Influence of callus irradiation with 60Co γ-rays on the cell ultrastructure of wheat

The calli of immature embryo derived from wheat were irradiated with 60Co γ-rays of different dosage and were fixed at different time after irradiation. The cell ultrastructure observed with electron microscope indicated that the non-irradiated calli had normal cell ultrastructure while the cell of calli irradiated with 500 R γ-rays suffered slight damages in three days after irradiation and repairing activities, including the increase of mitochondrion, the completion of crista structure and the development of endoplasmic reticulum were seen. On the 12th day after irradiation, the cell ultrastructure returned to normal state. When calli irradiated with 5000 R γ-rays, the cell ultrastructure were damaged seriously and became unclear, cell organs disintegrated, which finally leading to cell death. Considering the calli growth situation and the frequency of chromosomal variation in regenerated plants after irradiation, we suggest that 500 to 1000 R γ-rays be appropriate doses for callus irradiation in wheat