In the present study we aimed to observe the effects of different doses of colchicine during optimizing the appropriate time and dose on poly-ploid sunflower production. When the sunflower seeds germinated and cotiledonary leaves opened, cotton balls soaked in aqueous solutions of 0.2%, 0.4% and 0.6% colchicine were applied to apical shoots for 12 h in three sets for each concentration. The process was repeated three consecutive days. Morphological, anatomical and photosynthetic pig-ment analyses were performed. According to the results shoot length, stoma number, stoma size, total chlorophyll, chlorophyll a, b and carotenoid contents were decreased. In higher concentrations of 0.4% and 0.6% the reduction was more sensitive. Additionally, SEM results revealed some defects in pollen morphology. Although no pollen was produced in 0.6% colchicine treatment, the pollen grains were tied to each other forming a mass by exine wall bridges in 0.4% colchicine treatment. However these defects were rare in 0.2% colchicine. Our results demonstrated that 0.4% and 0.6% colchicine application for a duration of 12 h induced toxic effects on growth and development of sunflower seedlings.