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.
