Showing papers by "Institut national de la recherche agronomique published in 1992"
TL;DR: Analyzing an avirulent Tn917-lac mutant defective for actin polymerization showed that the actA gene encodes a surface protein necessary for bacterially induced actin assembly, and results indicate that it is a 610 amino acid protein with an apparent molecular weight of 90 kd.
815 citations
TL;DR: The authors present the results of an experiment defined to demonstrate the use of radar to retrieve forest biomass, finding the strong correlation of P-band backscatter intensity to forest biomass to be the most striking observation.
Abstract: The authors present the results of an experiment defined to demonstrate the use of radar to retrieve forest biomass. The SAR data were acquired by the NASA/JPL SAR over the Landes pine forest during the 1989 MAESTRO-1 campaign. The SAR data, after calibration, were analyzed together with ground data collected on forest stands from a young stage (eight years) to a mature stage (46 years). The dynamic range of the radar backscatter intensity from forest was found to be greatest at P-band and decreased with increasing frequencies. Cross-polarized backscatter intensity yielded the best sensitivities to variations of forest biomass. L-band data confirmed past results on good correlation with forest parameters. The most striking observation was the strong correlation of P-band backscatter intensity to forest biomass. >
803 citations
TL;DR: A membrane polypeptide involved in K+ transport in a higher plant was cloned by complementation of a yeast mutant defective in K+, with a complementary DNA library from Arabidopsis thaliana that conferred ability to grow on media with K+ concentration in the micromolar range and to absorb K+ (or 86Rb+) at rates similar to those in wild-type yeast.
Abstract: A membrane polypeptide involved in K+ transport in a higher plant was cloned by complementation of a yeast mutant defective in K+ uptake with a complementary DNA library from Arabidopsis thaliana. A 2.65-kilobase complementary DNA conferred ability to grow on media with K+ concentration in the micromolar range and to absorb K+ (or 86Rb+) at rates similar to those in wild-type yeast. The predicted amino acid sequence (838 amino acids) has three domains: a channel-forming region homologous to animal K+ channels, a cyclic nucleotide-binding site, and an ankyrin-like region.
665 citations
TL;DR: It is reported that aminopeptidase N, an ectoenzyme abundantly expressed at the apical membrane of the enterocytes, serves as a receptor for Transmissible gastroenteritis virus.
Abstract: Coronaviruses, like many animal viruses, are characterized by a restricted host range and tissue tropism. Transmissible gastroenteritis virus (TGEV), a major pathogen causing a fatal diarrhoea in newborn pig, replicates selectively in the differentiated enterocytes covering the villi of the small intestine. To investigate the molecular determinants of the infection, we characterized the surface molecule used by the virus for binding and entry into host cells. Here we report that aminopeptidase N, an ectoenzyme abundantly expressed at the apical membrane of the enterocytes, serves as a receptor for TGEV. Monoclonal antibodies were selected for their ability to block infection by TGEV of porcine cell lines. They recognized a brush-border membrane protein of M(r) 150K, which was identified as aminopeptidase N by amino-terminal sequencing. Two lines of evidence supported the view that the peptidase itself acts as a receptor. First, virions bound specifically to aminopeptidase N that was purified to homogeneity. Second, recombinant expression of aminopeptidase N conferred infectivity by TGEV to an otherwise non-permissive cell line.
590 citations
TL;DR: The low shut-off temperature of pVE6002 makes it a useful suicide vector for bacteria which are limited in their own temperature growth range and as the delivery vector for a transposon Tn10 derivative in Bacillus subtilis.
Abstract: We isolated a replication-thermosensitive mutant of the broad-host-range replicon pWV01. The mutant pVE6002 is fully thermosensitive above 35 degrees C in both gram-negative and gram-positive bacteria. Four clustered mutations were identified in the gene encoding the replication protein of pVE6002. The thermosensitive derivative of the related plasmid pE194 carries a mutation in the analogous region but not in the same position. Derivatives of the thermosensitive plasmid convenient for cloning purposes have been constructed. The low shut-off temperature of pVE6002 makes it a useful suicide vector for bacteria which are limited in their own temperature growth range. Using pVE6002 as the delivery vector for a transposon Tn10 derivative in Bacillus subtilis, we observed transposition frequencies of about 1%.
446 citations
TL;DR: This study exemplified the usefulness of mitochondrial DNA sequence analysis for estimating phylogenetic relationships within S. trutta populations by determining DNA sequence variation in segments of the mitochondrial control region for 151 individuals representing 24 populations.
Abstract: Summary
Throughout its natural range, the brown trout Salmo trutta L. exhibits a complex pattern of morphological and life-history variation. This has led to considerable taxonomic confusion, hampering the understanding of the evolutionary history of the species. To document the phylogenetic relationships among morphologically and geographically remote brown trout populations across western Europe, we determined the DNA sequence variation in segments of the mitochondrial control region for 151 individuals representing 24 populations. DNA was prepared for double-stranded sequencing by the polymerase chain reaction (PCR). Twenty-one variable nucleotide positions within a 640-bp fragment surveyed defined 12 genotypes differing by a mean of 7 nucleotide substitutions (range 1–12). Five major phylogenetic assemblages differing by mean sequence divergence estimates of 0.96 to 1.44% were identified. These groupings exhibited a strong spatial partitioning but lacked congruence with either ecological or morphological differentiation. Complete mitochondrial DNA (mtDNA) monomorphism across all Atlantic basin populations contrasted with the high interdrainage genetic diversity observed in more southerly populations. This study exemplified the usefulness of mitochondrial DNA sequence analysis for estimating phylogenetic relationships within S. trutta populations.
441 citations
Journal Article•
TL;DR: This paper is an overview of the main physical characteristics of the native starch granule, and a variation in the susceptibility of the starch granules to enzymatic digestion is explained by variations in the morphology of the granules and their crystalline organization.
Abstract: Starch, the most abundant component of the diet, is characterized by its variety as well as the versatility of its derivatives in foods. This paper is an overview of the main physical characteristics of the native starch granule. Three different levels of organization are presented: macromolecular structure, crystalline organization and ultrastructure. Starch consists of amylose and amylopectin. Amylose is an essentially linear polymer composed of alpha-1,4-linked D-anhydroglucose units (AGU); amylopectin is a branched polymer clustering a large amount of short linear chains by the linkage of alpha-1,6-bonds, constituting about 5% of the total glycosidic bonds. In the native starch granules, a large number of the macromolecular chains are organized in crystalline structures. Three forms have been found, the A, B and C patterns. So far only A and B starch crystals have been modelled. There is a variation in the susceptibility of the starch granules to enzymatic digestion. This is explained by variation in the morphology of the granules and their crystalline organization.
370 citations
TL;DR: The observations suggest that epidermal water relations may act as a modulator of the responses of stomata to ABA, and it is argued that such changes must be taken into account in studies or modeling of plant responses to drought stress.
Abstract: We investigated, under laboratory and field conditions, the possibility that increasing abscisic acid (ABA) concentrations and decreasing water potentials can interact in their effects on stomata. One experiment was carried out with epidermal pieces of Commelina communis incubated in media with a variety of ABA and polyethylene glycol concentrations. In the media without ABA, incubation in solutions with water potentials between −0.3 and −1.5 megapascals had no significant effect on stomatal aperture. Conversely, the sensitivity of stomatal aperture to ABA was trebled in solutions at −1.5 megapascals compared with sensitivity at −0.3 megapascals. The effect of the change in sensitivity was more important than the absolute effect of ABA at the highest water potential. In a field experiment, sensitivity of maize stomatal conductance to the concentration of ABA in the xylem sap varied strongly with the time of the day. We consider that the most likely explanation for this is the influence of a change in leaf or epidermal water potential that accompanies an increase in irradiance and saturation deficit as the day progresses. These observations suggest that epidermal water relations may act as a modulator of the responses of stomata to ABA. We argue that such changes must be taken into account in studies or modeling of plant responses to drought stress.
322 citations
TL;DR: Results in this study showed that loss of hydraulic conductivity occurred in stem segments pressurized in a pressure chamber while the xylem water was under positive pressure, consistent with the air-seeding hypothesis of how embolism are nucleated, but not with the nucleation of embolisms at hydrophobic cracks.
Abstract: Loss of hydraulic conductivity occurs in stems when the water in xylem conduits is subjected to sufficiently negative pressure. According to the air-seeding hypothesis, this loss of conductivity occurs when air bubbles are sucked into water-filled conduits through micropores adjacent to air spaces in the stem. Results in this study showed that loss of hydraulic conductivity occurred in stem segments pressurized in a pressure chamber while the xylem water was under positive pressure. Vulnerability curves can be defined as a plot of percentage loss of hydraulic conductivity versus the pressure difference between xylem water and the outside air inducing the loss of conductivity. Vulnerability curves were similar whether loss of conductivity was induced by lowering the xylem water pressure or by raising the external air pressure. These results are consistent with the air-seeding hypothesis of how embolisms are nucleated, but not with the nucleation of embolisms at hydrophobic cracks because the latter requires negative xylem water pressure. The results also call into question some basic underlying assumptions used in the determination of components of tissue water potential using "pressure-volume" analysis.
320 citations
TL;DR: Lactic acid bacteria can produce a variety of substances with antibacterial activity which are described in this article, including reuterin, which is a broad spectrum inhibitor active against Gram-positive and Gram-negative bacteria, yeasts, molds and protozoas.
Abstract: Summary - Lactic acid bacteria can produce a variety of substances with antibacterial activity which are described in this article. Non-peptide antibacterial substances are distinguished from bacteriocins, which have a proteinaceous active site. Among the former, reuterin produced by Lactobacillus reuteri is a broad spectrum inhibitor active against Gram-positive and Gram-negative bacteria, yeasts, molds and protozoas. It is a glycerol derivative, l3-hydroxypropionaldehyde. Bacteriocins can be produced by most lactic acid bacteria species and their spectrum of activity is generally restricted to organisms taxonomically close to the producer. The biochemical properties of bacteriocins, their structure and nature of their genetic determinants are highly variable. This literature review discusses the similarities and differences existing in this group of substances.
317 citations
TL;DR: This protocol was improved using the nopaline disarmed strain C58/pMP90 with the binary vector pBI121 and used to test three other vectors, finding that CaMV 70 promoter provided consistently higher level of gene expression than the other promoters in both callus and leaf tissues.
Abstract: Leaf or stem explants of a hybrid poplar clone (Populus tremula X Populus alba), sensitive to Agrobacterium tumefaciens, were co-cultivated either by an octopine or a nopaline disarmed A. tumefaciens modified strain. Transformed poplar shoots were readily regenerated from explants. The protocol was improved using the nopaline disarmed strain C58/pMP90 with the binary vector pBI121. This protocol was then used to test three other vectors. The first one, possessing a nptII gene fused to the CaMV 19S promoter, permitted regeneration of transformed shoots in presence of 50 to 100 mg/l kanamycin. The two other vectors carried an additional nptII gene under the control of the CaMV 35S or CaMV 35S promoter with a double enhancer sequence (CaMV 70). CaMV 70 promoter provided consistently higher level of gene expression than the other promoters in both callus and leaf tissues.
TL;DR: In this article, the authors proposed an empirical methodology for studying various (implicit or explicit) collusive behaviors on two strategic variables, which are price and advertising, in a differentiated market dominated by a duopoly.
Abstract: This paper proposes an empirical methodology for studying various (implicit or explicit) collusive behaviors on two strategic variables, which are price and advertising, in a differentiated market dominated by a duopoly. In addition to Nash or Stackelberg behaviors, we consider collusion on both variables, collusion on one variable and competition on the other, etc. Using data on the Coca-Cola and Pepsi-Cola markets from 1968 to 1986, full information maximum likelihood estimation of cost and demand functions are obtained allowing for various collusive behaviors. The collusive hypothesis is not rejected, and the best form of collusive behavior is selected via nonnested testing procedures. Using the best model, Lerner indices are computed for both duopolists to provide summary measures of market power. Finally, our approach is contrasted with the conjectural variation approach and is shown to give superior results.
TL;DR: It is shown that marker assisted selection may lead to a gain in time of about two generations, an efficiency below previous theoretical predictions, which is used to propose an optimal strategy for selection on the whole genome.
Abstract: We investigate the use of markers to hasten the recovery of the recipient genome during an introgression breeding program. The effects of time and intensity of selection, population size, number and position of selected markers are studied for chromosomes either carrying or not carrying the introgressed gene. We show that marker assisted selection may lead to a gain in time of about two generations, an efficiency below previous theoretical predictions. Markers are most useful when their map position is known. In the early generations, it is shown that increasing the number of markers over three per non-carrier chromosome is not efficient, that the segment surrounding the introgressed gene is better controlled by rather distant markers unless high selection intensity can be applied, and that selection on this segment first can reduce the selection intensity available for selection on non-carrier chromosomes. These results are used to propose an optimal strategy for selection on the whole genome, making the most of available material and conditions (e.g., population size and fertility, genetic map).
TL;DR: Two classes of glutathione transferases have been identified and purified from Musca domestica and the high activity found in an insecticide-resistant strain (Cornell R) is correlated with high level of GST1 transcript.
TL;DR: In this paper, the spectral and bidirectional reflectance of 26 soils was measured in the laboratory both with a field spectroradiometer (1000 narrow wavebands from 450 nm to 2450 nm) and a radiometer simulating TM channels (the five TM2, TM3, TM4, TM5, and TM7 broad bands).
TL;DR: In this paper, a differential absorption method, similar to the split window technique used over sea surfaces, can be adapted and used locally over land surfaces, which allows to derive land surface temperature with an accuracy better than 1.5 K.
Journal Article•
TL;DR: A better understanding of the enzymatic process enables the identification of the structural factors limiting hydrolysis: diffusion of enzyme molecules, porosity of solid substrate, adsorption of enzymes onto solid substrates, and the catalytic event.
Abstract: Foods appear as complex structures, in which starch may be present in different forms. These, including the molecular characteristics and the crystalline organization, depend on processing conditions and compositions of ingredients. The main changes in starch macro- and microstructures are the increase of surface area to volume ratio in the solid phase, the modification of the crystallinity as affected by gelatinization and gelation, and the depolymerization of amylose and amylopectin. Starch modification may be estimated by different methodologies, which should be selected according to the level of structure considered. When amylose and amylopectin are in solution, rapid and total hydrolysis leads to the formation of a mixture of linear oligosaccharides and branched alpha-limit dextrins. However, starch usually occurs in foods as solid structures. Structural factors of starchy materials influence their enzymic hydrolysis. A better understanding of the enzymatic process enables the identification of the structural factors limiting hydrolysis: diffusion of enzyme molecules, porosity of solid substrates, adsorption of enzymes onto solid substrates, and the catalytic event. A mechanistic modelling should be possible in the future.
TL;DR: Results confirm and extend observations made by Woloshuk et al. who showed that osmotin and a related protein from tomato had antifungal activity against the phytopathogen, Phytophthora infestans.
TL;DR: In this article, the degree of browning has been determined by the simultaneous measurements of soluble (absorbance at 400 nm) and insoluble (lightness) brown pigments.
Abstract: Phenolic compounds and polyphenol oxidase (PPO) activity in the fruits of 11 apple cultivars before and after bruising were studied in relation to their susceptibility to browning. The degree of browning has been determined by the simultaneous measurements of soluble (absorbance at 400 nm) and insoluble (lightness) brown pigments. The sum of these two expressing the extent of browning, closely correlated with the amount of phenolics (hydroxycinnamic derivatives and flavan-3-ols) degraded. Maturity did not appear to greatly influence the development of browning.
TL;DR: A set of oligonucleotide primers capable of amplifying full-length nuclear 17S and 25S ribosomal RNA genes, together with the Ribosomal internal transcribed spacer and intergenic spacer, have been designed and could be used for amplifying target sequences from a wide range of ectomycorrhizal genera.
Abstract: SUMMARY
There is a clear requirement to develop sensitive methods for detecting denned isolates of ectomycorrhizal fungi within the complex microbial communities of natural ecosystems and reforestation sites. We present a method that permits the rapid identification of an ectomycorrhizal isolate using enzymatic amplification (polymerase chain reaction) of DNA extracted either from pure cultures or ectomycorrhizas. A set of oligonucleotide primers capable of amplifying full-length nuclear 17S and 25S ribosomal RNA genes, together with the ribosomal internal transcribed spacer and intergenic spacer, have been designed and could be used for amplifying target sequences from a wide range of ectomycorrhizal genera. Length polymorphism in the amplified rDNA and restriction endonuclease analysis of nearly 6-0 kbp of amplified rDNA provided useful criteria for the rapid typing of isolates from different genera and species. Restriction endonuclease analysis of amplified DNA from 26 isolates representing four species of Laccaria (L. bicolor, L. laccata, L. proxima, L. tortilis) yielded up to 20 scored RFLPs and revealed interspecific and intraspecific polymorphism. Most of the polymorphisms were located within the regions corresponding to the internal transcribed spacer and intergenic spacer. The degree of variation observed was sufficient to discriminate several isolates from the same species. Genetic variation was correlated to some extent with geographical origin of the isolates. However, RFLPs of the rRNA genes cannot unambiguously discriminate all selected isolates within Laccaria species, requiring the development of additional DNA probes. Alone, or in combination with other DNA probes, the amplified rDNA genes may serve in the determination of pure fungal cultures and in the characterization of genetic variation of field ectomycorrhizal populations.
TL;DR: The vulnerability of a species to air embolism was found to be consistent with its ecophysiological behavior in the presence of water stress, drought-tolerant species being less vulnerable than drought-avoiding species.
Abstract: Hydraulic properties of xylem in seven species of conifer were studied during late winter and early spring 1991. Vulnerability to cavitation and air embolism was investigated using hydraulic conductivity and acoustic techniques. Embolisms were induced in branches excised from mature trees by air-drying them in the laboratory. Both techniques gave comparable results indicating that they both assess the same phenomenon. Within a tree, vulnerability was related to the permeability of the xylem, the largest stems tended to cavitate before the smallest ones when water deficits developed in a branch. Interspecific comparisons showed large differences in the xylem water potential needed to induce significant embolism, values ranged from -2.5 MPa in Pinus sylvestris to -4 MPa in Cedrus atlantica, but these differences did not correlate with differences in the xylem permeability of the species. The vulnerability of a species to air embolism was found to be consistent with its ecophysiological behavior in the presence of water stress, drought-tolerant species being less vulnerable than drought-avoiding species.
TL;DR: The data strongly suggest that the uniquely broad host range of NGR234 is mediated by the synthesis of a family of varied sulphated and non‐sulphated lipo‐oligosaccharide signals.
Abstract: Rhizobium species strain NGR234 is the most promiscuous known rhizobium. In addition to the non-legume Parasponia andersonii, it nodulates at least 70 genera of legumes. Here we show that the nodulation genes of this bacterium determine the production of a large family of Nod-factors which are N-acylated chitin pentamers carrying a variety of substituents. The terminal non-reducing glucosamine is N-acylated with vaccenic or palmitic acids, is N-methylated, and carries varying numbers of carbamoyl groups. The reducing N-acetyl-glucosamine residue is substituted on position 6 with 2-O-methyl-L-fucose which may be acetylated or sulphated or non-substituted. All three internal residues are N-acetylated. At pico- to nanomolar concentrations, these signal molecules exhibit biological activities on the tropical legumes Macroptilium and Vigna (Phaseoleae), as well as on both the temperate genera Medicago (Trifoliae) and Vicia (Viciae). These data strongly suggest that the uniquely broad host range of NGR234 is mediated by the synthesis of a family of varied sulphated and non-sulphated lipo-oligosaccharide signals.
TL;DR: Although it is not yet known whether the presence of retroelements is linked to the high level of variability found in plant genomes, it is now clear that retrotransposons are ancient and ubiquitous components of plant genomes.
TL;DR: In this article, the authors show that in the roughness sublayer, the momentum and/or scalar diffusivities are enhanced above their inertial layer values, which can be used for estimating heat and water vapour fluxes.
TL;DR: Different proposed pathways for carbohydrate metabolism are discussed, as well as recent molecular and genetic studies of the enzymes involved, for yogurt manufacture.
Abstract: to yogurt manufacture. The taxonomy of these bacteria is presented. Different proposed pathways for carbohydrate metabolism are then discussed, as weil as recent molecular and genetic studies of the enzymes involved. Acetaldehyde is the major aromatic compound in yogurt, and so the different pathways of its formation are briefly described. Recent studies have concerned threonine aldolase which catalyzes acetaldehyde synthesis by yogurt bacteria. Exocellular polysaccharides produced by lactic acid bacteria improve the texture of stirred and liquid yogurts. Some of the polysaccharides of yogurt bacteria are currently known and particular aspects of their production are discussed. Some other properties, le proteolysis, Iipolysis, urease, oxygen metabolism, are also briefly presented. Interactions between streptococci and lactobacilli are weil established, but more data are required for the complete characterization and control of mixed populations. In particular, Iittle is known about antimicrobial compounds produced by these microorganisms. Bacteriophages of yogurt bacteria are now weIl characterized, but liltle is known about Iysogeny in thermophilic streptococci. Finally, progress in genetics (on both plasmid and chromosomal DNA) is briefly discussed.
TL;DR: Diurnal course of A of well-watered trees exhibited sometimes important midday decreases in A related to high temperature and vapour pressure deficit, which may be considered as protective mechanisms adjusting activity of photosystem II to the electron requirement for photosynthesis.
Abstract: Adult trees of Quercus petraea were submitted to controlled water shortage in a natural stand near Nancy, France. Diurnal course of net CO2 assimilation rate (A) was measured in situ together with chlorophyll a fluorescence determined on dark adapted leaves. In 1990, trees experienced a strong water stress, with predawn and midday leaf water potentials below –2·0 and –3·0 MPa, respectively. Diurnal course of A of well-watered trees exhibited sometimes important midday decreases in A related to high temperature and vapour pressure deficit. Decreases in initial (Fo) and maximal (Fm) fluorescence and sometimes in photochemical efficiency of photosystem II (Fv/Fm) were observed and probably revealed the onset of mechanisms for thermal de-excitation. These mechanisms were shown to be sensitive to dithiothreitol. All these effects were reversible and vanished almost completely overnight. Therefore, they may be considered as protective mechanisms adjusting activity of photosystem II to the electron requirement for photosynthesis. Water stress amplified these reactions: A was strongly decreased, showing important midday depression; diurnal reductions in Fm and Fv/Fm were enhanced. The same trends were observed during summer 1991, despite a less marked drought. These protective mechanisms seemed very effective, as no photoinhibitory damage to PS II could be detected in either water stressed or control trees.
TL;DR: Knowledge of the different effects of photoperiod on neuroendocrine pathways and the reproductive activity in sheep and goats has allowed us to successfully apply light treatments to control seasonal reproductiveactivity in field conditions and in males raised in AI centres.
TL;DR: In this article, the spectral shifts characterized by the wavelength λi of the inflexion point in the red-edge region (670-780 nm) were analyzed using model simulations.
TL;DR: Glycoprotein hormones form a family of structurally related molecules that are among the most complex molecules possessing hormonal activities, and despite their extensive homologies, these hormones exhibit high specificities, indispensable for their respective and often coordinated physiological roles.
Abstract: Introduction THREE glycoprotein hormones are synthesized and secreted by the pituitary under hypothalamic control. Two of them are the gonadotropins, LH and FSH, and the third one is TSH. During gestation in primates and equidaes an additional gonadotropin, CG, is secreted by the placenta. Pituitary gonadotropins play pivotal roles in the control of reproductive function in both the female (1, 2) and the male (3) while the main role of TSH is in the control of thyroid gland activity (4). Although the human (h) and equine (e) CGs (the latter previously named PMSG) have been studied extensively, the full extent of their roles remains equivocal (5, 6). Glycoprotein hormones form a family of structurally related molecules that are among the most complex molecules possessing hormonal activities. Despite their extensive homologies, these hormones exhibit high specificities, indispensable for their respective and often coordinated physiological roles. The present review is an attempt to summarize and interpret t...
TL;DR: Stomatal conductance showed a tight relationship with xylem ABA, but not with the current leaf water status or with the concentration of ABA in the bulk leaf, suggesting that increased concentration of Xylem sap in response to stress can control the gas exchange of plants under field conditions.
Abstract: Stomatal conductance of individual leaves was measured in a maize field, together with leaf water potential, leaf turgor, xylem ABA concentration and leaf ABA concentration in the same leaves. Stomatal conductance showed a tight relationship with xylem ABA, but not with the current leaf water status or with the concentration of ABA in the bulk leaf. The relationship between stomatal conductance and xylem [ABA] was common for variations in xylem [ABA] linked to the decline with time of the soil water reserve, to simultaneous differences between plants grown on compacted, non-compacted and irrigated soil, and to plant-to-plant variability. Therefore, this relationship is unlikely to be fortuitous or due to synchronous variations. These results suggest that increased concentration of ABA in the xylem sap in response to stress can control the gas exchange of plants under field conditions.