Ultrastructural organization of leaves of transgenic tobacco overexpressing histone H1 from Arabidopsis thaliana

We investigated the anatomical and ultrastructural features of transgenic t obacco plants that overexpressed a gene of histone H1 from Arabidopsis thal iana. The overexpression of the heterologous gene resulted in more than a 2 .5-fold increase over the physiological level of the histone H1:DNA ratio i n chromatin. H1-overexpressing plants had a distinct mutant phenotype chara cterized by dwarf appearance and severely hampered flowering. These changes were accompanied by extensive and unusual heterochromatinization of nuclei occurring in all leaf parenchymal cells but not in leaf epidermal cells. T he observed anomalies in the growth rate and size of the cells and in nucle i/chloroplast proportions in histone H1-overexpressing plants suggest that the H1:DNA ratio can influence some specialized cellular functions involvin g the cytoskeleton, and nuclear/organellar interactions which are of import ance for the normal development of a plant. (C) 1999 Annals of Botany Compa ny.