Marine macroalgae exhibit phenotypic responses of their photosynthetic metabolism when grown at different temperatures. This thermal acclimation involves changes in cellular contents of photosynthetic enzymes and pigments that enable seaweeds to maintain similar rates of light-limited and light-saturated photosynthesis over a range of growth temperatures. Although these responses are undoubtedly a major reason for the biological success of seaweeds in low temperature environments, little is known about either the effect of temperature on the organization of the photochemical apparatus (e.g., number and size of chlorophyll- pigment complexes), or the processes that regulate thermal acclimation. This project will permit Dr. Davison to spend a year's sabbatical in 1993 working in the laboratories of Dr. P. G. Falkowski (Brookhaven National Laboratory) and Dr. E. Gantt (university of Maryland) to learn modern molecular, biochemical and biophysical techniques. These techniques will then be used to address the following questions about thermal acclimation of photosynthesis. 1. How is thermal acclimation regulated at the molecular level (i.e., transcription or translation)? 2. How rapidly does the acclimation response occur. 3. How does thermal acclimation affect the organization and function of the photochemical apparatus? For example, how does temperature affect the stoichiometry of the various components of the photosystems and the size and efficiency of energy transfer within the light- harvesting chlorophyll protein complexes? 4. Does the apparent similarity between thermal acclimation and photoacclimation indicate that they are regulated by the same mechanism? In particular, this project will test the hypothesis that thermal acclimation and photoacclimation are both regulated by the cellular energy budget. The techniques used will include: (i) antibodies and cDNA probes for measuring the cellular content and rates of synthesis (transcription) of mRNA that codes for the key proteins of the photosynthetic apparatus and contents and synthesis (translation) of these proteins, (ii) a pump-probe fluorometer and other biophysical techniques to measure the functional size of the light-harvesting antennae associated with photosystems I and II and to study energy transfer within and between chlorophyll-protein complexes, and (iii) immunocytochemistry to study the localization of components of the photochemical apparatus on the thylakoid membranes. The information obtained through this research should substantially increase our understanding of the physiological processes that enable seaweeds to achieve high rates of productivity in low temperature environments.
