UC Berkeley

As the global population continues to grow, optimizing photosynthetic light harvesting has emerged as an important route for increasing the production of food and bioenergy. Under periods of excess illumination, photosynthetic organisms initiate a suite of photoprotective mechanisms, collectively referred to as nonphotochemical quenching (NPQ), which thermally dissipate chlorophyll excited states. However, the molecular basis for NPQ is still unclear, partly due to overlapping dissipation mechanisms, shared molecular players, significant variation across species, and the difficulty of experimentally measuring dissipation in vivo and under physiologically relevant conditions. Additionally, while NPQ is thought to protect against downstream oxidative damage, there has been little direct investigation of the temporal and spatial connections between NPQ and reactive oxygen species, such as singlet oxygen, which is thought to be a toxic byproduct of photosynthesis though it may also play essential roles in intra-cellular signaling.

In this dissertation, I employ a suite of “snapshot” spectroscopic methods – including transient absorption, fluorescence lifetime, and electron paramagnetic resonance techniques – in order to better understand the complex operation of NPQ in intact photosynthetic systems. By applying these snapshot methods to a range of genetically altered plants and algae under dynamically changing illumination conditions, a more complete understanding of the complex in vivo operation of excitation energy dissipation is obtained, with particular emphasis on the roles of carotenoids, pH-sensing proteins, and oxidative species. These fundamental findings hold great promise for ongoing efforts to boost the biomass yields of natural photosynthesis as well as improve the sustainable production of bioenergy.