Tocopherol biosynthesis is enhanced in photomixotrophic sunflower cell cultures.

Two heterotrophic cell lines of sunflower (Helianthus annuus L.) of differing a-tocopherol biosynthetic capability, threefold higher in the high synthesizing cell line, HT, than in the low synthesizing one, LT, were previously identified. To investigate the relationship between a-tocopherol biosynthesis and photomixotrophic culture conditions, a new photomixotrophic sunflower cell line HS3 was established by selecting HT cells able to grow in the presence of a ten-fold reduced sucrose concentration in the culture medium. The photosynthetic properties of HS3 cells were characterized in comparison with HT and LT cells, revealing an increase in chlorophyll content, chloroplast number, and level of the photosynthesis related enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Furthermore, an enhanced expression of the gene encoding for the tocopherol biosynthetic enzyme geranyl-geranylpyrophosphate synthase was observed in HS3 cells. HS3 cells also revealed a 25% and a more than 3-fold higher tocopherol level than HT and LT, respectively, indicating a positive correlation between a-tocopherol biosynthesis of sunflower cell cultures and their photosynthetic properties