Calcium in the Root-hair Wall

Abstract

The walls of normal root hairs of white mustard, corn and tomato seedlings developed in moist air following seed treatment with ⁴⁵CaCl₂, were tested by radioautography for incorporated calcium. Radioactivity was absent or faint over the growing tips but became concentrated immediately behind this point. It extended back along the walls of the hairs, increasing in concentration towards the base. Since the hairs were subjected to plasmolysis and prolonged extraction with hot water prior to making the radioautographs, the distribution of radioactivity indicated the presence of bound ⁴⁵Ca. These findings are compatible with the view that gradual calcification is essential for the normal growth and form of the hair. Radioautographs of mustard root hairs produced in an aqueous solution of ⁴⁵CaCl₂ showed conspicuous radioactivity throughout the whole length of the hairs but particularly over the tips. Excessive wall calcification at the tips of these hairs could be the cause of their stunted growth.