Plants are ultimate harvesters of sunlight, the growth and development of which largely depend on abiotic and biotic environmental factors. Light is the most important factor influencing both energy metabolism and developmental processes of the photoautotrophic organisms. Plants have adopted efficient mechanisms to sense changes of light conditions and to induce adaptive processes in order to cope with environmental stresses and to raise plant fitness in natural growth conditions. Apart from the basic task in photosynthetic energy metabolism, chloroplasts are also the place for a numerous metabolic reactions including nitrogen and sulphur assimilation, biosynthesis of amino acids, lipids, hormones, cofactors and secondary metabolites that directly affect plant growth capacity. Redox signals are crucial in the control of these chloroplast functions. My project addresses to systemic analysis of chloroplast redox networks with specific focus on the plastidial members of thioredoxin protein family, and to molecular dissection of their function in plant development, control of chloroplast metabolism, determination of biomass yield and in relation to plant fitness. The aim of my research project is to discover the molecular mechanisms which are involved in the regulation of photosynthetic reactions under naturally fluctuating environmental conditions. The main goal is to identify the components, the modifications of which increase photosynthetic efficiency and thus productivity of plants and photosynthetic microbes.