Passive Phloem Loading

作物产量、对大气中高CO2的反应以及植物生长的其他方面部分地受到营养物质从叶片到植物远端部分（如根和谷物）的运输的限制和调节。这一过程的第一步，也是一个重要的控制点，涉及将糖和其他营养物质装载到长距离运输组织--韧皮部。迄今为止，已知两种韧皮部加载机制，这两种机制都需要代谢能量。在这个项目中，研究人员提出，还有第三种机制不需要能量，一种可能被多达一半的开花植物，特别是树木所使用的机制。这可以解释为什么一些树木能够在没有反馈抑制的情况下使用额外的大气CO2，这限制了草本作物在这些条件下的生长。这一假设将通过基因工程白杨来抑制活性韧皮部负载来检验。预测是，虽然这种抑制处理严重阻碍了主动加载的植物的生长，但它们对白杨几乎没有影响。改变通过连接植物细胞的细孔的运输方法，并作为病毒运动的传导通道，也将被探索。更广泛的影响包括：1）测试和潜在的重组植物养分运输的一个关键原则，即需要能量来装载韧皮部以准备出口; 2）确定一些植物如何比其他植物更有效地利用额外的CO2; 3）潜在的开发限制病毒在特定细胞界面上移动的转基因方法。教育更广泛的影响包括培训特殊的本科生在科学的职业生涯，领导监狱教育计划，教非生物专业的大型生物学入门课程，并为公众撰写科学文章。

Crop yield, responses to high CO2 in the atmosphere, and other aspects of plant growth are partially limited and regulated by the transport of nutrients from leaves to distant plants parts, such as roots and grain. The first step in this process, and an important control point, involves loading sugar and other nutrients into the long-distance transport tissue, the phloem. To date, two phloem-loading mechanisms are known, both of which require metabolic energy. In this project the investigators suggest that there is a third mechanism that does not require energy, one that may be used by as many as half of all flowering plants, especially trees. This could explain why some trees are able to use additional atmospheric CO2 without feedback inhibition, which limits growth of herbaceous crop plants under these conditions. The hypothesis will be tested by genetically engineering poplar trees to inhibit active phloem loading. The prediction is that, although such inhibitory treatments severely retard the growth of plants that load actively, they will have little, if any, effect on poplar. Methods of altering transport through the fine pores that connect plant cells, and serve as conducting channels for virus movement, will also be explored. Broader impacts include, 1) testing and potentially restructuring a key tenet of plant nutrient transport, namely that energy is required to load the phloem in preparation for export; 2) determining how some plants use additional CO2 more effectively than others; and 3) potentially developing a transgenic method of restricting virus movement across specific cellular interfaces. Educational broader impacts include training exceptional undergraduates for careers in science, leading a prison education program, teaching a large introductory biology course for non-biology majors, and writing scientific articles for the general public.