EVIDENCE THAT THE ROLE OF PLANT DEFENSINS IN RADISH DEFENSE RESPONSESIS INDEPENDENT OF SALICYLIC-ACID

Radish leaves contain two homologous 5-kDa plant defensins which accum ulate systemically upon infection by fungal pathogens (F.R.G. Terras e t al., 1995, Plant Cell 7: 573-588). Here we report on the molecular c loning of the cDNAs encoding the two pathogen-inducible plant defensin isoforms from radish (Raphanus sativus L.) leaves. Tissue-print and w hole-leaf electroblot immunostaining showed that the plant defensin pe ptides not only accumulate at high levels at or immediately around the infection sites in leaves inoculated with Alternaria brassicicola, bu t also accumulate in healthy tissue further away from the infection si tes and in non-infected leaves from infected plants. Gel blot analysis of RNA confirmed that expression of plant defensin genes is systemica lly triggered upon fungal infection whereas radish PR-I gene expressio n is only activated locally. In contrast to the radish PR-I gene(s), e xpression of the radish plant defensin genes was not induced by extern al application of salicylic acid. Activation of the plant defensin gen es, but not that of PR-I genes, occurred upon treatment with methyl ja smonate, ethylene and paraquat.