EVIDENCE FOR SOME SIGNAL-TRANSDUCTION ELEMENTS INVOLVED IN UV-LIGHT-DEPENDENT RESPONSES IN PARSLEY PROTOPLASTS

The signalling pathways used by UV-light are largely unknown. Using pr otoplasts from a heterotrophic parsley (Petroselinum crispum L.) cell culture that exclusively respond to UV-B light between 300 and 350 nm with a fast induction of genes encoding flavonoid biosynthetic enzymes , information was obtained about the UV-light signal transduction path way for chalcone synthase (CHS) and phenylalanine ammonia-lyase (PAL) gene expression. Pharmacological effecters which influence intracellul ar calcium levels, calmodulin and the activity of serine/threonine kin ases also changed the UV-light-dependent expression of these genes. Th is evaluation indicated the participation of these components on the U V-B-mediated signal transduction cascade to CHS. In contrast, neither membrane-permeable cyclic GMP nor the tyrosine kinase inhibitor genist ein affected CHS or PAL expression. Similar results were obtained in p rotoplasts, which have been transiently transformed with CHS-promoter/ GUS (beta-glucuronidase) reporter fusion constructs. The involvement o f calcium and calmodulin was further indicated in a cell-free light-re sponsive in vitro transcription system from evacuolated parsley protop lasts. In conclusion, there is evidence now that components of the UV- light-dependent pathway leading to the CHS-promoter are different from the previously characterized cGMP-dependent pathway to CHS utilized b y phytochrome in soybean (Glycine max) and tomato seedlings (Lycopersi con esculentum).