Teneur en ribulose-1,5-biphosphate carboxylase/oxygenase des feuilles de luzerne (Medicago sativa L.). Facteurs de variation genetiques et agronomiques

The content of ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) has been determined in leaves on the main stem of plants at the late budding stage by an immunochemical method. Starting from the stem top, the content of rubisco increases up to the leaf where the 1st inflorescence at the late budding stage is located (0 level) and then decreases towards the oldest part of the main stem (table I). Rubisco content of the 0 level leaf has been determined at the cutting (late budding) stages in 11 populations of alfalfa (table II, fig 1). Rubisco content varies much more than dry matter or nitrogen, and varies more between cutting stages than between populations (table III). Rubisco content does not seem to be correlated with dry matter or nitrogen content of the 0 level leaf (table IV), but ranges between 5 and 15% of the dry weight, depending on the population and on the cutting stage. The content of rubisco clearly increases from the first to the second cutting stage and remains nearly constant from the second to the fourth cutting stage in mediterranean type populations. With Flemish type populations, a maximum content is noted at the 2nd or 3rd cutting stage (fig 1). There is no simple correlation between these trends and the variations in climatic data (temperature, period of sunshine or radiation energy). Insofar as these results can be extended from a single leaf to the whole crop, they should have general consequences on the structure of plant nitrogen and on the way alfalfa is used for animal feeding, for dehydration or leaf protein extraction.

On a déterminé, par des dosages immunochimiques, la teneur en ribulose-1,5-bisphosphate carboxylase/oxygénase (rubisco) de feuilles situées sur la tige principale de plantes ayant atteint le stade «liseré violet». En partant du haut de la tige, cette teneur augmente jusqu’à la feuille à l’aisselle de laquelle est située la première inflorescence au stade «liseré violet» (rang 0) puis décroît régulièrement jusque vers la base de la tige. La teneur en rubisco de la feuille de rang 0 a été déterminée, aux époques de récolte, sur 11 génotypes. Elle ne semble pas corrélée aux teneurs en matière sèche ou en azote de cette feuille mais varie entre 5 et 15% de la teneur en matière sèche selon le cycle de récolte et le génotype. La teneur en rubisco augmente nettement entre le 1er et le 2e cycle puis reste sensiblement constante du 2e au 4e pour les types méditerranéens. Dans le cas des types flamands, on observe une teneur maximale marquée au 2e ou au 3e cycle.