Biology subjects

Nedbal, L.

Publications and source records attributed to Nedbal, L..

6 recordsLinked to original sources

bioRxiv2026

Frequency-domain identification of photosynthetic regulation under fluctuating light

Plant photosynthesis operates under naturally fluctuating light, yet its dynamic responses across timescales remain incompletely understood. Here, we apply sinusoidal light modulation as a controlled periodic input and analyze the response in the frequency domain, enabling quantitative system identification of photosynthetic dynamics. Using a minimal biochemical model of photosynthetic electron transport and regulation, we show that photosynthetic performance under fluctuating light differs systematically from that under constant illumination, even when the mean photon flux density is identical. Large-amplitude oscillations generate higher harmonics and alter time-averaged chlorophyll fluorescence, oxygen evolution, and non-photochemical quenching (NPQ), demonstrating that fluctuating light acts not merely as a perturbation but as a distinct physiological regime. For sufficiently small perturbations, the system behaves approximately linearly and can be characterized by transfer functions and Bode plots. We identify two dynamic regimes separated by a characteristic timescale of approximately 10 s. In the high-frequency domain, the response is governed by constitutive photochemical processes and reflects local steady-state properties, including the redox state of the plastoquinone pool. In the low-frequency domain, adaptive regulatory feedback dominates, particularly NPQ, which reshapes both the amplitude and phase of the photosynthetic response. Characteristic frequency-response features, including gain transitions and phase extrema, provide direct information about physiologically relevant quantities such as effective relaxation times and regulatory coupling strengths. We further introduce the concept of regulation fingerprints, defined as ratios of transfer functions between regulated and unregulated systems. These fingerprints reveal distinct spectral signatures of fast PsbS-dependent and slower zeaxanthin-dependent NPQ, enabling their quantitative separation and providing experimentally testable predictions for regulatory dynamics. Together, these results establish frequency-domain analysis as a general framework for probing, identifying, and testing the dynamic regulation of photosynthesis under fluctuating light. More broadly, they suggest that fluctuating illumination, often regarded as experimental noise, can instead serve as a structured probe of photosynthetic function in both laboratory and field environments.

plant biology↗

bioRxiv2025

Constitutive and regulatory responses of Arabidopsis thaliana to harmonically oscillating light

The rate of net CO2 uptake is proportional to dim light and saturates when the light exceeds the plant assimilation capacity. This simple relationship between constant light and photosynthesis becomes intriguingly complex when the light oscillates. The rates of photosynthesis may differ between the descending and ascending phases of light oscillation. This hysteresis changes with the frequency and amplitude of the light and reports on the dynamics of the photosynthetic reactions and their regulation. Here, we investigated the chlorophyll fluorescence response of Arabidopsis thaliana to light oscillating with three different amplitudes: 100-200, 100-400, and 100-800 mol photons{middle dot}m-2{middle dot}s-1, each with periods ranging from 1 s to 8 min. The light amplitudes and periods were chosen to represent light patterns often appearing in nature. Three genotypes were compared: wild-type Col-0 and npq1 and npq4 mutants that are incapacitated in the rapidly reversible energy-dependent non-photochemical quenching (qE). The experiments identified two major dynamic patterns. One was found in oscillation periods shorter than 30 s, characterized by constitutive non-linearity and hysteresis. The other was mainly formed by regulatory non-linearity and hysteresis, occurring when the oscillation periods were longer than 30 s. The mathematical model simulating the chlorophyll fluorescence dynamics qualitatively reproduced the constitutive and regulatory dynamic patterns observed in the experiments. The model simulations illustrated the dynamics of non-photochemical quencher activation, plastoquinone pool reduction, and lumen pH that form the constitutive and regulatory non-linearities. The model simulations provided mechanistic insight into molecular processes forming the plant response to oscillating light.

plant biology↗

bioRxiv2024

A novel dual-excitation pulse-amplitude-modulation fluorometer for investigating photosynthesis of plants

A modular instrument was developed to measure the fluorescence yield in plants subject to a combination of two harmonically-oscillating blue lights with independently controlled frequencies and phases.It uses the pulse-amplitude-modulation (PAM) method to measure the fluorescence yield independently of the plant irradiance. Compared to existing commercial instruments, it uses a higher measuring frequency ({approx} 60 kHz) and higher measuring flash irradiance. This enables averaging over a number of subsequent measurement data points to achieve a higher signal-to-noise ratio. The manuscript describes the design, testing, and characterization of the operational limits of the instrument. It identifies its current weaknesses and makes recommendations for improvements. It is accompanied by supplementary materials containing the electronic schematics and the source code. The instrument was used to study a plant response to a mixture of two oscillating lights. It resulted in an excellent signal-to-noise ratio of the measured fluorescent yield. The measurements clearly demonstrated that the fluorescence yield of a plant subject to a combination of two harmonically-oscillating lights is not the same as the sum of the responses to the two oscillating lights applied independently. The observed non-linearity leads to the important conclusion that the time- and frequency-domain cannot be connected by a Fourier transform. Therefore, the frequency-domain approach will yield novel information that is not redundant to the well-established time-domain measurements.

plant biology↗

bioRxiv2022

On the regulation of photosynthesis in pea leaves exposed to oscillating light.

Plants grow in nature often in fluctuating irradiance. In the laboratory, the dynamics of photosynthesis is usually explored by instantaneously exposing dark-adapted plants to constant light and detecting the dark-to-light transient, which is only a poor approximation of natural phenomena. Aiming at a better approximation, we exposed pea leaves to oscillating light and measured, during oscillations, changes in function of photosystem I and II and of the proton-motive force at the thylakoid membrane. The dynamics depends on the oscillation period, leaving information about the regulatory networks. As demonstrated for selected period of the oscillation of 60 s, the regulations try to keep reactions centres of photosystems I and II open. A possible evaluation of obtained data is presented and involvement of particular processes in regulation of photosynthesis is discussed. The forced oscillations provide information-rich fingerprint of complex regulatory networks. Further progress in understanding the networks is expected from experiments involving chemical interventions, plant mutants, and by using mathematical modelling and the system identification and system control tools, as already applied in other parts of science. HighlightMeasurement of photosynthetic signals during illumination of plants by light, whose intensity oscillates as sinus function provides information about regulation of photosynthesis in fluctuating light.

plant biology↗

bioRxiv2022

The dynamics of non-photochemical quenching and cyclic electron transport in A.thaliana exposed to harmonically oscillating light

In natural environments, plants are exposed to rapidly changing light. Maintaining photosynthetic efficiency while avoiding photodamage requires equally rapid regulation of photoprotective mechanisms. We asked what the operation frequency range of regulation is in which plants can efficiently respond to varying light. Chlorophyll fluorescence, P700, plastocyanin, and ferredoxin responses of wild-type Arabidopsis thaliana were measured in oscillating light of various frequencies. We also investigated the npq1 mutant lacking violaxanthin de-epoxidase, the npq4 mutant lacking PsbS-protein, and the mutants crr2-2, and pgrl1ab impaired in different pathways of the cyclic electron transport. The fastest was the PsbS-regulation responding to oscillation periods longer than 10s. Processes involving violaxanthin de-epoxidase dampened changes of chlorophyll fluorescence in oscillation periods of 2min or longer. Knocking out the PGRL1-PGR5 pathway strongly reduced variations of all monitored parameters, probably due to congestion in the electron transport. Incapacitating the NDH-like pathway only slightly changed the photosynthetic dynamics. Our observations are consistent with the assumption that non-photochemical quenching in slow light oscillations involves violaxanthin de-epoxidase to produce, presumably, a stationary, non-oscillating level of zeaxanthin. We interpret the observed dynamics of Photosystem I components as being formed in slow light oscillations partially by thylakoid remodeling that modulates the redox rates.

plant biology↗

bioRxiv2021

Photosynthesis dynamics and regulation sensed in the frequency domain

Foundations of photosynthesis research have been established mainly by studying the response of plants to changing light, typically to sudden exposure to a constant light intensity after a dark acclimation or light flashes. This approach remains valid and powerful, but can be limited by requiring dark acclimation before time-domain measurements and often assumes that rate constants determining the photosynthetic response do not change between the dark- and light-acclimation. We present experimental data and mathematical models demonstrating that these limits can be overcome by measuring plant responses to sinusoidally modulated light of varying frequency. By its nature, such frequency-domain characterization is performed in light-acclimated plants with no need for prior dark acclimation. Amplitudes, phase shifts, and upper harmonic modulation extracted from the data for a wide range of frequencies can target different kinetic domains and regulatory feedbacks. The occurrence of upper harmonic modulation reflects non-linear phenomena, including photosynthetic regulation. To support these claims, we present a frequency- and time-domain response in chlorophyll fluorescence emission of the green alga Chlorella sorokiniana in the frequency range 1000 - 0.001 Hz. Based on these experimental data and numerical as well as analytical mathematical models, we propose that frequency-domain measurements can become a versatile new tool in plant sensing. One sentence summaryIt is proposed to characterize photosynthesis in the frequency domain without the need for dark adaptation and, thus, without assumptions about the dark-to-light transition.

plant biology↗