Differentiation of embryogenic pollen in cold-treated buds ofNicotiana tabacum var. Badischer burley and nutritional requirements of the isolated pollen to form embryos

Summary Embryogenic pollen were selectively isolated from buds after cold treatment at 10 °C for 10 days; it was immaterial whether the buds were taken from short day and low temperature (SD and LT; 8 hours light, 18 °C) or long day and high temperature (LD and HT; 16 hours light, 24 °C) plants. However, in buds from SD and LT plants the differentiation of embryogenic pollen could be detected as early as 7 days after the cold treatment, and pollen from these plants formed embryos at higher frequency (up to 4% of cultured pollen) than those from LD and HT plants (up to 1% only).The embryogenic pollen, in isolated buds, differentiated by way of pollen dimorphism. During cold treatment a fraction of pollen remained small, retained clear cytoplasm and was capable of embryogenesis in comparison to gametophytic pollen which enlarged and acquired granular cytoplasm. In our experiments cold treatment was a key factor in the induction of pollen dimorphism. This aspect of cold treatment in pollen embryogenesis is reported for the first time and was possible on the basis of selection of embryogenic pollen by density gradient centrifugation. The ratio of embryogenic pollen was about one fifth of the total population.The nutritional requirements of isolated pollen for embryogenesis were rather simple. These pollen formed embryos which readily developed into plantlets on a mineral medium supplemented with sucrose provided the pH was 6.8.