Afin d’étudier l’impact de la surmaturation des poires sur les interactions parois-procyanidins, les parois et les procyanidines ont été isolées et caractérisées à partir d’une variété de poire à poiré à deux stade de maturité : mûres et surmatures. Leurs associations ont été quantifiées par la méthode des isothermes de Langmuir et par calorimétrie à titration isotherme.Les poires à poiré sont riches en procyanidines très polymérisées dont les unités constitutives sont principalement constituées de (-)-épicatéchine. Les parois du parenchyme et des cellules parenchymateuses sont principalement constituées de pectines hautement methylées et ramifiées alors que les parois des cellules pierreuses et de l’épiderme sont plutôt lignifiées et riches en hémicelluloses.La surmaturation n’induit pas de modification de la composition et ni de la distribution de la masse molaire des procyanidines. Par contre, la distribution des aggrégats de procyanidines dans les vacuoles change, de dispersée (poires mûres) à adjacente au tonoplaste (poire surmatures). Entre le stade mûr et surmature, les parois de poire perdent des chaînes latérales pectiques, principalement les chaînes d’arabinanes et de galactanes des parois du parenchyme et des cellules parenchymateuses.L'affinité des procyanidines vis-à-vis des parois diminue dans l’ordre suivant : cellules parenchymateuses> parenchyme>cellules pierreuses>épiderme d’après les isothermes de Langmuir. La quantité de procyanidines fixées sur les parois augmente avec la surmaturation surtout pour les parois de cellules pierreuses (et le parenchyme total). La calorimétrie à titration isotherme montre que la surmaturation induit également une modification du mécanisme de l’association parois-procyanidines en modifiant la balance hydrophile hydrophobe pour les cellules parenchymateuses.L'augmentation de la capacité d’adsorption des parois vis-à-vis des procyanidines à la surmaturation a été confirmée par des pressages de jus. Les jus de poires mûres sont plus riches en procyanidines que le jus extraits à partir poires surmatures alors que la concentration en procyanidines dans les fruits n’a pas changé. / In order to study overripening impact on cell wall–procyanidin interactions, perry pear cell walls and procyanidins were isolated and characterized at ripe and overripe stage. Their associations were quantified using Langmuir isotherms and isothermal titration calorimetry.Perry pears were rich in procyanidins with high degree of polymerization and their constitutive units were mainly (-)-epicatechin. Cell walls isolated from the whole flesh and parenchyma cells were characterized by extremely methylated pectin and highly branched rhamnogalacturonans whereas cell walls from stone cells and skin were more lignified and rich in hemicelluloses.Overripening did not modify procyanidin structure and molar mass distribution, but the distribution of the procyanidin-containg aggregates in the vacuoles was modified, from dispersed in ripe pears to close to the tonoplast in overripe pears. Between the ripe and overripe stage, pear cell walls lost pectic side chains, arabinans and galactan, mostly from cell walls isolated from parenchyma cells and the whole flesh.The affinity between procyanidins and cell walls decreased as follows: parenchyma cells > flesh > stone cells > skin as reported by Langmuir isotherms. The amount of bound procyanidins increased at the overripe stage notably for the cell walls from stone cells and whole flesh. Isothermal titration calorimetry indicated that overripening induced the modification of cell wall binding mechanism especially for parenchyma cells where interactions were driven by hydrophobic interactions.The increase of procyanidin binding capacity at the overripe stage was confirmed by juice pressing where overripe pear juices were poorer in procyanidins than ripe pear juices whereas fruit procyanidin contents did not change with overripening.

Reproduction in vertebrates, including fishes, is under control of the brain-pituitary-gonad (BPG) axis. The female three-spined stickleback, Gasterosteus aculeatus, produces egg clutches at intervals of a few days and spawns them in a nest built by male. Following ovulation, eggs are stored in the ovarian cavity surrounded by the ovarian fluid (OF). If spawning or spontaneous release do not occur, the eggs can undergo overripening, a phenomenon occurring both in nature and captivity. In this PhD thesis, the changes of reproductive hormones and vitellogenesis were studied at overripening of eggs and over the natural spawning cycle. OF properties were also examined at overripening of eggs and after treatment with sex steroids. Plasma levels of steroids: testosterone (T), estradiol (E2), 17,20β-dihydroxypregn-4-en-3-one (17,20β-P) and 17,20β,21-trihydroxypregn-4-en-3-one (17,20β,21-P) were measured by radioimmunoassay, and relative mRNA levels of the pituitary gonadotropins (fsh-β/lh-β), brain gonadotropin-releasing hormones (gnrh2/gnrh3) and kisspeptin and its receptor (kiss2/gpr54) by qPCR. Overripening of eggs was accompanied with a significant reduction in most of endocrine parameters of BPG axis (T, E2, 17,20β-P; lh-β; kiss2, gpr54). Low level of hormones could be advantageous for the overripe egg-bound females, since this would reduce further ovulations giving higher chances to survive and reproduce again. Over the 3-day spawning cycle, T and E2 were highly correlated, showed cyclicity with low levels at ovulation and increasing from 24 and 6 hours post-spawning (hps), respectively. Spawning may give rise to this increase as these rises did not occur if release of the eggs does not happen (overripe females). A peak at pituitary lh-β mRNA levels appeared 48 hps, a day before the next ovulation. No significant changes were found for the other studied hormones. Vitellogenesis was studied by measurement of the vitellogenin mRNA levels in the liver by qPCR. The levels were highest at 24 and 48 hps and were positively correlated to both E2 and T over the cycle. However, changes were small suggesting a rather continuous vitellogenesis over the stickleback spawning cycle which could be an advantage for a multiple spawner with a limited spawning season. Overripening reduced vitellogenin mRNA levels but did not abolish it. OF amount was diminished in overripe females and had a lower viscocity but higher dry weight and protein levels than in non-overripe ovulated females, suggesting that changes in OF properties are related to the egg overripening. The effects of steroids were studied using Silastic capsules. T and 17,20β-P induced an increase of OF amount, but protein levels were only increased in 17,20β-P-treated females, proposing a role of this steroid in the control of OF secretion. 1-D SDS-PAGE showed that OF contained several proteins, some of them came from eggs, but no consistent differences between groups. Concluding, the knowledge of the reproductive physiological changes is important for understanding their essential roles in the production of viable eggs in this species but also in the reproductive physiology of female fishes in general. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p>