The Function of Intermediary Cells in Leaves

9419703 Turgeon 韧皮部装载是一种运输过程，其中由叶肉细胞合成的碳水化合物被转移到叶子的维管组织（韧皮部），为长距离易位到其他器官做准备。 Turgeion 博士针对除蔗糖外还易位水苏糖的物种提出了一种新的韧皮部装载模型。 可能有三分之一的双子叶植物物种属于这一类。 根据该模型，蔗糖从叶肉细胞扩散到小静脉中的一种特殊类型的伴细胞（中间细胞）中，并在那里转化为水苏糖。 扩散通过连接束鞘细胞和中间细胞的许多分支胞间连丝发生。 水苏糖积聚在中间细胞和筛元素中，因为它太大而无法扩散回叶肉。 该奖项支持对中间细胞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，并且这种收缩是区分一个方向上的蔗糖和另一个方向上的水苏糖运输的可能位点。 冷冻固定将用于保存胞间连丝结构，并将在碳水化合物含量减少之前和之后的成熟叶子中进行研究。 使用膜特异性染料进行的共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）是否源自液泡系统或内质网。 这些研究将集中于甜瓜和西葫芦，但也可能采用其他水苏糖易位物种。

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.