Enhancing effects of simulated microgravity on Agrobacterium-infected frequency of tobacco callus.

Under the condition of rotation-induced gravity compensation, the time course of interaction between Agrobacteriun tumefaciens and tobacco callus was investigated by means of a scanning electronic microscope. Resulted from repeated experiments, it was found that callus induced from tobacco leaves under simulated microgravity was easier to be infected by A. tumefaciens than controls. Analyses with a scanning electronic microscope indicated that A. tumefaciens were instantly detected on the surface of cell in the first 5 min, that is, A. tumefaciens are liable to interrecognize with callus cell upon contact with each other. With the proceeding of co-culture, the infection efficiency of A. tumefaciens was correspondingly increased. When the time reached 6 h, the fiber was formed between A. tumefaciens and callus cell. In our experiment, the erecting rotating state was taken as the control to exclude the interference of rotating. In this case, A. tumefaciens did not adsorb on calli until 3 h of co-culture, and fiber was only observed as late as 16 h. Statistic data showed that A. tumefaciens-infected frequency of the callus under the action of microgravity was elevated to 176% over that of control.