Abstract: Cytological and statistical studies on the effects of exogenous Ca2 + on in vitro pollen tube growth and generative nucleus (GN) division of tobacco (Nicotiana tabacum L. ) were conducted in an artificial experimental system. Under normal cultured conditions, the rate of GN division increased logarithmically in general, and reaches the climax at about 10 - 18 h. Among the treatments with various Ca2 + concentrations, 10- 3 mol/L was the optimal concentration for pollen tube growth, whereas other Ca2+ concentrations showed increasing inhibitory effect with the time of culture. Generally, Ca2 + concentrations at 10-2 and 10-3 mol/L favored GN division more than the others. Compared with 10-3 mol/L Ca2 + concentration at 10-2 mol/L benefitiated GN division at earlier stage of the treatment, but afterwards showed inhibitory effect gradually. Besides, the authors designed another series of experiments, in which 10-2, 10-1 mol/L Ca2+ (final concentrations) or 2,10 mmol/L EG-TA was respectively added to the medium containing 10-3 mol/L Ca2+ at 10 h of culture. Pollen tube growth was inhibited by the high Ca2+ treatments, especially being severely effected by 10-l mol/L Ca2 + from which wall, thickening of the tube tip, amitotic division of GN leading to micronucleus formation occurred. 10-2 mol/L Ca2 + treatment, however, promoted GN division at the earlier stage of treatment ( 10 - 12 h). EGTA treatments inhibited both pollen tube growth and GN division.

Key words: Nicotiana tabacum, Pollen tube growth, Generative nucleus division, Exogenous calcium ion