Studies on the Changes in the Volume and Proliferation Rate of Cells during Embryogenesis of in vitro cultured Pollen Grains of Nicotiana tabacum L.

Abstract

Summary The rate of increase in cell number and the changes in cell volume during the embryogenesis of Nicotiana pollen grains cultured in vitro were studied. At the initial stage of the pollen culture, the embryogenic pollen grains consisted on the average of 4.3 cells per grain, the mean diameter of which was 36.6 ,um. After three days of culture the average cell number per grain increased five-fold with little change in grain size indicating a rapid decrease in individual cell volume. During the early globular-embryo stage (45-90 ,um in diameter) the increase in both cell volume and cell number per embryo was observed, but during the late globular-embryo stage (90-120 um in diameter), individual cell volume decreased again. The average times required for cell doubling in the initial stage of embryogenesis and in the early and late globular-embryo stages were 31.3, 32.4, and 18.1 hr respectively. Continuous observations revealed that the polarity of future embryos was determined by the site where the exine burst open.