In eggplant (Solanum melongena L., cv, Pusa Purple Long), explants from different regions of the leaf showed significant differences for embryogenic potential, Discs from the apical region of leaves yielded more somatic embryos than those from the basal region, Apical discs showed consistently higher polyamine titres than the basal discs, Putrescine treatment promoted somatic embryogenesis and at 0.5 mM it caused a remarkable increase (c. 6-fold) in a number of somatic embryos, accompanied by an increased putrescine titre, On the other hand, spermidine and spermine had no stimulatory effect on embryogenesis; rather they were inhibitory at higher concentrations. All tested inhibitors of polyamine biosynthesis such as difluoromethylarginine, difluoromethylornithine, methylglyoxal bis (guanylhydrazone) and bis (cyclohexylammonium) sulphate significantly inhibited somatic embryogenesis, Difluoromethylarginine blocked somatic embryogenesis by lowering endogenous polyamine contents (particularly putrescine) and such inhibitory effects were totally restored by exogenous putrescine (0.5 mM), concomitant with the revival of endogenous PA concentrations. These results demonstrate (i) a positive correlation between the spatial distribution of free and conjugated polyamines and the embryogenic capacity of an explant and (ii) putrescine caused the promotion of somatic embryogenesis, suggesting the intricate regulatory role of polyamines, specifically putrescine, in somatic embryogenesis in eggplant.
