Influence of auxin on the establishment of bilateral symmetry in monocots

Abstract

SummaryTo study the influence of auxin on the shift from radial to bilateral symmetry during monocot embryogenesis, the fate of young wheat (Triticurn aestivum L.) zygotic embryos has been manipulated in vitro by adding auxins, an auxin transport inhibitor and an auxin antagonist to the culture medium. The two synthetic auxins used, 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), induced identical phenotypes. In the most severe cases, the shift from radial to bilateral symmetry was blocked resulting in continuous uniform radial growth. The natural auxin indole-3-acetic acid (IAA) induced the same phenotype. The effect of 2,4,5-T and 2,4-D depended on their concentrations and on the developmental stage of the isolated embryos. In the presence of 2,3,5-triiodobenzoic acid (TIBA), an auxin transport inhibitor, the overall embryo symmetry was abnormal. The relative position of the shoot apical meristem in comparison with the scutellum was anomalous. The quality of shoot apical meristem and the scutellum differentiation was altered compared with normal developed embryos. No root meristem was differentiated. The effect of TIBA depends on its concentration and on the developmental stage of the isolated embryos. By contrast, 2-(pchlorophenoxy)-2-methylpropionic acid (PCIB) which is described as an auxin antagonist, has no visible direct effect on the embryonic symmetry. These observations indicate that auxin influences the change from radial symmetry to embryonic polarity during monocot embryogenesis. A model of auxin action during early wheat embryo development is proposed.

Histological changes in banana explants, cv. Nanicão (Musa spp., Group AAA), submitted to different auxins for induction of somatic embryogenesis

“…However, conversion of these embryos into plants did not occur, probably due to a lack of development of the shoot apical meristem. Similar results were obtained by Lee et al (1997) with banana somatic embryos, and Nickle & Yeung (1993) with Daucus carota L.. Fischer & Neuhaus (1996) observed that the shoot apex development of Triticum aestivum L.. induced in 2,4,5-T was interrupted due to the vacuolization of the cells in the meristem. According to these authors, the establisment of polarity represents the initial stage of development of embryonic structures in monocots: the embryonary axis and the scutellum.…”

“…Auxin polar transport in the globular embryo is essential for the establishment of polarity (Liu et al 1993). Polarity can be affected if auxin is evenly distributed in the embryo tissues due to an increase in the auxin endogenous level, which can occur by the application of endogenous auxin through the culture medium (Fischer & Neuhaus 1996).…”

ABP1 is required for organized cell elongation and division in Arabidopsis embryogenesis

“…For example, manipulation of the amount and spatial distribution of auxin (Liu et al 1993;Fischer and Neuhaus 1996;Hadfi et al 1998) in developing zygotic embryos phenocopies development observed in a number of embryo defective mutants (Mayer et al 1991). Many em-bryo-patterning mutants have altered auxin sensitivities or are associated with auxin signal transduction (Hardtke and Berleth 1998;Hammann et al 1999;Hobbie et al 2000) beginning as early as the primary zygotic division.…”

ZmPIN1-Mediated Auxin Transport Is Related to Cellular Differentiation during Maize Embryogenesis and Endosperm Development

“…Studies from wheat (Triticum aestivum) zygotic embryos indicate that heterogeneous auxin distribution plays an analogous role in monocot embryonic pattern formation (Fischer and Neuhaus, 1996;Fischer-Iglesias et al, 2001).…”