The Function of Intermediary Cells in Leaves

[9419703]韧皮部装载是叶肉细胞合成的碳水化合物转移到叶片维管组织（韧皮部），为长距离转运到其他器官做准备的运输过程。Turgeion博士提出了一种新的韧皮部负荷模型，用于那些除了蔗糖外还转运水苏糖的物种。可能三分之一的双子叶植物属于这一组。根据这个模型，蔗糖从叶肉细胞扩散到小静脉中的一种特殊类型的伴侣细胞（中间细胞），并在那里转化为水苏糖。扩散通过将束鞘细胞与中间细胞连接在一起的许多分枝间连丝发生。水苏糖在中间细胞和筛元中积累，因为它太大而不能扩散回叶肉中。该奖项支持中间细胞间连丝超微结构动力学的实验研究。这些胞间连丝在中间细胞一侧特别狭窄，这种狭窄可能是区分蔗糖在一个方向上的运输和水苏糖在另一个方向上的运输的地方。冷冻将用于保存胞间连丝结构，这将在碳水化合物含量减少前后的成熟叶片中进行研究。膜特异性染料的共聚焦显微镜研究将确定中间细胞中的小液泡（可能参与糖通过细胞的运输）是来自液泡系统还是内质网。这些研究将集中在甜瓜和葫芦上，但其他水苏糖易位物种也可能被利用。

9419703 Turgeon Phloem loading is the transport process in which carbohydrate, synthesized by mesophyll cells, is transferred to the vascular tissue (phloem) of leaves in preparation for long-distance translocation to other organs. A new model of phloem loading has been put forward by Dr. Turgeion for those species that translocate stachyose in addition to sucrose. Possibly one-third of all dicotyledonous species are in this group. According to this model, sucrose diffuses from the mesophyll cells into a specialized type of companion cell (the intermediary cell) in the minor veins and is converted there into stachyose. Diffusion occurs through numerous branched plasmodesmata linking bundle sheath cells to intermediary cells. The stachyose accumulates in the intermediary cells and sieve elements because it is too large to diffuse back into the mesophyll. This award supports experimental studies into the dynamics of intermediary cell phlasmodesmata ultrastructure. These plasmodesmata are especially narrow on the intermediary cell side and this constriction is the possible site of discrimination between transport of sucrose in one direction and stachyose in the other. Cryofixation will be used to preserve plasmodesmata structure, which will be studied in mature leaves before and after a reduction in carbohydrate content. Confocal microscope investigations with membrane- specific dyes will determine whether the small vacuoles in intermediary cells, which may be involved in transport of sugar through the cell, originate from the vacuolar system or the endoplasmic reticulum. These studies will concentrate on Cucumis melo and Cucurbita pepo but other stachyose-translocation species may also be employed.