Wobus U, Weber H
Abt. Molekulare Genetik, Institut für Pflanzengenetik und Kulturpflanzenforschung, Gatersleben, Germany.
Biol Chem. 1999 Jul-Aug;380(7-8):937-44. doi: 10.1515/BC.1999.116.
Higher plants as sessile organisms react very flexible to environmental changes and stresses and use metabolites like glucose, sucrose and nitrate not only as nutrients but also as signals as part of their life strategies. The role of metabolites as signal molecules has attracted considerable interest during recent years. Data reviewed here for developing plant seeds suggest a trigger function of especially sugars also in development in that metabolic regulatory control can override developmental regulation, i.e., the developmental programme only continues normally if a certain metabolic state is sensed at a given time point in a given cell or tissue. Several experimental strategies have provided mainly correlative evidence that certain sugar levels and/or the resulting changes in osmotic values are necessary within defined tissues or cells to maintain a distinct stage of differentiation or to proceed with the developmental programme. In young legume seeds, but certainly also in other tissues, a high hexose (probably mainly glucose) level seems to maintain the capacity of cells to divide whereas - later in seed development - a certain sucrose level is necessary to induce storage-associated cell differentiation. A major determinant of embryo hexose levels in young legume seeds is an apoplastic invertase preferentially expressed in the inner cell layers of the seed coat. The enzyme cleaves the incoming photoassimilate sucrose into glucose and fructose. During development the tissue harbouring the invertase is degraded in a very specific spatial and temporal pattern as part of the developmental programme and is thus creating steep glucose gradients within the cotyledons. These gradients can be measured at nearly cellular resolution and were found to be correlated positively with cell division rate and negatively with cell differentiation and storage activities. A hexose and a sucrose transporter accumulating only in the epidermal cell layer of the cotyledons seem to be essential in creating and maintaining these gradients. To gain further insights into the role of metabolites, especially sugars, as triggers of developmental processes we foremost have to identify receptor molecules already characterised in yeast, and to describe and understand the signal transduction networks involved.
高等植物作为固着生物，对环境变化和胁迫反应非常灵活，它们将葡萄糖、蔗糖和硝酸盐等代谢物不仅用作营养物质，还作为信号，这是其生命策略的一部分。近年来，代谢物作为信号分子的作用引起了相当大的关注。这里回顾的有关发育中植物种子的数据表明，尤其是糖类在发育过程中也具有触发功能，即代谢调节控制可以超越发育调节，也就是说，只有在给定的细胞或组织中，在特定时间点感知到特定的代谢状态时，发育程序才能正常继续。几种实验策略主要提供了相关证据，表明在特定组织或细胞内，特定的糖水平和/或由此产生的渗透压变化对于维持特定的分化阶段或推进发育程序是必要的。在幼嫩的豆科植物种子中，但其他组织肯定也是如此，高己糖（可能主要是葡萄糖）水平似乎维持细胞分裂的能力，而在种子发育后期，一定的蔗糖水平对于诱导与储存相关的细胞分化是必要的。幼嫩豆科植物种子中胚己糖水平的一个主要决定因素是一种质外体转化酶，它优先在种皮的内层细胞中表达。该酶将进入的光合产物蔗糖裂解为葡萄糖和果糖。在发育过程中，含有转化酶的组织作为发育程序的一部分，以非常特定的时空模式降解，从而在子叶内形成陡峭的葡萄糖梯度。这些梯度可以在接近细胞分辨率的水平上测量，并且发现与细胞分裂速率呈正相关，与细胞分化和储存活动呈负相关。一种仅在子叶表皮细胞层积累的己糖和蔗糖转运蛋白似乎对于建立和维持这些梯度至关重要。为了进一步深入了解代谢物，尤其是糖类作为发育过程触发因素的作用，我们首先必须鉴定酵母中已经表征的受体分子，并描述和理解所涉及的信号转导网络。
