Carbohydrate metabolism in rice during callus induction and shoot regeneration induced by osmotic stress

We are interested in the cellular physiological events taking place during shoot regeneration in rice (Oryza sativa L. cv. Tainan 5) callus induced by osmotic stress. At first, the sucrose and starch metabolisms in rice callus were studied because carbohydrates are the main energy source in plant tissue culture. The results showed that fresh weight, water content, cellular water, and osmotic potentials all decreased significantly in highly regenerable callus which was induced on MS basal medium supplemented with 10 μM 2,4-D and 0.6 M mannitol (TN5-M 6 ). Besides, the starch and soluble sugar contents in TN5-M 6 callus were higher than in un-regenerable callus, induced on the same medium without mannitol. Then, a sudden increase of glucose content was found in TN5-M 6 the first day after the callus was transferred to regeneration medium. Simultaneously, the activities of sucrolytic enzymes, sucrose synthase, and acid invertase were higher, and they may have responded to the increase of glucose content. It is suggested that the sudden increase of glucose content may play an important role in shoot regeneration.