Asexual embryogenesis and plant regeneration in Quercus

Red oaks (Quercus rubra L.) were regenerated via direct and indirect asexual embryogenesis from immature zygotic embryo tissues. Late heart and early cotyledonary explants cultured in light on modified MS medium proved to be most embryogenic. Embryoids arose from explants cultured on various combinations of 2,4-D and BA. However, the highest percentages of normal polar embryoids were produced by explants cultured on growth-regulator-free media. Epicotyl dormancy of embryoids was overcome by desiccation (air drying and use of an osmoticum) and rehydration treatments. Asexual plantlet development paralleled developmental changes associated with seed germination. White oak (Quercus alba L.) embryoids were also regenerated, but failed to germinate.     

Establishment and characterization of American elm cell suspension cultures

Cell suspension cultures of Dutch elm disease (DED)-tolerant and DED-susceptible American elms clones have been established and characterized as prerequisites for contrasts of cellular responses to pathogen-derived elicitors. Characteristics of cultured elm cell growth were monitored by A₇₀₀ and media conductivity. Combined cell growth data for all experiments within a genotype showed relatively low variances and between-genotype contrasts during repeated passages showed no significant differences. Subculturing exponentially growing cells at 8–14 day intervals, within readily measured parameters of media conductivity (4.95–4.2 mmhos) and cell concentration (≥ 1.4 A₇₀₀), consistently resulted in repeatable profiles of elm cell growth and minimized lag phase. Culture cells were essentially homogeneous after 5 subculture passages and their overall appearance was stable. We conclude that the described procedure resulted in consistent cultures suitable for elicitor treatment experiments. This revised version was published online in June 2006 with corrections to the Cover Date.