The Function of Intermediary Cells in Leaves

9419703金枪鱼韧皮部的运输过程是由叶肉细胞合成的碳水化合物转移到叶片的维管组织(韧皮部)，为远距离运输到其他器官做准备的过程。Turgeion博士提出了一种新的韧皮部装载模型，用于那些除了蔗糖外还运输水苏糖的物种。所有双子叶植物物种中可能有三分之一属于这一类。根据这个模型，蔗糖从叶肉细胞扩散到细脉中的一种特殊类型的伴生细胞(中间细胞)，并在那里转化为水苏糖。扩散通过许多分枝的胞间连丝将束鞘细胞连接到中间细胞。由于水苏糖太大而不能扩散回叶肉中，所以水苏糖聚集在中间细胞和筛分分子中。该奖项支持对中间细胞横纹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，这种收缩可能是蔗糖向一个方向运输和水苏糖向另一个方向运输的区别部位。冷冻固定将被用来保存胞间连丝结构，这将在碳水化合物含量减少之前和之后的成熟叶片中进行研究。共聚焦显微镜用膜特异的染料研究将确定中间细胞中的小空泡是否起源于空泡系统或内质网，这些小空泡可能参与糖在细胞中的运输。这些研究将集中在甜瓜和西葫芦上，但也可能使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.