Geoperception in primary and lateral roots of Phaseolus vulgaris (Fabaceae). II. Intracellular distribution of organelles in columella cells

A morphometric analysis of the ultrastructures of columella cells in primary and lateral roots of Phaseolus vulgaris was performed to determine the precise location of cellular components in these cells. Roots were fixed in situ to preserve the in vivo ultrastructure of the cells. All cellular components in columella cells of both types of roots were distributed asymmetrically. The nucleus and vacuome were located primarily in the middle third of both types of columella cells. Dictyosomes, mitochondria, and amyloplasts were most abundant in the lower third of the columella cells in both types of roots. The distribution of amyloplasts was the most asymmetrical of all cellular components examined, with the lower third of the columella cells containing approximately 90% of the relative volume of amyloplasts in both types of roots. The distribution of cellular components in columella cells of primary roots was not significantly different from that of columella cells of lateral roots. These results indicate that differences in georesponsiveness of primary and lateral roots of P. vulgaris are probably due to factors other than the ultrastructures of their individual columella cells.