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Toluidine blue O (TBO) is a phenothiazine dye that, due to its photochemical characteristics and high affinity for biomembranes, has been revealed as a new photosensitizer (PS) option for antimicrobial photodynamic therapy (PDT). This points to a possible association with membranous organelles like mitochondrion. Therefore, here we investigated its effects on mitochondrial bioenergetic functions both in the dark and under photostimulation. Two experimental systems were utilized: (a) isolated rat liver mitochondria and (b) isolated perfused rat liver. Our data revealed that, independently of photostimulation, TBO presented affinity for mitochondria. Under photostimulation, TBO increased the protein carbonylation and lipid peroxidation levels (up to 109.40 and 119.87%, respectively) and decreased the reduced glutathione levels (59.72%) in mitochondria. TBO also uncoupled oxidative phosphorylation and photoinactivated the respiratory chain complexes I, II, and IV, as well as the F

Elevar a produtividade e prolongar a vida útil dos frutos do morangueiro estão entre os principais objetivos dos produtores. A cultura do morango possui grande importância e a crescente competitividade no setor olerícola e o aumento da demanda pela cultura estimulou a procura dos agricultores por reguladores à base de giberelinas. Uma das funções da aplicação de fitormônios ou reguladores vegetais é promover precocidade ou atraso no florescimento e maturação dos pseudofrutos do morangueiro. Outra é obter aumentos no tamanho e na quantidade de pseudofrutos. A aplicação das giberelinas é realizada em diversas culturas, de acordo com o estágio de interesse do vegetal. Dessa forma, visando aumentar a produtividade, avaliamos os efeitos da aplicação foliar do fitorregulador Progibb 40%, em morango cultivado em sistema semi-hidropônico sobre: quantidade de flores e quantidade de pseudofrutos. Para o delineamento experimental utilizou-se blocos inteiramente casualizados. Foi realizado o plantio das mudas da variedade San Andreas e cultivadas em sistema semi-hidropônico, abastecidas via fertirrigação para o suprimento de água e nutrientes. A aplicação de fitorregulador Progibb 40% foi realizada 30 dias após o plantio das mudas, em dose de 25 Mm. A avaliação da quantidade de flores e pseudofrutos foi realizada em contagem manual, semanalmente. Os fatores temperatura e fotoperíodo e sua relação entre ambos ou com o ambiente, influenciaram no comportamento fisiológico da cultura. A aplicação do regulador proporcionou aumento no número de flores e de pseudofrutos, evidenciando uma eficiência para aumento de produtividade.

Biofuels produced from lignocellulosic biomass provide energy security and reduce greenhouse gas emissions with positive impacts on sustainability. Lignocellulose byproducts are expected to impact the production of cellulosic ethanol. However, lignin is a major factor imposing biomass recalcitrance to saccharification. Although structural phenolics can be removed from lignocellulosic biomass, physical and chemical pretreatments are expensive. In turn, the structure and composition of lignin is very flexible. Up- and downregulation of genes and, thereby, enzymes involved in core and non-core lignin biosynthesis can reduce lignin content and improve biomass saccharification. Alternatively, insertion of heterologous genes to the phenylpropanoid pathway may lead to the incorporation of alternative monomers into lignin, creating desirable properties and preserving the biological roles of lignin with a positive effect on saccharification. Studies reporting the effect of fine regulation on lignin structures are mapping how plants can be transformed to enhance saccharification while preserving productivity. Based on these findings and events, this review updates the state-of-art changes in lignin biosynthesis to improve saccharification efficiency. The main findings reported over the last decade were summarized to permit researchers an overview of this relevant scientific subject.

Maize (Zea mays) caffeate 3-O-methyltransferase (ZmaysCOMT, EC 2.1.1.68), a key enzyme of the phenylpropanoid pathway, catalyzes the O-methylation of caffeic acid to ferulic acid, a precursor of lignin polymer and a crucial component of the cell wall structure. Plant cell wall recalcitrance is due to lignin, and the discovery of specific inhibitors of ZmaysCOMT could be useful to increase the digestibility of the lignocellulose biomass and improve the production of cellulosic biofuels. In this work, we have modeled the three-dimensional structure of ZmaysCOMT and prospected promising inhibitors by using virtual screening techniques. A set of 1668 putative candidates was screened from a virtual library and docked in the active site of the enzyme, and nitecapone was selected as one of the most promising enzyme inhibitors. Details of the mode of inhibition were assessed by in silico simulation and in vitro assays of nitecapone on the enzyme. In comparison with the nitecapone-free control, kinetics parameters showed different values of Vmax and KM, suggesting a kinetic profile such as mixed inhibition of the ZmaysCOMT. In brief, we suggest that the nitecapone-induced inhibition of ZmaysCOMT may serve as a non-transgenic strategy to explore the biosynthesis of ferulic acid and lignin, their relationships with the recalcitrance of lignocellulosic biomass, and, possibly, to improve bioethanol production.

The diversity of secondary compounds in the plant kingdom is huge. About 200,000 compounds are known, which are grouped into amines, non-protein amino acids, peptides, alkaloids, glucosinolates, cyanogenic glucosides, organic acids, terpenoids, quinones, polyacetylenes, and phenolics. The group of phenolic compounds consists of polyphenols, oligophenols and monophenols or simple phenolic compounds such as benzoic and cinnamic acids and their hydroxylated derivatives. Among the thousands of compounds present in ecological interactions, simple phenolic acids are the most abundant in soils, and many are described as allelochemicals. Given the physiological and biochemical importance of these compounds, we review their biosynthesis and metabolic actions in plants.

An additional reaction of the plant phenylpropanoid pathway is that catalyzed by coniferyl aldehyde dehydrogenase (HCALDH) to form cytosolic ferulic acid from coniferaldehyde. Because ferulic acid anchors lignin in cell wall polysaccharides and causes cell wall recalcitrance, the HCALDH inhibition could be a prominent target to release fermentable sugars from lignocellulose biomass and improve the saccharification efficiency. Here, we evaluated the role of the flavanone glycoside naringin (NRG), prospected in silico, as a selective inhibitor of the HCALDH of Zea mays (ZmaysHCALDH). A homotetrameric structural model in the absence of ligands was used for evaluations. The stability of the ZmaysHCALDH–NRG complex was checked via molecular dynamics simulation of the apo form (Apo–HCALDH) and that bonded to the inhibitor (NRG–HCALDH), both for the tetrameric form. The conformation bound to NRG varied less in relation to the apo form, and thus could be considered more stable. To obtain kinetic parameters, activities of a partially purified ZmaysHCALDH preparation were determined in vitro using high performance liquid chromatography. In comparison to the NRG-free control, Vmax and Km data suggested a kinetic profile of uncompetitive inhibition with respect to the substrate coniferyl aldehyde. In brief, this combinatorial in silico and in vitro approach suggest that NRG-induced inhibition of ZmaysHCALDH may be an attractive strategy to explore new clues regarding the phenylpropanoid pathway, the role of ferulic acid in the cell wall and, and mainly the digestibility of lignocellulosic biomass for biorefinery purposes.

Coniferyl aldehyde dehydrogenase (CALDH) catalyzes the oxidation of coniferyl aldehyde to ferulic acid. Because ferulic acid has a relevant role in the structure and recalcitrance of the cell wall, inhibition of CALDH can reduce its levels and increase the digestibility of lignocellulosic biomass. We prospected in silico a selective inhibitor of CALDH of Zea mays. The ZmaysCALDH gene was identified by homology with the corresponding gene of Arabidopsis thaliana. The sequence was translated and analyzed, and the quaternary structure was modeled. A set of 20 putative inhibitors were screened from a virtual library and docked in the active site of ZmaysCALDH, and daidzin (DZN) was selected as an enzyme inhibitor. The stability of the ZmaysCALDH–DZN complex was evaluated by molecular dynamics simulations of the monomeric and tetrameric forms. For evaluation of kinetic analysis, ZmaysCALDH activity was determined in vitro by high-performance liquid chromatography. In comparison to the DZN-free control, the data obtained indicated constant Vmax and enhanced Km. Altogether, in silico and in vitro findings indicated that DZN inhibited ZmaysCALDH competitively. The DZN-induced inhibition of ZmaysCALDH could be a valuable and promising approach to studies on ferulic acid biosynthesis and saccharification of lignocellulosic biomass.

Lignocellulosic biomass is an abundant renewable feedstock, rich in polysaccharides that are covalently linked with lignin. In this study, biomass composition of nine forage grasses revealed the role of lignin in biomass recalcitrance. We determined the profiles of cell wall-bound phenolics, lignin, monosaccharides, enzymatic saccharification, and the chemical fingerprints using Fourier transform infrared (FTIR) and Raman spectroscopies. Coastcross and Tifton 85, both bermuda grass cultivars, showed lower lignin content and higher saccharification at 2 h and 72 h of enzymatic hydrolysis, supporting their use as valuable sources of carbohydrates for ethanol production. Principal component analysis (PCA) of thirteen different cell wall traits revealed that lignin was a hierarchical factor in reduced saccharification of forage grasses. As such, lignin content could be used as a marker for the selection of grass cultivars for genetic engineering programs for improved sustainable biofuel production.

The current study sought to evaluate the acute effects of phloretin (PH) on metabolic pathways involved in the maintenance of glycemia, specifically gluconeogenesis and glycogenolysis, in the perfused rat liver. The acute effects of PH on energy metabolism and toxicity parameters in isolated hepatocytes and mitochondria, as well as its effects on the activity of a few key enzymes, were also evaluated. PH inhibited gluconeogenesis from different substrates, stimulated glycogenolysis and glycolysis, and altered oxygen consumption. The citric acid cycle activity was inhibited by PH under gluconeogenic conditions. Similarly, PH reduced the cellular ATP/ADP and ATP/AMP ratios under gluconeogenic and glycogenolytic conditions. In isolated mitochondria, PH inhibited the electron transport chain and the F

Lignin is a technological bottleneck to convert polysaccharides into fermentable sugars, and different strategies of genetic-based metabolic engineering have been applied to improve biomass saccharification. Using maize seedlings grown hydroponically for 24 h, we conducted a quick non-transgenic approach with five enzyme inhibitors of the lignin and tricin pathways. Two compounds [3,4-(methylenedioxy)cinnamic acid: MDCA and 2,4-pyridinedicarboxylic acid: PDCA] revealed interesting findings on root growth, lignin composition, and saccharification. By inhibiting hydroxycinnamoyl-CoA ligase, a key enzyme of phenylpropanoid pathway, MDCA decreased the lignin content and improved saccharification, but it decreased root growth. By inhibiting flavone synthase, a key enzyme of tricin biosynthesis, PDCA decreased total lignin content and improved saccharification without affecting root growth. PDCA was three-fold more effective than MDCA, suggesting that controlling lignin biosynthesis with enzymatic inhibitors may be an attractive strategy to improve biomass saccharification.

Cellulosic ethanol production will decrease our dependence on fossil fuels, positively impacting global warming, energy security, and urban pollution. In the last few years, our group has screened a few enzyme inhibitors of the phenylpropanoid pathway. We have shown that when some enzyme inhibitors are sprayed in young plants, they increase the lignocellulose saccharification in the long term at the workbench scale. Here, we screened five aromatic compounds for their ability to improve the saccharification of maize plants. Benzohydrazide increased saccharification in a broad range of concentrations in growth-room experiments, and it was selected for field-scale assays. At 20 g ha−1 (500 μM, 300 L ha−1), benzohydrazide increased by 33 and 46%, respectively, the saccharification of lignocellulose from maize leaves and stems. When the lignocellulose biomass of maize plants, sprayed with benzohydrazide or not, was submitted to hydrogen peroxide–acetic acid delignification pretreatment, benzohydrazide increased the saccharification by up to 76%. Benzohydrazide did not significantly affect any other biometric (length or fresh and dry weights) or biochemical (lignin, monolignols, structural hydroxycinnamates) parameters assessed. In brief, benzohydrazide could be used to improve saccharification in agroenergy crops.

Cadmium (Cd) inhibits soybean root growth, but its exact mode of action is still not completely understood. We evaluated the effects of Cd on growth, mitochondrial respiration, lipid peroxidation, total phenols, glutathione, and activities of lipoxygenase (LOX), superoxide dismutase (SOD), and catalase (CAT) in soybean roots. In primary roots, Cd stimulated KCN-insensitive respiration and KCN-SHAM-insensitive respiration, indicating the involvement of the alternative oxidase (AOX) pathway, while it decreased KCN-sensitive respiration, suggesting an inhibition of the cytochrome oxidase pathway (COX). In isolated mitochondria, Cd uncoupled the oxidative phosphorylation since it decreased state III respiration (coupled respiration) and ADP/O and respiratory control ratios, while it increased state IV respiration (depletion of exogenously added ADP). The uncoupling effect increased extramitochondrial LOX activity, lipid peroxidation, and oxidized and reduced glutathione, which induced an antioxidant response with enhanced SOD and CAT activities. In brief, our findings reveal that Cd acts as an uncoupler of the mitochondrial oxidative phosphorylation in soybean roots, disturbing cellular respiration and inducing oxidative cellular stress.

Pyruvate orthophosphate dikinase (PPDK) catalyzes the conversion of pyruvate to phosphoenolpyruvate, and its activity is essential to maintain photosynthetic CO2 assimilation in C4 plants. Thus, it has been described as a promising target for the development of selective herbicides for C4 weeds. We evaluated whether bromoacetic acid, a known PPDK inhibitor of Clostridium symbiosum, can also inhibit the PPDK of a C4 plant, maize, in in vitro experiments. We also evaluated the effects of foliar application of 0.5–10 mM bromoacetic acid on the leaf pyruvate content and gas exchange of maize plants. Bromoacetic acid reduced maize PPDK activity in vitro in a dose-dependent manner; the degree of inhibition ranged from 13.6 to 73.6% with 0.5–10 mM bromoacetic acid. The foliar application of bromoacetic acid increased the leaf pyruvate content, suggesting that this compound may also inhibit PPDK activity in vivo. As a consequence, impairments to the gas exchange parameters of maize plants were noted, with a marked reduction in the photosynthetic rate and an increase in the intercellular CO2 concentration. Despite the abrupt decrease in stomatal conductance and transpiration, the plants showed large dehydration and reduction of leaf fresh weight after 48 h of application to bromoacetic acid. Our data allow us to affirm that bromoacetic acid has a potent herbicidal effect on a C4 plant, maize; the most likely mechanism of action is the inhibition of PPDK.

Titanium dioxide (TiO2) nanoparticles (NPs) are the most widely released nanomaterials in the environment and are considered an emerging contaminant. Although the phytotoxicity mechanism of TiO2 NPs on plants involves the elevated generation of reactive oxygen species (ROS), it is still not well established in soybean. Herein, we evaluated the effects of 250–1000 mg L−1 TiO2 NPs on seed germination, growth, content of ROS, lipid peroxidation, and activity of antioxidant enzymes in roots of soybean plants. Our data revealed that up to 1000 mg L−1 TiO2 NPs did not affect soybean seed germination. Transmission electron microscopy images and determinations of zeta potential and hydrodynamic diameter of a suspension of TiO2 NPs demonstrated that they form aggregates, favoring their adsorption to the root surface with consequent physical damage. The main deleterious effects noted on roots were reduced cell viability, reduced root hair number, striated aspect of root apexes, and reduced fresh and dry weights of roots. In disagreement with other studies, plant exposure to TiO2 NPs reduced the level of total ROS and lipid peroxidation, probably due to increased superoxide dismutase (SOD) activity. Altogether, our data suggest that the toxicity mechanism of TiO2 NPs on soybean roots involves physical damage resulting from their adsorption to the root surface, but not the generation of ROS.

Azure A (AA) is a cationic molecule of the class of phenothiazines that has been applied in vitro as a photosensitising agent in photodynamic antimicrobial chemotherapy. It is a di-demethylated analogue of methylene blue (MB), which has been demonstrated to be intrinsically and photodynamically highly active on mitochondrial bioenergetics. However, as far as we know, there are no studies about the photodynamic effects of AA on mammalian mitochondria. Therefore, this investigation aimed to characterise the intrinsic and photodynamic acute effects of AA (0.5 40 μM) on isolated rat liver mitochondria, isolated hepatocytes, and isolated perfused rat liver. The effects of AA were assessed by evaluating several parameters of mitochondrial bioenergetics, oxidative stress, cell viability, and hepatic energy metabolism. The photodynamic effects of AA were assessed under simulated hypoxic conditions, a suitable way for mimicking the microenvironment of hypoxic solid tumour cells. AA interacted with the mitochondria and, upon photostimulation (10 min of light exposure), produced toxic amounts of reactive oxygen species (ROS), which damaged the organelle, as demonstrated by the high levels of lipid peroxidation and protein carbonylation. The photostimulated AA also depleted the GSH pool, which could compromise the mitochondrial antioxidant defence. Bioenergetically, AA photoinactivated the complexes I, II, and IV of the mitochondrial respiratory chain and the F1FO–ATP synthase complex, sharply inhibiting the oxidative phosphorylation. Upon photostimulation (10 min of light exposure), AA reduced the efficiency of mitochondrial energy transduction and oxidatively damaged lipids in isolated hepatocytes but did not decrease the viability of cells. Despite the useful photobiological properties, AA presented noticeable dark toxicity on mitochondrial bioenergetics, functioning predominantly as an uncoupler of oxidative phosphorylation. This harmful effect of AA was evidenced in isolated hepatocytes, in which AA diminished the cellular ATP content. In this case, the cells exhibited signs of cell viability reduction in the presence of high AA concentrations, but only after a long time of incubation (at least 90 min). The impairments on mitochondrial bioenergetics were also clearly manifested in intact perfused rat liver, in which AA diminished the cellular ATP content and stimulated the oxygen uptake. Consequently, gluconeogenesis and ureogenesis were strongly inhibited, whereas glycogenolysis and glycolysis were stimulated. AA also promoted the release of cytosolic and mitochondrial enzymes into the perfusate concomitantly with inhibition of oxygen consumption. In general, the intrinsic and photodynamic effects of AA were similar to those of MB, but AA caused some distinct effects such as the photoinactivation of the complex IV of the mitochondrial respiratory chain and a diminution of the ATP levels in the liver. It is evident that AA has the potential to be used in mitochondria-targeted photodynamic therapy, even under low oxygen concentrations. However, the fact that AA directly disrupts mitochondrial bioenergetics and affects several hepatic pathways that are linked to ATP metabolism, along with its ability to perturb cellular membranes and its little potential to reduce cell viability, could result in significant adverse effects especially in long-term treatments.

Aluminum oxide (Al2O3) nanoparticles (NPs) are among the nanoparticles most used industrially, but their impacts on living organisms are widely unknown. We evaluated the effects of 50–1000 mg L−1 Al2O3 NPs on the growth, metabolism of lignin and its monomeric composition in soybean plants. Al2O3 NPs did not affect the length of roots and stems. However, at the microscopic level, Al2O3 NPs altered the root surface inducing the formation of cracks near to root apexes and damage to the root cap. The results suggest that Al2O3 NPs were internalized and accumulated into the cytosol and cell wall of roots, probably interacting with organelles such as mitochondria. At the metabolic level, Al2O3 NPs increased soluble and cell wall-bound peroxidase activities in roots and stems but reduced phenylalanine ammonia-lyase activity in stems. Increased lignin contents were also detected in roots and stems. The Al2O3 NPs increased the p-hydroxyphenyl monomer levels in stems but reduced them in roots. The total phenolic content increased in roots and stems; cell wall-esterified p-coumaric and ferulic acids increased in roots, while the content of p-coumaric acid decreased in stems. In roots, the content of ionic aluminum (Al+3) was extremely low, corresponding to 0.0000252% of the aluminum applied in the nanoparticulate form. This finding suggests that all adverse effects observed were due to the Al2O3 NPs only. Altogether, these findings suggest that the structure and properties of the soybean cell wall were altered by the Al2O3 NPs, probably to reduce its uptake and phytotoxicity.

Cell walls of grasses have ferulic acid (FA) ester-linked to the arabinosyl substitutions of arabinoxylan (AX). Feruloyl esterases (FAE) are carboxylic acid esterases that release FA from cell walls and synthetic substrates. Despite the importance of FA for cell wall recalcitrance and in response to biotic and abiotic stresses, the physiological function of plant FAEs remains unclear. Here, we developed a simple method for the determination of FAE activity (ZmFAE) in maize using the total protein extract and investigated its role in regulating the feruloylation of cell wall. The method includes a single protein extraction and enzymatic reaction with protein concentration as low as 65 μg at 35 °C for 30 min, using methyl ferulate as the substrate. The methodology allowed the determination of the apparent Km (392.82 μM) and Vmax (79.15 pkat mg−1 protein). We also found that ZmFAE activity was correlated (r = 0.829) with the levels of FA in seedling roots, plant roots and leaves of maize. Furthermore, the exposure to osmotic stress resulted in a 50% increase in ZmFAE activity in seedling roots. These data suggest that FAE-catalyzed reaction is important for cell wall feruloylation during plant development and in response to abiotic stress. We conclude proposing a model for the feruloylation and deferuloylation of AX, which explains the role of FAE in regulating the levels of ester-linked FA. Our model might orient further studies investigating the role of plant FAEs and assist strategies for genetic engineering of grasses to obtain plants with reduced biomass recalcitrance.

20 páginas.- 8 figuras.- 4 tablas.- 77 referencias.- Additional supporting information may be found online in the Supporting Information section at the end of this article or in https://onlinelibrary.wiley.com/action/downloadSupplement?doi=10.1111%2Fpce.13805&file=pce13805-sup-0001-supinfo.docx, Although cell wall polymers play important roles in the tolerance of plants to abiotic stress, the effects of salinity on cell wall composition and metabolism in grasses remain largely unexplored. Here, we conducted an in‐depth study of changes in cell wall composition and phenolic metabolism induced upon salinity in maize seedlings and plants. Cell wall characterization revealed that salt stress modulated the deposition of cellulose, matrix polysaccharides and lignin in seedling roots, plant roots and stems. The extraction and analysis of arabinoxylans by size‐exclusion chromatography, 2D‐NMR spectroscopy and carbohydrate gel electrophoresis showed a reduction of arabinoxylan content in salt‐stressed roots. Saponification and mild acid hydrolysis revealed that salinity also reduced the feruloylation of arabinoxylans in roots of seedlings and plants. Determination of lignin content and composition by nitrobenzene oxidation and 2D‐NMR confirmed the increased incorporation of syringyl units in lignin of maize roots. Salt stress also induced the expression of genes and the activity of enzymes enrolled in phenylpropanoid biosynthesis. The UHPLC–MS‐based metabolite profiling confirmed the modulation of phenolic profiling by salinity and the accumulation of ferulate and its derivatives 3‐ and 4‐O‐feruloyl quinate. In conclusion, we present a model for explaining cell wall remodeling in response to salinity., Conselho Nacional de Desenvolvimento Científico e Tecnológico, Grant/Award Number: GM/GD ‐ 141076/2016‐0; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Grant/Award Numbers: PDSE ‐ 88881.188627/2018‐01, PDSE ‐ 88881.188639/2018‐01; Czech Science Foundation, Grant/Award Number: 18‐07563S; European Regional Development Fund; Ministerio de Economía y Competitividad, Agencia Estatal de Investigación, Grant/Award Number: AGL2017‐83036‐R; Ministry of Education, Youth and Sports of the Czech Republic, Grant/Award Number: CZ.02.1.01/0.0/0.0/16_019/0000827

Grass cell walls have hydroxycinnamic acids attached to arabinosyl residues of arabinoxylan (AX), and certain BAHD acyltransferases are involved in their addition. In this study, we characterized one of these BAHD genes in the cell wall of the model grass Setaria viridis. RNAi silenced lines of S. viridis (SvBAHD05) presented a decrease of up to 42% of ester-linked p-coumarate (pCA) and 50% of pCA-arabinofuranosyl, across three generations. Biomass from SvBAHD05 silenced plants exhibited up to 32% increase in biomass saccharification after acid pre-treatment, with no change in total lignin. Molecular dynamics simulations suggested that SvBAHD05 is a p-coumaroyl coenzyme A transferase (PAT) mainly involved in the addition of pCA to the arabinofuranosyl residues of AX in Setaria. Thus, our results provide evidence of p-coumaroylation of AX promoted by SvBAHD05 acyltransferase in the cell wall of the model grass S. viridis. Furthermore, SvBAHD05 is a promising biotechnological target to engineer crops for improved biomass digestibility for biofuels, biorefineries and animal feeding.

According to the literature, methylene blue (MB) is a photosensitizer (PS) with a high affinity for mitochondria. Therefore, several studies have explored this feature to evaluate its photodynamic effects on the mitochondrial apoptotic pathway under normoxic conditions. We are aware only of limited reports regarding MB's photodynamic effects on mitochondrial energy metabolism, especially under hypoxic conditions. Thus, the purposes of this study were to determine the direct and photodynamic acute effects of MB on the energy metabolism of rat liver mitochondria under hypoxic conditions and its direct acute effects on several parameters linked to energy metabolism in the isolated perfused rat liver. MB presented a high affinity for mitochondria, irrespective of photostimulation or proton gradient formation. Upon photostimulation, MB demonstrated high in vitro oxidizing species generation ability. Consequently, MB damaged the mitochondrial macromolecules, as could be evidenced by the elevated levels of lipid peroxidation and protein carbonyls. In addition to generating a pro-oxidant environment, MB also led to a deficient antioxidant defence system, as indicated by the reduced glutathione (GSH) depletion. Bioenergetically, MB caused uncoupling of oxidative phosphorylation and led to photodynamic inactivation of complex I, complex II, and F1FO-ATP synthase complex, thus decreasing mitochondrial ATP generation. Contrary to what is expected for an ideal PS, MB displayed appreciable dark toxicity on mitochondrial energy metabolism. The results indicated that MB acted via at least three mechanisms: direct damage to the inner mitochondrial membrane; uncoupling of oxidative phosphorylation; and inhibition of electron transfer. Confirming the impairment of mitochondrial energy metabolism, MB also strongly inhibited mitochondrial ATP production. In the perfused rat liver, MB stimulated oxygen consumption, decreased the ATP/ADP ratio, inhibited gluconeogenesis and ureogenesis, and stimulated glycogenolysis, glycolysis, and ammoniagenesis, fully corroborating its uncoupling action in intact cells, as well. It can be concluded that even under hypoxic conditions, MB is a PS with potential for photodynamic effect-induced mitochondrial dysfunction. However, MB disrupts the mitochondrial energy metabolism even in the dark, causing energy-linked liver metabolic changes that could be harmful in specific circumstances.

Nonprotein amino acids are widely distributed in the plants. They constitute a numerous group of secondary metabolites and represent a relevant reservoir of nitrogen and carbon. Among them, L-3,4-dihydroxyphenylalanine (L-DOPA) and 3,4-dihydroxyphenethylamine (dopamine) possess relevant physiological and biochemical effects on plants. L-DOPA, a strong allelochemical released by Mucuna plants into soils, is a precursor of many alkaloids, melanin, and catecholamines such as norepinephrine (noradrenaline) and epinephrine (adrenaline). In plants, dopamine is produced via hydroxylation of tyramine or decarboxylation of L-DOPA. Because L-DOPA and dopamine reveal striking roles in plant communication and signaling, we revise in this chapter the state of current knowledge on their biosynthesis, oxidation, functions, and prooxidant and antioxidant activities.

Grasses producing trans-aconitic acid, a geometric isomer of cis-aconitic acid, are often used in Glycine max rotation systems. However, the effects of trans-aconitic acid on Glycine max are unknown. We conducted a hydroponic experiment to evaluate the effects of 2.5–10 mM trans-aconitic acid on Glycine max growth and photosynthesis. The results revealed that the enhanced H2O2 production in the roots increased the membrane permeability and reduced the water uptake. These effects culminated with a reduced stomatal conductance (gs), which seems to be the main cause for a decreased photosynthetic rate (A). Due to low gs, the limited CO2 assimilation may have overexcited the photosystems, as indicated by the high production of H2O2 in leaves. After 96 h of incubation, and due to H2O2-induced damage to photosystems, a probable non-stomatal limitation for photosynthesis contributed to reducing A. This is corroborated by the significant decrease in the quantum yield of electron flow through photosystem II in vivo (ΦPSII) and the chlorophyll content. Taken together, the damage to the root system and photosynthetic apparatus caused by trans-aconitic acid significantly reduced the Glycine max plant growth.