Morphological characteristics and function of hilum in safflower seed germination

This research was carried out to clarify the germination characteristics with reference to hard seed coat in safflower. Morphologically, seed coat surface has hilum and micropyle which were evident during seed development stage. In the flower of developing seeds, the hilum area is connected with placenta of maternal tissue while the micropyle area is connected with the style of pistil. When the seeds imbibed, the hilum surface began to crack and the embryo protrudes through the hilum. To investigate the route for moisture absorption and gas exchange on the seed coat, the hilum and the micropyle were artificially sealed by paraffin. The seeds whose hilum were sealed could not germinate, which indicates that the exchange of moisture and oxygen takes place through hilum in safflower seeds. The germination was tested at 15°C, 20°C, and 25°C by three substrates with different moisture conditions; top of paper method (hilum submerged in water), between-paper method, and soil seeding. The germination percentages were 31.3% at 15°C, 15.7% at 20°C and 6.0% at 25°C in the top of paper method; and 45.5% at 15°C, 30.0% at 20°C and 14.0% at 25°C in the between-paper method; and 80.0% at 15°C, 77.0% at 20°C and 78.0% at 25°C in the soil seeding, respectively. When the internal structure of hilum was investigated through SEM, it was found out consisting of vascular bundle element. In conclusion, the hilum of safflower seed was closely related with water absorption and gas exchange during initial germination process.