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水平升高的环境中时，常见的反应是叶片加速衰老。在正常的衰老过程中，叶片的净光合作用速率逐渐下降，并伴随着一种名为Rubisco的关键酶的下降。这种酶负责固定二氧化碳；Rubisco也是叶片中最普遍的蛋白质，占可溶叶片蛋白质的70%。由于叶子处于植物年龄的基础，并最终脱落，蛋白质分解产物被运输到植物的其他地方，以合成新的蛋白质。一个结果是，在包括杨树在内的一些物种中，臭氧胁迫下植物的幼嫩组织实际上可能会表现出Rubisco浓度和相关净光合作用的短暂、相对增加。这一反应被认为对空气污染造成的伤害提供了一些补偿。植物生长在一个复杂的环境中，通常有其他限制。由于Rubisco作为一种蛋白质提供了氮素的内部来源，研究人员感兴趣的是确定土壤中的氮素限制是否会增强这些臭氧反应。这个问题具有相关性，因为许多生长在自然生态系统中的植物都是在养分有限的土壤中发现的。人们正在开发模型来尝试和预测植物对多种胁迫的反应。这些模型的本质是了解植物如何将压力降至最低，以及哪些条件将影响植物的反应方式。这些研究的结果将有助于改进这些模型。在这些研究中，杂交杨树植物将被长期剂量的臭氧处理。我们将跟踪树冠底部和树冠叶片的发育和老化。我们将重点关注Rubisco状态的变化，并将蛋白质的合成和降解与氮素的可用性联系起来。

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.