Competence versus Recalcitrance for in Vitro Regeneration
Plant regeneration from tissue cultures of many species has been reported so far, but various groups, families and genera are still regarded as recalcitrant, and tools susceptible to distinguish as early in culture as possible the regeneration-competent cells and tissues from those that will never regenerate would be of interest, whatever the regeneration pathway. We have examined various cytological parameters to identify those that might serve as early indicators of cell competence to undergo somatic embryogenesis and/or organogenesis. Water potential of the culture medium declined preceding the onset of embryogenesis while intracellular osmolarity and cell surface increased concomitantly in embryogenic cells. In addition, cellulose accumulated in the walls of non-embryogenic cells while cell walls became thinner with onset of embryogenesis, and diminished further as embryos matured. In parallel experiments, the cytogenetic, proteomic and molecular processes governing the competence for embryogenesis and/or organogenesis from plant cells were studied with Arabidopsis thaliana, and more recently also with Medicago truncatula and pea, both by flow cytometry, immuno-cytohistology, mono and bidimensional electrophoresis and comparing insertion mutants and RNAis with their respective wild types. The implications of these results when applying biotechnology approaches for grain legume breeding, and in terms of plant regeneration competence in general are discussed.
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