ENDOGENOUS PHYTOHORMONES OF ETIOLATED CORN SEEDLINGS

Solid-phase immunoenzymatic analysis and biological test procedure hav e been used to determine the content of free and bound IAA, zeatin + z eatin riboside, ABA, and gibberellins (in GA3 equivalents) in 13 organ s and growth zones of 4-day etiolated corn seedlings. The greatest con tent of free IAA and ABA is in the distal part of the primary root and in the coleoptile tip. The remainder of the root houses the greatest content of zeatin + zeatin riboside and GA. The content of GA is one o r two orders of magnitude lower than levels of the other phytohormones . Bound phytohormones in most cases are present in tissues in concentr ations close to those of free forms. Each organ and zone is characteri zed by a definite content and ratio of phytohormones, which enables th e theory of positional information to be used to explain the behavior of cells and tissues in these organs and zones. To be specific, tissue s with high meristematic activity (root tip, leaf intercalary meristem , coleoptile node) are characterized by a high ratio of cytokinins to IAA (> 1).