No abstract

We investigated the effect of the physical state of the nutrient medium on the induction of somatic embryogenesis on cell cultures derived from coffee (Coffea arabica L.). Non-embryogenic callus tissues were pulsed initially with 50 lM 6-benzyladenine (BA) for 6, 24 or 48 h in half-strength liquid Murashige and Skoog (MS) medium. After pretreatment, calli were transferred to agar-solidified halfstrength MS medium supplemented with 50 lM BA ('standard induction medium'). Control callus tissues were incubated directly on the solid standard induction medium. Callus growth was promoted by longer pretreatment periods. Formation of globular somatic embryos was observed on callus tissues pretreated with BA for 24 or 48 h, which developed fully to cotyledonary-stage within only 2 weeks after transfer to agar-solidified medium supplemented with BA. No embryo formation occurred in control cultures. Pretreatment with BA in liquid medium was associated with changes in the redox status of cultured cells, such as alterations of the ascorbate-glutathione redox systems and the accumulation of free radicals and oxidized lipids, as well as the possible reduction of cytochrome c-mediated apoptotic pathways. In particular, the induction of somatic embryogenesis was highly positively correlated (r 2 = 0.822) with the accumulation of protein carbonyls. The physiological role of BA as an inducer of both embryonic differentiation and cellular death is discussed.

We investigated a possible relationship between the levels of reactive oxygen species (ROS) and the stimulation of frond division of the aquatic plant Spirodela polyrrhiza (duckweed) during a 7-day experimental culture period. In particular, we monitored superoxide concentration using a state-of-the-art cell biosensor. A considerable reduction in ROS and superoxide concentration was observed during the first 2 days of culture, whereas duckweed cultures achieved near exponential growth rates after the second day. In addition, apoptotic markers such as the cytoplasmic concentration of cytochrome c, mitochondrial membrane depolarization and the activity of caspase-3 declined during the culture period and at least before daughter frond maturation. We suggest that S. polyrrhiza frond division may have been stimulated by the observed reduction of free radicals and the associated avoidance of cell apoptotic pathways in cultured plants.