GENE ACTIVATION IN SUSPENSION-CULTURED CELLS OF ARABIDOPSIS-THALIANA DURING BLUE-LIGHT-DEPENDENT PLANTLET REGENERATION

In cell-suspension cultures of Arabidopsis thaliana (L.) Heynh., trans fer to auxin-free medium initiates regeneration leading to the formati on of numerous rootlets around day 5. This process is promoted by cont inuous irradiation of the cell cultures with blue light (400-500 nm) w hile red light (600-700 nm) is ineffective in this respect. During the course of this process, two mRNA species, encoding, respectively, cha lcone synthase and a plasmalemma channel protein, transiently accumula te. A second temporary increase in the steady-state level of these mRN As is correlated with the onset of chloroplast development after 13-17 d of blue-light exposure of the cell cultures. During this cellular d ifferentiation process a number of mRNAs start to accumulate which spe cify prominent plastid proteins: the small and the large subunits of r ibulose-1,5-bisphosphate carboxylase/oxygenase (SSU and LSU), respecti vely the light-harvesting chlorophyll-a/b protein II (LHCPII). These f indings are in accordance with those obtained with carrot suspension c ultures where a clear sequence of development, i.e. the formation of s omatic embryos followed by blue-light-dependent chloroplast differenti ation, has also been observed.