Hormonal status of maize initial explants and of the embryogenic and non-embryogenic callus cultures derived from them as related to morphogenesis invitro

Endogenous hormone levels (indole-3-acetic acid [IAA], abscisic acid [ABA], gibberellins(1,3) and (20) [GAs], zeatin/zeatin riboside [Z/ZR] and N-6[De lta (2)-isopentenyl] adenine/N-6[Delta (2)-isopentenyl] adenosine; [iP/iPA] ) were analysed in immature maize zygotic embryos of two maize (Zea mays L. ) genotypes, known for their distinct ability to generate embryogenic (E) c allus. No differences were found among genotypes in the hormone contents of the embryos. These embryos were also used as initial explants to establish callus cultures. E and non-embryogenic (NE) calli were obtained from the c ompetent genotype (A188), while only NE callus was produced by the incompet ent one (B73). The morphogenetic competence of each callus type was evaluat ed by transferring some segments to regeneration conditions. When analysing the endogenous hormone levels in the various callus types generated in eac h genotype, it was found that only differences in the IAA levels accounted for variations in the morphogenic properties of the calli. Higher levels of endogenous IAA were typical of embryogenic callus cultures. It was also ob served, that a loss in the embryogenic competence of the calli, due to a pr olonged time of culture, occurred concomitantly with a reduction in the IAA levels, practically to the levels found in the non-embryogenic calli. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.