The role of N metabolism in organogenesis and growth was studied using tobacco pith callus. Callus was cultured on a solid medium containing 10 μM (1.75 mg/l) IAA and 2 μM (0.43 mg/l) kinetin for 56 days. In the growth experiment, ratios of NH4+-N to NO3--N (0:60, 20:40, 30:30, 40:20 and 60:0 mM) were supplied by (NH4)2 SO4 and KNO3. Callus and media were analyzed for inorganic N. Callus supported by 30:30 and 40:20 media removed the highest amounts of NH4+-N and NO3--N from the media and exhibited organogenesis. Final dry weight was greatest in callus supported by the 30:30 medium. In the organogenesis experiment, the transfer history of the inoculum source affected N uptake, organogenesis and growth. Inorganic N was supplied by NH4NO3 and KNO3-. The net uptake of NH4+-N and NO3--N was lower in shoot-forming than in root-forming and non-organogenic callus subculture from 7-day-old stock cultures. The final pH of the medium supporting shoot-forming callus was lowest. Growth, on a dry weight basis, was lowest in shoot-forming callus. Callus subculture from 60-day-old stock cultures formed no shoots.
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