Summary
The root apex of barley,Hordeum vulgare cv. Proctor, is a structure which undergoes a number of gross morphological and ultrastructural changes from the normal patterns of development when grown under a small degree of applied mechanical constraint (2 × 104 Pa.). The root cap is generally smaller and thus does not confer to the root meristem the same degree of protection as caps growing in an uncompacted medium. Associated with this loss of peripheral cells is a reduction in the volume of mucigel in contact with the root apex.
In many impeded caps, the planes of division in the calyptrogen are often neither transverse nor longitudinal. There is a reduction in both the number of amyloplasts and starch grains per amyloplast in the columella, but any statolith function of these must not be impaired since the root remains geotropically responsive. The patterns of accumulation of polysaccharide in the walls of peripheral cells as a result of Golgi activity are modified by mechanical impedance.
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Wilson, A.J., Robards, A.W. Some observations of the effects of mechanical impedance upon the ultrastructure of the root caps of barley. Protoplasma 101, 61–72 (1979). https://doi.org/10.1007/BF01293435
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DOI: https://doi.org/10.1007/BF01293435