Developmental biology

Abstract

Unlike animals, higher plants continue to generate new organs and tissues throughout their postembryonic life. This ongoing process is achieved through the activity of specific domains formed during embryogenesis at the two poles of developing embryos which have capacity to continuously renew themselves: the shoot and root apical meristems, respectively. The word "meristem" derives from the Greek "merizein", meaning "to divide" (Evans and Barton, 1997). Both shoot and root meristems add permanently new organs to the growing plant body and generate all the progeny cells that are required for tissue and organ differentiation. During the last decade, considerable progress has been made in the understanding of both shoot and root morphogenesis. A range of genes has been isolated from developmental mutants, namely from Arabidopsis thaliana, Antirrhinum majus, Zea mays and Nicotiana tabacum, and their temporal and spatial patterns of expression have been established using molecular biology techniques, so that we have now a better view of how shoot and root morphogenesis and development are controlled at cell, tissue and organ levels of organization. It is clear that each developmental step from embryogenesis to flowering, and each type of organ and tissue, is the result of the coordinated expression of sets of specific and developmentally-regulated genes. As a consequence for tissue culture, it can be expected a consideration of what genes are expressed in the initial explants, and how developmental genes are controlled by hormones and other components of culture media, would be helpful to improve the monitoring of in vitro manipulation. There is no doubt that the recent findings will have consequences for a better understanding of the processes of adventitious regeneration in tissue culture and the recently isolated genes will certainly serve as new tools to investigate these processes.