Plant Cell Metabolism Research Articles

VIABILITY AND MORPHOLOGY OF HUMAN DENTAL PULP STEM CELLS IN THE PRESENCE OF CITRUS PECTIN

Pectin is a galacturonic acid rich heteropolysaccharide which regulates plant cell metabolism. Plenty of fresh fruits and fruit pomaces from fruit juice production can be used as a raw material in commercial pectin production. Pectin occupies a large global market size especially in food industry and the utilization of waste materials for obtaining pectin molecules as a high value-added product makes it very favorite industrial material. Besides food industry, pectin is gaining attention in tissue engineering and drug development studies. In this study, the effects of citrus pectin on viability and morphology of human dental pulp stem cell (hDPSC) were investigated. The cells were cultured in the presence of pectin in culture medium (0.43, 0.85 and 1.7 mg/mL) for eight days. Resazurin application and MTT assay were applied on day one and eight for cellular viability. Cellular morphology was investigated by invert phase contrast microscope, live/dead cell staining and F-actin/nucleus immunofluorescence staining. MTT analysis results indicated that the viability of hDPSCs decreased significantly due to dissolved pectin in culture medium at applied concentrations. There was no significant morphological difference in the cells under invert phase contrast microscope and no significant staining difference in live/dead cell staining images. On the other hand, F-actin/nucleus staining showed that there were some condensed and crescent cell nuclei in the pectin applied groups when compared to the control groups which may be related to apoptosis. In conclusion, the viability of hDPSCs decreased and crescent cell nuclei formation was observed due to the presence of citrus pectin in the cell culture medium.

The AtGSTU7 gene influences glutathione-dependent seed germination under ABA and osmotic stress in Arabidopsis

Glutathione S-transferases (GSTs) play important roles in metabolism and detoxification of plant cells. However, their functions during development are less well understood. Arabidopsis AtGSTU7 (AT2G29420) encodes a Tau class GST. Here we provide the AtGSTU7 was abundantly expressed in seeds and in roots at an early stage of germination. AtGSTU7 expression was repressed by exogenous ABA and promoted by osmotic stress. A null mutant of AtGSTU7 (atgstu7) accumulated higher contents of reduced GSH and decreased amounts of endogenous H2O2 in seedlings. The atgstu7 plants showed decreased osmotic tolerance during seed germination, which was influenced by GSH and ABI3 gene expression. The results suggested that AtGSTU7 involvement in seed germination is mediated by GSH–ROS homeostasis and ABA signaling.

Litter decomposition process dramatically declines the allelopathy of Solidago canadensis L. on the seed germination and seedling growth of Lactuca sativa L.

A variety of invasive alien species (IAS) can trigger distinct allelopathy on the seed germination and seedling growth (SGeSGr) of native plant species (NPS) mainly through the released allelochemicals. However, the decomposition process of IAS litters may affect their allelopathy on SGeSGr of NPS because part of the allelochemicals will be released during the litter decomposition process, especially under heavy metal pollution. This study focuses on the impacts of the litter decomposition process of the notorious IAS Solidago canadensis L. on its allelopathy on SGeSGr of NPS Lactuca sativa L. under cadmium (Cd) pollution. The decomposition process signally declines the allelopathy of S. canadensis litters on SGeSGr of L. sativa likely because partial allelochemicals in S. canadensis litters discharged during the decomposition process. Cd addition noticeably rises the allelopathy of S. canadensis litters on SGeSGr of L. sativa probably because Cd can reduce plant growth largely via the improved lipid membrane permeability and the induced reactive oxygen molecules which is unfavorable to plant cell metabolism. This phenomenon may also be attributed to the weak acid properties of one of the most abundant allelochemicals in S. canadensis litters, i.e., phenolics (particularly polyphenols), can improve the solubility and the toxicity of Cd.

Correlative evidence for co-regulation of phosphorus and carbon exchanges with symbiotic fungus in the arbuscular mycorrhizal Medicago truncatula.

Research efforts directed to elucidation of mechanisms behind trading of resources between the partners in the arbuscular mycorrhizal (AM) symbiosis have seen a considerable progress in the recent years. Yet, despite of the recent developments, some key questions still remain unanswered. For example, it is well established that the strictly biotrophic AM fungus releases phosphorus to- and receives carbon molecules from the plant symbiont, but the particular genes, and their products, responsible for facilitating this exchange, are still not fully described, nor are the principles and pathways of their regulation. Here, we made a de novo quest for genes involved in carbon transfer from the plant to the fungus using genome-wide gene expression array targeting whole root and whole shoot gene expression profiles of mycorrhizal and non-mycorrhizal Medicago truncatula plants grown in a glasshouse. Using physiological intervention of heavy shading (90% incoming light removed) and the correlation of expression levels of MtPT4, the mycorrhiza-inducible phosphate transporter operating at the symbiotic interface between the root cortical cells and the AM fungus, and our candidate genes, we demonstrate that several novel genes may be involved in resource tradings in the AM symbiosis established by M. truncatula. These include glucose-6-phosphate/phosphate translocator, polyol/monosaccharide transporter, DUR3-like, nucleotide-diphospho-sugar transferase or a putative membrane transporter. Besides, we also examined the expression of other M. truncatula phosphate transporters (MtPT1-3, MtPT5-6) to gain further insights in the balance between the "direct" and the "mycorrhizal" phosphate uptake pathways upon colonization of roots by the AM fungus, as affected by short-term carbon/energy deprivation. In addition, the role of the novel candidate genes in plant cell metabolism is discussed based on available literature.

Analysis of Protein Synthesis in Cucumber Leaves after Inoculation with Corynespora cassiicola: A Proteomic Approach.

Cucumber target leaf spot (TLS) disease caused by Corynespora cassiicola has become one of the most important fungal foliar diseases of cultivated cucumbers. However, the defense mechanisms of cucumber plants (Cucumis sativus) against C. cassiicola are still poorly understood. Here, proteins from resistant cucumber plants were analyzed using iTRAQ (isobaric tags for relative and absolute quantification) method. A total of 286 differentially expressed proteins were identified (p < 0.05, ratio > 1.2 or < 0.83) 6 and 24 h after pathogen inoculation in the resistant cultivar Jinyou 38 (the data are available via ProteomeXchange; identifier, PXD012903). Some of the early responses to C. cassiicola infection were revealed, and four factors related to the resistance of cucumber plants to TLS were discovered. First, the proteomic approach revealed modulation of signaling pathways in resistant cucumber plants in response to C. cassiicola infection. Second, the plant immune system recognizes the pathogen and initiates expression of immune response proteins, including those related to plant defense, stress response, signal transduction, cell metabolism, and redox regulation. Third, C. cassiicola activates common stress response pathways; in particular, mildew resistance locus O (MLO) proteins were found to play a crucial role in the TLS prevention. Fourth, rapid activation of the carbohydrate and secondary metabolic pathways, modification and reinforcement of cell walls, and adjustment of the apoplastic environment to the highly stressful conditions were crucial in the cucumber resistance to TLS. Overall, our data contribute to the understanding of interactions between plants and their pathogens and provide new insight into molecular processes involved in the resistance of cucumber plants to disease.

Magneto-Priming Improved Nutraceutical Potential and Antimicrobial Activity of Momordica charantia L. Without Affecting Nutritive Value.

The need for some economic strategies for increased growth and nutraceuticals of medicinal plants is well acknowledged now. It was hypothesized that external magnetic field treatment (MFT) of seeds affecting internal magnet of cells may affect growth and metabolism. In this study, seeds were subjected to pre-sowing magnetic field (50mT at 5mm for 5s). At vegetative stage, the leaf growth, chlorophyll content, catalase (CAT), peroxidase (POD), amino acids, proteins, flavonoids, soluble sugars, total soluble phenolics, carotenoids, anthocyanins, phenolic profile (HPLC based), and antimicrobial activity of leaves (in terms of the minimum inhibitory concentration against Staphylococcus aureus and Pseudomonas aeruginosa) were studied. Yield was evaluated for nutritive components in fruit (peel+pulp) and peel. MFT improved germination percentage, growth, leaf chlorophyll, antimicrobial activity, peel amino acids, phenolics, and POD with negligible effect on fruit nutritive value. Moreover, photosynthetic pigments and cinnamic acid exhibited direct correlation with antimicrobial potential against both pathogens. However, sinapic acid showed positive correlation against Staphylococcus aureus only. Cinnamic acid, coumaric acid, syringic acid, and quercetin were in direct correlation against Pseudomonas aeruginosa; it was directly correlated with total flavonoids too. In conclusion, magnetic field can be used to manipulate plant cell metabolism promising improvement of growth, antimicrobial activity, and phenolics of interest.

Comparative Studies on the Role of Organic Biostimulant in Resistant and Susceptible Cultivars of Rice Grown under Saline Stress - Organic Biostimulant Alleviate Saline Stress in Tolerant and Susceptible Cultivars of Rice

Plants are sessile organisms that experience various abiotic stresses during their lifespan and try to adapt to these environmental stresses by manipulating their physiological, biochemical, cellular, and molecular mechanisms. Salinity is one of the important abiotic stress that affects the metabolism and physiology of plant cells that leads to serious damage to crops and productivity. We investigated the response of two contrasting (salt susceptible and tolerant) cultivars during saline stress by modulating its effect with the application of an important natural biostimulant panchagavya (PG). The results showed that the salinity stress greatly influenced and negatively affects the plant growth, biochemical attributes, and induces the expression of various genes in both cultivars. Furthermore, we assessed the effect of PG alone and by amending with NaCl to alleviate the saline stress which showed a significant enhancement of biochemical and physiological characteristics in both cultivars. Furthermore, we assessed the response of seven autophagy associated gene (ATG1, ATG3, ATG4, ATG6, ATG7, ATG8, and ATG9), BAX Inhibitor -1 (BI-1), Mitogen activated Protein Kinase–1 (MAPK-1), WRKY53, Catalase -1 (CAT-1), Superoxide Dismutase (SOD), and Glutathione Peroxidase (GPX) genes in rice that displayed the differential expression pattern during saline stress in both cultivars. We concluded that saline stress can be manipulated by the application of PG and positively regulate the physiological, biochemical, and gene expression response in salt-susceptible and -tolerant rice cultivars. Furthermore, the current study also suggested that salinity is a mutifactorial and multigenic response. Autophagy and programmed cell death regulated along with salinity and was helpful in adapting the tolerance against the stress condition.

The Mitochondrial Endonuclease M20 Participates in the Down-Regulation of Mitochondrial DNA in Pollen Cells.

Maintaining the appropriate number of mitochondrial DNA (mtDNA) molecules is crucial for supporting mitochondrial metabolism and function in both plant and animal cells. For example, a substantial decrease in mtDNA levels occurs as a key part of pollen development. The molecular mechanisms regulating mtDNA copy number are largely unclear, particularly with regard to those that reduce mtDNA levels. Here, we identified and purified a 20-kD endonuclease, M20, from maize (Zea mays) pollen mitochondria. We found M20 to be an His-Asn-His/Asn (H-N-H/N) nuclease that degrades linear and circular DNA in the presence of Mg2+ or Mn2+ Arabidopsis (Arabidopsis thaliana) AtM20, which shared high sequence similarity with maize M20, localized to the mitochondria, had a similar H-N-H/N structure, and degraded both linear and circular DNA. AtM20 transcript levels increased during pollen development, in parallel with a rapid reduction in mtDNA. Clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 genome-editing techniques were used to generate knockout lines of AtM20 (atm20), which exhibited a significant delay in the reduction in mtDNA levels in pollen vegetative cells but normal mtDNA levels in somatic cells. The delayed reduction in pollen mtDNA levels was rescued by the transgenic expression of AtM20 in atm20 plants. This study thus uncovers an endonucleolytic DNase in plant mitochondria and its crucial role in reducing mtDNA levels, pointing to the complex mechanism regulating mtDNA levels in plants.

Carbon dioxide induces minor antioxidant responses in Eucalyptus urophylla chloroplasts

Minor effect on the chloroplast antioxidant proteins was detected in Eucalyptus urophylla cultivated in high-CO2 atmosphere. Global climate change can significantly alter plant cell metabolism. A higher atmospheric CO2 scenario may be beneficial for C3 plants through the stimulation of photosynthesis. This predicted increase in the rate of carbon assimilation may also increase the expression of enzymes involved in the antioxidant cellular defense. Here, we studied the responses of the chloroplastic antioxidant system of Eucalyptus urophylla plants cultivated in a high-CO2 condition. Plants exposed to a high concentration (980 ppm) of CO2 showed an increase in the H2O2 concentration and MDA content in relation to those cultivated at 410 and 680 ppm. With the discovery proteomics approach used herein, we identified 19 chloroplastic antioxidant proteoforms and pinpointed differentially regulated isoforms of an ascorbate peroxidase and a superoxidase dismutase upon cultivation in a high-CO2 atmosphere. Our data indicate that the CO2 stimulus induces only minor changes in the antioxidant metabolism of E. urophylla chloroplasts.

Melatonin Antagonizes Jasmonate-Triggered Anthocyanin Biosynthesis in Arabidopsis thaliana

As a plant-specific flavonoid type metabolite, anthocyanin is an important plant-sourced nutrition. Although the anthocyanin biosynthesis pathway has been revealed, how to modulate anthocyanin production by endogenous molecules is still elusive. Here, we investigated the role of melatonin in anthocyanin biosynthesis in the reference plant Arabidopsis thaliana and found that melatonin suppresses anthocyanin synthesis. Moreover, melatonin was able to significantly inhibit jasmonate-stimulated anthocyanin production. Unexpectedly, melatonin could not repress the jasmonate-triggered JAZ protein degradation that is a key event for relaying jasmonate signaling. The expression of jasmonate-induced marker genes or other jasmonate-related phenotypes were not discernibly changed in the presence of melatonin. These results indicate that the antagonization of jasmonate-induced anthocyanin synthesis by melatonin does not occur through the abrogation of jasmonate signaling. Furthermore, we found that melatonin does not trigger anthocyanin catabolism. Finally, we supplied anthocyanin biosynthesis precursors to examine their roles in anthocyanin biosynthesis and found that melatonin most likely acts before the dihydrokaempferol production step. Our work illustrates that melatonin plays a negative role in the induction of anthocyanin biosynthesis and sheds new light on the role of melatonin in plant cell metabolism.

Stereo-Specific Transcript Regulation of the Polyamine Biosynthesis Genes by Enantiomers of Ornithine in Tobacco Cell Culture.

BackgroundOrnithine (Orn) plays an essential role in the metabolism of plant cells through incorporation in polyamines biosynthesis, the urea cycle and nitrogen metabolism. Physiological response of the plant cells to its two enantiomers have not been widely investigated yet.ObjectivesThis study aimed to evaluate effect of ornithine enantiomers on expression of certain polyamine (PAs) biosynthetic genes in tobacco cells.Materials and MethodsSuspension-cultured tobacco cells were treated with different concentrations of L- and D- Orn for 24 h. Cell viability was assayed by Evans Blue and hydrogen peroxide content. The changes of gene expression were analyzed by semi-quantitative RT-PCR.ResultsExogenous D-Orn resulted in enhancement of expression of genes involved in Orn, arginine and S-adenosyl methionine metabolism. Additionally, exogenous D-Orn treatment resulted in sustained viability of cultured tobacco cells and normal levels of hydrogen peroxide were maintained. Supplied L-Orn increased the hydrogen peroxide level and lowered viability of cells. Treatment with L-Orn had a negative effect on the transcript levels for most analyzed PA-related genes. It was also illustrated that transcription of putrescine methyl transferase, key enzyme for nicotine production, was highly upregulated by L-Orn.ConclusionsBased on the results, D-Orn was shown to have a stereo-selective function in regulation of the PAs-related genes.

Ties that bind: the integration of plastid signalling pathways in plant cell metabolism.

Plastids are critical organelles in plant cells that perform diverse functions and are central to many metabolic pathways. Beyond their major roles in primary metabolism, of which their role in photosynthesis is perhaps best known, plastids contribute to the biosynthesis of phytohormones and other secondary metabolites, store critical biomolecules, and sense a range of environmental stresses. Accordingly, plastid-derived signals coordinate a host of physiological and developmental processes, often by emitting signalling molecules that regulate the expression of nuclear genes. Several excellent recent reviews have provided broad perspectives on plastid signalling pathways. In this review, we will highlight recent advances in our understanding of chloroplast signalling pathways. Our discussion focuses on new discoveries illuminating how chloroplasts determine life and death decisions in cells and on studies elucidating tetrapyrrole biosynthesis signal transduction networks. We will also examine the role of a plastid RNA helicase, ISE2, in chloroplast signalling, and scrutinize intriguing results investigating the potential role of stromules in conducting signals from the chloroplast to other cellular locations.

A novel Meloidogyne incognita chorismate mutase effector suppresses plant immunity by manipulating the salicylic acid pathway and functions mainly during the early stages of nematode parasitism

Meloidogyne incognita is the most economically important plant‐parasitic nematode. Meloidogyne incognita manipulates plant cell development and metabolism by injecting effectors from the oesophageal glands into the plant host. Chorismate mutase (CM) is one such effector that may contribute to successful parasitism by M. incognita. This investigation identified and functionally characterized a novel CM effector, Mi‐CM‐3, which is more similar to CMs from bacteria than from other phytoparasitic nematodes. Spatial and temporal expression assays showed Mi‐cm‐3 mRNA accumulates specifically in the subventral oesophageal glands and transcription is up‐regulated during the early parasitic stages of the nematode. In planta gene silencing of Mi‐cm‐3 attenuated nematode parasitism. In addition, Mi‐cm‐3 could fully restore the full virulence phenotype of the pathogenic bacterium Xanthomonas oryzae pv. oryzae by complementation when it was introduced into a mutant strain carrying a deletion in the CM gene. Transient expression of Mi‐CM‐3 caused a reduction in levels of salicylic acid (SA) and mRNA of gene PR1 in Nicotiana benthamiana in response to oomycete pathogen Phytophthora capsici infection, while confocal observations showed that Mi‐CM‐3 was localized within the cytoplasm and the nucleus, but not the plastids, of transfected N. benthamiana leaf cells. Constitutive expression of Mi‐CM‐3 in N. benthamiana plants inhibited root growth and increased susceptibility to M. incognita infection. These results provide direct experimental evidence to show that Mi‐CM‐3 may play an important role in suppressing plant immunity by regulating the SA pathway during the early parasitic stage of M. incognita so as to promote nematode parasitism.

Citrus Limonoid Glucosyltransferase: AKey Player For Natural Debittering And Anticancerous Potential

Citrus fruits and juices are rich source of health benefitting phytochemicals which play a vital role in balanced diet and disease prevention. Citrus limonoids and flavonoids are the major phytochemicals which are of great interest in pharmaceutical industries because of their demonstrated anticancerous, antioxidant, anti-inflammatory, hormonal stimulation, antibacterial and antiviral actions. Citrus limonoid biosynthetic pathway contains an important regulatory limonoid glucosyltransferase enzyme (LGT). LGT is the natural debittering enzyme encoded by a single copy gene which has been isolated from different Citrus spp. This enzyme is mainly responsible for conversion of all limonoid aglycones (mostly bitter) to their corresponding glucosides (mostly nonbitter) but only during late fruit developmental stage of citrus. Citrus LGT belongs to glycosyltransferase super family whose members are the wide managers to catalyze the transfer of sugar molecules to their acceptor molecules to play several key modifications in plant secondary metabolites. These reveal great significance value in plant cell metabolism especially in detoxification of xenobiotics, production and storage of natural products. Despite to the fact that over expression of LGT in citrus will lead to reduce the delayed bitterness caused by limonin (an aglycone) but in addition will enhance the accumulation of limonoid glucosides in fruits. Further, recent studies suggest that citrus limonoids especially glucosides have shown importance against brain, pancreas, colon, and breast cancers. Thus, future studies should be focused on utilizing the potential of LGT present in citrus plants in terms of anticancerous properties as well as reducing the delayed bitterness problem important for citrus juice industry

Calorimetrically Determined U(VI) Toxicity in Brassica napus Correlates with Oxidoreductase Activity and U(VI) Speciation.

Radioecological studies depend on the quantitative toxicity assessment of environmental radionuclides. At low dose exposure, the life span of affected organisms is barely shortened, enabling the transfer of radionuclides through an almost-intact food chain. Lethality-based toxicity estimates are not adequate in this regime because they require higher concentrations. However, increased radionuclide concentration alters its speciation, rendering the extrapolation to the low dose exposure chemically inconsistent. Here, we demonstrate that microcalorimetry provides a sensitive real-time monitor of toxicity of uranium (in the U(VI) oxidation state) in a plant cell model of Brassica napus. We introduce the calorimetric descriptor "metabolic capacity" and show that it correlates with enzymatically determined cell viability. It is independent of physiological models and robust against the naturally occurring fluctuations in the metabolic response to U(VI) of plant cell cultures. In combination with time-resolved laser-induced fluorescence spectroscopy and thermodynamic modeling, we show that the plant cell metabolism is affected predominantly by hydroxo-species of U(VI) with an IC50 threshold of ∼90 μM. The data emphasize the yet-little-exploited potential of microcalorimetry for the speciation-sensitive ecotoxicology of radionuclides.

Nicotinamide; antioxidative and DNA hypomethylation effects in plant cells

The effects of nicotinamide (NIC) and its natural plant metabolites nicotinic acid (NIA) and trigonelline (TRIG) were studied with respect to defense in plant cell cultures. NIC and NIA could protect against oxidative stress damage caused by 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH), which generates free radicals. Damage was analyzed as DNA strand breaks in cell cultures of Pisum sativum (garden pea), Daucus carota (carrot), Populus tremula L. × P. tremuloides (hybrid aspen) and Catharanthus roseus (Madagascar periwinkle), monitored by single cell gel electrophoresis (comet assay), and assays of cell leakage in C. roseus. The activities of aconitase and fumarase enzymes, which have key roles in energy metabolism, were analyzed in P. sativum cultures after treatment with NIC or NIA. Aconitase activity was increased by NIA, and fumarase activity was increased by both compounds. These compounds were shown to promote glutathione metabolism in P. sativum cultures, and NIC was shown to have a global DNA hypomethylating effect. Neither TRIG nor poly(ADP-ribose) polymerase (PARP) inhibitor 3-aminobenzamide offered any protection against DNA damage or cell leakage, nor did they promote aconitase or fumarase activities, or glutathione metabolism. By this broad approach addressing multiple biochemical factors and different plant species, we demonstrate that NIC and NIA protect plant cells from oxidative stress, and that NIC clearly exerts an epigenetic effect; decreased DNA methylation. This indicates that these compounds have important roles in the regulation of metabolism in plant cells, especially in connection to stress.

Identification of two frataxin isoforms in Zea mays: Structural and functional studies

Frataxin is a ubiquitous protein that plays a role in Fe-S cluster biosynthesis and iron and heme metabolism, although its molecular functions are not entirely clear. In non-photosynthetic eukaryotes, frataxin is encoded by a single gene, and the protein localizes to mitochondria. Here we report the presence of two functional frataxin isoforms in Zea mays, ZmFH-1 and ZmFH-2. We confirmed our previous findings regarding plant frataxins: both proteins have dual localization in mitochondria and chloroplasts. Physiological, biochemical and biophysical studies show some differences in the expression pattern, protection against oxidants and in the aggregation state of both isoforms, suggesting that the two frataxin homologs would play similar but not identical roles in plant cell metabolism. In addition, two specific features of plant frataxins were evidenced: their ability to form dimers and their tendency to undergo conformational change under oxygen exposure.

Discovery and Characterization of the 3-Hydroxyacyl-ACP Dehydratase Component of the Plant Mitochondrial Fatty Acid Synthase System.

We report the characterization of the Arabidopsis (Arabidopsis thaliana) 3-hydroxyacyl-acyl carrier protein dehydratase (mtHD) component of the mitochondrial fatty acid synthase (mtFAS) system, encoded by AT5G60335. The mitochondrial localization and catalytic capability of mtHD were demonstrated with a green fluorescent protein transgenesis experiment and by in vivo complementation and in vitro enzymatic assays. RNA interference (RNAi) knockdown lines with reduced mtHD expression exhibit traits typically associated with mtFAS mutants, namely a miniaturized morphological appearance, reduced lipoylation of lipoylated proteins, and altered metabolomes consistent with the reduced catalytic activity of lipoylated enzymes. These alterations are reversed when mthd-rnai mutant plants are grown in a 1% CO2 atmosphere, indicating the link between mtFAS and photorespiratory deficiency due to the reduced lipoylation of glycine decarboxylase. In vivo biochemical feeding experiments illustrate that sucrose and glycolate are the metabolic modulators that mediate the alterations in morphology and lipid accumulation. In addition, both mthd-rnai and mtkas mutants exhibit reduced accumulation of 3-hydroxytetradecanoic acid (i.e. a hallmark of lipid A-like molecules) and abnormal chloroplastic starch granules; these changes are not reversible by the 1% CO2 atmosphere, demonstrating two novel mtFAS functions that are independent of photorespiration. Finally, RNA sequencing analysis revealed that mthd-rnai and mtkas mutants are nearly equivalent to each other in altering the transcriptome, and these analyses further identified genes whose expression is affected by a functional mtFAS system but independent of photorespiratory deficiency. These data demonstrate the nonredundant nature of the mtFAS system, which contributes unique lipid components needed to support plant cell structure and metabolism.

Transformation of plastids in soil-shaded lowermost hypocotyl segments of bean (Phaseolus vulgaris) during a 60-day cultivation period.

The maintenance but substantial transformation of plastids was found in lowermost hypocotyl segments of soil-grown bean plants (Phaseolus vulgaris cv. Magnum) during a 60-day cultivation period. Although the plants were grown under natural light-dark cycles, this hypocotyl segment was under full coverage of the soil in 5-7 cm depth, thus it was never exposed to light. The 4-day-old plants were fully etiolated: amyloplasts, occasionally prolamellar bodies, protochlorophyllide (Pchlide) and protochlorophyll (Pchl) were found in the hypocotyls of these young seedlings. The 633 and 654 nm bands in the 77 K fluorescence emission spectra indicated the presence of Pchlide and Pchl pigments. During aging, both the Pchlide and Pchl contents increased, however, the Pchl to Pchlide ratio gradually increased. In parallel, the contribution of the 654 nm form decreased and in the spectra of the 60-day-old samples, the main band shifted to 631 nm, and a new form appeared with an emission maximum at 641 nm. The photoactivity had been lost; bleaching took place at continuous illumination. The inner membranes of the plastids disappeared, the amount of starch storing amyloplasts decreased. These data may indicate the general importance of plastids for plant cell metabolism, which can be the reason for their maintenance. Also the general heterogeneity of plastid forms can be concluded: in tissues not exposed to light, Pchl accumulating plastids develop and are maintained even for a long period.

Derivation of an Effective Model for Metabolic Processes in Living Cells Including Substrate Channeling

A system of reaction-diffusion equations in a multi-component medium with nonlinear flux-conditions and additional reaction-diffusion equations on the interfaces is considered. The model is motivated by metabolic processes in living cells. Especially, we are interested in modeling the central carbon metabolism in plant cells, with particular emphasis on metabolite channeling. The nonlinear reaction terms arising in the equations and boundary conditions are described by structural conditions, which are fulfilled by the kinetics of multi-species enzymatic reactions encountered in cellular metabolism. Starting from a mathematical model at subcellular level, where cellular structures like organelles are resolved, we derive an effective approximations for the cellular processes, by letting the scale parameter given by the ratio between the size of organelles and that of the cell going to zero. To show convergence of the nonlinear terms, we use homogenization concepts developed in Gahn, Neuss-Radu, and Knabner (SIAM J. Appl. Math. 76, 1819–1843 [21]), based on estimates for the shifting operator for Banach-space-valued functions.