Photosynthesis is not only vital for plant growth and survival but also indicative of plant-environment interactions. This research was designed to analyze photoelectron kinetics and its dependence on environmental factors. This project included three parts: I. Modeling of photoelectron transport, II. Techniques for enhanced parameter estimation, and III. Methodology development for evaluating drought and herbicide stresses.
In Part I, two models were developed for the photoelectron transport process in the early stage of photosystem II (PSII) with delayed fluorescence (DF) as a measurable output. Using the combinational redox state of plastoquinone A and B (QA and QB) in a reaction center as state variables leads to a five-state model that is conditionally linear. This model was used to observe some interesting characteristics of plastoquinone kinetics. Using the redox state of individual QA and QB results in a three-state nonlinear model that is nonlinear but compact. Both models were validated through experiments. The models could effectively predict DF emission and the estimated parameters correctly reflected the expected changes induced by drought and DCMU ([3-(3,4-dichlorophenyl)-1,1-dimethylurea], a commonly used herbicide).
In Part II, techniques were developed to overcome difficulties in system parameter estimation resulting from: (1) lack of direct measurements, (2) limited liberty in implementing rich perturbations, and (3) plant circadian. The identifiability of linear time-invariant systems with only initial condition responses was analyzed for systems with only one measurable state (OMS) and n measurable states (NMS). For an OMS system, n initial condition responses are necessary for uniquely determining the system matrix. Explicit formulations and a non-recursive algorithm are developed for both OMS and NMS systems. A recurrent-pulse excitation method was devised to achieve perturbation richness by executing simple pulses. The technique allowed determination of model parameters that would otherwise be difficult to determine uniquely. DF emission was found to follow a 24-hour circadian cycle, which adds an unwanted variation in DF measurements. A technique was proposed to filter and thus minimize the circadian influence.
In Part III, methodologies were developed to evaluate drought and DCMU stresses based on DF measurements. DF dependence on the availability of electron donors (water) was modeled and analyzed by using the system models. This yielded an effective way to define and measure water deficiency as the deficit in PSII photoelectron generation efficiency from the maximum achievable by supplemental water diffusion. This deficit could be effectively evaluated from measured DF emissions. Both theoretical analysis and experimental results showed that long-term DF emission following an excitation pulse was proportional to reaction centers without DCMU binding. This resulted in an effective plant-based technique for measuring DCMU concentrations.
|School:||University of Missouri - Columbia|
|School Location:||United States -- Missouri|
|Source:||DAI-B 72/08, Dissertation Abstracts International|
|Subjects:||Agricultural engineering, Environmental engineering|
|Keywords:||Biosensors, Delayed fluorescence, Drought, Photosystem II|
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