A Morphometric Analysis of the Ultrastructure of Columella Statocytes in Primary Roots of Zea mays L.

A morphometric analysis of the ultrastructure of columella statocytesin primary roots of Zea mays was performed to determine theprecise location of cellular organelles in graviperceptive cells.Vacuoles occupy the largest volume in the cell (11.4 per centof the protoplasm). The nucleus (9.51 per cent), amyloplasts(7.57 per cent), mitochondria (3.42 per cent), spherosomes (2.13per cent) and dictyosomes (0.55 per cent) occupy progressivelysmaller volumes of the statocytes. All organelles are distributedasymmetrically within the cell. Amyloplasts, spherosomes anddictyosomes are found in greatest numbers (and relative volumes)in the lower (i.e. ‘bottom’) third of the cell.The largest numbers and relative volumes of mitochondria arein the lower and middle thirds of the cell. Nuclei tend to befound in the middle third of the statocytes. Only the hyaloplasmis concentrated in the upper (i.e. ‘top’) thirdof Z. mays statocytes. When the sedimentation of amyloplasts(and the resulting exclusion of other organelles from the lowerthird of the cell) is corrected for, all cellular constituentsremain asymmetrically distributed within the cell. Therefore,the sedimentation of amyloplasts alone is not responsible forthe differential distribution of other cellular organelles inZ. mays statocytes. The quantitative ultrastructure of Z. maysstatocytes is discussed relative to the graviperceptive functionof these cells. Zea mays, corn, maize, root cap, stereology, columella, statocytes, graviperception, ultrastructure