A novel type of photosynthesis has recently been discovered in the submersed aquatic plant Hydrilla verticillata. Photosynthesis, the biochemical process by which plants transform carbon dioxide and water into carbohydrate, has been shown to occur by two primary reaction sequences commonly designated as the C3 and C4 pathways. All photosynthetic organisms utilize the C3 pathway, however, a few, including corn and sugar cane, also possess the C4 reaction sequence and are among the most productive plants known. What makes Hydrilla unique is the ability of an individual plant to switch from C3 to C4 photosynthesis depending upon environmental conditions. This project will utilize a powerful combination of plant physiological and ecological methods in both greenhouse and field studies to 1) quantify the environmental conditions associated with the C4 state in the field, 2) determine the environmental cues that induce the C4 state, 3) compare the photosynthetic and productivity rates of C3 and C4 Hydrilla plants, 4) determine the environmental conditions under which C4 photosynthesis benefits growth, and 5) determine the importance of C4 photosynthesis to the overall productivity of this plant. Hydrilla is native to tropical Africa and Asia. It was introduced into Florida during the early 1960's by the aquarium plant industry, and because of its prolific growth currently threatens freshwater resources throughout the southern United States. Therefore, elucidation of its photosynthetic physiology may contribute knowledge important for the control of this noxious weed. Such knowledge may also facilitate breeding efforts to introduce desirable C4 traits into C3 crop plants and possibly increase crop yield. Furthermore, understanding the environmental conditions that induce C4 photosynthesis in this plant may give insights into the forces that resulted in the evolution of C4 photosynthesis in flowering plants.
