Plasmodesmata and Phloem Loading

该项目支持对叶中韧皮部装载机制的鉴定研究。 光合作用产生的糖被装载到小脉的韧皮部，输出到生长器官。 有两种已知的韧皮部装载机制。 质外体装载涉及跨膜运输，而共质体装载完全通过连接胞间连丝的细胞质发生。 能够区分这些机制是很重要的，因为它们受到环境压力的抑制，可能是以不同的方式。 根据目前的范例，质外体和共质体加载物种可以可靠地确定胞间连丝计数。 在这项调查中要测试的另一种假设是，质外体加载是普遍的，除了那些物种，易位水苏糖，或类似大小的其他碳水化合物，并通过聚合物捕获负载。 韧皮部装载的研究，主要是对氯汞苯磺酸的跨膜运输的特异性抑制的基础上，将进行5个物种，易位蔗糖，但已被pueretically确定为共质体装载的基础上，胞间连丝计数。 预测这些植物通过质外体装载。 进一步的研究将进行测试的假设，小脉韧皮部的胞间连丝的频率反映了整体的胞间连丝数量在叶中，取决于植物的生长习性，并不一定与韧皮部的生理。

This project supports studies on the identification of phloem loading mechanisms in leaves. Sugars manufactured by photosynthesis are loaded into the phloem of minor veins for export to growing organs. There are two known phloem loading mechanisms. Apoplastic loading involves trans-membrane transport while symplastic loading takes place entirely through the plasmodesmata-connected cytoplasm. It is important to be able to distinguish between these mechanisms because they are inhibited by environmental stress, presumably in different ways. According to the current paradigm, apoplastic- and symplastic-loading species can be identified reliably by plasmodesmatal counts. An alternative hypothesis to be tested in this investigation is that apoplastic loading is universal, except for those species that translocate stachyose, or other carbohydrates of similar size, and load by polymer trapping. Phloem loading studies, based primarily on the specific inhibition of trans-membrane transport by p-chloromercuribenzenesulfonic acid, will be conducted on five species that translocate sucrose but have been putatively identified as symplastic loaders on the basis of plasmodesmatal counts. The prediction is that these plants load via the apoplast. Further studies will be conducted to test the hypothesis that plasmodesmatal frequencies in minor vein phloem reflect overall plasmodesmatal numbers in leaves, depending on plant growth habit, and are not necessarily related to phloem physiology.