Combining Borrmann and weak-beam diffraction images to study defects in a high-quality CdTe(Zn) crystal

In this work, synchrotron radiation rocking curve imaging (RCI) is used to visualize and characterize dislocations and second-phase defects in a highly perfect and absorbing CdTe(Zn) crystal. This technique requires recording a series of Bragg diffracted images along the rocking curve to produce maps of the `local' integrated intensity, full width at half-maximum and peak position. The diffraction conditions of the reported experiment are such that anomalous transmission (Borrmann effect) is a crucial ingredient for the formation of the image of the defects. The images recorded and maps produced allow the investigation of a series of topics that, to the authors' knowledge, have not been previously studied. The first of these topics is the variation of the position and width of the Borrmann image of a defect when sitting on the peak and on the flanks of the diffraction curve. The second topic is the way Borrmann images show up on the usual RCI maps. The final topic is the combination of Borrmann and weak-beam images to infer the depth of the defect within the crystal.

Performance and Limitations of Phosphate Quantification: Guidelines for Plant Biologists

Phosphate (Pi) is a macronutrient that is essential for plant life. Several regulatory components involved in Pi homeostasis have been identified, revealing a very high complexity at the cellular and subcellular levels. Determining the Pi content in plants is crucial to understanding this regulation, and short real-time(33)Pi uptake imaging experiments have shown Pi movement to be highly dynamic. Furthermore, gene modulation by Pi is finely controlled by localization of this ion at the tissue as well as the cellular and subcellular levels. Deciphering these regulations requires access to and quantification of the Pi pool in the various plant compartments. This review presents the different techniques available to measure, visualize and trace Pi in plants, with a discussion of the future prospects.

Corrigendum to: Metabolomic characterisation of the functional division of nitrogen metabolism in variegated leaves

Many horticultural and natural plant species have variegated leaves, that is, patchy leaves with green and non-green or white areas. Specific studies on the metabolism of variegated leaves are scarce and although white (non-green) areas have been assumed to play the role of a 'nitrogen store', there is no specific studies showing the analysis of nitrogenous metabolites and the dynamics of nitrogen assimilation. Here, we examined the metabolism of variegated leaves of Pelargonium × hortorum. We show that white areas have a larger N : C ratio, more amino acids, with a clear accumulation of arginine. Metabolomic analyses revealed clear differences in the chemical composition, suggesting contrasted metabolic commitments such as an enhancement of alkaloid biosynthesis in white areas. Using isotopic labelling followed by nuclear magnetic resonance or liquid chromatography/mass spectrometry, we further showed that in addition to glutamine, tyrosine and tryptophan, N metabolism forms ornithine in green area and huge amounts of arginine in white areas. Fine isotopic measurements with isotope ratio mass spectrometry indicated that white and green areas exchange nitrogenous molecules but nitrogen export from green areas is quantitatively much more important. The biological significance of the metabolic exchange between leaf areas is briefly discussed.

An overview of the metabolic differences between Bradyrhizobium japonicum 110 bacteria and differentiated bacteroids from soybean (Glycine max) root nodules: an in vitro 13C- and 31P-nuclear magnetic resonance spectroscopy study

Bradyrhizobium japonicum is a symbiotic nitrogen-fixing soil bacteria that induce root nodules formation in legume soybean (Glycine max.). Using (13)C- and (31)P-nuclear magnetic resonance (NMR) spectroscopy, we have analysed the metabolite profiles of cultivated B. japonicum cells and bacteroids isolated from soybean nodules. Our results revealed some quantitative and qualitative differences between the metabolite profiles of bacteroids and their vegetative state. This includes in bacteroids a huge accumulation of soluble carbohydrates such as trehalose, glutamate, myo-inositol and homospermidine as well as Pi, nucleotide pools and intermediates of the primary carbon metabolism. Using this novel approach, these data show that most of the compounds detected in bacteroids reflect the metabolic adaptation of rhizobia to the surrounding microenvironment with its host plant cells.

Short-term effects of CO(2) and O(2) on citrate metabolism in illuminated leaves

Although there is now a considerable literature on the inhibition of leaf respiration (CO(2) evolution) by light, little is known about the effect of other environmental conditions on day respiratory metabolism. In particular, CO(2) and O(2) mole fractions are assumed to cause changes in the tricarboxylic acid pathway (TCAP) but the amplitude and even the direction of such changes are still a matter of debate. Here, we took advantage of isotopic techniques, new simple equations and instant freeze sampling to follow respiratory metabolism in illuminated cocklebur leaves (Xanthium strumarium L.) under different CO(2) /O(2) conditions. Gas exchange coupled to online isotopic analysis showed that CO(2) evolved by leaves in the light came from 'old' carbon skeletons and there was a slight decrease in (13) C natural abundance when [CO(2) ] increased. This suggested the involvement of enzymatic steps fractionating more strongly against (13) C and thus increasingly limiting for the metabolic respiratory flux as [CO(2) ] increased. Isotopic labelling with (13) C(2) -2,4-citrate lead to (13) C-enriched Glu and 2-oxoglutarate (2OG), clearly demonstrating poor metabolism of citrate by the TCAP. There was a clear relationship between the ribulose-1,5-bisphosphate oxygenation-to-carboxylation ratio (v(o) /v(c) ) and the (13) C commitment to 2OG, demonstrating that 2OG and Glu synthesis via the TCAP is positively influenced by photorespiration.

Metabolomic characterisation of the functional division of nitrogen metabolism in variegated leaves

Many horticultural and natural plant species have variegated leaves, that is, patchy leaves with green and non-green or white areas. Specific studies on the metabolism of variegated leaves are scarce and although white (non-green) areas have been assumed to play the role of a 'nitrogen store', there is no specific studies showing the analysis of nitrogenous metabolites and the dynamics of nitrogen assimilation. Here, we examined the metabolism of variegated leaves of Pelargonium×hortorum. We show that white areas have a larger N:C ratio, more amino acids, with a clear accumulation of arginine. Metabolomic analyses revealed clear differences in the chemical composition, suggesting contrasted metabolic commitments such as an enhancement of alkaloid biosynthesis in white areas. Using isotopic labelling followed by nuclear magnetic resonance or liquid chromatography/mass spectrometry, we further showed that in addition to glutamine, tyrosine and tryptophan, N metabolism forms ornithine in green area and huge amounts of arginine in white areas. Fine isotopic measurements with isotope ratio mass spectrometry indicated that white and green areas exchange nitrogenous molecules but nitrogen export from green areas is quantitatively much more important. The biological significance of the metabolic exchange between leaf areas is briefly discussed.

A simple and efficient method for the long-term preservation of plant cell suspension cultures

BACKGROUND

The repeated weekly subculture of plant cell suspension is labour intensive and increases the risk of variation from parental cells lines. Most of the procedures to preserve cultures are based on controlled freezing/thawing and storage in liquid nitrogen. However, cells viability after unfreezing is uncertain. The long-term storage and regeneration of plant cell cultures remains a priority.

RESULTS

Sycamore (Acer pseudoplatanus) and Arabidopsis cell were preserved over six months as suspensions cultures in a phosphate-free nutrient medium at 5°C. The cell recovery monitored via gas exchange measurements and metabolic profiling using in vitro and in vivo 13C- and 31P-NMR took a couple of hours, and cell growth restarted without appreciable delay. No measurable cell death was observed.

CONCLUSION

We provide a simple method to preserve physiologically homogenous plant cell cultures without subculture over several months. The protocol based on the blockage of cell growth and low culture temperature is robust for heterotrophic and semi-autotrophic cells and should be adjustable to cell lines other than those utilised in this study. It requires no specialized equipment and is suitable for routine laboratory use.

Experimental evidence of phosphoenolpyruvate resynthesis from pyruvate in illuminated leaves

Day respiration is the cornerstone of nitrogen assimilation since it provides carbon skeletons to primary metabolism for glutamate (Glu) and glutamine synthesis. However, recent studies have suggested that the tricarboxylic acid pathway is rate limiting and mitochondrial pyruvate dehydrogenation is partly inhibited in the light. Pyruvate may serve as a carbon source for amino acid (e.g. alanine) or fatty acid synthesis, but pyruvate metabolism is not well documented, and neither is the possible resynthesis of phosphoenolpyruvate (PEP). Here, we examined the capacity of pyruvate to convert back to PEP using (13)C and (2)H labeling in illuminated cocklebur (Xanthium strumarium) leaves. We show that the intramolecular labeling pattern in Glu, 2-oxoglutarate, and malate after (13)C-3-pyruvate feeding was consistent with (13)C redistribution from PEP via the PEP-carboxylase reaction. Furthermore, the deuterium loss in Glu after (2)H(3)-(13)C-3-pyruvate feeding suggests that conversion to PEP and back to pyruvate washed out (2)H atoms to the solvent. Our results demonstrate that in cocklebur leaves, PEP resynthesis occurred as a flux from pyruvate, approximately 0.5‰ of the net CO(2) assimilation rate. This is likely to involve pyruvate inorganic phosphate dikinase and the fundamental importance of this flux for PEP and inorganic phosphate homeostasis is discussed.

Over-expression of PHO1 in Arabidopsis leaves reveals its role in mediating phosphate efflux

Inorganic phosphate (Pi) homeostasis in multi-cellular eukaryotes depends not only on Pi influx into cells, but also on Pi efflux. Examples in plants for which Pi efflux is crucial are transfer of Pi into the xylem of roots and release of Pi at the peri-arbuscular interface of mycorrhizal roots. Despite its importance, no protein has been identified that specifically mediates phosphate efflux either in animals or plants. The Arabidopsis thaliana PHO1 gene is expressed in roots, and was previously shown to be involved in long-distance transfer of Pi from the root to the shoot. Here we show that PHO1 over-expression in the shoot of A. thaliana led to a two- to threefold increase in shoot Pi content and a severe reduction in shoot growth. (31) P-NMR in vivo showed a normal initial distribution of intracellular Pi between the cytoplasm and the vacuole in leaves over-expressing PHO1, followed by a large efflux of Pi into the infiltration medium, leading to a rapid reduction of the vacuolar Pi pool. Furthermore, the Pi concentration in leaf xylem exudates from intact plants was more than 100-fold higher in PHO1 over-expressing plants compared to wild-type. Together, these results show that PHO1 over-expression in leaves leads to a dramatic efflux of Pi out of cells and into the xylem vessel, revealing a crucial role for PHO1 in Pi efflux.

Uncoupling phosphate deficiency from its major effects on growth and transcriptome via PHO1 expression in Arabidopsis

Inorganic phosphate (Pi) is one of the most limiting nutrients for plant growth in both natural and agricultural contexts. Pi-deficiency leads to a strong decrease in shoot growth, and triggers extensive changes at the developmental, biochemical and gene expression levels that are presumably aimed at improving the acquisition of this nutrient and sustaining growth. The Arabidopsis thaliana PHO1 gene has previously been shown to participate in the transport of Pi from roots to shoots, and the null pho1 mutant has all the hallmarks associated with shoot Pi deficiency. We show here that A. thaliana plants with a reduced expression of PHO1 in roots have shoot growth similar to Pi-sufficient plants, despite leaves being strongly Pi deficient. Furthermore, the gene expression profile normally triggered by Pi deficiency is suppressed in plants with low PHO1 expression. At comparable levels of shoot Pi supply, the wild type reduces shoot growth but maintains adequate shoot vacuolar Pi content, whereas the PHO1 underexpressor maintains maximal growth with strongly depleted Pi reserves. Expression of the Oryza sativa (rice) PHO1 ortholog in the pho1 null mutant also leads to plants that maintain normal growth and suppression of the Pi-deficiency response, despite the low shoot Pi. These data show that it is possible to unlink low shoot Pi content with the responses normally associated with Pi deficiency through the modulation of PHO1 expression or activity. These data also show that reduced shoot growth is not a direct consequence of Pi deficiency, but is more likely to be a result of extensive gene expression reprogramming triggered by Pi deficiency.

Co-chaperone BAG3 and adenovirus penton base protein partnership

The BAG family of Hsp70/Hsc70 co‐chaperones is characterised by the presence of a conserved BAG domain at the carboxyl‐terminus. BAG3 protein is the only member of this family containing also the N‐terminally located WW domain. We describe here the identification of adenovirus (Ad) penton base protein as the first BAG3 partner recognising BAG3 WW domain. Ad penton base is the viral capsid constituent responsible for virus internalisation. It contains in the N‐terminal part two conserved PPxY motifs, known ligands of WW domains. In cells producing Ad penton base protein, cytoplasmic endogenous BAG3 interacts with it and co‐migrates to the nucleus. Preincubation of BAG3 with Ad base protein results in only slight modulation of BAG3 co‐chaperone activity, suggesting that this interaction is not related to the classical BAG3 co‐chaperone function. However, depletion of BAG3 impairs the cell entry of the virus and viral progeny production in Ad‐infected cells, suggesting that the interaction between virus penton base protein and cellular co‐chaperone BAG3 positively influences virus life cycle. These results thus demonstrate a novel host–pathogen interaction, which contributes to the successful infectious life cycle of adenoviruses. In addition, these data enrich our knowledge about the multifunctionality of the BAG3 co‐chaperone. J. Cell. Biochem. 111: 699–708, 2010. © 2010 Wiley‐Liss, Inc.

Early response of plant cell to carbon deprivation: in vivo 31P-NMR spectroscopy shows a quasi-instantaneous disruption on cytosolic sugars, phosphorylated intermediates of energy metabolism, phosphate partitioning, and intracellular pHs

• In plant cells, sugar starvation triggers a cascade of effects at the scale of 1-2 days. However, very early metabolic response has not yet been investigated. • Soluble phosphorus (P) compounds and intracellular pHs were analysed each 2.5 min intervals in heterotrophic sycamore (Acer pseudoplatanus) cells using in vivo phosphorus nuclear magnetic resonance ((31)P-NMR). • Upon external-sugar withdrawal, the glucose 6-P concentration dropped in the cytosol, but not in plastids. The released inorganic phosphate (Pi) accumulated transiently in the cytosol before influx into the vacuole; nucleotide triphosphate concentration doubled, intracellular pH increased and cell respiration decreased. It was deduced that the cytosolic free-sugar concentration was low, corresponding to only 0.5 mM sucrose in sugar-supplied cells. • The release of sugar from the vacuole and from plastids is insufficient to fully sustain the cell metabolism during starvation, particularly in the very short term. Similarly to Pi-starvation, the cell's first response to sugar starvation occurs in the cytosol and is of a metabolic nature. Unlike the cytoplasm, cytosolic homeostasis is not maintained during starvation. The important metabolic changes following cytosolic sugar exhaustion deliver early endogenous signals that may contribute to trigger rescue metabolism.

Metabolic and structural rearrangement during dark-induced autophagy in soybean (Glycine max L.) nodules: an electron microscopy and 31P and 13C nuclear magnetic resonance study

The effects of dark-induced stress on the evolution of the soluble metabolites present in senescent soybean (Glycine max L.) nodules were analysed in vitro using (13)C- and (31)P-NMR spectroscopy. Sucrose and trehalose were the predominant soluble storage carbons. During dark-induced stress, a decline in sugars and some key glycolytic metabolites was observed. Whereas 84% of the sucrose disappeared, only one-half of the trehalose was utilised. This decline coincides with the depletion of Gln, Asn, Ala and with an accumulation of ureides, which reflect a huge reduction of the N(2) fixation. Concomitantly, phosphodiesters and compounds like P-choline, a good marker of membrane phospholipids hydrolysis and cell autophagy, accumulated in the nodules. An autophagic process was confirmed by the decrease in cell fatty acid content. In addition, a slight increase in unsaturated fatty acids (oleic and linoleic acids) was observed, probably as a response to peroxidation reactions. Electron microscopy analysis revealed that, despite membranes dismantling, most of the bacteroids seem to be structurally intact. Taken together, our results show that the carbohydrate starvation induced in soybean by dark stress triggers a profound metabolic and structural rearrangement in the infected cells of soybean nodule which is representative of symbiotic cessation.

Phosphate (Pi) starvation effect on the cytosolic Pi concentration and Pi exchanges across the tonoplast in plant cells: an in vivo 31P-nuclear magnetic resonance study using methylphosphonate as a Pi analog

In vivo (31)P-NMR analyses showed that the phosphate (Pi) concentration in the cytosol of sycamore (Acer pseudoplatanus) and Arabidopsis (Arabidopsis thaliana) cells was much lower than the cytoplasmic Pi concentrations usually considered (60-80 mum instead of >1 mm) and that it dropped very rapidly following the onset of Pi starvation. The Pi efflux from the vacuole was insufficient to compensate for the absence of external Pi supply, suggesting that the drop of cytosolic Pi might be the first endogenous signal triggering the Pi starvation rescue metabolism. Successive short sequences of Pi supply and deprivation showed that added Pi transiently accumulated in the cytosol, then in the stroma and matrix of organelles bounded by two membranes (plastids and mitochondria, respectively), and subsequently in the vacuole. The Pi analog methylphosphonate (MeP) was used to analyze Pi exchanges across the tonoplast. MeP incorporated into cells via the Pi carrier of the plasma membrane; it accumulated massively in the cytosol and prevented Pi efflux from the vacuole. This blocking of vacuolar Pi efflux was confirmed by in vitro assays with purified vacuoles. Subsequent incorporation of Pi into the cells triggered a massive transfer of MeP from the cytosol to the vacuole. Mechanisms for Pi exchanges across the tonoplast are discussed in the light of the low cytosolic Pi level, the cell response to Pi starvation, and the Pi/MeP interactive effects.

Amino acid changes during sunflower infection by the necrotrophic fungus B. cinerea

Metabolic changes that occur in host tissues during a necrotrophic plant/fungal interaction have been poorly investigated. Whereas carbon metabolism reprogramming and photosynthesis disturbances have been studied, data on plant amino acids stores during infection are scarce. Here we report an analysis of sunflower cotyledon amino acid content during infection with the necrotrophic fungus Botrytis cinerea, by using (13)C-NMR spectroscopy. A rapid disappearance of plant amino acids was observed, most probably due to fungal assimilation. In order to explore amino acid changes due to host reaction, we investigated the amino acid content in healthy and invaded region of infected leaves. During the course of infection, glutamate store was affected at distance in the non invaded region. Glutamate depletion was correlated to an enhanced sunflower glutamate dehydrogenase (GDH) transcription level in the area invaded by pathogen. Our data suggest that glutamate could be transferred to the invaded region to supply nitrogen. Such a strategy could delay cell death, and consequently disturb fungal progression in plant tissues.

Accumulation of 2-C-methyl-D-erythritol 2,4-cyclodiphosphate in illuminated plant leaves at supraoptimal temperatures reveals a bottleneck of the prokaryotic methylerythritol 4-phosphate pathway of isoprenoid biosynthesis

Metabolic profiling using phosphorus nuclear magnetic resonance ((31)P-NMR) revealed that the leaves of different herbs and trees accumulate 2-C-methyl-D-erythritol 2,4-cyclodiphosphate (MEcDP), an intermediate of the methylerythritol 4-phosphate (MEP) pathway, during bright and hot days. In spinach (Spinacia oleracea L.) leaves, its accumulation closely depended on irradiance and temperature. MEcDP was the only (31)P-NMR-detected MEP pathway intermediate. It remained in chloroplasts and was a sink for phosphate. The accumulation of MEcDP suggested that its conversion rate into 4-hydroxy-3-methylbut-2-enyl diphosphate, catalysed by (E)-4-hydroxy-3-methylbut-2-enyl diphosphate synthase (GcpE), was limiting under oxidative stress. Indeed, O(2) and ROS produced by photosynthesis damage this O(2)-hypersensitive [4Fe-4S]-protein. Nevertheless, as isoprenoid synthesis was not inhibited, damages were supposed to be continuously repaired. On the contrary, in the presence of cadmium that reinforced MEcDP accumulation, the MEP pathway was blocked. In vitro studies showed that Cd(2+) does not react directly with fully assembled GcpE, but interferes with its reconstitution from recombinant GcpE apoprotein and prosthetic group. Our results suggest that MEcDP accumulation in leaves may originate from both GcpE sensitivity to oxidative environment and limitations of its repair. We propose a model wherein GcpE turnover represents a bottleneck of the MEP pathway in plant leaves simultaneously exposed to high irradiance and hot temperature.

Dynamic carbon transfer during pathogenesis of sunflower by the necrotrophic fungus Botrytis cinerea: from plant hexoses to mannitol

The main steps for carbon acquisition and conversion by Botrytis cinerea during pathogenesis of sunflower cotyledon were investigated here. A sequential view of soluble carbon metabolites detected by NMR spectroscopy during infection is presented. Disappearance of plant hexoses and their conversion to fungal metabolites were investigated by expression analysis of an extended gene family of hexose transporters (Bchxts) and of the mannitol pathway, using quantitative PCR. In order to analyse the main fungal metabolic routes used by B. cinerea in real time, we performed, for the first time, in vivo NMR analyses during plant infection. During infection, B. cinerea converts plant hexoses into mannitol. Expression analysis of the sugar porter gene family suggested predominance for transcription induced upon low glucose conditions and regulated according to the developmental phase. Allocation of plant hexoses by the pathogen revealed a conversion to mannitol, trehalose and glycogen for glucose and a preponderant transformation of fructose to mannitol by a more efficient metabolic pathway. Uptake of plant hexoses by B. cinerea is based on a multigenic flexible hexose uptake system. Their conversion into mannitol, enabled by two simultaneously expressed pathways, generates a dynamic intracellular carbon pool.

Cross tolerance to heavy-metal and cold-induced photoinhibiton in leaves of Pisum sativum acclimated to low temperature

Under high light intensity, low temperatures as well as heavy metals induce photoinhibition of PSII and oxidative stress in leaves. Since cold acclimation of leaves ameliorates their capacity of antioxidative defence, cross tolerance between cold-induced and heavy metal-induced photoinhibition was investigated in pea leaves grown at either 22 °C or 6 °C. The experimental conditions were chosen to induce a uniform level of short-term photoinhibition at low temperature or in the presence of CuSO4 or CdCl2 in leaves grown at 22 °C. Under all conditions photoinhibition of PSII was lower in cold-acclimated (6°C-grown) than in non-acclimated (22°C-grown) pea leaves. In darkness PSII was not affected by all treatments. Other parameters like catalase activity, chlorophyll content and metabolite contents were most sensitive to CuSO4, but less affected by CdCl2 and low temperature treatments. Strong oxidation of ascorbate and concomitant loss of catalase activity showed the enhanced oxidative stress in CuSO4-treated leaves. Generally, all measured parameters were less affected in cold-acclimated leaves than in non-acclimated leaves under all experimental conditions. Cold-acclimated pea leaves contained higher levels of ascorbate and particularly of glutathione and a higher capacity to keep the primary electron acceptor of PSII more oxidised. Incubation with heavy metals caused a nearly complete loss of reduced glutathione. It is suggested that reduced glutathione served as a source for phytochelatin synthesis. The extraordinarily high glutathione content in cold-acclimated pea leaves might therefore increase their ability to chelate heavy metals and thus to protect leaves from heavy-metal induced damage.

Metabolic processes sustaining the reviviscence of lichen Xanthoria elegans (Link) in high mountain environments

To survive in high mountain environments lichens must adapt themselves to alternating periods of desiccation and hydration. Respiration and photosynthesis of the foliaceous lichen, Xanthoria elegans, in the dehydrated state were below the threshold of CO2-detection by infrared gas analysis. Following hydration, respiration totally recovered within seconds and photosynthesis within minutes. In order to identify metabolic processes that may contribute to the quick and efficient reactivation of lichen physiological processes, we analysed the metabolite profile of lichen thalli step by step during hydration/dehydration cycles, using 31P- and 13C-NMR. It appeared that the recovery of respiration was prepared during dehydration by the accumulation of a reserve of gluconate 6-P (glcn-6-P) and by the preservation of nucleotide pools, whereas glycolytic and photosynthetic intermediates like glucose 6-P and ribulose 1,5-diphosphate were absent. The large pools of polyols present in both X. elegans photo- and mycobiont are likely to contribute to the protection of cell constituents like nucleotides, proteins, and membrane lipids, and to preserve the integrity of intracellular structures during desiccation. Our data indicate that glcn-6-P accumulated due to activation of the oxidative pentose phosphate pathway, in response to a need for reducing power (NADPH) during the dehydration-triggered down-regulation of cell metabolism. On the contrary, glcn-6-P was metabolised immediately after hydration, supplying respiration with substrates during the replenishment of pools of glycolytic and photosynthetic intermediates. Finally, the high net photosynthetic activity of wet X. elegans thalli at low temperature may help this alpine lichen to take advantage of brief hydration opportunities such as ice melting, thus favouring its growth in harsh high mountain climates.

Metabolic processes and carbon nutrient exchanges between host and pathogen sustain the disease development during sunflower infection by Sclerotinia sclerotiorum

Interactions between the necrotrophic fungus Sclerotinia sclerotiorum and one of its hosts, Helianthus annuus L., were analyzed during fungal colonization of plant tissues. Metabolomic analysis, based on (13)C- and (31)P-NMR spectroscopy, was used to draw up the profiles of soluble metabolites of the two partners before interaction, and to trace the fate of metabolites specific of each partner during colonization. In sunflower cotyledons, the main soluble carbohydrates were glucose, fructose, sucrose and glutamate. In S. sclerotiorum extracts, glucose, trehalose and mannitol were the predominant soluble carbon stores. During infection, a decline in sugars and amino acids was observed in the plant and fungus total content. Sucrose and fructose, initially present almost exclusively in plant, were reduced by 85%. We used a biochemical approach to correlate the disappearance of sucrose with the expression and the activity of fungal invertase. The expression of two hexose transporters, Sshxt1 and Sshxt2, was enhanced during infection. A database search for hexose transporters homologues in the S. sclerotiorum genome revealed a multigenic sugar transport system. Furthermore, the composition of the pool of reserve sugars and polyols during infection was investigated. Whereas mannitol was produced in vitro and accumulated in planta, glycerol was exclusively produced in infected tissues and increased during colonization. The hypothesis that the induction of glycerol synthesis in S. sclerotiorum exerts a positive effect on osmotic protection of fungal cells and favors fungal growth in plant tissues is discussed. Taken together, our data revealed the importance of carbon-nutrient exchanges during the necrotrophic pathogenesis of S. sclerotiorum.

Protein transduction into human cells by adenovirus dodecahedron using WW domains as universal adaptors

BACKGROUND

Direct protein transduction is a recent technique that involves use of peptide vectors. In this study, we demonstrate that adenovirus dodecahedron (Dd), a virus-like particle devoid of DNA and able to penetrate cells with high efficiency, can be used as a vector for protein delivery.

METHODS

Taking advantage of Dd interaction with structural domains called WW, we have elaborated a universal adaptor to attach a protein of interest to this vector.

RESULTS

A tandem of three WW structural domains derived from the Nedd4 protein enables the formation of stable complexes with Dd, without impairing its endocytosis efficiency. Our protein of interest fused to the triple WW linker is delivered by the dodecahedron in 100% of cells in culture with on average more than ten million molecules per cell.

CONCLUSION

These data demonstrate the great potential of adenovirus dodecahedron in combination with WW domains as a protein transduction vector.

Methyl-beta-D-glucopyranoside in higher plants: accumulation and intracellular localization in Geum montanum L. leaves and in model systems studied by 13C nuclear magnetic resonance

Using (13)C-NMR, methyl-beta-D-glucopyranoside (MeG) was characterized as a major compound in the leaves of the alpine herb Geum montanum L. MeG continuously accumulated during the life span of G. montanum leaves, and accounted for up to 20% of the soluble carbohydrates in aged overwintering leaves, without being reallocated during senescence. Incubating intact plant tissues, culture cells, and purified organelles with (13)C-labelled substrates showed that MeG was synthesized in the cytosol of cells, directly from glucose and methanol molecules. There was no contribution of the C-1 pathway. MeG was subsequently stored in the vacuole without being re-exported to the cytoplasm. All the dicots tested contained the enzymatic machinery permitting MeG synthesis from methanol and glucose, but the plants accumulating this compound at concentrations higher than 1 micromol g(-1) wet wt were mainly members of the Rosaceae family belonging to the Rosoideae subfamily. It is suggested that the synthesis of MeG may contribute to reduce the accumulation in the cytoplasm of methanol and its derived compounds.

Cytosolic pH regulates root water transport during anoxic stress through gating of aquaporins

Flooding of soils results in acute oxygen deprivation (anoxia) of plant roots during winter in temperate latitudes, or after irrigation, and is a major problem for agriculture. One early response of plants to anoxia and other environmental stresses is downregulation of water uptake due to inhibition of the water permeability (hydraulic conductivity) of roots (Lp(r)). Root water uptake is mediated largely by water channel proteins (aquaporins) of the plasma membrane intrinsic protein (PIP) subgroup. These aquaporins may mediate stress-induced inhibition of Lp(r) but the mechanisms involved are unknown. Here we delineate the whole-root and cell bases for inhibition of water uptake by anoxia and link them to cytosol acidosis. We also uncover a molecular mechanism for aquaporin gating by cytosolic pH. Because it is conserved in all PIPs, this mechanism provides a basis for explaining the inhibition of Lp(r) by anoxia and possibly other stresses. More generally, our work opens new routes to explore pH-dependent cell signalling processes leading to regulation of water transport in plant tissues or in animal epithelia.

Novel partner proteins of adenovirus penton

Each of the 12 vertices of the adenovirus virion is made of penton, the complex of two oligomeric proteins: a pentameric penton base anchored in the capsid and an antenna-like trimeric fiber extending outwards. Adenovirus penton plays an essential role in the infection of host cells because it is indispensable for virus attachment and internalization. The initial interactions of penton with the primary and secondary receptors are well described. In contrast with that, the role of the penton components downstream of the initial cell contact is not known. This work shows for the first time that two adenovirus structural proteins, fiber and base, are able to interact intimately with different classes of cellular targets. In the case of penton base, a protein responsible for virus internalization, the partners include three ubiquitin-protein ligases that are involved in protein turnover, cell cycle control and endocytosis. Another base protein partner, BAG3, is involved in controlling Hsc70 chaperone activity. Virus attachment protein, fiber, interacts with many different partners, some of them involved in signal transduction and cell growth. Further work will illustrate the implications of these interactions for both the viral and cellular life cycles.

Cold- and light-induced changes of metabolite and antioxidant levels in two high mountain plant species Soldanella alpina and Ranunculus glacialis and a lowland species Pisum sativum

Leaves of the two cold-acclimated alpine plant species Ranunculus glacialis and Soldanella alpina and, for comparison, of the non-acclimated lowland species Pisum sativum were illuminated with high light intensity at low temperature. The light- and cold-induced changes of antioxidants and of the major carbon and phosphate metabolites were analysed to examine which metabolic pathways might be limiting in non-acclimated pea leaves and whether alpine plants are able to circumvent such limitation. During illumination at low temperature pea leaves accumulated high quantities of sucrose, glucose-6-phosphate, fructose-6-phosphate, mannose-6-phosphate and phosphoglycerate (PGA) whereas ATP/ADP-ratios decreased. Although the PGA content also increased in leaves of R. glacialis the other metabolites did not accumulate and ATP/ADP-ratios remained fairly constant in either alpine species. These data indicate a inorganic phosphate (Pi)-limitation in the chloroplasts of pea leaves but not in the alpine species. However, the total phosphate pool and the percentage of free Pi were highest in pea and did not change during illumination in cold. In contrast, free Pi contents declined markedly in R. glacialis leaves, suggesting that Pi is available for metabolism in this species. In S. alpina leaves contents of ascorbate and glutathione doubled in light and cold, while the contents of sugars did not increase. Obviously, S. alpina leaves can use assimilated carbon for ascorbate synthesis, rather than for the synthesis of sugars. A high capacity for ascorbate synthesis might prevent the accumulation of mannose-6-phosphate and Pi-limitation.

Adenovirus dodecahedron allows large multimeric protein transduction in human cells

Adenovirus dodecahedron is a virus-like particle composed of only two viral proteins of human adenovirus serotype 3 that are responsible for virus attachment and internalization. We show here that this dodecameric particle, devoid of genetic information, efficiently penetrates human cells and can deliver large multimeric proteins such as immunoglobulins.

Reversibility of cold- and light-stress tolerance and accompanying changes of metabolite and antioxidant levels in the two high mountain plant species Soldanella alpina and Ranunculus glacialis

Two high mountain plants Soldanella alpina (L.) and Ranunculus glacialis (L.) were transferred from their natural environment to two different growth conditions (22 degrees C and 6 degrees C) at low elevation in order to investigate the possibility of de-acclimation to light and cold and the importance of antioxidants and metabolite levels. The results were compared with the lowland crop plant Pisum sativum (L.) as a control. Leaves of R. glacialis grown for 3 weeks at 22 degrees C were more sensitive to light-stress (defined as damage to photosynthesis, reduction of catalase activity (EC 1.11.1.6) and bleaching of chlorophyll) than leaves collected in high mountains or grown at 6 degrees C. Light-stress tolerance of S. alpina leaves was not markedly changed. Therefore, acclimation is reversible in R. glacialis leaves, but constitutive or long-lasting in S. alpina leaves. The different growth conditions induced significant changes in non-photochemical fluorescence quenching (qN) and the contents of antioxidants and xanthophyll cycle pigments. These changes did not correlate with light-stress tolerance, questioning their role for light- and cold-acclimation of both alpine species. However, ascorbate contents remained very high in leaves of S. alpina under all growth conditions (12-19% of total soluble carbon). In cold-acclimated leaves of R. glacialis, malate represented one of the most abundant compounds of total soluble carbon (22%). Malate contents declined significantly in de-acclimated leaves, suggesting a possible involvement of malate, or malate metabolism, in light-stress tolerance. Leaves of the lowland plant P. sativum were more sensitive to light-stress than the alpine species, and contained only low amounts of malate and ascorbate.

Reversibility of cold- and light-stress tolerance and accompanying changes of metabolite and antioxidant levels in the two high mountain plant species Soldanella alpina and Ranunculus glacialis

Two high mountain plants Soldanella alpina (L.) and Ranunculus glacialis (L.) were transferred from their natural environment to two different growth conditions (22 degrees C and 6 degrees C) at low elevation in order to investigate the possibility of de-acclimation to light and cold and the importance of antioxidants and metabolite levels. The results were compared with the lowland crop plant Pisum sativum (L.) as a control. Leaves of R. glacialis grown for 3 weeks at 22 degrees C were more sensitive to light-stress (defined as damage to photosynthesis, reduction of catalase activity (EC 1.11.1.6) and bleaching of chlorophyll) than leaves collected in high mountains or grown at 6 degrees C. Light-stress tolerance of S. alpina leaves was not markedly changed. Therefore, acclimation is reversible in R. glacialis leaves, but constitutive or long-lasting in S. alpina leaves. The different growth conditions induced significant changes in non-photochemical fluorescence quenching (qN) and the contents of antioxidants and xanthophyll cycle pigments. These changes did not correlate with light-stress tolerance, questioning their role for light- and cold-acclimation of both alpine species. However, ascorbate contents remained very high in leaves of S. alpina under all growth conditions (12-19% of total soluble carbon). In cold-acclimated leaves of R. glacialis, malate represented one of the most abundant compounds of total soluble carbon (22%). Malate contents declined significantly in de-acclimated leaves, suggesting a possible involvement of malate, or malate metabolism, in light-stress tolerance. Leaves of the lowland plant P. sativum were more sensitive to light-stress than the alpine species, and contained only low amounts of malate and ascorbate.

Glycerophosphocholine metabolism in higher plant cells. Evidence of a new glyceryl-phosphodiester phosphodiesterase

Glycerophosphocholine (GroPCho) is a diester that accumulates in different physiological processes leading to phospholipid remodeling. However, very little is known about its metabolism in higher plant cells. (31)P-Nuclear magnetic resonance spectroscopy and biochemical analyses performed on carrot (Daucus carota) cells fed with GroPCho revealed the existence of an extracellular GroPCho phosphodiesterase. This enzymatic activity splits GroPCho into sn-glycerol-3-phosphate and free choline. In vivo, sn-glycerol-3-phosphate is further hydrolyzed into glycerol and inorganic phosphate by acid phosphatase. We visualized the incorporation and the compartmentation of choline and observed that the major choline pool was phosphorylated and accumulated in the cytosol, whereas a minor fraction was incorporated in the vacuole as free choline. Isolation of plasma membranes, culture medium, and cell wall proteins enabled us to localize this phosphodiesterase activity on the cell wall. We also report the existence of an intracellular glycerophosphodiesterase. This second activity is localized in the vacuole and hydrolyzes GroPCho in a similar fashion to the cell wall phosphodiesterase. Both extra- and intracellular phosphodiesterases are widespread among different plant species and are often enhanced during phosphate deprivation. Finally, competition experiments on the extracellular phosphodiesterase suggested a specificity for glycerophosphodiesters (apparent K(m) of 50 microM), which distinguishes it from other phosphodiesterases previously described in the literature.

Questioning the role of salicylic acid and cytosolic acidification in mitogen-activated protein kinase activation induced by cryptogein in tobacco cells

Elicitors of plant defence reactions, oligogalacturonides and cryptogein, an elicitin produced by Phytophthora cryptogea, were previously shown to induce a rapid and transient activation of two mitogen-activated protein kinases (MAPKs) in cells of tobacco [ Nicotiana tabacum L. cv. Xanthi; A. Lebrun-Garcia et al. (1998) Plant J 15:773-781]. We verified that these two MAPKs correspond to the salicylic acid-induced protein kinase (SIPK) and the wound-induced protein kinase (WIPK). The involvement of salicylic acid (SA) in cryptogein-induced MAPK activation was investigated using transgenic NahG tobacco cells expressing the salicylate hydroxylase gene and thus unable to accumulate SA. The large and sustained activation of both MAPKs by cryptogein was maintained in transgenic cells compared with non-transgenic tobacco cells. Moreover, weak acids, namely SA, 4-hydroxybenzoic acid, an ineffective analogue of SA in plant resistance, and butyric acid acidified the cytosol, a physiological event also induced by cryptogein, but activated both MAPKs only slightly and transiently in tobacco cells. These results indicate that MAPK activation by cryptogein is not mediated by SA, that cytosolic acidification can be transduced by MAPKs, and that in cryptogein-treated cells, cytosolic acidification should contribute poorly to MAPK activation.

Origin of the cytoplasmic pH changes during anaerobic stress in higher plant cells. Carbon-13 and phosphorous-31 nuclear magnetic resonance studies

We tested the contribution of nucleoside triphosphate (NTP) hydrolysis, ethanol, and organic acid syntheses, and H(+)-pump ATPases activity in the acidosis of anoxic sycamore (Acer pseudoplatanus) plant cells. Culture cells were chosen to alter NTP pools and fermentation with specific nutrient media (phosphate [Pi]-deprived and adenine- or glycerol-supplied). In vivo (31)P- and (13)C-nuclear magnetic resonance (NMR) spectroscopy was utilized to noninvasively measure intracellular pHs, Pi, phosphomonoesters, nucleotides, lactate, and ethanol. Following the onset of anoxia, cytoplasmic (cyt) pH (7.5) decreased to 6.8 within 4 to 5 min, whereas vacuolar pH (5.7) and external pH (6.5) remained stable. The NTP pool simultaneously decreased from 210 to <20 nmol g(-1) cell wet weight, whereas nuceloside diphosphate, nucleoside monophosphate, and cyt pH increased correspondingly. The initial cytoplasmic acidification was at a minimum in Pi-deprived cells containing little NTP, and at a maximum in adenine-incubated cells showing the highest NTP concentration. Our data show that the release of H(+) ions accompanying the Pi-liberating hydrolysis of NTP was the principal cause of the initial cyt pH drop and that this cytoplasmic acidosis was not overcome by H(+) extrusion. After 15 min of anoxia, a partial cyt-pH recovery observed in cells supplied with Glc, but not with glycerol, was attributed to the H(+)-consuming ATP synthesis accompanying ethanolic fermentation. Following re-oxygenation, the cyt pH recovered its initial value (7.5) within 2 to 3 min, whereas external pH decreased abruptly. We suggest that the H(+)-pumping ATPase located in the plasma membrane was blocked in anoxia and quickly reactivated after re-oxygenation.

Metabolism of methanol in plant cells. Carbon-13 nuclear magnetic resonance studies

Using (13)C-NMR, we demonstrate that [(13)C]methanol readily entered sycamore (Acer pseudoplatanus L.) cells to be slowly metabolized to [3-(13)C]serine, [(13)CH(3)]methionine, and [(13)CH(3)]phosphatidylcholine. We conclude that the assimilation of [(13)C]methanol occurs through the formation of (13)CH(3)H(4)Pte-glutamate (Glu)(n) and S-adenosyl-methionine, because feeding plant cells with [3-(13)CH(3)]serine, the direct precursor of (13)CH(2)H(4)Pte-Glu(n), can perfectly mimic [(13)CH(3)]methanol for folate-mediated single-carbon metabolism. On the other hand, the metabolism of [(13)C]methanol in plant cells revealed assimilation of label into a new cellular product that was identified as [(13)CH(3)]methyl-beta-D-glucopyranoside. The de novo synthesis of methyl-beta-D-glucopyranoside induced by methanol did not require the formation of (13)CH(3)H(4)Pte-Glu(n) and was very likely catalyzed by a "transglycosylation" process.

Glycine and serine catabolism in non-photosynthetic higher plant cells: their role in C1 metabolism

Glycine and serine are two interconvertible amino acids that play an important role in C1 metabolism. Using 13C NMR and various 13C-labelled substrates, we studied the catabolism of each of these amino acids in non-photosynthetic sycamore cambial cells. On one hand, we observed a rapid glycine catabolism that involved glycine oxidation by the mitochondrial glycine decarboxylase (GDC) system. The methylenetetra- hydrofolate (CH2-THF) produced during this reaction did not equilibrate with the overall CH2-THF pool, but was almost totally recycled by the mitochondrial serine hydroxymethyltransferase (SHMT) for the synthesis of one serine from a second molecule of glycine. Glycine, in contrast to serine, was a poor source of C1 units for the synthesis of methionine. On the other hand, catabolism of serine was about three times lower than catabolism of glycine. Part of this catabolism presumably involved the glycolytic pathway. However, the largest part (about two-thirds) involved serine-to-glycine conversion by cytosolic SHMT, then glycine oxidation by GDC. The availability of cytosolic THF for the initial SHMT reaction is possibly the limiting factor of this catabolic pathway. These data support the view that serine catabolism in plants is essentially connected to C1 metabolism. The glycine formed during this process is rapidly oxidized by the mitochondrial GDC-SHMT enzymatic system, which is therefore required in all plant tissues.

Transport, Compartmentation, and Metabolism of Homoserine in Higher Plant Cells. Carbon-13- and phosphorus-31-nuclear magnetic resonance studies Carbon-13- and Phosphorus-31-Nuclear Magnetic Resonance Studies

The transport, compartmentation, and metabolism of homoserine was characterized in two strains of meristematic higher plant cells, the dicotyledonous sycamore (Acer pseudoplatanus) and the monocotyledonous weed Echinochloa colonum. Homoserine is an intermediate in the synthesis of the aspartate-derived amino acids methionine, threonine (Thr), and isoleucine. Using 13C-nuclear magnetic resonance, we showed that homoserine actively entered the cells via a high-affinity proton-symport carrier (Km approximately 50-60 mum) at the maximum rate of 8 +/- 0.5 mumol h-1 g-1 cell wet weight, and in competition with serine or Thr. We could visualize the compartmentation of homoserine, and observed that it accumulated at a concentration 4 to 5 times higher in the cytoplasm than in the large vacuolar compartment. 31P-nuclear magnetic resonance permitted us to analyze the phosphorylation of homoserine. When sycamore cells were incubated with 100 mum homoserine, phosphohomoserine steadily accumulated in the cytoplasmic compartment over 24 h at the constant rate of 0.7 mumol h-1 g-1 cell wet weight, indicating that homoserine kinase was not inhibited in vivo by its product, phosphohomoserine. The rate of metabolism of phosphohomoserine was much lower (0.06 mumol h-1 g-1 cell wet weight) and essentially sustained Thr accumulation. Similarly, homoserine was actively incorporated by E. colonum cells. However, in contrast to what was seen in sycamore cells, large accumulations of Thr were observed, whereas the intracellular concentration of homoserine remained low, and phosphohomoserine did not accumulate. These differences with sycamore cells were attributed to the presence of a higher Thr synthase activity in this strain of monocot cells.

Early Events Induced by the Elicitor Cryptogein in Tobacco Cells: Involvement of a Plasma Membrane NADPH Oxidase and Activation of Glycolysis and the Pentose Phosphate Pathway

Application of the elicitor cryptogein to tobacco (cv Xanthi) is known to evoke external medium alkalinization, active oxygen species production, and phytoalexin synthesis. These are all dependent on an influx of calcium. We show here that cryptogein also induces calcium-dependent plasma membrane depolarization, chloride efflux, cytoplasm acidification, and NADPH oxidation without changes in NAD+ and ATP levels, indicating that the elicitor-activated redox system, responsible for active oxygen species production, uses NADPH in vivo. NADPH oxidation activates the functioning of the pentose phosphate pathway, leading to a decrease in glucose 6-phosphate and to the accumulation of glyceraldehyde 3-phosphate, 3- and 2-phosphoglyceric acid, and phosphoenolpyruvate. By inhibiting the pentose phosphate pathway, we demonstrate that the activation of the plasma membrane NADPH oxidase is responsible for active oxygen species production, external alkalinization, and acidification of the cytoplasm. A model is proposed for the organization of the cryptogein responses measured to date.

Early Events Induced by the Elicitor Cryptogein in Tobacco Cells: Involvement of a Plasma Membrane NADPH Oxidase and Activation of Glycolysis and the Pentose Phosphate Pathway

Application of the elicitor cryptogein to tobacco (cv Xanthi) is known to evoke external medium alkalinization, active oxygen species production, and phytoalexin synthesis. These are all dependent on an influx of calcium. We show here that cryptogein also induces calcium-dependent plasma membrane depolarization, chloride efflux, cytoplasm acidification, and NADPH oxidation without changes in NAD+ and ATP levels, indicating that the elicitor-activated redox system, responsible for active oxygen species production, uses NADPH in vivo. NADPH oxidation activates the functioning of the pentose phosphate pathway, leading to a decrease in glucose 6-phosphate and to the accumulation of glyceraldehyde 3-phosphate, 3- and 2-phosphoglyceric acid, and phosphoenolpyruvate. By inhibiting the pentose phosphate pathway, we demonstrate that the activation of the plasma membrane NADPH oxidase is responsible for active oxygen species production, external alkalinization, and acidification of the cytoplasm. A model is proposed for the organization of the cryptogein responses measured to date.

Adenovirus dodecahedron, a new vector for human gene transfer

Recombinant adenovirus is one of most efficient delivery vehicles for gene therapy. However, the initial enthusiasm for the use of recombinant adenovirus for gene therapy has been tempered by strong immune responses that develop to the virus and virus-infected cells. Even though recombinant adenoviruses are replication-defective, they introduce into the recipient cell, together with the gene of interest, viral genetes that might lead to fortuitous recombination if the recipient is infected by wild-type adenovirus. We propose the use of a dodecahedron made of adenovirus pentons or penton bases as an alternative vector for human gene therapy. The penton is a complex of two oligomeric proteins, a penton base and fiber, involved in the cell attachment, internalization, and liberation of virus into the cytoplasm. The dodecahedron retains many of the advantages of adenovirus for gene transfer such as efficiency of entry, efficient release of DNA from endosomes, and wide range of cell and tissue targets. Because it consists of only one or two adenovirus proteins instead of the 11 contained in an adenovirus virion and it does not contain the viral genome, it is potentially a safer alternative to recombinant adenovirus.

Cooperation and Competition between Adenylate Kinase, Nucleoside Diphosphokinase, Electron Transport, and ATP Synthase in Plant Mitochondria Studied by 31P-Nuclear Magnetic Resonance

Nucleotide metabolism in potato (Solanum tuberosum) mitochondria was studied using 31P-nuclear magnetic resonance spectroscopy and the O2 electrode. Immediately following the addition of ADP, ATP synthesis exceeded the rate of oxidative phosphorylation, fueled by succinate oxidation, due to mitochondrial adenylate kinase (AK) activity two to four times the maximum activity of ATP synthase. Only when the AK reaction approached equilibrium was oxidative phosphorylation the primary mechanism for net ATP synthesis. A pool of sequestered ATP in mitochondria enabled AK and ATP synthase to convert AMP to ATP in the presence of exogenous inorganic phosphate. During this conversion, AK activity can indirectly influence rates of oxidation of both succinate and NADH via changes in mitochondrial ATP. Mitochondrial nucleoside diphosphokinase, in cooperation with ATP synthase, was found to facilitate phosphorylation of nucleoside diphosphates other than ADP at rates similar to the maximum rate of oxidative phosphorylation. These results demonstrate that plant mitochondria contain all of the machinery necessary to rapidly regenerate nucleoside triphosphates from AMP and nucleoside diphosphates made during cellular biosynthesis and that AK activity can affect both the amount of ADP available to ATP synthase and the level of ATP regulating electron transport.

Ultrastructural and biochemical characterization of autophagy in higher plant cells subjected to carbon deprivation: control by the supply of mitochondria with respiratory substrates

Autophagy triggered by carbohydrate starvation was characterized at both biochemical and structural levels, with the aim to identify reliable and easily detectable marker(s) and to investigate the factors controlling this process. Incubation of suspension cells in sucrose-free culture medium triggered a marked degradation of the membrane polar lipids, including phospholipids and galactolipids. In contrast, the total amounts of sterols, which are mainly associated with plasmalemma and tonoplast membranes, remained constant. In particular, phosphatidylcholine decreased, whereas phosphodiesters including glycerylphosphorylcholine transiently increased, and phosphorylcholine (P-Cho) steadily accumulated. P-Cho exhibits a remarkable metabolic inertness and therefore can be used as a reliable biochemical marker reflecting the extent of plant cell autophagy. Indeed, whenever P-Cho accumulated, a massive regression of cytoplasm was noticed using EM. Double membrane-bounded vacuoles were formed in the peripheral cytoplasm during sucrose starvation and were eventually expelled into the central vacuole, which increased in volume and squeezed the thin layer of cytoplasm spared by autophagy. The biochemical marker P-Cho was used to investigate the factors controlling autophagy. P-Cho did not accumulate when sucrose was replaced by glycerol or by pyruvate as carbon sources. Both compounds entered the cells and sustained normal rates of respiration. No recycling back to the hexose phosphates was observed, and cells were rapidly depleted in sugars and hexose phosphates, without any sign of autophagy. On the contrary, when pyruvate (or glycerol) was removed from the culture medium, P-Cho accumulated without a lag phase, in correlation with the formation of autophagic vacuoles. These results strongly suggest that the supply of mitochondria with respiratory substrates, and not the decrease of sucrose and hexose phosphates, controls the induction of autophagy in plant cells starved in carbohydrates.

Human adenovirus serotype 3 (Ad3) and the Ad3 fiber protein bind to a 130-kDa membrane protein on HeLa cells

The fiber protein of adenovirus mediates the interaction of adenovirus with cell membrane receptors. We have produced the Ad3 fiber protein in the baculovirus expression system. Biochemical, morphological and functional analyses showed that the recombinant fiber was properly folded and functionally competent. The specific binding of Ad3 virus to two HeLa membrane proteins of 130 and 100 kDa was demonstrated with an overlay protein binding assay. In the same assay, Ad3 fiber only recognized the 130-kDa protein. Divalent cations seemed to be important for the interaction of both virus and fiber with these proteins.

Multiple effects of glycerol on plant cell metabolism. Phosphorus-31 nuclear magnetic resonance studies

The effects of glycerol on plant cell metabolism were studied with sycamore (Acer pseudoplatanus L.) cells using 31P nuclear magnetic resonance spectroscopy. After a long period of sucrose starvation, the addition of 50 mM glycerol to the medium did not restore the original glucose-6-P pool and led to a rapid accumulation of sn-glycerol-3-P in the cytoplasmic compartment. The synthesis of sn-glycerol-3-P was rapid and occurred first at the expense of cytoplasmic P(i). Accumulated sn-glycerol-3-P competitively inhibited glucose-6-phosphate isomerase activity when fructose-6-P was the varied substrate. Such a situation prevented the rapid recycling of triose phosphates back to hexose phosphates and led to an arrest of the functioning of the cytosolic and plastidial pentose phosphate pathways. Under these conditions, the flow of carbon to drive cell respiration derived almost exclusively from glycerol, and this polyalcohol was not used as a source of carbon skeletons for biosynthesis. Glycerol also induced the accumulation of O-phosphohomoserine in the cytoplasmic compartment as long as the cell culture medium contained sucrose. Finally glycerol added to sucrose-starved cells stopped the accumulation of phosphocholine (Roby, C., Martin J.-B., Bligny, R., and Douce, R. (1987) J. Biol. Chem. 262, 5000-5007) and prevented a further decline in the uncoupled rate of O2 consumption by the cells (Journet, E. P., Bligny, R., and Douce, R. (1986) J. Biol. Chem. 261, 3193-3199). These last observations strongly suggest that glycerol prevented the triggering of autophagy induced by sucrose starvation in sycamore cells.

Metabolism of malate in bovine adrenocortical mitochondria studied by 13C-NMR spectroscopy

13C-NMR spectroscopy was used to study the metabolism of [13C]malate in bovine coupled adrenocortical mitochondria. The most apparent difference between the mitochondria from steroidogenic tissues and mitochondria from other tissues is the presence, in addition to the normal respiratory chain, of a second electron-transport system responsible for steroid hydroxylation. [13C]malate was synthesized from [13C]succinate by isolated adrenocortical mitochondria. The basic functional suspension consisted of oxygenated mitochondria to which were added ADP, inorganic phosphate (Pi) and [13C]malate, both in the absence or presence of the steroid substrate, deoxycorticosterone. These mitochondria synthesized [13C]citrate and [13C]pyruvate from [13C]malate. The 13C labeling of these two metabolites demonstrated an important role of the malic enzyme and the kinetics depended on the presence of the steroid substrate; the citric acid cycle was stopped during the hydroxylation pathway. The addition of cyanide, a strong inhibitor of the respiratory chain, confirmed an increased malic enzyme activity when hydroxylation occurred, since pyruvate was trapped by formation of a cyanohydrin. The relative enzymic activities of malic enzyme and isocitrate dehydrogenase were compared, both in the absence or presence of the steroid substrate, by supplementing the basic suspension with unlabeled exogenous metabolites, such as pyruvate or oxaloacetate.

13C nuclear magnetic resonance studies of malate and citrate synthesis and compartmentation in higher plant cells

The synthesis of malate and citrate by sycamore cells (Acer pseudoplatanus L.) perfused with KH13CO3 was analyzed using 13C NMR. To perform in vivo experiments, cells were compressed in a 25-mm tube and perfused with an arrangement enabling tight control of the circulating nutrient medium. An original method using paramagnetic Mn2+ that induced a complete loss of the vacuolar malate and citrate signals was developed to discriminate between cytoplasmic and vacuolar pools of malate and citrate. Our results indicated the following. (a) The accumulation of appreciable amounts of malate in sycamore cells required rather high (1 mM) concentrations of bicarbonate at all the pH values tested. (b) Malate was equally labeled at C-1 and C-4, suggesting that malate labeled at C-1 was produced by randomization of C-1 and C-4 by mitochondrial fumarase. Indeed, the separation of the intact organelles from the lysed protoplasts indicated that fumarase activity was essentially limited to the mitochondria. Similarly, citrate was equally enriched at C-1 and C-5 + C-6 carboxyls. (c) Malate appeared first in the cytoplasmic compartment; and when a threshold of cytoplasmic malate concentration was attained, malate molecules were expelled into the vacuole, where they accumulated. On the other hand, citrate accumulated steadily in the vacuole. Pulse-chase experiments demonstrated the central role played by the tonoplast in governing the vacuolar influx of citrate and the permanent exchange of malate between the cytoplasm and the vacuole.

Effect of glyphosate on plant cell metabolism. 31P and 13C NMR studies

The effect of glyphosate (N-phosphonomethyl glycine; the active ingredient of Roundup herbicide) on plant cells metabolism was analysed by 31P and 13C NMR using suspension-cultured sycamore (Acer pseudoplatanus L) cells. Cells were compressed in the NMR tube and perfused with an original arrangement enabling a tight control of the circulating nutrient medium. Addition of 1 mM glyphosate to the nutrient medium triggered the accumulation of shikimate (20-30 mumol g-1 cell wet weight within 50 h) and shikimate 3-phosphate (1-1.5 mumol g-1 cell wet weight within 50 h). From in vivo spectra it was demonstrated that these two compounds were accumulated in the cytoplasm where their concentrations reached potentially lethal levels. On the other hand, glyphosate present in the cytoplasmic compartment was extensively metabolized to yield aminomethylphosphonic acid which also accumulated in the cytoplasm. Finally, the results presented in this paper indicate that although the cell growth was stopped by glyphosate the cell respiration rates and the level of energy metabolism intermediates remained unchanged.

Regulation of intracellular pH values in higher plant cells. Carbon-13 and phosphorus-31 nuclear magnetic resonance studies

The regulation of the cytoplasmic and vacuolar pH values (pHc and pHv) in sycamore (Acer pseudoplatanus L.) cells was analyzed using 31P and 13C nuclear magnetic resonance spectroscopy. Suspension-cultured cells were compressed in the NMR tube and perfused with the help of an original arrangement enabling a tight control of the pH (external pH, pHe) of the carefully oxygenated circulating nutrient medium. Intracellular pH values were measured from the chemical shifts of: CH2-linked carboxyl groups of citric acid below pH 5.7; orthophosphate between pH 5.7 and 8.0; 13C-enriched bicarbonate over pH 8.0. pHc and pHv were independent of pHe over the range 4.5-7.5. In contrast intracellular pH values decreased rapidly below pHe 4.5 and increased progressively at pHe over 7.5. There was an acceleration in the rate of O2 consumption accompanied with a decrease in cytoplasmic ATP concentration as pHe decreased. When the rate of O2 consumption was approaching the uncoupled O2 uptake rate, a loss of pHc control was observed. It is concluded that as pHe decreased, the plasma membrane ATPase consumed more and more ATP to reject the invading H+ ions in order to maintain pHc at a constant value. Below pHe 4.5 the efficiency of the H+ pump to react to back leakage of H+ ions became insufficient, leading to an acidification of pHc and to an alkalinization of pHe. On the other hand, over pHe 7.5 a passive influx of OH- ions was observed, and pHc increased proportionally to the increase of pHe. Simultaneously appreciable amounts of organic acids (malate and citrate) were synthesized by cells during the course of the alkalinization of the cytoplasmic compartment. The synthesis of organic acids which partially counteract the alkalinization of the cytoplasmic compartment may result from a marked activation of the cytoplasmic phosphoenolpyruvate carboxylase induced by an increase in cytoplasmic bicarbonate concentration. The fluctuations of pHv followed a similar course to that of pHc. It is concluded that the vacuole, which represents a potentially large H+ ions reservoir, can counteract H+ (or OH-) ion invasion observed at acidic (or alkaline) pHe contributing to the homeostasis of pHc.