Root Cap Inhibitor Formation in Isolated Root Caps ofZea mays

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Abstract
Root caps were isolated and cultured aseptically on various defined media. Under appropriate culture conditions plus suitable illumination a substance able to produce a positive geotropic response (i.e. a downward bending of roots) was formed in isolated root caps. The presence of this substance, or root cap inhibitor, was assessed by substituting cultured caps in place of caps of dark-grown roots. Normally these roots if kept in continuous darkness will not respond to gravity (i.e. no bending). Optimal root cap inhibitor production occurs on a relatively simple medium, lacking sucrose, but supplemented with 10−9 M IAA. Protein synthesis is necessary for inhibitor production and/or expression, whereas DNA synthesis is not.