LAUSR

De-etiolation of plant seedlings is controlled by a complex system of light and hormonal signaling. This process is accompanied by chloroplast development and initiation of chlorophyll biosynthesis leading to cotyledon greening. In this study, peculiaritis of regulation of expression of the key genes encoding enzymes of chlorophyll biosynthesis in wild type plants and mutants of perception and transduction of blue light in Arabidopsis thaliana (L.) Heynh. during cytokinin (CK)-dependent greening of seedlings were investigated. Inactivation of blue-light signaling components (СRY1, CRY2 and HY5) led to retarded chlorophyll accumulation and decrease of the expression of the key genes responsible for its biosynthesis. Exogenous application of cytokinin accelerated de-etiolation of wild type and knockout-mutants cry1cry2 and hy5 seedlings that was manifested itself in elevating chlorophyll a fluorescence and higher level of transcripts of a number of genes involved in chlorophyll biosynthesis. Taken together the results may provide evidence for the significant contribution of blue-light signaling to the greening regulation at early steps of de-etiolation of seedlings and involvement of HY5 protein in realization of the positive effect of CK at early steps of photomorphogenesis.