In Vitro Organogenesis

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The ability of plant cells and tissues to de-differentiate and give rise to shoots and roots under appropriate conditions forms the basis of modern day plant biotechnology. The key event in the generation of new functional shoots and roots is the formation of apical meristems. Apical meristems are responsible for tissue and organ formation of the primary plant body - the mother of all cells in plants. Although recent advances have been made in understanding apical meristem formation and function during normal plant development, we still do not fully understand meristem formation leading to root and shoot development from an in vitro environment. The overall goal of this research program is to provide a mechanistic understanding of in vitro meristem and organ formation. We have devised new protocols for shoot regeneration by using Arabidopsis zygotic embryos at the walking-stick stage and root tips as explants. Our protocol differs from the conventional procedure in that the shoot induction medium contains abscisic acid (ABA). This results in the formation of a green organogenic callus wherefrom shoots will consistently develop. This precise identification of the organogenic callus allows us to study the process of shoot formation in detail. Moreover, our use of Arabidopsis allows us to take advantage of the many available transformed lines and defined antibodies to study details of the developmental processes with confidence. The objectives of the proposed research are (1) to study the ontogeny of the organogenic callus and to characterize the organogenic cells that are responsible for shoot formation, (2) to study the structural and molecular events associated with shoot formation, (3) to study changes in the distribution and levels of hormones during the course of shoot organogenesis, and (4) to study the mode of action of ABA in the regeneration process. As Professor Ian Sussex stated in his review (Cell 56: 225, 1989) "The meristems make the plant". Without the formation of functional meristems, one cannot claim to have any biotechnological success in any system. The results obtained will provide a sound theoretical understanding of apical meristem formation and improved designs of protocols for biotechnology.