Citrus limon seedlings without functional chloroplasts are unable to induce phenylalanine ammonia-lyase in response to inoculation with Alternaria alternata

Summary A light-dependent bleaching of plastids was induced in lemon seedlings through cultivation in the presence of the herbicide Norfluorazon (NFZ). Also, etiolated seedlings were obtained by cultivation under continuous dark conditions. When both types of seedlings were challenged with Alternaria alternata conidia, they were unable to induce phenylalanine ammonia-lyase, PAL (E.C. 4.3.1.5.)- Cell ultrastructure of control seedlings showed the presence of chloroplasts, while NFZ-treated lemon seedlings showed altered chloroplasts and in etiolated seedlings only proplastids were observed. In addition, CO 2 assimilation was not detected in NFZ-treated and etiolated seedlings, as compared to controls.