Direct gene transfer to protoplasts of two genotypes of Asparagus officinalis L. by electroporation.

Callus-derived protoplasts of two genotypes of asparagus (Asparagus officinalis L.) were electroporated to introduce the β-glucuronidase gene (GUS). The level of GUS transient gene expression and the viability of the protoplasts were influenced by the voltage and duration of the electric pulse. The transient expression level was enhanced by increasing the plasmid DNA concentration and by the presence of polyethylene glycol (PEG) in the electroporation medium. A considerable increase in GUS activity was observed in presence of both PEG and upon heat-shock treatments compared to PEG treatment alone. An optimal level of GUS activity was obtained after electroporation with a capacitive discharge of 500 V/cm and 94 ms duration in both genotypes. The two genotypes differed in their responses to in vitro culture and also showed variable levels of transient expression. The present technique was found to be suitable to obtain transgenic plants as the histochemical GUS assay revealed GUS activity in the protoplast-derived micro-colonies as well as in callus tissues.