A global non-invasive methodology for the phenotyping of potato under water deficit conditions using imaging, physiological and molecular tools

BACKGROUND

Drought is a major consequence of global heating that has negative impacts on agriculture. Potato is a drought-sensitive crop; tuber growth and dry matter content may both be impacted. Moreover, water deficit can induce physiological disorders such as glassy tubers and internal rust spots. The response of potato plants to drought is complex and can be affected by cultivar type, climatic and soil conditions, and the point at which water stress occurs during growth. The characterization of adaptive responses in plants presents a major phenotyping challenge. There is therefore a demand for the development of non-invasive analytical techniques to improve phenotyping.

RESULTS

This project aimed to take advantage of innovative approaches in MRI, phenotyping and molecular biology to evaluate the effects of water stress on potato plants during growth. Plants were cultivated in pots under different water conditions. A control group of plants were cultivated under optimal water uptake conditions. Other groups were cultivated under mild and severe water deficiency conditions (40 and 20% of field capacity, respectively) applied at different tuber growth phases (initiation, filling). Water stress was evaluated by monitoring soil water potential. Two fully-equipped imaging cabinets were set up to characterize plant morphology using high definition color cameras (top and side views) and to measure plant stress using RGB cameras. The response of potato plants to water stress depended on the intensity and duration of the stress. Three-dimensional morphological images of the underground organs of potato plants in pots were recorded using a 1.5 T MRI scanner. A significant difference in growth kinetics was observed at the early growth stages between the control and stressed plants. Quantitative PCR analysis was carried out at molecular level on the expression patterns of selected drought-responsive genes. Variations in stress levels were seen to modulate ABA and drought-responsive ABA-dependent and ABA-independent genes.

CONCLUSIONS

This methodology, when applied to the phenotyping of potato under water deficit conditions, provides a quantitative analysis of leaves and tubers properties at microstructural and molecular levels. The approaches thus developed could therefore be effective in the multi-scale characterization of plant response to water stress, from organ development to gene expression.

Different mechanisms of nucleation and self-organization of droplets in ferroelectric smectic membranes

New mechanisms of droplet nucleation and self-organization in ferroelectric membranes are described. The droplets may be accompanied by different number of topological defects (zero, one, two) whose location may be on the droplet boundary or in the membrane. Nucleation and self-organization of droplets with total topological charge S = 0 , S = + 1 and S = - 1 were investigated. We found that an S = - 1 topological defect may be the center of both droplet nucleation and chain formation. This mechanism of chaining drastically differs from the droplet self-organization described earlier which is realized by attraction of droplet-defect pairs. Our observations demonstrate new possibilities for manipulating the inclusions and their self-organization in smectic membranes.

Interaction of surfaces in smectic membranes and their instability near thinning transitions

We report measurements of the interaction between surfaces of the presmectic membrane above the temperature of transition to the phase without layer ordering. Investigations were performed employing cholesteric droplets embedded in the membrane in the temperature range of thinning transitions. Upon heating, the difference between the membrane tension and surface tension of the bulk sample decreases sufficiently, which leads to membrane instability. After the thinning transition, the membrane returns to a stable state with a larger value of surface interaction.

Correlation between dielectric and optical measurements in the smectic-C(*)(alpha) phase

We present optical and dielectric measurements in the smectic-C(*)(alpha) (SmC(*)(alpha)) phase of three homologues of an alkoxy benzoate series. Two different behaviors are observed depending on the values and the temperature evolution of the azimuthal angle difference alpha between two adjacent layers. For moderate values of alpha, the Goldstone mode is predominant over the whole SmC(*)(alpha) phase. For large values of alpha, we can distinguish the soft mode near the SmA*-SmC(*)(alpha) phase transition and the Goldstone mode at lower temperatures. In this case, discontinuities are also observed at the SmC(*)(alpha)-SmA* phase transition. These dielectric features are correlated with optical properties using simulations based on the discrete phenomenological "clock model."

Self-organization of N(*) inclusions in SmC(*) free-standing films

The behaviour of freely suspended smectic-C* ( SmC(*)) films at the bulk SmC(*)-cholesteric ( N(*)) phase transition has been investigated using polarized-reflected-light microscopy. Our experimental observations show that above the bulk SmC(*)- N(*) phase transition the N(*) order appears in different ways according to the film thickness. In thin films, the conventional layer-by-layer thinning occurs. In films of intermediate thickness N(*) inclusions nucleate inside the SmC(*) film. The distortions of the in-plane orientational order of the SmC(*) host phase induce elastic interactions between the inclusions and lead to their self-organization in chain-like structures. Both the dynamic of the chaining and the parameters driving the equilibrium distance between the inclusions in the chain are investigated. In thick films, N(*) fingers grow inside the film. The influence of the experimental conditions on the various processes is analysed.

Molecular characterization of partial trisomy 16q24.1-qter: clinical report and review of the literature

We describe a 3(1/2)-year-old girl with psychomotor and mental retardation; dysmorphic features, including a high forehead with bitemporal narrowing; a broad nasal bridge and a broadened nose; downslanting palpebral fissures; abnormal ears; vertebral abnormalities; cardiac defect; genital hypoplasia; and anal abnormalities. The karyotype of our patient (550 bands) was normal. Molecular cytogenetic techniques, including comparative genomic hybridization (CGH) and fluorescence in situ hybridization (FISH), revealed that this girl was a carrier of a de novo derivative chromosome 7 arising from a cryptic t(7;16)(p22.3;q24.1) translocation generating a trisomy 16q24.1-qter and a 7p22.3-pter deletion. FISH with a series of specific chromosome 7p and 16q probes allowed us to delineate the chromosome 7 breakpoint between YAC660G6 (WD7S517) and YAC848A12 (D7S521, D7S31, and WI-4829) and the chromosome 16 breakpoint between BAC457K7 (D42053) and BAC44201 (SGC30711). The comparison of the clinical features of our patient with those of 2 cases of pure terminal 7p deletion and 28 cases of trisomy 16q reported in the literature allowed us to establish the following phenotype-genotype correlation for trisomy of the long arm of chromosome 16: distinctive facies (high/prominent forehead, bitemporal narrowing, periorbital edema in the neonatal period); severe mental retardation; vertebral, genital, and anal abnormalities to 16q24; distal joint contractures and camptodactyly to 16q23; cleft palate and renal anomalies to 16q22; beaked nose and gall bladder agenesis to 16q21; gut malrotation; lung and liver anomalies to 16q13; and behavior abnormalities to band 16q11-q13.

Genetic diversity in european and Argentinian cultivated potatoes (Solanum tuberosum subsp. tuberosum) detected by inter-simple sequence repeats (ISSRs)

In this study, the use of inter-simple sequence repeats (ISSR) to assess genetic diversity between cultivated potatoes (Solanum tuberosum subsp. tuberosum) is reported. ISSR technology rapidly reveals high polymorphic fingerprints and thus determines the genetic diversity among potato cultivars. Nine primers were selected according to the number of amplified markers and the level of polymorphism detected. Three primers (GAG(CAA)5, CTG(AG)8, and (AG)8) were used to cluster the 28 potato accessions and 77 polymorphic markers were sufficient to identify all of the accessions. Among the 15 simple sequence repeat (SSR) motifs tested, the most abundant were CAA and AG. Argentinian- and European-grown potatoes were easily distinguished, with a higher level of genetic diversity among potatoes from Argentina. An ISSR study using a limited number of cultivars and very few primers clearly differentiated between all cultivars, thus ISSR was revealed to be a good tool for the genetic identification of potato and for future germplasm-management programs.

Comparative genomic hybridisation in mentally retarded patients with dysmorphic features and a normal karyotype

Segmental aneusomy for small chromosomal regions has been shown to be a common cause of mental retardation and multiple congenital anomalies. A screening method for such chromosome aberrations that are not detected using standard cytogenetic techniques is needed. Recent studies have focused on detection of subtle terminal chromosome aberrations using subtelomeric probes. This approach however excludes significant regions of the genome where submicroscopic rearrangements are also liable to occur. The aim of the present study was to evaluate the efficiency of comparative genomic hybridisation (CGH) for screening of submicroscopic chromosomal rearrangements. CGH was performed in a cohort of 17 patients (14 families) with mental retardation, dysmorphic features and a normal karyotype. Five subtle unbalanced rearrangements were identified in 7 patients. Subsequent FISH studies confirmed these results. Although no interstitial submicroscopic rearrangement was detected in this small series, the study emphasises the value of CGH as a screening approach to detect subtle chromosome rearrangements in mentally retarded patients with dysmorphic features and a normal karyotype.

Interactions between colloidal inclusions in two-dimensional smectic-C* films

We report an experimental study of colloidal inclusions in free-standing films of smectic-C* liquid crystal. The inclusions are cholesteric droplets that form above the bulk smectic-C*-7cholesteric transition temperature. Each droplet confined in a two-dimensional (2D) system, is accompanied by a topological defect. The distortions of the in-plane orientational order of the smectic-C* film induce elastic interactions between the droplets. As in 3D water nematic emulsions, a short-range repulsion and a long-range dipolar attraction govern the stability of the inclusions and lead to their organization in chainlike structures. Our results are in agreement with recent theoretical predictions.

Formation of string defects at thinning transitions in smectic-C* free-standing films

The layer thinning transitions in freely suspended smectic-C* films have been investigated. The defect structure formed by stringlike lines was observed just before the thinning transitions. The string defects disappear after the thinning transition and appear again near the temperature of the next thinning transition. These results clearly indicate that thin free-standing films at the thinning transitions are slightly below the melting temperature of the interior layers.

Assessment of sex chromosome aneuploidy in sperm nuclei from 47,XXY and 46,XY/47,XXY males: comparison with fertile and infertile males with normal karyotype

Sex chromosome aneuploidy was assessed in spermatozoa from a 47,XXY male and a 46,XY/47,XXY male using three colour fluorescence in-situ hybridization (FISH) and compared with two control groups. The first group included subjects of proven fertility and the second infertile males with normal constitutional karyotype. The frequencies of XX and YY disomic, XY hyperhaploid and diploid spermatozoa were significantly increased in the 47,XXY male compared to subjects from the two control groups (P < 0.0001). For the 46,XY/47,XXY sample, the same results were observed, except that the incidence of YY disomic spermatozoa did not differ significantly from the rate obtained in infertile patients. The frequency of sex chromosome aneuploidy did not differ significantly between the 47,XXY and the 46,XY/47,XXY males, except for XX disomic sperm nuclei which was higher in the 47,XXY patient. The frequency of chromosome 12 disomy was also increased in the two XXY individuals (0.42 and 0.49% respectively; P < 0.0001). The meiotic abnormalities observed in the two XXY patients arose through segregation errors in XY germ cells. The increased number of meiotic non-disjunctions observed in the germ cells of infertile males may be a common feature of the deficient oligo- or azoospermic testis. Patients with Klinefelter's syndrome with oligozoospermia have an increased risk of both sex chromosome and autosome aneuploidy in their progeny.

Multicritical behaviors and an induced twist grain boundary phase in a binary liquid crystalline mixture

We report here the composition-temperature phase diagram of a mixture between n=9 and n=16 terms of a chiral tolans series shortly noted nF(2)BTFO1M7. This diagram constitutes an experimental illustration of one of the three theoretical phase diagrams predicted by the Renn and Lubensky's model. The pure compounds n=9 and n=16 exhibit, respectively, the phase sequences Cry-Sm-C*-Sm-A-TGB(A)-N*-BP-I and Cry-Sm-C*-N*-BP-I, where TGB refers to a twist grain boundary phase. Phases identification and transition temperatures, at atmospheric pressure, have been determined by both optical microscopy and photothermal methods. The experimental phase diagram shows the disappearance of Sm-A and TGB(A) mesophases and the appearance of a TGB(C) phase when the n=16 composition increases. Four of the five multicritical points theoretically anticipated by Renn and Lubensky are pointed out.

[Microdeletion of 22q11 and conotruncal cardiopathies: contribution of prenatal diagnosis]

OBJECTIVE

We report our experience on prenatal diagnosis of 22q11 deletion by fluorescent in situ hybridation (FISH).

PATIENTS AND METHODS

From February 1997 to April 1998, prenatal diagnosis of 22q11 deletion was performed in 13 cases of congenital conotruncal heart defects. FISH was carried out using D22S75 DiGeorge's chromosome region probe.

RESULTS

Microdeletions of 22q11 were detected in 4 fetuses with tetralogy of Fallot (3 cases) and pulmonary atresia with ventricular septal defect (1 case). Termination of pregnancy was performed in two cases for severe congenital heart defect. A third malformed fetus died immediately after a blood sampling procedure. The last fetus, with a tetralogy of Fallot malformation, was born and underwent corrective cardiac surgery. The dysmorphic features of this fetus was suggestive of DiGeorge's syndrome, and the development status was normal.

CONCLUSION

Prenatal detection of 22q11 only played a minor role in the decision to terminate the pregnancy in our study.

Relationship between clinical phenotype, semen parameters and aneuploidy frequency in sperm nuclei of 50 infertile males

The purpose of this study was to analyse the frequency of disomy for chromosomes 1, 13, 14, 18, 21, 22, X and Y in sperm nuclei of 50 infertile men and 10 healthy probands of proven fertility. Semen parameters (sperm count, global motility and morphology), urological clinical examination, genital ultrasound and lymphocyte karyotyping were performed for each patient. Disomy frequency was established by fluorescence in situ hybridization by using whole chromosome paint probes. The mean rate of disomy for the various autosomes studied was higher in infertile males than in subjects of proven fertility. Interchromosomal and interindividual differences in the disomy frequency were observed between the 50 patients. The mean frequency of homodisomy YY and heterodisomy XY was increased in spermatozoa of patients with low semen quality parameters (0.24% and 0.54%, respectively). The disomy frequency in infertile males was directly correlated with the severity of oligospermia. However, no relationship was established between aneuploidy rate, sperm motility, morphology or clinical phenotype. These results support the hypothesis that, during spermatogenesis of males with sperm parameter alterations, a decreased frequency of meiotic chromosome pairing and crossing over may lead to spermatogenesis arrest at the meiosis stage and/or to an increase of meiotic nondisjunctions. Meiotic arrest in some germ cells may be responsible for oligospermia and nondisjunctions in other cells for aneuploidy in mature male gametes.

Fluorescence in situ hybridization with chromosome paint probes: a novel approach to assess aneuploidy in human sperm nuclei

PURPOSE

Fluorescence in situ hybridization (FISH) using whole-chromosome paint probes was performed to evaluate disomy and diploidy frequency for chromosomes 1, 18, 19, and 22 in human sperm nuclei.

METHODS

Ten subjects of proven fertility and normal spermatic parameters were included in the study. A dual-color FISH method was carried out.

RESULTS

A total of 157,896 spermatozoa was scored. The mean frequencies of disomic sperm for chromosomes 1, 18, 19, and 22 were 0.22% (range, 0.19 to 0.28%), 0.24% (range, 0.14 to 0.37%), 0.22% (range, 0.17 to 0.30%), and 0.25% (range, 0.21 to 0.29%), respectively. The mean frequency of diploidy was 0.14% (range, 0.09 to 0.18%). No interindividual and interchromosomal variations in the aneuploidy frequency were observed between the different subjects.

CONCLUSIONS

FISH with whole-chromosome paint probes provides a novel and efficient approach for disomy assessment in human sperm nuclei.

Assessment of autosome and gonosome disomy in human sperm nuclei by chromosome painting

Disomy and diploidy frequencies for autosomes 1-22 and the gonosomes were assessed in 299,442 sperm nuclei from four normal fertile men by chromosome painting. This novel approach allowed us to perform a specific and sensitive detection of each chromosome. A minimum of 5000 sperm nuclei per subject were evaluated for each chromosome by dual colour fluorescence in situ hybridization. The disomy rate proved to be similar for all the autosomes (0.24%) and the diploidy rate varied from 0.12% to 0.15%. No interchromosomal or interindividual differences in the frequency of disomic and diploid sperm nuclei were observed between the four subjects. The mean frequency of XX-, YY- and XY-bearing spermatozoa was estimated to 0.17%, 0.17% and 0.32%, respectively. This strategy constitutes a new approach for detecting aneuploidy in human sperm nuclei and suggests an equal repartition of non-disjunction among chromosomes in male gametes.

Effects of the Ca2+ antagonist RO 40-5967 on endothelium-dependent responses of isolated arteries

Experiments were designed to determine whether the Ca2+ channel inhibitor RO 40-5967 [(1S,2S)-2-[2-[[3-(2-benzimidazolyl)propyl]methylamine]ethyl]-6- fluoro-1,2,3,4-tetrahydro-1-isopropyl-2-naphthyl methoxyacetate dihydrochloride] causes endothelium-dependent relaxations or inhibits endothelium-dependent contractions of isolated blood vessels. Rings of dog femoral, carotid, and basilar arteries and of rat aorta, with and without endothelium, were suspended in conventional organ chambers for measurement of isometric force. During contractions evoked by phenylephrine (full alpha 1-adrenergic agonist), St 587 (partial alpha 1-adrenergic agonist) and endothelin-1 (ET), RO 40-5967 caused concentration-dependent relaxations of rings of dog femoral arteries; the relaxations to RO 40-5967 were greater in rings with endothelium than in those without endothelium. Nitro-L-arginine (NLA) and methylene blue (MB) inhibited the endothelium-dependent component of the response to RO 40-5967 during contractions to phenylephrine (PE) St 587 and ET. The endothelium-dependent relaxations evoked by RO 40-5967 during contractions to PE were not affected by diltiazem in the femoral artery, suggesting that this effect of the compound may not be related to its calcium channel inhibitor properties. Under bioassay conditions, RO 40-5967 stimulated release of relaxing factors from the endothelium of canine carotid arteries; the response of the detector tissues was inhibited by MB. In strips of canine femoral artery with endothelium, in which membrane potential of vascular smooth muscle cells (VSMC) was recorded with glass microelectrodes, RQ 40-5967 did not cause endothelium-dependent hyperpolarizations.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell-free hemoglobin reverses the endotoxin-mediated hyporesponsivity of rat aortic rings to alpha-adrenergic agents

Hemoglobin (Hbg) and lysates of red blood cells act as vasoconstrictors in isolated vessels by a mechanism that may involve nitric oxide (NO.) scavenging. To determine if such a mechanism indeed occurs, we investigated the effects of cell-free Hgb, modified Hgp (met Hgb and cyan met Hgb), and red blood cells on the formation of NO. induced by endotoxin in rat aorta. Incubation of rat aortic rings with endotoxin induced a delayed and prolonged release of NO. that resulted in a decrease in the contractile response to phenylephrine. Hgb significantly potentiated contractions to phenylephrine in control rings and also reversed the hyporeactivity to this alpha 1-agonist in endotoxin-treated rings with and without endothelium. Lysed red blood cells but not whole red blood cells shifted the concentration-contraction response curves to phenylephrine significantly to the right in endotoxin-treated preparations. Neither picket-fence porphyrin-albumin (PFP-albumin) or metheme-albumin affected the contractile response to phenylephrine. Oxidation of Hgb to met Hgb did not alter the contractions to an alpha 1-agonist in endotoxin-treated rings. In contrast, the formation of cyan met Hgb abolished the action of Hgb on the vascular reactivity of endotoxin-treated preparations. Together, these results demonstrate that free Hgb can scavenge NO. produced in endotoxin-treated vascular tissue and that the ability to bind NO. requires a cell-free form of Hgb with an intact heme center capable of undergoing redox reactions.

Antagonistic effects of S9871 or (imidazolinyl-2)-2-dihydro 2,3 benzofurane and its stereoisomers on some central and peripheral actions of alpha 2-agonists

(+/-) and (+), but not (-) S9871 are new alpha 2-adrenoceptor selective antagonists. The effect of the racemic mixture and of the stereoisomers on cardiovascular and sedative responses to clonidine have been studied in rats and chickens, respectively. Blockade of central alpha 2-adrenoceptors was also measured as a recovery of the sympathoinhibitory effect induced by intravenous administration of B-HT 933 (azepexole). The potency profiles of these agents established in the central nervous system were confirmed in studies using the vas deferens in situ in the pithed rat. (+/-) and (+) S9871 blocked and antagonized some centrally mediated effects of clonidine such as the depressor response to both intravenous and intracerebroventricular administration. However, the return of arterial pressure to the control value, after intravenous administration of (-) S9871, does not result from an antagonistic action on alpha 2-adrenoceptors, since the depressor effects of clonidine were not blocked, but could be explained by alpha-agonistic properties of (-) S9871. (+/-) and (+) S9871 also blocked and antagonized the hypotensive and bradycardic action induced by intravenous administration of B-HT 933. The loss of the righting reflex induced by clonidine in the chicken was prevented by (+/-) and (+) S9871, as shown by a shift of the dose-response curve to clonidine to the right by both agents; on the contrary, (-) S9871 potentiated the sedation induced by clonidine. In the pithed rat, intravenously administered (+/-) and (+) S9871 fully antagonized the inhibitory effects of clonidine on the electrically induced contractions of the vas deferens. These observations are consistent with a selective alpha 2-adrenoceptors antagonistic effect of (+/-) and (+) S9871 at central and peripheral alpha 2-adrenoceptors.

Stereoselectivity of central alpha-adrenoceptors involved in sleep induced by clonidine in chickens

The stereoselectivity of central alpha 2-adrenoceptors involved in sleep induced in chicks by clonidine, suggested by the results observed with the stereoisomers of idazoxan, was further investigated with the stereoisomers of (imidazolinyl-2)-2-dihydro-2,3-benzofurane (S9871) and those of (imidazolinyl-2)-2-benzocyclobutane (S10089). As for the stereoisomers of idazoxan, there was not a good separation between the effects of the stereoisomers of S10089. In contrast, there was a clearcut separation between the effects of (+)S9871 (antagonist) and (-)S9871 (no effect against the action of clonidine). Therefore, these results strongly support the view that central alpha 2-adrenoceptors which mediate sedation are stereoselective for alpha 2-antagonists.

Pre- and postsynaptic alpha-adrenoceptor blocking properties of a new dihydrobenzofurane derivative (imidazolinyl-2)-2-dihydro 2,3 benzofurane (S 9871) and its stereoisomers in rats

In the present investigation, the alpha-adrenoceptor blocking effect of (imidazolinyl-2)-2-dihydro 2,3 benzofurane or S 9871 and its stereoisomers was studied. In the pithed rat (+/-) and (+) S 9871 competitively antagonized the pressor effects of azepexole and clonidine more effectively than those of cirazoline and phenylephrine. (-) S 9871 only blocked the pressor response of the alpha 1-agonists used: phenylephrine and cirazoline. (+/-) and (+) S 9871 antagonized the inhibitory effects of clonidine on the increase in heart rate produced by stimulation of the sympathetic efferent fibres of the thoracic spinal cord. (-) S 9871 was twenty times less potent on the decrease in heart rate induced by clonidine. On the vas deferens of the rat, (+/-) and (+) S 9871 appeared to be more potent than (-) S 9871 in antagonizing the inhibitory effects of clonidine on the twitch response produced by electrical stimulation. Therefore, (+/-) and (+) S 9871 appear to be more preferential for alpha 2-adrenoceptors than for alpha 1-adrenoceptors; in contrast (-) S 9871 appears to be selective for alpha 1-adrenoceptors. (+/-) and (+) S 9871 appears to be one of the most selective agents for blocking alpha 2-adrenoceptors.

[Interactions between alpha 1, alpha 2 and beta receptors in the blood pressure effects of adrenaline and noradrenaline in the dog]

In anaesthetized dog, the adrenaline induced hypertension is reversed by both alpha 1- and alpha 2-adrenoceptor blocking agents such as AR-C 239 and yohimbine. After alpha 1 or alpha 2 and beta-blockade, adrenaline induced again an increase in blood pressure. This hypertensive effect was suppressed by an alpha 2-adrenoceptor blocking agent when an alpha 1-adrenoceptor blocking was responsible for the reversal of adrenaline-induced hypertension, and conversely. After beta-blockade, both alpha 1- and alpha 2-adrenoceptor blockade is necessary for suppressing any tensional effect of adrenaline. On the other hand, alpha 1- and alpha 2-adrenoceptor blockade are both required to prevent beta-blockade from restoring adrenaline hypertensive effect. Similar effects were observed wih noradrenaline. In fact, only a significant decrease of the noradrenaline-induced hypertension was observed after each alpha-blocker. Both alpha 1- and alpha 2-adrenoceptor blocking agent also significantly inhibited the hypertension induced by noradrenaline. For completely suppressing the effect of noradrenaline on blood pressure, a combination of alpha 1, alpha 2 and beta-blockade is necessary. These results are compatible with a stimulation by adrenaline and noradrenaline of both alpha 1- and alpha 2-adrenoceptors to produce increase in blood pressure.

Hysteresis, oscillations, and pattern formation in realistic immobilized enzyme systems

Hysteresis, oscillations, and pattern formation in realistic biochemical systems governed by P.D.E.s are considered from both numerical and mathematical points of view. Analysis of multiple steady states in the case of hysteresis, and bifurcation theory in the cases of oscillations and pattern formation, account for the observed numerical results. The possibility to realize these systems experimentally is their main interest, thus bringing further arguments in favor of theories explaining basic biological phenomena by diffusion and reaction.

The kinetic behavior of an artificial bienzyme membrane

Artificial membranes bearing immobilized enzymes can be used to study some effects of membrane structure on enzyme kinetic behavior. The bienzyme system described is a mixture of beta-glucosidase and glucose oxidase. Gluconolactone, the product of thesecond enzyme, is an inhibitor of the first one. The resulting feedback effect has been compared using a mixed two-enzyme membrane, two separated one-enzyme membranes, and astirred bienzyme solution. The feedback effect is quicker and more efficient in the two-enzyme membrane than in solution; it is slower and less efficient in the case of the separated one-enzyme membranes. Effects of enzyme proximity in the structure are discussed. Conclusions are drawn concerning the efficiency of feedback mechanisms when enzymes are embedded within a single structure.

Kinetic studies dealing with an immobilized bienzyme system

The binding of enzymes into artificial membranes makes possible a study of the interaction between membrane structure and enzyme kinetics within a simple context. Artificial protein membranes bearing a bienzyme system (xanthine oxidase, uricase) are produced by using a co-crosslinking method. The inhibition of uricase was shown to be dependent not only on the concentration of inhibitor in the bulk solution, but also on the kinetic properties of the membrane-bound enzymes. In the presence of xanthine oxidase inside the structure the uricase inhibition by xanthine is less important than in solution. Under defined conditions the activity was found to be higher in the presence of inhibitor than in its absence. Due to diffusion limitations this specific bienzyme system is more efficient when immobilized inside a membrane than when in solution.