Previous Section Next Section Introduction Sunlight is the most abundant source of energy available on Earth, and it is used by photosynthetic organisms to fix inorganic carbon into organic molecules and produce biomass. In addition, ATPase synthesizes ATP from the trans-thylakoid proton gradient generated by the photosynthetic electron transport.
Photosynthesis is the biological process that converts solar energy into chemical energy, providing the raw materials for growth, development, and reproduction of plants, algae, and photosynthetic bacteria.
These diverse photoautotrophs are the major primary producers of organic matter and the ultimate source of food for nearly all life on Earth. My long-term research goals are to understand how photosynthetic energy conversion works, how it is regulated, and how it might be improved to help meet the world's needs for food and fuel.
My lab uses a wide array of experimental organisms and interdisciplinary approaches to investigate fundamental questions about assembly, regulation, and dynamics of photosynthesis. In particular, we have focused on a pair of model organisms that diverged from each other around the time that fungi diverged from animals: By comparing how photosynthesis works in diverse organisms, we hope to uncover general design principles of natural photosynthesis as well as unique adaptations to different environments.
Light response curves for photosynthesis compared with the rate of light absorption. Pmax, maximum rate of photosynthesis.
Krishna Niyogi Figure 2: Chlorophyll fluorescence image of an F2 population of Arabidopsis plants in which a mutation affecting nonphotochemical quenching is segregating. Krishna Niyogi Figure 3: False-color image of photosystem II efficiency in colonies of Chlamydomonas mutants that are unable to do photosynthesis.
Robert Calderon Regulation of Photosynthetic Light Harvesting The actual efficiency of photosynthetic light utilization in nature is relatively low, mainly because algae and plants are unable to use most of the light energy that they absorb. The rate of photosynthesis typically reaches a maximum Pmax at a light intensity well below that of full sunlight Figure 1.
Therefore, most of the photons that are absorbed by an algal cell or plant leaf end up being wasted. Photoprotective mechanisms that regulate light harvesting by dissipating excess light energy as heat have evolved to minimize generation of oxidizing molecules that would otherwise inhibit photosynthesis and growth.
We have made major contributions to understanding the regulation of photosynthesis by identifying and characterizing mutants of both Chlamydomonas and Arabidopsis that are defective in nonphotochemical quenching NPQwhich regulates light harvesting in nearly all photosynthetic eukaryotes Figure 2.
The mutant analysis helped to define the carotenoid pigments zeaxanthin and lutein that are involved in NPQ and showed that a photosystem II protein of previously unknown function, PsbS, is necessary for the main component of NPQ in Arabidopsis.
We are also investigating the possibility of improving photosynthesis by altering NPQ. Singlet Oxygen Signaling Aerobic organisms, from bacteria to plants and animals, have evolved sensing, signaling, and protective mechanisms to cope with various reactive oxygen species that are inevitably generated as products of intracellular and extracellular reactions.
Singlet oxygen is a short-lived, highly reactive oxygen species that is generated under excess light in the photosystem II reaction center, where it can inhibit photosynthesis. We discovered that Chlamydomonas exhibits an acclimation response to singlet oxygen stress that enables cells to survive singlet oxygen levels that would otherwise be lethal.
This response involves retrograde signaling from the chloroplast that regulates nuclear gene expression. To dissect the signal transduction pathway involved in sensing and responding to singlet oxygen, my lab has studied mutants that are unable to acclimate to singlet oxygen, as well as mutants that are constitutively more resistant to singlet oxygen.
Analysis of these mutants has led to the identification of putative transcription factors that control the acclimation response, and we are using genome-wide approaches to define their targets.
Dynamics of Photosynthetic Membranes and Protein Complexes The light-dependent reactions of oxygenic photosynthesis in algae and plants are catalyzed by a series of membrane protein complexes in chloroplasts. Although high-resolution structures are now available for the major complexes, a thorough understanding of the dynamic processes of photosynthetic membrane biogenesis, regulation, and repair is lacking.
To gain insight into how specific pigments, proteins, lipids, and cofactors are assembled into a functional photosynthetic membrane, my lab has isolated hundreds of new Chlamydomonas mutants that affect photosynthesis. We have found mutants affecting key reactions in chlorophyll biosynthesis and nearly every step of carotenoid biosynthesis, in addition to mutants that affect specific photosynthetic complexes.
For example, mutants that are defective in photosystem II activity were identified by imaging of chlorophyll fluorescence based on their lack of variable fluorescence Figure 3.
Through genetic and biochemical analysis of these mutants, we are uncovering novel factors that are necessary for photosystem II assembly.
Biogenesis, regulation, and repair of the photosynthetic apparatus in chloroplasts involve nano- to microscale reorganization of the photosynthetic membrane and its protein complexes. Working with an outstanding team of experts in advanced imaging, spectroscopy, and computational modeling, my lab aims to obtain a detailed molecular description of the organization and dynamics of the photosynthetic membrane at different levels of spatiotemporal resolution.
These approaches are integrated with development of new imaging methods in collaboration with Naomi Ginsberg [UC Berkeley and Berkeley Lab] and parallel modeling and theoretical efforts in collaboration with Phillip Geissler [UC Berkeley and Berkeley Lab]which will provide insights into the fundamental biophysical mechanisms governing protein interactions and the partitioning of protein complexes in the photosynthetic membrane.
As of March 11, Scientist Profile.combination of picosecond lifetime analysis and variable ﬂuorescence technique, we examined the dynamics of NPQ activation upon transition from dark to high light.
Analysis of heat-induced limitations using Maxi-Imaging-PAM and Dual-PAM Ulrich Schreiber and Christof Klughammer.
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1 Introduction. Different forms of non-photochemical quenching (NPQ) can be induced by illumination depending on light inten-sity and the physiological state of the investigated sam- Photochemical quantum yield. Y(ND). Testing accommodations are changes to the regular testing environment and auxiliary aids and services 2 that allow individuals with disabilities to demonstrate their true aptitude or achievement level on standardized exams or other high-stakes tests.
Nov 07, · This tutorial demonstrates how to add formulas and cascade a data analysis with Oracle Planning and Budgeting Cloud.
Using Smart View, you learn how to add f. NPQ Analysis Essay Sample. Estimate the qualified product or market potential It has two methods to estimate the qualified product or market potential the first is NPQ formula and the second is market build-up approach.
Product Quantity Analysis (Pq Analysis) 1 Definition An analysis over say several months of the demand for different products from a plant. The volume and variety is shown on a Pareto Diagram.
Products are sometimes classed into runners, repeaters and strangers. This information helps design the production method to suit the product e.g. high.