Integrated Studies on Cellular and Physiological Roles of Higher Plant Plasmodesmata

在植物中，细胞与细胞之间的接触是由称为胞间连丝的特殊细胞器建立的。 这些独特的细胞质桥将器官（如叶子）内细胞的原生质相互连接，形成共质状态，这增强了代谢物和信息分子的交换。 近年来，遗传学、分子生物学、细胞学和生理学的研究提供了直接证据，证明胞间连丝具有介导蛋白质和核酸（RNA和DNA）等大分子物质转运的能力。 重要的是，已经表明核酸以核蛋白复合物的形式在细胞间移动。 基于这些研究，新出现的概念是胞间连丝已经进化为（a）增强特定器官内发生的生化过程的功效，和（B）通过选择性运输信息分子促进生理和发育事件的协调。 为了更好地了解植物对这些胞间连丝功能施加控制的机制，描述了实验，该实验将允许鉴定和克隆参与植物细胞之间大分子选择性运输的组成部分。 将采取综合方法来实现这一目标，并将结合使用生物化学，细胞，分子和超微结构技术。 用于鉴定参与细胞质和核质之间蛋白质运输的组分的方法将被整合到这些实验中。 分子伴侣的具体参与蛋白质和核蛋白运输的整个过程中，并通过胞间连丝也将进行探讨。 注意力将集中在一类称为热休克蛋白质的细胞质伴侣。 这些研究将与高等植物维管系统中存在的共质途径的分析相结合。 该维管系统由木质部和韧皮部组成，木质部将水和矿物质营养物质从根传导到植物的气生区域，韧皮部将固定的碳（糖）和氮（氨基酸）转运到发育中的器官。 韧皮部的输导组织由两种细胞组成，即伴胞和筛分子。 连接这些细胞类型的胞间连丝在这个长距离易位系统的运作中发挥重要作用。 将进行实验，以确定在遗传水平上，植物可以控制这一关键的共质途径的方式，从叶片的光合组织，一直到韧皮部传导组织。 这些研究将提供一个框架，了解植物如何利用韧皮部长距离易位系统，以编排过程在整个植物水平。

In plants, cell-to-cell contact is established by special intercellular organelles, termed plasmodesmata. These unique cytoplasmic bridges interconnect the protoplasm of the cells within an organ, such as a leaf, forming a symplasmic state, which potentiates the exchange of both metabolites and information molecules. In recent years, genetic, molecular, cellular and physiological studies provided direct evidence that plasmodesmata have the capacity to mediate the transport of macromolecules, such as proteins and nucleic acids (RNA and DNA). Importantly, it has been shown that nucleic acids move cell to cell in the form of nucleoprotein complexes. Based on these studies, the emerging concept is that plasmodesmata have evolved to (a) enhance the efficacy of biochemical processes occurring within specific organs, and (b) facilitate the coordination of both physiological and developmental events, via the selective trafficking of information molecules. To better understand the mechanisms by which plants exert control over these plasmodesmal functions, experiments are described that will allow identification and cloning of the component parts involved in the selective trafficking of macromolecules between plant cells. An integrated approach will be taken to achieve this goal, and will incorporate the use of biochemical, cellular, molecular and ultrastructural techniques. Methods developed for the identification of the components involved in protein trafficking between the cytoplasm and the nucleoplasm will be integrated into these experiments. The specific involvement of chaperones in the overall process of protein and nucleoprotein transport to and through plasmodesmata will also be explored. Attention will be focused on a class of cytoplasmic chaperones termed the heat shock proteins. These studies will be integrated with an analysis of the symplasmic pathway that exists within the vascular system of higher plants. This vascular system is comprised of the xylem, which conducts water and mineral nutrients from the root to the aerial regions of the plant, and the phloem, which translocates fixed carbon (sugars) and nitrogen (amino acids) to developing organs. Two cell types, the companion cells and the sieve elements, form the conducting tissue of the phloem. The plasmodesmata that interconnect these cell types fulfill an important function in the operation of this long-distance translocation system. Experiments will be conducted to identify, at the genetic level, ways by which the plant can control this pivotal symplasmic route, from the photosynthetic tissues of the leaf, all the way to the phloem conducting tissue. These studies will provide a framework for understanding how the plant employs the phloem long-distance translocation system to orchestrate processes at the whole-plant level.