Plant Meristems and Organogenesis: The New Era of Plant Developmental Research

摘要

The principles behind the process of body formation in multicellular organisms have long intrigued biologists. Body formation in owering plants is initiated from a single zygotic cell.Proliferation of the cell leads to the formation of an embryo, inwhich two distinctive meristems (groups of stem cells), theembryonic shoot apical meristem (SAM) and the root apicalmeristem (RAM), as well as other embryonic tissues and organs,begin to form. After germination, the SAM develops shootorgans and tissues by proliferation and differentiation of cellsin peripheral regions, whereas the RAM differentiates severaltypes of root tissues in proximal and distal directions to formthe root proper and the root cap, respectively. Both meristemsmaintain the stem cell population by self-renewal. The lateralroot meristem and the axial meristem are formed de novoduring plant growth. After a period of vegetative growth, owering (or oral transition) is induced in response to environmental conditions such as daylength, leading to a change in theSAM from a vegetative meristem to a reproductive meristem.Following gamete formation and fertilization, a zygote begins anew life cycle. Numerous intensive studies with the model systems Arabidopsis thaliana and rice (Oryza sativa) have attempted to understand the molecular frameworks thatcontrol these developmental processes, and a number of keygenes and biologically active molecules have been identied.However, the networks that regulate these molecules, and themolecular and cellular mechanisms of shoot and root development, remain to be fully understood: several factors that mediate between cell division and plant development have beenidentied that may lead to innovative conceptual advancements in developmental biology in general; and, it is generallyaccepted that plant growth is modulated by signaling molecules such as origen through long-distance vascular-basedtransport systems; however, the molecular identity of thesesystems is largely unknown.