CITRUS LIMON SEEDLINGS WITHOUT FUNCTIONAL CHLOROPLASTS ARE UNABLE TO INDUCE PHENYLALANINE AMMONIA-LYASE IN RESPONSE TO INOCULATION WITH ALTERNARIA-ALTERNATA

A light-dependent bleaching of plastids was induced in lemon seedlings through cultivation in the presence of the herbicide Norfluorazon (NF Z). Also, etiolated seedlings were obtained by cultivation under conti nuous dark conditions. When both types of seedlings were challenged wi th Alternaria alternata conidia, they were unable to induce phenylalan ine ammonia-lyase, PAL (E.C. 4.3.1.5.). Cell ultrastructure of control seedlings showed the presence of chloroplasts, while NFZ-treated lemo n seedlings showed altered chloroplasts and in etiolated seedlings onl y proplastids were observed. In addition, CO2 assimilation was not det ected in NFZ-treated and etiolated seedlings, as compared to controls.