Modelling and simulation of chlorophyll fluorescence from photosystem II as affected by temperature

Determination of Fv /Fm from Chlorophyll a Fluorescence without Dark Adaptation by an LSSVM Model

Evaluation of photosynthetic quantum yield is important for analyzing the phenotype of plants. Chlorophyll a fluorescence (ChlF) has been widely used to estimate plant photosynthesis and its regulatory mechanisms. The ratio of variable to maximum fluorescence, F_v /F_m , obtained from a ChlF induction curve, is commonly used to reflect the maximum photochemical quantum yield of photosystem II (PSII), but it is measured after a sample is dark-adapted for a long time, which limits its practical use. In this research, a least-squares support vector machine (LSSVM) model was developed to explore whether F_v /F_m can be determined from ChlF induction curves measured without dark adaptation. A total of 7,231 samples of 8 different experiments, under diverse conditions, were used to train the LSSVM model. Model evaluation with different samples showed excellent performance in determining F_v /F_m from ChlF signals without dark adaptation. Computation time for each test sample was less than 4 ms. Further, the prediction performance of test dataset was found to be very desirable: a high correlation coefficient (0.762 to 0.974); a low root mean squared error (0.005 to 0.021); and a residual prediction deviation of 1.254 to 4.933. These results clearly demonstrate that F_v /F_m , the widely used ChlF induction feature, can be determined from measurements without dark adaptation of samples. This will not only save experiment time but also make F_v /F_m useful in real-time and field applications. This work provides a high-throughput method to determine the important photosynthetic feature through ChlF for phenotyping plants.

Development of a minimized model structure and a feedback control framework for regulating photosynthetic activities

In this work, the main activities of the plant photosynthesis process are discussed to yield a minimized mathematical model structure with photosystem II (PSII) chlorophyll a fluorescence (ChlF) as a measurable output. After experimental validation of the model structure, we demonstrate that the states of the photosynthetic process may be observed by using this model and the extended Kalman filter method. We then show a feedback control framework that can be used to alter a given photosynthetic activity. The control framework is demonstrated with an example in which PSII ChlF is used as the feedback signal and light intensity is used as a controllable process input to regulate plastoquinone reduction. Although there are caveats, and further research is needed, the results lay the groundwork for further research on novel methods for optimization and regulation of photosynthetic activities, with a goal for sustainability.

Photosynthesis: basics, history and modelling

BACKGROUND

With limited agricultural land and increasing human population, it is essential to enhance overall photosynthesis and thus productivity. Oxygenic photosynthesis begins with light absorption, followed by excitation energy transfer to the reaction centres, primary photochemistry, electron and proton transport, NADPH and ATP synthesis, and then CO2 fixation (Calvin-Benson cycle, as well as Hatch-Slack cycle). Here we cover some of the discoveries related to this process, such as the existence of two light reactions and two photosystems connected by an electron transport 'chain' (the Z-scheme), chemiosmotic hypothesis for ATP synthesis, water oxidation clock for oxygen evolution, steps for carbon fixation, and finally the diverse mechanisms of regulatory processes, such as 'state transitions' and 'non-photochemical quenching' of the excited state of chlorophyll a.

SCOPE

In this review, we emphasize that mathematical modelling is a highly valuable tool in understanding and making predictions regarding photosynthesis. Different mathematical models have been used to examine current theories on diverse photosynthetic processes; these have been validated through simulation(s) of available experimental data, such as chlorophyll a fluorescence induction, measured with fluorometers using continuous (or modulated) exciting light, and absorbance changes at 820 nm (ΔA820) related to redox changes in P700, the reaction centre of photosystem I.

CONCLUSIONS

We highlight here the important role of modelling in deciphering and untangling complex photosynthesis processes taking place simultaneously, as well as in predicting possible ways to obtain higher biomass and productivity in plants, algae and cyanobacteria.

Modelling and simulation of chlorophyll fluorescence from PSII of a plant leaf as affected by both illumination light intensities and temperatures

The emission of chlorophyll fluorescence (ChlF) from photosystem II (PSII) of plant leaves the couple with photoelectron transduction cascades in photosynthetic reactions and can be used to probe photosynthetic efficiency and plant physiology. Because of population increase, food shortages, and global warming, it is becoming more and more urgent to enhance plant photosynthesis efficiency by controlling plant growth rate. An effective model structure is essential for plant control strategy development. However, there is a lack of reporting on modelling and simulation of PSII activities under the interaction of both illumination light intensities and temperatures, which are the two important controllable factors affecting, plant growth, especially for a greenhouse. In this work, the authors extended their work on modelling photosynthetic activities as affected by light and temperature to cover both the interaction effects of illumination light intensities and temperature on ChlF emission. Experiments on ChlF were performed under different light intensities and temperatures and used to validate the developed model structure. The average relative error between experimental data and model fitting is <0.3%, which shows the effectiveness of the developed model structure. Simulations were performed to show the interaction effect of light and temperature effects on photosynthetic activities.

Sensing Plant Physiology and Environmental Stress by Automatically Tracking Fj and Fi Features in PSII Chlorophyll Fluorescence Induction

Following a step excitation, chlorophyll fluorescence (ChlF) from photosystem II (PSII) of a dark-adapted photosynthetic organism exhibits the well-known OJIP pattern. The OJIP induction has been widely used in plant science and agriculture engineering. While the J and I phases are related to transitions of photochemical reaction redox states, characteristic fluorescence intensities at the two phases (F_j and F_i ) are often treated at fixed time points in routine measurement and thus do not account for variations in plant and experimental conditions, this (1) neglects the differences in the time of appearance of these phases, which is potentially useful information for characterizing plant status and environmental factors, and (2) leads to errors in measured F_j and F_i values in the many publications. In this work, an alternative method for consistent measurement of F_j and F_i was presented. The proposed method measures the curvatures in the OJIP curve and automatically tracks the characteristic transition points under variable sample and experimental conditions. Experiments were carried out to demonstrate the concept and classification capabilities of the method. This research has established a new framework to analyze ChlF and has enhanced the application capability of ChlF. It is expect useful in analysis ChlF from PSII.