Gene activation in suspension-cultured cells of Arabidopsis thaliana during blue-light-dependent plantlet regeneration

In cell-suspension cultures of Arabidopsis thaliana (L.) Heynh., transfer to auxin-free medium initiates regeneration leading to the formation of numerous rootlets around day 5. This process is promoted by continuous irradiation of the cell cultures with blue light (400–500 nm) while red light (600–700 nm) is ineffective in this respect. During the course of this process, two mRNA species, encoding, respectively, chalcone synthase and a plasmalemma channel protein, transiently accumulate. A second temporary increase in the steady-state level of these mRNAs is correlated with the onset of chloroplast development after 13–17 d of blue-light exposure of the cell cultures. During this cellular differentiation process a number of mRNAs start to accumulate which specify prominent plastid proteins: the small and the large subunits of ribulose-1,5-bisphosphate carboxylase/oxygenase (SSU and LSU), respectively the light-harvesting chlorophyll-a/b protein II (LHCPII). These findings are in accordance with those obtained with carrot suspension cultures where a clear sequence of development, i.e. the formation of somatic embryos followed by bluelight-dependent chloroplast differentiation, has also been observed.Abbreviations AthH2 intrinsic membrane protein of Arabidopsis thaliana (gene) - CHS chalcone-synthase - 2,4-D 2,4-dichlorophenoxyacetic acid - EFR energy fluence rate - LHCPII cab light harvesting chlorophyll-a/b protein of photosystem II (gene) - LSU rbcL large subunit of Rubisco - SSU rbcS small subunit of Rubisco - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase Dedicated to Prof. Wolfhart Rüdiger on the occasion of this 60th birthdayThe research was supported by the Deutsche Forschungsgemeinschaft. We thank Mrs. I. Liebscher for her competent assistance. For the generous gift of cloned gene sequences we thank Prof. Dr. G. Link (Pflanzliche Zellphysiologie, Bochum, Germany), Dr. A. Batschauer (Biologisches Institut II/Botanik, Freiburg, Germany) and Dr. B. Weißhaar (MPI für Züchtungsforschung, Köln, Germany).