Ultrastructural Organization of Leaves of Transgenic Tobacco Overexpressing Histone H1 from Arabidopsis thaliana

We investigated the anatomical and ultrastructural featuresof transgenic tobacco plants that overexpressed a gene of histoneH1 from Arabidopsis thaliana. The overexpression of the heterologousgene resulted in more than a 2.5-fold increase over the physiologicallevel of the histone H1:DNA ratio in chromatin. H1-overexpressingplants had a distinct mutant phenotype characterized by dwarfappearance and severely hampered flowering. These changes wereaccompanied by extensive and unusual heterochromatinizationof nuclei occurring in all leaf parenchymal cells but not inleaf epidermal cells. The observed anomalies in the growth rateand size of the cells and in nuclei/chloroplast proportionsin histone H1-overexpressing plants suggest that the H1:DNAratio can influence some specialized cellular functions involvingthe cytoskeleton, and nuclear/organellar interactions whichare of importance for the normal development of a plant. Copyright1999 Annals of Botany Company Transgenic tobacco plant, histone H1 overexpression, heterochromatinization.