Endogenous hormone concentrations and embryogenic callus development in wheat

Immature zygotic embryos of two wheat (Triticum aestivum L.) genotypes, kno wn for their different ability to generate embryogenic callus, were used as initial explants to establish callus cultures. Embryogenic and non-embryog enic calluses were obtained from the competent genotype (`Combi'), while on ly non-embryogenic callus was produced by the incompetent one (`Devon'). Th e morphogenetic competence of each callus type was evaluated by transferrin g some segments to regeneration conditions. The endogenous hormone concentr ations (free indole-3-acetic acid [IAA], abscisic acid [ABA], gibberellins (1), (3) and (20) [GAs], zeatin/zeatin riboside [Z/ZR] and N-6[Delta (2)-is opentenyl] adenine/ N-6[Delta 2-isopentenyl] adenosine; [iP/iPA]) of the in itial explants were determined by means of radio-immunoassay and showed tha t the only difference was the higher concentration of ABA found in the embr yos of the most competent genotype; whose embryos showed a reduced rate of precocious germination. When analysing the endogenous hormone concentration s in the various callus types generated in each genotype, it was found that only differences in the free IAA concentrations were associated with varia tions in the morphogenic properties of the calluses. Higher concentrations of endogenous free IAA were typical of embryogenic callus cultures. It was also observed that a loss in the embryogenic competence of the calluses, du e to a prolonged time of culture, occurred concomitantly with a reduction i n free IAA concentrations, practically to the concentrations found in the n on-embryogenic calluses.