Photosynthesis utilizes energy from the sun to power photochemical reactions that store energy in chemical bonds, creating the basis of our food chain. As the world population continues to grow, the projected demand for crops is increasing at a higher rate than current agricultural techniques can produce. Altering dynamics around how plants and algae protect themselves from changes in light levels has been proven to increase crop yields. Light levels are constantly changing in nature due to shifts in canopies, weather events, seasons, and photosynthetic organisms need rapidly reversible mechanisms to adjust to sudden changes between high and low light levels. In high light (HL) conditions, excess energy is unable to participate in photochemistry and is instead dissipated through non-photochemical quenching (NPQ) as heat, minimizing reactive oxygen species formation. But, if these NPQ pathways are not de-activated, energy is lost even in low light conditions, leading to an underutilization of light. Plants and algae need to balance photochemistry and photoprotection to maximize efficient energy use in all light conditions. However, NPQ pathways can be slow to turn on and off. By understanding these processes more fully, photosynthesis can be optimized by increasing organisms’ responsiveness to light.
In this dissertation, my research focuses on understanding the role that each unique molecular component of NPQ contributes to the overall summation of photoprotection. NPQ is incredibly diverse across photosynthetic organisms—as will be discuss in Chapter 1—yet there are several key features that are nearly universal. These components would be pH-sensing proteins and the xanthophyll cycle. In addition to experiments, we have created a model using these two molecular components as a basis to inform our understanding of the dynamics of these NPQ components in response to all types of light environments, which is explored in Chapter 2. The model is quantitative and predictive, which is helpful in determining the limits of photosynthetic yield improvements when parameterized to a specific organism. The model in turn has highlighted unique attributes of the xanthophyll cycle, particularly the role of antheraxanthin in photoprotective memory (Chapter 3). We explore the effect of two-state verses three-state xanthophyll cycles further in Chapter 4. By creating a flexible model based on the biochemical components of NPQ, we can expand this work to crop plants and other organisms to predict how changes in relevant NPQ pathways might affect the expression and dynamics of photoprotection.
