Les anthocyanes constituent une composante importante de la qualité des fruits rouges, particulièrement pour le raisin noir, et pour la couleur des vins qui en dérivent. La biosynthèse des anthocyanes est déterminée par des facteurs génétiques et affectée par des facteurs environnementaux, notamment la lumière. Pour la plupart des cépages, la pellicule des baies est le tissu principal ou exclusif accumulant les anthocyanes. Notre travail analyse les effets de la lumière et du génotype sur la biosynthèse des anthocyanes. Le matériel végétal que nous avons utilisé était constitué de cépages teinturiers, qui accumulent des anthocyanes dans la pellicule et dans la pulpe, et de populations hybrides. Dix-neuf anthocyanes mono-glycosylées ont été identifiés dans sept tissus colorés du cépage teinturier Yan-73 (V. vinifera). La composition et la concentration en anthocyanes varient selon les organes et le stade de développement. Les anthocyanes de la pellicule incluent principalement les dérivés de la malvidine, alors que les dérivés de la péonidine sont les plus abondants dans la pulpe. Les dérivés de malvidine et de péonidine prédominent dans le rachis, les pédicelles des baies, les limbes foliaires, les nervures et les pétioles, et dans l‘écorce à la base du cep. Les concentrations des anthocyanes dans les pellicules, la pulpe, le rachis et les pédicelles augmentent rapidement à partir de la véraison, ou une semaine après la véraison. Elles sont élevées dans les limbes foliaires jeunes et sénescents, et faibles dans les feuilles en expansion et les feuilles adultes. Elles ne varient pas beaucoup au cours de la saison dans les nervures et les pétioles, ou dans l‘écorce. Les cépages ont pu être distingués selon leur réponse à des traitements d‘exclusion de la lumière imposés de la nouaison à la maturité en entourant les grappes par des boîtes opaques. Le cépage non teinturier ―Gamay‖ à peau rouge accumule très peu d‘anthocyanes dans la pellicule en absence de lumière. Au contraire, les cultivars teinturiers, ‗Yan-73‘ et ‗Gamay Fréaux‘ (mutant teinturier de ‘Gamay’) accumulent des anthocyanes aussi bien dans la pellicule que dans la pulpe et présentent une coloration sombre même en absence de lumière... / Anthocyanins are an important component of red fruit quality, especially for grape berries, and for the color of the wines made from these berries. Anthocyanin biosynthesis is determined by genetic factors and affected by environmental factors, especially sunlight. For most grape cultivars, the berry skin is the main or only tissue accumulating anthocyanins. The present work investigates the effects of light and grape genotype on anthocyanin biosynthesis. We used teinturier grape cultivars (also called dyers, which synthesize anthocyanins in both skin and pulp) and its hybrid population as plant materials. Nineteen monoglucoside anthocyanins were identified in seven colored tissues of the teinturier cultivar Yan-73 (V. vinifera). Anthocyanin composition and concentration varied among grape organs and with developmental stage. Skin anthocyanins were mainly composed of malvidin derivatives, while peonidin derivatives were the most abundant anthocyanins in the pulp. Both malvidin and peonidin derivatives were predominant in rachis, berry pedicels, leaf lamina, vein and petioles, and living bark at the base of the shoot. The concentration of anthocyanins in berry skin, pulp, rachis and pedicels rapidly increased starting from veraison on, or one week after veraison. Anthocyanin concentrations were high in young and senescing leaf lamina and low in expanding and mature lamina. They did not vary much throughout the growing season in the leaf veins and petiole tissues, or in the bark. Grape cultivars could be distinguished by their response to sunlight exclusion treatments imposed from fruit set to maturity by surrounding the clusters with opaque boxes. The red-skinned non-teinturier cultivar Gamay could barely accumulate anthocyanins in berry skin under sunlight exclusion. In contrast, teinturier cultivars, Yan-73 and Gamay Fréaux (teinturier mutant of Gamay) accumulated anthocyanins in both skin and pulp and showed dark color even under sunlight exclusion...

Infection of barley (Hordeum vulgare) leaves with the rust fungus, Puccinia hordei, causes changes in the host protein synthesis. This thesis analyses these changes in the barley cultivar Triumph following inoculation of 7-day-old leaves with either a virulent or an avirulent race of P. hordei. The initial approach was to isolate membrane-bound polysomes from infected leaves, translate them in vitro and analyse the translation products. These products include the integral membrane proteins which were expected to be involved in the response of the host to the pathogen. A method based on differential centrifugation in the presence of a ribonuclease-inhibiting buffer was developed for separating membrane-bound polysomes from the rest of the cytoplasmic polysomes. Membrane-bound polysomes were found to comprise one fifth of the total polysomes in the leaves. Analysis of the translation products of membrane-bound polysomes by SDS-PAGE showed them to be of higher average molecular weight than those from free polysomes. Comparison of polypeptides produced by membrane-bound polysomes from healthy and inoculated plants showed some differences however the low yield of membrane-bound polysomes made it difficult to obtain conclusive results. Thus it was decided to isolate total polysomes by including 1% Triton X-100 in the extraction buffer. Polysomes were extracted from 12 to 72 h after inoculation. Infection caused a decline in yield of polysomes during this period when compared with healthy leaves of the same age. Polysomes isolated 16 h after inoculation with the virulent race were 20% less efficient at translation than polysomes from control leaves. In contrast polysome isolated from leaves inoculated with the avirulent race were 20% more efficient. Analysis of the labelled translation products by SDS-PAGE and fluorography showed relative increases in the synthesis of some proteins by 16 h after inoculation with either race when compared to products from healthy leaves. Protein synthesis in the infected plants was further analysed by in vivo labelling and one- and two-dimensional PAGE. The fluorographs revealed increased synthesis of a group of proteins from 58 to 116 kDa starting 12 h after inoculation with either race of P. hordei; confirming the results from the polysome translations. Two polypeptides with molecular weights of about 66 kDa were found to increase following infection only with the virulent race. By three days after inoculation with either fungal race the most obvious change in protein synthesis was a marked decrease in the synthesis of the two most prominent polypeptides with molecular weights of 15 and 51 kDa which were considered to be the subunits of ribulose bisphosphate carboxylase. The elicitor hypothesis, in attempting to explain cultivar-specific resistance in plants, postulates that resistance is controlled by the interaction of specific fungal elicitors and plant receptors and that this interaction which only occurs between resistant hosts and avirulent pathogens triggers specific gene expression leading to resistance. This hypothesis does not fit the situation in the barley-P. hordei interaction as protein synthesis showed similar changes following infection with either a virulent or an avirulent race.