Partial Production of A Normal Morphological Phenocopy in the Zea Mays L. Mutant, Ramosa-1

ZEA MAYS L. Mutant plants carrying the ramosa-1 (ra-1) gene which effects inflorescence development, were treated with aqueous solutions of several growth substances. Some plants treated with TIBA exhibited tassels with a reduced ra-1 phenotype. Several plants treated with GA produced ears showing little branching. Discussion is centered on evidence which supports the idea that hormone metabolism is part of a genetic control system governing maize inflorescence development at various stages in the pathway. Although the development of numerous flowers and inflorescences have been described in considerable morphological detail, very little information is currently available concerning the biochemical and physiological aspects of the growth and differentiation of floral organs. To fully understand the morphogenesis of floral development we must be concerned with the relationships between form, metabolism and hereditary information. Apical meristems are generally in a sustained embryonic condition. Morphogenesis continues in an active shoot apex thus providing an excellent experimental system for the study of plant development. A special problem which has attracted a number of investigators is the transformation of a vegetative shoot apex into a reproductive shoot apex. Through various experimental techniques, many of which disturb the normal metabolic activities of apical meristems-for example, by surgical operations (Snow and Snow, 1947; Wardlaw, 1959, 1963; Ball, 1960, 1963) by x-ray treatments (Stein and Steffensen, 1959) by tissue culture (Petru and Retovsky, 1957); and by application of natural and synthetic growth substances (Phinney, 1956, 1961 ; Nickerson, 1960; Anderson, 1963) results indicate that many cells in an embryonic condition can be deflected from their normal destiny. Another useful technique has been to substitute a mutant allele for its normal counterpart. Suitability of mutant genes for experimental studies of development was aptly explained by Phinney and West ( 1960). Experimental alteration, by gene substitution, of events leading to normal development of Zea mays L. inflorescence has led to the idea that an indispensable relay system of gene action must occur at specific stages in maize inflorescence development (See Postlethwait and Nelson's Fig. 1, 1964). A similar hypothesis was also proposed by Heslop-Harrison ( 1961) on the basis of studies involving inflorescence development of Zea mays. 1 Univ. of Northern Iowa, Cedar Falls, Iowa.