EAGER: Elucidation of the Potential for CAM Photosynthesis in the C4 Halophyte Spinifex littoreus, a Succulent Asian Grass with Enormous Agricultural Potential

最近，PI和国际合作者发现台湾的一种沿海草具有非常不寻常的光合作用类型，植物利用这种机制来制造食物（它们的和我们的）。这种类型的光合作用只在另外一小群植物中被发现，科学家们仍然对其意义感到困惑。这一发现特别有趣，因为这种植物是一种草，而这种不同寻常的光合作用的一个结果是节省了大量的水。从农业的角度来看，这两个观察结果变得更加有趣，因为世界上大部分地区？5 .粮食作物来自禾草，而这类禾草的灌溉正在耗尽世界上的水库/含水层，并在需水量超过供应的地方造成困难。拟议研究的重点是草，它很可能为全世界节约用水和减少灌溉需求提供一种遗传基础。PI提出的直接工作包括对这种草不寻常的光合作用进行实地和实验室调查，目的是确定在什么条件下它最能表达其保水生理。这项研究为进一步的遗传和农业工作奠定了基础。尽管目前已知的具有CAM光合作用的物种来自30多个不同的植物科，但在现存最大的科之一Poaceae（禾本科）中还没有报道过具有CAM光合作用的物种。然而，PI和他的同事们的初步研究发现，在多肉盐生草Spinifex littoralis（一种生长在整个东南亚沿海地区的C4物种）中，天冬酸代谢（CAM）的水平是可变的。这是目前所知的第一个关于豆科植物多肉质和CAM的报道。拟议研究的目标是确定为什么CAM是可变的，以及哪些环境因素在促进这种多肉C4草中最大程度的CAM中最重要。叶片气体交换、可滴定酸度和PEP羧化酶活性的日模式将在野外和实验室中在不同的光照、水分状况和土壤盐度条件下进行监测。本研究的植物样本来自台湾不同生境的不同种群，包括有竞争者和没有竞争者的种群。要进行的其他测量包括使用PAM荧光法的光能利用效率、叶片组织解剖（特别是多肉化程度）和叶片水势。此外，拟议的研究与分子植物生理学家合作，包括初步工作，旨在确定如何最好地准备将这种植物用于遗传目的，目标是将CAM基因转移到农业谷物物种中。

Recently, the PI and international collaborators discovered that a coastal grass in Taiwan has a very unusual type of photosynthesis, the mechanism that plants use to make food (theirs and ours). This type of photosynthesis has only been found in one other small group of plants, and scientists are still puzzled by its significance. This discovery is particularly interesting because the plant is a grass, and one consequence of its unusual type of photosynthesis is a considerable savings of water. These two observations become even more interesting from an agricultural perspective because most of the world?s grain crops derive from grasses, and irrigation of such grasses is depleting world reservoirs/aquifers and creating difficulties wherever such water demands exceed supply. The grass that is the focus of the proposed research may well provide a source of the genetic underpinnings for conserving water and reducing irrigation demands worldwide. The immediate work proposed by the PI comprises field and laboratory investigations of the unusual photosynthesis in this grass with the goal of determining under what conditions it most expresses its water-conservative physiology. This research lays the groundwork for further genetic and agricultural work.Although species with CAM photosynthesis are now known from over 30 different plant families, no species in one of the largest extant families, the Poaceae (grasses), has been reported as having CAM. Preliminary research by the PI and his colleagues, however, has discovered variable levels of Crassulacean Acid Metabolism (CAM) in the succulent halophytic grass, Spinifex littoralis, a C4 species that grows in coastal areas throughout Southeast Asia. This is the first known report of succulence and of CAM in a species of Poaceae. The goals of the proposed research are to determine why CAM is variable and which environmental factors are most important in promoting the greatest degree of CAM in this succulent C4 grass. Diurnal patterns of leaf gas exchange, titratable acidity, and PEP carboxylase activity will be monitored in the field and in the lab under varying conditions of irradiance, water status, and soil salinity. Plants for these investigations will be sampled from different populations in different habitats in Taiwan, including those with and without competitors. Other measurements to be made include light-use efficiency using PAM fluorometry, leaf tissue anatomy (especially degree of succulence), and leaf water potential. In addition, the proposed research, in collaboration with molecular plant physiologists, includes preliminary work designed to determine how best to prepare use of this plant for genetic purposes with the goal of transferring CAM genes to agricultural grain species.