Improved Agrobacterium-mediated transformation of sunflower (Helianthus annuus L.): assessment of macerating enzymes and sonication.

Agrobacterium -mediated transformation of shoot apices of sunflower (Helianthus annuus L.) was evaluated following wounding by cell-wall-digesting enzymes and sonication. The frequency of explants with regenerated shoots expressing GUS (beta-glucuronidase) or GFP (green fluorescent protein) increased following treatment with the macerating enzymes cellulase Onozuka R-10 and pectinase Boerozym M5, whereas treatment with macerozyme R-10 had a negative effect. When a combination of cellulase (0.1%) and pectinase (0.05%) was used, the rate of explants with uniformly GUS-positive shoots increased at least twofold. The transient expression of reporter genes was also enhanced using sonication (50 MHz; 2, 4 and 6 s), but stable expression in regenerated shoots following 4 weeks of selection did not increase with this treatment. Enzyme treatment alone (0.1% cellulase and 0.05% pectinase) was superior to a combined treatment of sonication and enzymes with respect to stable transformation. Polymerase chain reaction analyses of shoots recovered by grafting from transformation experiments using GFP as the reporter gene demonstrated the stable integration of the transgene. Regenerated plants were fertile and seeds could be harvested.