Characteristics of Citrus cell cultures during undifferentiated growth on sucrose and somatic embryogenesis on galactose

Growth of willow-leaf mandarin (Citrus deliciosa Ten.)nucellar callus cultures without embryo formation was supported on sucrose as the sole carbon source. Somatic embryogenesis was obtained by substituting galactose for sucrose at the same concentration (0.15 M). A histocytological study revealed proliferation of young globular embryos during the first half of the 18-day culture cycle, irrespective of the carbon source. However, during the second half of the cycle, further embryo development failed in cell cultures on sucrose-containing medium. The rate of cell growth and the carbohydrate depletion of the medium were 3-fold higher on sucrose than on galactose-containing medium. Cell suspensions on sucrose differed by an increase in calcium, phosphorus, magnesium and potassium utilization soon after subculturing, followed by a sharp decrease. Finally, the phosphorus utilization rate per g dry weight formed was 2-fold higher in cell cultures on galactose during the second half of the culture cycle, coinciding with further embryo ontogenesis.