9320335 Cooksey The long term goal of this research is to understand the regulation of adhesion, motility and chemotaxis in diatoms of the genus Amphora. This project will expand on preliminary observations that calcium plays a role in the regulation of these processes. Preliminary results indicate that a certain level of extracellular calcium is necessary for adhesion and motility and that Amphora responds chemotactically to simple sugars and glutamate. Calcium has a pivotal role as a second messenger in control of numerous biological processes. This ion is responsible for signal-response coupling in animal, plant, and other cells during such physiological processes as secretion and the development of cellular polarity. The availability of calcium-sensitive fluorescent probes such as Fura-2, Indo-1, Fluo-3 has made possible the direct visualization of spatial and temporal changes in cytosolic free calcium in single cells using confocal laser scanning microscopy, and changes in intracellular calcium can be detected in suspensions of synchronized cells using an appropriate spectrofluorimeter. Research supported by this Small Grant for Exploratory Research will establish the experimental conditions for applying these important experimental tools in studies of the role of calcium in regulation of cell adhesion, motility, and chemotaxis in diatoms. These tools will then be used to study the effects of external calcium and sugars that promote chemotaxis on intracellular free calcium levels as part of a longer term study of the control of physiological processes by calcium in these, rather primitive, eukaryotes. %%% Marine diatoms are responsible for more than half of the world's replacement oxygen. The diatoms that are the subject of this research grow attached to illuminated surfaces in the nearshore benthic zone. Whether chemotaxis is a common property of these organisms is not known. Although diatoms are green algae and can carry out photosynthesis, ma ny diatoms from this niche also can use some simple sugars and amino acids to support their growth. If, as suggested by preliminary observations, they can sense chemical gradients of these compounds in the sediment pore water and move toward higher concentrations, these diatoms could be important in turnover of dissolved organic carbon in illuminated sediments. Yet, despite the potential importance of these organisms, very little is known about the mechanisms of their responses to stimuli such as organic compounds. This Small Grant for Exploratory Research will be used to lay the experimental groundwork for studies of the signal transduction pathways regulating diatom adhesion, motility, and chemotaxis. The longer term results of this research will not only fill a gap in knowledge of the mechanisms by which these little-understood organisms respond to environmental signals, but should also provide new insights into their ecological role in the nearshore food web. ***
