Study of carbon metabolism in plants: from enzymes to the organism, from physiology to stress.

Plant carbon metabolism has been approached with two different focuses: study the biochemistry of enzymes in vitro and understanding the physiological role of enzymes in vivo. In both cases physiological and stress conditions were considered. The Chapter 1 is a comprehensive introduction on primary carbon metabolism, from photosynthesis to starch and sucrose metabolism. In addition, two insights are provided on carbon metabolism under abiotic stress and regulation of carbon metabolism. Starting with CO2 fixation, an enzyme of Calvin-Benson cycle has been characterized. In Chapter 2, the crystallographic structures and regulatory properties of phosphoribulokinase from the green algae Chlamydomonas reinhadtii and the plant Arabidopsis thaliana have been studied. The structure have been solved in collaboration with the Dr. Simona Fermani of Department of Chemistry "G. Ciamician" (University of Bologna) and Dr. Stephane D. Lemaire (CNRS - Paris). Then in Chapter 3 the regulation of the α-amylase 3 (AtAMY3) of Arabidopsis thaliana by glutathione has been characterized. The chapter focuses on glutathionylation, a post-translational redox modifications which can occur when oxidative stress raises inside cellular compartments. The last two chapters illustrate two studies on Arabidopsis thaliana plants. In Chapter 5 the adaptation of carbon metabolism to osmotic stress has been investigated using T-DNA lines for enzymes involved in carbon metabolism which are not essential for normal plant physiology. In the last chapter, Chapter 6, the focus went back to physiological conditions and three T-DNA lines for the three Arabidopsis dikinases have been studied. Although GWD1 has been examined several times and in different species, the other two dikinases, PWD and GWD2, remained poorly studied. In this analysis, the development of plants carrying T-DNA insertions has been monitored and different parameters on seeds and plants have been evaluated to understand the function of GWD1, PWD and GWD2 along the plant life cycle