Callus of the tumor hybrid of Nicotiana glauca × N. langsdorffii grew better on agar in flasks than on liquid medium in flasks or on agar medium in Petri dishes. Asymmetric callus without roots produced small leaves and parenchyma cells were the most common type of cell. Few meristematic clusters were present, but these were very active during exponential and deceleration growth phases. The volume of their nucleoli, which were large and stained intensely, was used as a marker of the cell cycle. Shortly after transplantation the tissue divided synchronously, but thereafter it became asynchronous. An investigation of nucleic acids and polyamines showed that subcultures initiated a rapid synthesis and accumulation of DNA; thereafter the levels of tRNA and rRNA increased, especially in the deceleration phase, the amount of tRNA always being higher than rRNA. The polyamines putrescine and spermidine are always in larger amounts than in the normal tissue, and spermine could be detected in trace amounts. Their metabolism is correlated with arginine levels, the most important precursor of putrescine. Polyamine levels increased several fold during the deceleration phase, their increase being positively correlated with increased levels of nucleic acids, mainly during the very beginning of the subculture and, then during the deceleration phase.
Tobacco mild green mosaic virus found naturally infecting Nicotiana glauca in Brazil
