Abstract
Sunflower oil is widely consumed in France and Spain. This oil has a good reputation among consumers, due to its high polyunsaturated fatty acid content. Thirty years after its discovery, the oleic mutation (high C18:1 contents) has now reached agricultural production, with fast increasing surfaces for the last three years. The challenge is now the production of very high oleic (> 90%) sunflowers and new fatty acid profiles, such as high linoleic, palmitic, stearic or stearic + oleic hybrids, which are of high interest for chemistry or food industry. The problem is now the stability of the expression in varying genetic backgrounds, and the understanding of environmental effects. Minor components are also a main strength of sunflower oil: its high tocopherols (Vitamin E) content (0,5 to 1%) is all the more interesting for nutritionists that they be almost exclusively α-tocopherol (> 95%), which is the most vitaminic active component. Nowadays, the unraveling of tocopherols biosynthesis and its key points of regulation is in progress. New tocopherol profiles have been recently obtained. Higher protective effects are attributed to γ- or δ-tocopherols. They could increase the stability of oils or margarines. Genetic progress for total content is possible, as in sunflower like in other oilseed crops, heritability is rather high (> 0.7). Sunflower oil also contains twice as much phystosterols as olive oil (3 vs 1,5%), and mainly β-sitosterol. Major mutations of this pathway can induce penalizing phenotypic modifications: 1) campesterol is the precursor of plant hormones brassinosteroids, and 2) stigmasterol/campesterol ratio is also implied in plant growth regulation. However, hybrids can significantly differ in their total content. Either for fatty acids or minor components, breeding programs for new profiles, or higher contents, need high throughout oil extraction and analysis. Chemometric analysis offer interesting solutions despite their need of large sets of reference analysis.
Highlights
Le tournesol est essentiellement cultivé pour son huile, bien qu’une petite partie des graines soit directement consommée en alimentation humaine ou animale
Parallèlement, la méthylation finale qui donne les formes α et β- tocophérols pourrait être catalysée par là même tocophérol méthyl transférase (VTE4) (Hofius et Sonnewald, 2003 ; DellaPenna et Pogson, 2006)
L’élucidation du déterminisme de cette mutation en montre aussi les faiblesses, les mécanismes de silencing sont souvent instables et répondent de manière très variable au fond génétique dans lequel ils sont introduits
Summary
Les acides gras sont stockés sous la forme de triacyglycérols (TAG) : leur synthèse est donc liée à celle du glycérol-3-phosphate (G3P) qui constitue une des étapes limitantes de leur accumulation. Les carbones sont ainsi ajoutés deux par deux, sous la forme de groupe acétyle, pour obtenir un complexe palmitoyl (C16:0)-ACP ou stéaroyl (C18:0)ACP. La lysophosphatidic acid acyl transferase (LPAAT) a une plus grande affinité pour les chaînes insaturées, c’est donc l’acide oléique qui prend cette position. Au niveau de la membrane du réticulum, l’acide oléique placé en sn-2 sur une PC peut subir une nouvelle désaturation par une enzyme membranaire, la FAD2, qui génère un oméga-6 linoléoyl-PC (C18:2). Les acyl-CoA libres dans le réticulum endoplasmique peuvent être allongés pour former des acides gras à très longue chaîne (plus de 18 carbones).
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