We aim to identify "new" chaperone and assembly factors of the oxygen-evolving complex, Photosystem II (PSII). Current knowledge of the structure and components of PSII is quite comprehensive, yet little is known about the complex assembles or disassembles for repair, and even less about how its function is fine-tuned for optimal performance under fast and ever-changing light and temperature conditions. We will use our newly developed meristematic cell line to grow Arabidopsis in liquid cell cultures in which the plants are not differentiated into root, leaf and stem. In this system the assembly and greening of the photosynthetic protein complexes are slowed, presenting us, for the first time, with an opportunity to dissect in detail the assembly process and to identify some of the "missing" components. The liquid culture system allows us to grow the cells in the presence of metal isotopes; in combination with MS analyses, this will provide information on the timing and nature of their incorporation. These in vitro analyses will be combined with fluorescence correlation spectroscopy (FCS) to perform single molecule/cell analysis in vivo. This unique combination will enable identification of new chaperones, revealing new perspectives on their interaction in living plant cells. A deeper knowledge of the regulatory mechanism within the chloroplast protein complexes will facilitate the development of new tools for targeted plant breeding to increase biomass and stress resistance.