Role of Nitrogen in Compensatory Response of Hybrid Poplar to Ozone-Induced Accelerated Foliar Senescence

9631030佩尔：当植物生长在地面空气污染物臭氧含量升高的环境中时，一种常见的反应是叶子加速老化。在正常的衰老过程中，叶片的净光合作用速率逐渐下降，同时一种称为Rubisco的关键酶也在减少。这种酶负责固定二氧化碳；Rubisco也是叶片中最普遍存在的蛋白质，占可溶性叶蛋白的70%。当植物基部的叶子衰老并最终脱落时，蛋白质分解产物被运送到植物的其他地方合成新的蛋白质。一个结果是，在一些物种中，包括杨树，臭氧胁迫植物的幼嫩组织实际上可能表现出短暂的Rubisco浓度和相关的净光合作用的相对增加。这种反应被认为对空气污染损害提供了一定的补偿。植物生长在复杂的环境中，通常还有其他限制。由于Rubisco作为一种蛋白质，提供了氮的内部来源，研究人员对确定土壤中氮的限制是否会增强这些臭氧反应感兴趣。这个问题具有相关性，因为在自然生态系统中生长的许多植物都是在营养有限的土壤中发现的。人们正在开发模型，试图预测植物对多种胁迫的反应。这些模型中固有的是对植物如何将压力最小化以及什么条件会影响植物反应方式的理解。这些研究的结果将有助于改进这些模型。在这些研究中，杂交杨树将用慢性剂量的臭氧处理。我们将跟踪树冠基部和树冠叶片的发育和老化。我们将重点关注Rubisco的变化状态，并将蛋白质的合成和降解与氮的可用性联系起来。

9631030 Pell When plants are grow in an environment with elevated ground levels of the air pollutant, ozone, a common response is accelerated aging of foliage. During the normal aging process, foliage exhibits a gradual decline in rate of net photosynthesis accompanied by a decrease in a key enzyme known as Rubisco. This enzyme is responsible for fixation of carbon dioxide; Rubisco is also the most ubiquitous protein in the leaf accounting for up to 70% of soluble leaf protein. As leaves at the base of a plant age and eventually abscise, protein breakdown products are transported elsewhere in the plant for synthesis of new protein. One result is that in some species, including poplar, young tissue of ozone-stressed plants may actually exhibit a transitory, relative increase in Rubisco concentration and associated net photosynthesis. This response is thought to provide some compensation to the air pollution injury. Plants grow in a complex environment, often with other limitations. Since Rubisco, as a protein, provides an internal source of nitrogen, the investigators are interested in determining whether nitrogen limitation in the soil might enhance these ozone responses. The question has relevance since many plants growing in the natural ecosystem are found in nutrient limited soils. Models are being developed to try and predict plant responses to multiple stresses. Inherent in these models is an understanding of how plants minimize stress and what conditions will influence the way plants respond. The results of these studies will aid in the refinement of these models. In these studies hybrid poplar plants will be treated with chronic doses of ozone. We will follow the development and aging of leaves at the base and crown of the canopy. We will focus on the changing status of Rubisco and relate synthesis and degradation of the protein to availability of nitrogen.