PARENT SESSION
Posters P5C Biosynthesis and assembly: Pigments. Abstracts (643-659)

High pressure: A tool to study volumetric changes during greening of etiolated leaves. Katalin Solymosi^*,1, László Smeller^{2, 3}, Judit Fidy^{2, 3}, Béla Böddi¹, ¹ Department of Plant Anatomy, Eötvös University, Budapest, Hungary² Department of Biophysics and Radiation Biology, Semmelweis University, Budapest, Hungary³ MTA-SE Research Group for Biophysics, Hungarian Academy of Science, Budapest, Hungary

ABSTRACT- In angiosperms, a key step of chlorophyll biosynthesis is the light-induced transformation of protochlorophyllide into chlorophyllide driven by NADPH:protochlorophyllide oxidoreductase (POR). After phototransformation, the fluorescence emission maximum of the newly formed chlorophyllide undergoes a spectral blue shift, which indicates the rearrangement of the enzyme macrodomains and the etioplast inner membranes. These processes can be observed with fluorescence spectroscopy. The appearance of chlorophyllide fluorescence and the decline in protochlorophyllide fluorescence were measured in the function of time after irradiation. The kinetical curves were fitted with exponentials and the activation volume of phototransformation was determined from the pressure dependence of the rate constants at 20 °C. The activation volume was 1.7 ml/mol, indicating that the formation of a H-bond/molecule has decisive role in the structural changes. Pressure also influenced the spectral blue shift of chlorophyllide (Shibata shift). At 20 °C, this process was almost completely inhibited above 100 MPa. At 40 °C, 400-500 MPa was needed to slow down this process. Based on the data obtained at high pressures, two components of the blue shift could be distinguished. The first was almost pressure independent; a slow blue shift proceeded even at very high pressures. The second was pressure dependent and had an activation volume of 43±11 ml/mol and 35±1.5 ml/mol at 20 °C and 40 °C, respectively. The first component was interpreted as a result of minor conformational changes of the POR enzyme followed by molecular movements of the newly formed chlorophyllide. The second component may be due to major molecular movements occurring in the lipid system of the membrane and in the chlorophyllide-protein complexes reflecting changes in the tertiary structure of proteins. Directly or indirectly, the whole process can be influenced by structural changes of the membrane lipids, too.

KEY WORDS: chlorophyllide, protochlorophyllide, phototransformation, shibata shift