A new culture method for the injection of tobacco mesophyll protoplasts has been established. The protoplasts are embedded in a thin layer of alginate and are nourished from the medium in the underlying basis layer. In the alginate layer the protoplasts regenerate to calli at a frequency of up to 80%. Embedded protoplasts can be selected either with 50 mg l-1 kanamycin or 5 mg l-1 paromomycin. Single resistant cells can be recovered from about 10,000 sensitive cells in one alginate layer. Injection of the neo gene (coding for neomycin phosphotransferase II) into protoplast derived single cells in the alginate layer results in kanamycin resistant colonies that can be regenerated to mature plants. These plants express the neomycin phosphotransferase as shown by enzyme activity assay. The integration of the transgene into the plant genome could be proved by Southern hybridization to high molecular weight DNA. With this culture method 100 cells can be injected per hour. Transformation frequencies range from 2 to 20%. In crossing experiments, it was shown that the foreign gene is transmitted to the next generation in a Mendelian fashion.

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A flexible, comparatively inexpensive system based on a liquid nitrogen‐cooled slow‐scan CCD (charge coupled device) camera is presented, which can be employed for quantitative low‐light (bioluminescence, chemiluminescence or fluorescence) imaging. Using this camera system and the firefly luciferase (LUC) as a screenable marker, transgenic tobacco lines have been produced by direct gene transfer. Bioluminescence emitted from single tobacco cells transiently expressing the firefly luciferase gene (Luc) as well as from stably transformed calli, regenerated shoots, plantlets and T1 seedlings could be monitored in vivo with no effect on the viability of the material analysed. The patterns of light emission from sections through Luc‐expressing leaves and bioluminescent single protoplasts isolated from such leaves were also imaged microscopically. The assay used to detect in vivo LUC activity was optimized by quantifying bioluminescence emitted from Luc‐expressing tobacco protoplasts and leaves incubated in different substrate solutions and determining the kinetics of light emission during incubation in the substrate solution.

Barley zygote protoplasts were mechanically isolated, embedded in agarose droplets, and microinjected with a rice actin promoter Act1-gusA-nos gene construct. On average 62% of the cells survived the injection and of these 55% continued development into embryo-like structures and eventually to plants. PCR screening for the presence of a 307-bp fragment in the middle of the gusA gene showed that on average 21% of the derived structures contained this fragment. However, among the hundreds of injected zygotes, derived structures and regenerants we only found significant GUS expression in two cases (embryo-like structures nine days after injection). Two lines of green plants, derived from zygotes microinjected with linearized plasmid (line A147-1) or an isolated Act1-gusA-nos gene cassette (line A166-h) proved to be transgenic. Line A147-1 appeared to contain a single and intact copy of the expression cassette but a PCR based progeny analysis indicated the presence of additional shorter fragments of the cassette. Line A166-h appeared to contain a single fragment of the gusA gene that was transferred to the progeny as a single Mendelian trait. One additional fragment of the gusA gene was identified in this line. The present data show that transformation of barley by microinjection of DNA into isolated zygotes is feasible but also that gene expression rarely is achieved, possibly due to degradation of the introduced DNA.

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