The effect of culture temperature on the morphogenetic response of Arachis hypogaea was studied. Cotyledons were cultivated on MS medium supplemented with 110 pM 6-benzyladenine. Leaf explants were cultivated in the presence of the same growth regulator at 22 ~tM. Cuhures were incubated at temperatures of 25, 28, and 35 + 5 ° C. Both direct organogenesis from cotyledons and development of organogenic calluses from leaves showed optimal rates at 35 + 5 ° C. The highest frequency of elongation of buds into shoots from leaf-derived calluses occurred in the presence of 5 ~M AgNO~. At the best culture temperature, an average of 95% of shoots formed roots on growth-regulator-free MS medium. Plants were successfully transferred to soil, showing normal phenotypes.

Direct gene transfer into peanut intact embryonic leaflets was performed through electroporation. In transient bglucuronidase expression assays, maximal expression was obtained by using pulses of 625 V cm 21 in EPRm (modified electroporation) buffer supplemented with 75 mM NaCl. Kanamycin-resistant plants were obtained, and the presence of the nptII gene was demonstrated by PCR analysis. The positive effect of electroporation on the efficiency of in vitro regeneration was demonstrated. Explants submitted to field strengths between 500 and 625 V cm 21 displayed a significantly increased number of shoots and originated faster growing calluses relative to control explants. Whereas in control explants callus formation occurred only at the petiolule, electroporated leaflets developed additional organogenic calluses on the foliar lamina.