Events

Light Harvesting by Photosystem II in the Thykaloid Membrane of Plants

August 27, 2015 at 10:30 am, Room 66-360

Dr. Kapil Amarnath
Harvard University

Abstract: Photosystem II (PSII), which provides the electrons that power photosynthesis, is crucial to a leaf’s ability to efficiently and robustly harvest sunlight into chemical energy. In dim light, sunlight absorbed by pigments in the antenna complexes of PSII is rapidly transferred to the reaction centers and trapped for long term storage as chemical energy with >80% quantum efficiency. In high light, to avoid photodamage, absorbed sunlight is dissipated safely as heat by nonphotochemical quenching mechanisms. However, how PSII’s functionality arises from its structure has remained a major question since its discovery nearly 70 years ago. A major challenge has been the multiscale nature of PSII light harvesting, which covers time scales from femtoseconds to minutes and length scales from angstroms to hundreds of nanometers. In this talk, we explain the high efficiency of PSII light harvesting by building the first model of the photosystem II (PSII) membrane that correctly incorporates the quantum effects previously observed in individual complexes. We show that excitation moves diffusively through the antenna with a diffusion length of 50 nm until it reaches a reaction center, where charge separation serves as an energetic trap. To understand PSII’s NPQ mechanisms, we developed a new technique, fluorescence lifetime snapshots, which allows us to perform time correlated single-photon counting on whole leaves as they acclimate to changes in light intensity. We constrain the possible mechanisms of NPQ by fitting snapshot data with our PSII model.

Bio: I grew up in Nashville, TN, where I began my career in science by working in my parents’ lab, doing analytical chemistry. I then attended MIT, where I worked for JoAnne Stubbe for my UROP, and gained an interest in biological mechanism. For graduate school, I joined Graham Fleming’s lab at UC Berkeley, where I studied the biophysical mechanisms of light harvesting in green algae and leaves. I am currently a postdoc studying the systems biology of cyanobacteria at Harvard and would like to move from natural to artificial light harvesting materials.