthesis of citric was found from the middle of maturation onwards. In mesocarp, however, malic, quinic, and citric acids peaked in the middle of maturation, whereas fumaric acid notably increased towards ripening. In epicarp, the maximum for the quinic and malic was found at the beginning of ripening and maturation, respectively. In the seed, all soluble sugars (SS) studied peaked at the middle of maturation, and while fructose and glucose (the most abundant SS) tended to be stored during ripening, sucrose (the most abundant in the edible part of fruit) decreased. All the SS studied tend to increase in mesocarp and epicarp throughout maturation and ripening. [ABSTRACT FROM AUTHOR]

Plant species and cultivars elicit a diverse array of sophisticated metabolic and developmental strategies to enhance phosphorus (P) solublization and acquisition from P-deficient rooting media. Scavenging of phosphate (Pi) from extracellular sparingly soluble P sources may be aided by organic acids (OAs) exudation and root-mediated pH changes under a P-stress environment. Root exudates were collected to quantify short-term (4 h, 8 h) carboxylate exudation using hydroponically grown Brassica cultivars. Malic and citric acids were the dominant OAs and efficient cultivars exuded 2–3-fold more OAs than inefficient cultivars under P-deficient conditions. However, the exudation rate of both resistant and sensitive cultivars decreased with time. Experiments in nutrient solution were conducted to evaluate growth responses and the P solublization and acquisition ability of six genetically diverse Brassica cultivars. Pre-germinated seedlings were grown in nutrient solution containing ammonium di-hydrogen phosphate (AP), tri-calcium phosphate (TCP) and rock phosphate (RP) (TCP at 0.2 g L−1 and RP at 2 g L−1, in a bid to maintain deficiently buffered solution-P concentration) as different P sources. The cultivars exhibited substantial growth differences ( P < 0.001) in terms of biomass accumulation, P acquisition and P utilization efficiency (PUE). Biomass production correlated significantly ( P < 0.01) with their shoot P uptake and PUE at both P sources, indicating that cultivars efficient in P solublization accumulated more biomass. Higher P uptake by all cultivars was significantly related to the drop in root medium pH, which was presumably owing to H+ efflux from the roots supplied with TCP and RP. Higher shoot dry matter of the cultivars at TCP was related to better P acquisition ability, which in turn was related to higher Ca uptake. Thus, cultivars with efficient Ca accumulation ability can acquire higher amounts of P from P-deficient soils and can adapt well to such low-P soil conditions. [ABSTRACT FROM AUTHOR]

Malic acid production, degradation, and storage during fruit development have been modelled. The model assumes that malic acid content is determined essentially by the conditions of its storage in the mesocarp cells, and provides a simplified representation of the mechanisms involved in the accumulation of malate in the vacuole and their regulation by thermodynamic constraints. Solving the corresponding system of equations made it possible to predict the malic acid content of the fruit as a function of organic acids, potassium concentration, and temperature. The model was applied to peach fruit, and parameters were estimated from the data of fruit development monitored over 2 years. The predictions were in good agreement with experimental data. Simulations were performed to analyse the behaviour of the model in response to variations in composition and temperature. [ABSTRACT FROM PUBLISHER]

Although total titratable acidity levels in ‘Hayward’ kiwifruit appear quite stable during storage at 0 °C under New Zealand conditions it is known that citric acid levels decline but malic acid levels are maintained. By contrast, malic acid levels tend to increase with storage at 4 °C. These observations formed the basis of a sensory comparison of fruit stored at 0, 4, and 10 °C which were also analysed for acidity, sweetness, and the individual acid concentrations during 6 weeks of storage. The fruit were ripened to equivalent firmness, and presented to sensory panellists. Acid perception increased at 4 °C, which correlated with an increase in malic acid concentration, but also with a decline in sweetness perception, soluble solids content, and dry matter in fruit stored at 4 and 10 °C compared to fruit stored at 0 °C. Although fruit were presented to panellists at equivalent fruit firmness (4.4–7.3N), the results were further confounded by changes in perceived texture in fruit held at the warmer temperatures. Ratings for core firmness, flesh firmness, and fibrous flesh texture increased in the fruit at 4 and 10 °C compared to fruit at 0 °C. Storage at 4 and 10 °C also led to an increase in stalky, woody flavours compared to storage at 0 °C. Findings for an increase in the perception of acidity from fruit stored at 4 °C could not be unequivocably attributed to the changes in acidity occurring during storage. However, they were consistent with findings from pulp experiments, where malic and citric acid had been added to ‘Hayward’ kiwifruit pulp.The results had implications for the storage of ‘Hayward’ kiwifruit at less than optimum fruit temperatures and raised interesting questions about the changes in metabolism occurring in fruit at the three temperatures studied. [Copyright &y& Elsevier]

Cis -dioxo hydrogenmalato tungstates(VI) Δ-Na 2 [WO 2 ( S -Hmal) 2 ]·4H 2 O 1 , and Na 2 [WO 2 ( R , S -Hmal) 2 ] 2 (H 3 mal = malic acid) have been prepared from the reactions of excess S- malic acid and R , S -malic acid respectively, with sodium tungstate at ambient temperature. Both complexes were characterized by elemental analyses, conductivity measurement, optical rotation, UV-Vis, IR and NMR spectroscopy. Complex 1 was obtained with predetermined helical chirality at the metal center for a Δ- cis -configuration, which is established by single crystal X-ray diffraction. The crystal is orthorhombic, space group P 2 1 2 1 2 1 , with unit cell parameters: a = 7.9545(6), b = 10.7440(8), c = 21.045(2)Å, V = 1798.6(2)Å 3 , Z = 4, D c = 2.215 g cm -3 , F (000) = 1152, R = 0.031, R w = 0.034. Single crystal X-ray diffraction reveals that the cis- dioxo tungstate 1 is octahedrally coordinated by the S -malate through the deprotonated α-hydroxy and α-carboxylate groups, while the β-carboxylic acid groups remain uncomplexed. [ABSTRACT FROM AUTHOR]

Two enzymes, lactate oxidase and malate dehydrogenase, were used in the construction of working electrodes for the amperometric determination of lactic and malic acid in wine. Preparation of the enzyme matrices had to satisfy two technologies: thick-film printing and sol–gels. The matrices were thus complex printing inks, consisting principally of gel precursors, graphite, cellulosic binder and enzyme. After mixing, the inks were printed before gel formation. The electrodes responded to standard solutions of lactic and malic acids. In combination with the method of standard addition, the electrodes were able to provide estimates of the concentrations of lactic and malic acids in some white wines. [Copyright &y& Elsevier]

Reaction of sodium or potassium molybdate and excess malic acid in a wide range of pH values (pH 4.0–7.0) resulted in the isolation of two cis-dioxo-bis(malato)-Mo(VI) complexes, viz. Na3[MoO2H(S-mal)2] and K3[MoO2H(S-mal)2]·H2O (H3mal=malic acid). The sodium complex is also characterized by an X-ray structure analysis, showing that the mononuclear Mo units are linked together via very strong symmetric CO2···H··· O2C-hydrogen bond [2.432(5) A˚], forming a polymeric chain. The molybdenum atoms are quasi-octahedrally coordinated by two cis-oxo groups and two bidentate malate ligands via its alkoxy and α-carboxyl groups, while the β-carboxylic and carboxylate groups remain uncomplexed, as the coordination of vicinal carboxylate and alkoxide of homocitrate in FeMo cofactor of nitrogenase. The absolute configuration of the metal center in this S-malato complex is assigned as Λ and the homochirality within the chain is established as a homochiral form ···ΛS–ΛS–ΛS–ΛS···. It is proposed that the chiral configuration of the metal center in wild-type FeMo-co biosynthesis might be induced by the early coordination of the chiral R-homocitric acid, while a mixture of raceme might be obtained in the biosynthesis of NifV− FeMo-cofactor. The absolute configuration of wild-type FeMo-cofactor is assigned as ΔR. [ABSTRACT FROM AUTHOR]

Polymeric S-malate nickel(II) [Δ-Ni(S-Hmal)(H2O)2]n·nH2O (1) was prepared from the reaction of nickel chloride and malate salt. By prolonging the reaction time and heating, the kinetic monomeric product cis-[Ni(S-H2mal)2(H2O)2]·2H2O (2) can be converted into the thermodynamic polymeric product 1. The coordination polymer is linked strongly by the tetradentate malate ligand, forming an homochiral zigzag chain. It is proposed that the chiral metal center of the complex may also be involved in the enantioselective synthesis as well as the chiral ligand. [Copyright &y& Elsevier]

All of the features of crassulacean acid metabolism (CAM) and most characteristics of C4 photosynthesis are exhibited by stomatal guard cells. It is proposed that CAM and possibly also C4 photosynthesis result from the expression in photosynthetic cells of genetic information which is expressed only in guard cells of C3 plants. [ABSTRACT FROM AUTHOR]

Summary Electrophysiological studies using the patch-clamp technique were performed on isolated vacuoles from leaf mesophyll cells of the crassulacean acid metabolism (CAM) plant Kalanchoë daigremontiana to characterize the malate transport system responsible for nocturnal malic acid accumulation. In the presence of malate on both sides of the membrane, the current–voltage relations of the tonoplast were dominated by a strongly inward-rectifying anion-selective channel that was active at cytoplasmic-side negative voltages. Rectification of the macroscopic conductance was reflected in the voltage-dependent gating of a 3-pS malate-selective ion channel, which showed a half-maximal open probability at -43 mV. Also, the time-averaged unitary currents following a step to a negative voltage corresponded to the time-dependent kinetics of the macroscopic currents, suggesting that the activity of this channel underlies the anion-selective inward rectifier. The inward rectifier showed saturation kinetics with respect to malate (apparent K m of 2.5 mm malate2- activity), a selectivity sequence of fumarate2- > malate2- > Cl- > maleate2– ≈ citrate3– , and greater activity at higher pH values (with an apparent pK of 7.1 and maximum activity at around pH 8.0). All these properties were in close agreement with the characteristics of malate transport observed in isolated tonoplast vesicles. Further, 100 µm niflumate reversibly blocked the activity of the 3-pS channel and inhibited both macroscopic currents and malate transport into tonoplast vesicles to the same extent. The macroscopic current densities recorded at physiological voltages and the estimated channel density of 0.2 µm-2 are sufficient to account for the observed rates of nocturnal malic acid accumulation in this CAM plant, suggesting that the 3-pS, inward-rectifying, anion-selective... [ABSTRACT FROM AUTHOR]