间充质干细胞表达趋化因子及受体的相关生物学功能

间充质干细胞(mesenchymal stem cells,MSCs)是一群存在于骨髓间质和其他组织间质的干细胞,表达CD34和CD133.近来研究发现,存在于骨髓的间充质干细胞除了能支持造血,向骨细胞、软骨细胞和脂肪细胞进行多向分化外,其分泌的趋化因子及其相关受体在MSCs的信号转导、维持内环境的稳定、损伤修复、免疫调节、支持造血等功能中也发挥了关键性的作用.     

Cell Differentiation and Organ Initiation at the Shoot Apical Meristem

Plants continuously generate organs at the flanks of their shoot apical meristems (SAMs). The patterns in which these organs are initiated, also called patterns of phyllotaxis, are highly stereotypic and characteristic for a particular species or developmental stage. This stable, predictable behaviour of the meristem has led to the idea that organ initiation must be based on simple and robust mechanisms. This conclusion is less evident, however, if we consider the very dynamic behaviour of the individual cells. How dynamic cellular events are coordinated and how they are linked to the regular patterns of organ initiation is a major issue in plant developmental biology.     

植物茎尖分生组织分化调控机制研究进展

茎尖分生组织是位于植物顶端具有持续分化能力的组织,通过细胞分裂、分化产生茎、叶和花等器官,形成植株地上部分。茎尖分生组织在分化过程中受外界环境因素、内源激素水平和分子调控等影响,表现出明显变化。该文综合国内外近年来有关茎尖分生组织分化调控的研究进展,从茎尖分生组织的形态结构和环境影响因素,以及激素调控和分子调控等方面,对茎尖分生组织分化活动的研究进行综述,并对目前研究现状存在问题及未来研究方向进行了分析和展望。     

Control of Rice Embryo Development,Shoot Apical Meristem Maintenance,and Grain Yield by a Novel Cytochrome P450

Angiosperm seeds usually consist of two major parts： the embryo and the endosperm. However, the molec- ular mechanism（s） underlying embryo and endosperm development remains largely unknown, particularly in rice, the model cereal. Here, we report the identification and functional characterization of the rice GIANT EMBRYO （GE） gene. Mutation of GE resulted in a large embryo in the seed, which was caused by excessive expansion of scuteUum cells. Post-embryonic growth of ge seedling was severely inhibited due to defective shoot apical meristem （SAM） mainte- nance. Map-based cloning revealed that GE encodes a CYP78A subfamily P450 monooxygenase that is localized to the endoplasmic reticulum. GE is expressed predominantly in the scutellar epithelium, the interface region between embryo and endosperm. Overexpression of GE promoted cell proliferation and enhanced rice plant growth and grain yield, but reduced embryo size, suggesting that GE is critical for coordinating rice embryo and endosperm development. Moreover, transgenic Arabidopsis plants overexpressing AtCYP78AlO, a GE homolog, also produced bigger seeds, implying a con- served role for the CYP78A subfamily of P450s in regulating seed development. Taken together, our results indicate that GE plays critical roles in regulating embryo development and SAM maintenance.     

Feedback from Lateral Organs Controls Shoot Apical Meristem Growth by Modulating Auxin Transport

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Morphogenesis and Patterning at the Organ Boundaries in the Higher Plant Shoot Apex

Formation of lateral organ primordia from the shoot apical meristem creates boundaries that separate the primordium from surrounding tissue. Morphological and gene expression studies indicate the presence of a distinct set of cells that define the boundaries in the plant shoot apex. Cells at the boundary usually display reduced growth activity that results in separation of adjacent organs or tissues and this morphological boundary coincides with the border of different cell identities. Such morphogenetic and patterning events and their spatial coordination are controlled by a number of boundary-specific regulatory genes. The boundary may also act as a reference point for the generation of new meristems such as axillary meristems. Many of the genes involved in meristem initiation are expressed in the boundary. This review summarizes the cellular characters of the shoot organ boundary and the roles of regulatory genes that control different aspects of this unique region in plant development.     

Primary Root Growth and the Pattern of Root Apical Meristem Organization are Coupled

Root apical meristems (RAMs) in dicotyledonous plants have two organizational schemes; closed (with highly organized tiers) and open (tiers lacking or disorganized). These schemes are commonly believed to remain unchanged during the growth of the root axis. Individual roots are commonly thought to have indeterminate growth. We challenge these two generalizations through the study of five species with closed apical organization: Clarkia unguiculata L., Oxalis corniculata L., Dianthus caryophyllus L., Blumenbachia hieronymi Urb., and Salvia farinaceae Benth. cv. Strata. These roots have phased growth patterns where early growth is followed by deceleration, after which the initial cells stop dividing, elongation ceases, and the root reaches its determinate length. At or before reaching determinacy, the root apical meristem stops maintaining its closed organization and becomes less organized. These observations will be placed in context with observations from the literature to suggest two new generalizations, namely, that apical organization does change over the growth phases of roots, and that roots are determinate.     

Formation, Maintenance and Function of the Shoot Apical Meristem in Rice

In higher plants, the process of embryogenesis establishes the plant body plan (body axes). On the basis of positional information specified by the body axes, the shoot apical meristem (SAM) and root apical meristem (RAM) differentiate at fixed positions early in embryogenesis. After germination, SAM and RAM are responsible for the development of the above-ground and below-ground parts, respectively, of the plant. Because of the importance of SAM function in plant development, the mechanisms of SAM formation during embryogenesis and of SAM maintenance and function in post-embryonic development are priority questions in plant developmental biology. Recent advances in molecular and genetic analysis of morphogenetic mutations in Arabidopsis have revealed several components required for SAM formation, maintenance and function. Although these processes are fundamental to the life cycle of every plant, conservation of the components does not explain the diversity of plant morphologies. Rice is used as a model plant of the grass family and of monocots because of the progress in research infrastructure, especially the collection of unique mutations and genome information. In comparison with the dicot Arabidopsis, rice has many unique organs or processes of development. This review summarizes what is known of the processes of SAM formation, maintenance and function in rice.     

Plant stem cells and their regulations in shoot apical meristems

Stem cells in plants, established during embryogenesis, are located in the centers of the shoot apical meristem (SAM) and the root apical meristem (RAM). Stem cells in SAM have a capacity to renew themselves and to produce new organs and tissues indefinitely. Although fully differentiated organs such as leaves do not contain stem cells, cells in such organs do have the capacity to re-establish new stem cells, especially under the induction of phytohormones in vitro. Cytokinin and auxin are critical in creating position signals in the SAM to maintain the stem cell organizing center and to position the new organ primordia, respectively. This review addresses the distinct features of plant stem cells and focuses on how stem cell renewal and differentiation are regulated in SAMs.