Passive Phloem Loading

作物产量、对大气中二氧化碳含量高的反应以及植物生长的其他方面在一定程度上受到营养物质从叶片到远端植物部位（如根和谷物）的运输的限制和调节。这个过程的第一步，也是一个重要的控制点，包括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，已知两种韧皮部负荷机制，两者都需要代谢能量。在这个项目中，研究人员提出了第三种不需要能量的机制，这种机制可能被多达一半的开花植物，尤其是树木所利用。这可以解释为什么一些树木能够利用额外的大气二氧化碳而没有反馈抑制，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杨树来检验，以抑制活性韧皮部负荷。预测是，尽管这种抑制处理严重阻碍了主动负荷植株的生长，但它们对杨树的影响很小，如果有的话。还将探索通过连接植物细胞并作为病毒运动的传导通道的细孔改变运输的方法。更广泛的影响包括：1)测试并可能重构植物养分运输的一个关键原则，即在准备出口时需要能量来装载韧皮部；2)确定一些植物如何比其他植物更有效地利用额外的二氧化碳；3)潜在地开发一种限制病毒在特定细胞界面上移动的转基因方法。更广泛的教育影响包括培养杰出的本科生从事科学事业，领导监狱教育计划，为非生物学专业教授大型生物学入门课程，以及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.