Sink-Source Transition in Tobacco Leaves

高等植物的叶片在成熟时从汇转化为光同化物的来源。本实验室已经证明，停止烟草的光同化物输入(库阶段结束)与正碳平衡的实现是一致的，但不是由于实现了正碳平衡。这表明韧皮部的卸载是共生的(通过胞间连丝)，当胞间连丝与周围细胞的连接丢失或被阻断时，韧皮部的卸荷就停止了。阻止共生体流动也将允许韧皮部的细胞通过防止渗漏来获得出口所需的高溶质含量。以往的研究结果支持卸荷是被动的和共塑性的假说。还将进行额外的实验，通过测试打破胞间连丝连接的效果，用高pH和抑制剂处理防止共体运输，以及改进目前对卸载途径的形态计量学分析，以允许使用溶质通量数据来刺激运输，进一步证实烟草汇叶片中的共生体韧皮部卸载途径。将进行高分辨率的EM研究，以确定沿卸载路径的胞间连丝是否被物理阻塞。韧皮部加载也将被研究，以确定是否涉及质外体步骤。%这些对发育中的叶片的生理和结构的研究提供了关于光合作用中糖是如何产生的信息首先储存在叶子中，然后被动员起来形成谷粒和果实。这对于更好地理解作物生产力具有明显的意义。令人惊讶的是，还有多少植物结构有待阐明。该项目正在填补植物生物学领域的一个重要信息空白。

Leaves of higher plants are converted from sinks to sources of photoassimilate as they mature. This lab has shown that termination of photoassimilate import (end of the sink phase) in tobacco is coincident with, but not due to, achievement of positive carbon balance. This suggests that phloem unloading is symplastic (through plasmodesmata) and ceases when plasmodesmatal connections to surrounding cells are either lost or blocked. Interruption of symplastic flow would also allow the cells of the phloem to achieve the high solute content needed for export by preventing leakage. Prior results support the hypothesis that unloading is passive and symplastic. Additional experiments will be conducted to further substantiate the symplastic phloem unloading route in tobacco sink leaves by testing the effects of breaking plasmodesmatal connections, preventing symplastic transport with high pH and inhibitor treatments, and refining the present morphometric analysis of the unloading pathway to allow stimulation of transport using data on solute flux. High resolution EM studies will be conducted to determine whether plasmodesmata along the unloading pathway become physically obstructed. Phloem loading will also be studied to determine whether an apoplastic step is involved.%%% These studies on the physiology and structure of a developing leaf are providing information on how sugars made during photosynthesis are first stored in leaves and then mobilized to form grains and fruits. This has obvious implications for a better understanding of crop productivity. It is surprising how much plant structure remains to be elucidated. This project is filling an important information gap in plant biology.***//