Expression of Chalcone Synthase Genes in Coleoptiles and Primary Leaves of Secale cereale L. after Induction by UV Radiation: Evidence for a UV‐Protective Role of the Coleoptile*

Four chalcone synthase (CHS; EC 2.3.1.74) clones from rye were isolated and characterized. Two of these clones were used for analysis of CHS gene activities in response to ultraviolet and visible radiation in the coleoptile and the primary leaf of the rye seedling. The time‐dependence of CHS gene activation and the spatial distribution of CHS were studied by investigation of enzyme activities and CHS mRNA levels, including in situ RNA hybridization. In the primary leaf strong induction of CHS gene activity was localized in the epidermal layers and only marginally found in the mesophyll. The coleoptile showed an even higher response to UV irradiation, but CHS gene activity was evenly distributed throughout the tissues. It is suggested that, in addition to its function as a mechanical protection for the primary leaf during seed germination and seedling emergence through the soil, the coleoptile may also protect the emerging seedling from harmful radiation.