STRUCTURE OF COLUMELLA CELLS IN PRIMARY AND LATERAL ROOTS OF HELIANTHUS ANNUVS (COMPOSITAE)

Primary and lateral roots of sunflower (Helianthus annuus) were fixed in situ and the ultrastructures of their columella cells determined using stereology. The relative volumes of cellular components and the distribution of organelles in columella cells of primary and lateral roots were not significantly different. All organelles were distributed asymmetrically in columella cells of both types of roots. Nuclei tended to be located in the upper third of the cells, while vacuoles tended to be located in the middle third. Amyloplasts, dictyosomes and mitochondria were most frequent in the lower third of columella cells in both types of roots. These results suggest that the differential responses to gravity of primary and lateral roots of H. annuus are probably due to factors other than the ultrastructures of their columella cells.