Francis Dennis, Halford Nigel G
School of Biosciences, Cardiff University, PO Box 915, CF72 9DU, Cardiff, UK.
Plant Mol Biol. 2006 Apr;60(6):981-93. doi: 10.1007/s11103-005-5749-3.
Plants need nutrient to grow and plant cells need nutrient to divide. The meristems are the factories and cells that are left behind will expand and differentiate. However, meristems are not simple homogenous entities; cells in different parts of the meristem do different things. Positional cues operate that can fate cells into different tissue domains. However, founder/stem cells persist in specific locations within the meristem e.g. the quiescent centre of root apical meristem (RAM) and the lower half of the central zone of the shoot apical meristem (SAM). Given the complexity of meristems, do their cells simply respond to a diffusing gradient of photosynthate? This in turn begs the question, why do stem cell populations tend to have longer cell cycles than their immediate descendants given that like all other cells they are directly in the path of diffusing nutrient? In this review, we have examined the extent to which nutrient sensing might be operating in meristems. The scene is set for sugar sensing, the plant cell cycle, SAMs and RAMs. Special emphasis is given to the metabolic regulator, SnRK1 (SNF1-related protein kinase 1), hexokinase and the trehalose pathway in relation to sugar sensing. The unique plant cell cycle gene, cyclin-dependent kinase B1;1 may have evolved to be particularly responsive to sugar signalling pathways. Also, the homeobox gene, STIMPY, emerges strongly as a link between sugar sensing, plant cell proliferation and development. Flowering can be influenced by sucrose and glucose levels and both meristem identity and organ identity genes could well be differentially sensitive to sucrose and glucose signals. We also describe how meristems deal with extra photosynthate as a result of exposure to elevated CO2. What we review are numerous instances of how developmental processes can be affected by sugars/nutrients. However, given the scarcity of knowledge we are unable to provide uncontested links between nutrient sensing and specific activities in meristems.
植物生长需要养分，植物细胞分裂也需要养分。分生组织是“工厂”，而留下来的细胞会生长和分化。然而，分生组织并非简单的同质实体；分生组织不同部位的细胞功能各异。位置线索发挥作用，可使细胞分化为不同的组织区域。不过，起始细胞/干细胞在分生组织内的特定位置持续存在，例如根顶端分生组织（RAM）的静止中心以及茎顶端分生组织（SAM）中央区的下半部分。鉴于分生组织的复杂性，其细胞是否仅仅对光合产物的扩散梯度做出反应呢？这进而引出一个问题：鉴于干细胞群体与所有其他细胞一样直接处于养分扩散路径上，为何它们的细胞周期往往比其直接后代更长？在本综述中，我们研究了养分感知在分生组织中发挥作用的程度。文中介绍了糖感知、植物细胞周期、茎顶端分生组织和根顶端分生组织的相关情况。特别强调了与糖感知相关的代谢调节因子SnRK1（SNF1相关蛋白激酶1）、己糖激酶和海藻糖途径。独特的植物细胞周期基因细胞周期蛋白依赖性激酶B1;1可能已进化为对糖信号通路具有特别的响应性。此外，同源异型盒基因STIMPY作为糖感知、植物细胞增殖与发育之间的联系而备受关注。开花会受到蔗糖和葡萄糖水平的影响，分生组织特征基因和器官特征基因很可能对蔗糖和葡萄糖信号具有不同的敏感性。我们还描述了分生组织如何应对因暴露于高浓度二氧化碳而产生的额外光合产物。我们综述了众多发育过程如何受糖类/养分影响的实例。然而，鉴于知识的匮乏，我们无法提供养分感知与分生组织中特定活动之间无争议的联系。
