Nejvíce citovaný článek - PubMed ID 25569797
Parameters of photosynthetic energy partitioning
The rate of net CO2 uptake is proportional to dim light and saturates when the light exceeds the plant's 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 μmol photons m-2 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 hysteresis and non-linearity. The other was mainly formed by regulatory 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 plastoquinone pool reduction and variables affecting non-photochemical quenching that form the constitutive and regulatory hysteresis types. The model simulations provided mechanistic insights into molecular processes forming the plant response to oscillating light.
- Klíčová slova
- chlorophyll fluorescence, frequency domain, harmonics, mathematical model, photosynthesis,
- MeSH
- Arabidopsis * účinky záření fyziologie metabolismus genetika MeSH
- chlorofyl metabolismus MeSH
- fluorescence MeSH
- fotosyntéza účinky záření fyziologie MeSH
- proteiny huseníčku metabolismus genetika MeSH
- světlo * MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- chlorofyl MeSH
- proteiny huseníčku MeSH
Quantitative measurement of light intensity is a key step in ensuring the reliability and the reproducibility of scientific results in many fields of physics, biology, and chemistry. The protocols presented so far use various photoactive properties of manufactured materials. Here, leaves are introduced as an easily accessible green material to calibrate light intensity. The measurement protocol consists in monitoring the chlorophyll fluorescence of a leaf while it is exposed to a jump of constant light. The inverse of the characteristic time of the initial chlorophyll fluorescence rise is shown to be proportional to the light intensity received by the leaf over a wide range of wavelengths and intensities. Moreover, the proportionality factor is stable across a wide collection of plant species, which makes the measurement protocol accessible to users without prior calibration. This favorable feature is finally harnessed to calibrate a source of white light from exploiting simple leaves collected from a garden.
- Klíčová slova
- actinometry, fluorescence, green materials, irradiance, light intensity, photoactive materials,
- Publikační typ
- časopisecké články MeSH
The present paper aims to open discussion on the information content, physical mechanism(s), and measuring protocols to determine the partitioning of the absorbed light energy in oxygenic photosynthetic organisms. Revisiting these questions is incited by recent findings discovering that PSII, in addition to its open and closed state, assumes a light-adapted charge-separated state and that chlorophyll a fluorescence induction (ChlF), besides the photochemical activity of PSII, reflects the structural dynamics of its reaction center complex. Thus, the photochemical quantum yield of PSII cannot be determined from the conventional ChlF-based protocol. Consequently, the codependent quantity - the quantum yield of the so-called nonregulatory constitutive nonphotochemical quenching (npq) - loses its physical meaning. Processes beyond photochemistry and regulatory npq should be identified and characterized by multifaceted studies, including ChlF. Such investigations may shed light on the putative roles of dissipation and other energy-consuming events in the stress physiology of photosynthetic machinery.
- Klíčová slova
- Fv/Fm, chlorophyll a fluorescence, constitutive nonregulatory dissipation, nonphotochemical quenching, quantum yield, structural dynamics,
- Publikační typ
- časopisecké články MeSH
Woody plant areal encroachment is pervasive throughout the Southern Great Plains, USA. The ability of woody plants to dissipate excess solar radiation - dynamically over the day and sustained periods without recovery overnight - is key for maintaining photosynthetic performance during dry stretches, but our understanding of these processes remains incomplete. Photosynthetic performance and energy dissipation were assessed for co-occurring encroachers on the karst Edwards Plateau (Juniperus ashei, Prosopis glandulosa, and Quercus fusiformis) under seasonal changes in water status. Only J. ashei experienced mild photoinhibition from sustained energy dissipation overnight while experiencing the lowest photochemical yields, minimal photosynthetic rates, and the highest dynamic energy dissipation rates at midday during the dry period - indicating susceptibility to photosynthetic downregulation and increased dissipation under future drought regimes. Neither other encroacher experienced sustained energy dissipation in the dry period, though P. glandulosa did experience marked reductions in photosynthesis, photochemical yields, and increased regulatory dynamic energy dissipation.
- Klíčová slova
- carbon cycling, drought avoider, drought tolerant, grasslands, nonphotochemical quenching, savannas,
- Publikační typ
- časopisecké články MeSH
Plants growing in nature often experience fluctuating irradiance. However, in the laboratory, the dynamics of photosynthesis are usually explored by instantaneously exposing dark-adapted plants to constant light and examining the dark-to-light transition, which is a poor approximation of natural phenomena. With the aim creating a better approximation, we exposed leaves of pea (Pisum sativum) to oscillating light and measured changes in the functioning of PSI and PSII, and of the proton motive force at the thylakoid membrane. We found that the dynamics depended on the oscillation period, revealing information about the underlying regulatory networks. As demonstrated for a selected oscillation period of 60 s, the regulation tries to keep the reaction centers of PSI and PSII open. We present an evaluation of the data obtained, and discuss the involvement of particular processes in the regulation of photosynthesis. The forced oscillations provided an information-rich fingerprint of complex regulatory networks. We expect future progress in understanding these networks from experiments involving chemical interventions and plant mutants, and by using mathematical modeling and systems identification and control tools.
- Klíčová slova
- Pisum sativum, Fluctuating light, forced oscillations, pea, photosynthesis, photosystem I and II, proton motive force, regulation,
- MeSH
- fotosyntéza fyziologie MeSH
- fotosystém I (proteinový komplex) metabolismus MeSH
- fotosystém II (proteinový komplex) * metabolismus MeSH
- hrách setý * metabolismus MeSH
- listy rostlin metabolismus MeSH
- rostliny metabolismus MeSH
- světlo MeSH
- transport elektronů fyziologie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- fotosystém I (proteinový komplex) MeSH
- fotosystém II (proteinový komplex) * MeSH
To cope with biotic and abiotic stress conditions, land plants have evolved several levels of protection, including delicate defense mechanisms to respond to changes in the environment. The benefits of inducible defense responses can be further augmented by defense priming, which allows plants to respond to a mild stimulus faster and more robustly than plants in the naïve (non-primed) state. Priming provides a low-cost protection of agriculturally important plants in a relatively safe and effective manner. Many different organic and inorganic compounds have been successfully tested to induce resistance in plants. Among the plethora of commonly used physicochemical techniques, priming by plant growth regulators (phytohormones and their derivatives) appears to be a viable approach with a wide range of applications. While several classes of plant hormones have been exploited in agriculture with promising results, much less attention has been paid to cytokinin, a major plant hormone involved in many biological processes including the regulation of photosynthesis. Cytokinins have been long known to be involved in the regulation of chlorophyll metabolism, among other functions, and are responsible for delaying the onset of senescence. A comprehensive overview of the possible mechanisms of the cytokinin-primed defense or stress-related responses, especially those related to photosynthesis, should provide better insight into some of the less understood aspects of this important group of plant growth regulators.
- Klíčová slova
- ROS, chlorophyll fluorescence, cytokinin, photosynthesis, priming, stomata, stress,
- Publikační typ
- časopisecké články MeSH
- přehledy MeSH
Oxygenic photosynthesis takes place in thylakoid membranes (TM) of cyanobacteria, algae, and higher plants. It begins with light absorption by pigments in large (modular) assemblies of pigment-binding proteins, which then transfer excitation energy to the photosynthetic reaction centers of photosystem (PS) I and PSII. In green algae and plants, these light-harvesting protein complexes contain chlorophylls (Chls) and carotenoids (Cars). However, cyanobacteria, red algae, and glaucophytes contain, in addition, phycobiliproteins in phycobilisomes that are attached to the stromal surface of TM, and transfer excitation energy to the reaction centers via the Chl a molecules in the inner antennas of PSI and PSII. The color and the intensity of the light to which these photosynthetic organisms are exposed in their environment have a great influence on the composition and the structure of the light-harvesting complexes (the antenna) as well as the rest of the photosynthetic apparatus, thus affecting the photosynthetic process and even the entire organism. We present here a perspective on 'Light Quality and Oxygenic Photosynthesis', in memory of George Christos Papageorgiou (9 May 1933-21 November 2020; see notes a and b). Our review includes (1) the influence of the solar spectrum on the antenna composition, and the special significance of Chl a; (2) the effects of light quality on photosynthesis, measured using Chl a fluorescence; and (3) the importance of light quality, intensity, and its duration for the optimal growth of photosynthetic organisms.
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 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 dark and light acclimation. We show 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 nonlinear phenomena, including photosynthetic regulation. To support these claims, we measured chlorophyll fluorescence emission of the green alga Chlorella sorokiniana in light that was sinusoidally modulated 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 tool in plant sensing.
Leaf senescence, accompanied by chlorophyll breakdown, chloroplast degradation and inhibition of photosynthesis, can be suppressed by an exogenous application of cytokinins. Two aromatic cytokinin arabinosides (6-benzylamino-9-β-d-arabinofuranosylpurines; BAPAs), 3-hydroxy- (3OHBAPA) and 3-methoxy- (3MeOBAPA) derivatives, have recently been found to possess high anti-senescence activity. Interestingly, their effect on the maintenance of chlorophyll content and maximal quantum yield of photosystem II (PSII) in detached dark-adapted leaves differed quantitatively in wheat (Triticum aestivum L. cv. Aranka) and Arabidopsis (Arabidopsisthaliana L. (Col-0)). In this work, we have found that the anti-senescence effects of 3OHBAPA and 3MeOBAPA in wheat and Arabidopsis also differ in other parameters, including the maintenance of carotenoid content and chloroplasts, rate of reduction of primary electron acceptor of PSII (QA) as well as electron transport behind QA, and partitioning of absorbed light energy in light-adapted leaves. In wheat, 3OHBAPA had a higher protective effect than 3MeOBAPA, whereas in Arabidopsis, 3MeOBAPA was the more efficient derivative. We have found that the different anti-senescent activity of 3OHBAPA and 3MeOBAPA was coupled to different ethylene production in the treated leaves: the lower the ethylene production, the higher the anti-senescence activity. 3OHBAPA and 3MeOBAPA also efficiently protected the senescing leaves of wheat and Arabidopsis against oxidative damage induced by both H2O2 and high-light treatment, which could also be connected with the low level of ethylene production.
- Klíčová slova
- Arabidopsis, chlorophyll fluorescence, cytokinin derivative, ethylene, oxidative stress, photosystem II, phytohormone, senescence, wheat,
- MeSH
- Arabidopsis účinky léků růst a vývoj metabolismus MeSH
- cytokininy farmakologie MeSH
- ethyleny metabolismus MeSH
- fotosyntéza MeSH
- listy rostlin účinky léků růst a vývoj metabolismus MeSH
- pšenice účinky léků růst a vývoj metabolismus MeSH
- regulátory růstu rostlin farmakologie MeSH
- stárnutí buněk * MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- cytokininy MeSH
- ethylene MeSH Prohlížeč
- ethyleny MeSH
- regulátory růstu rostlin MeSH
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.
- Klíčová slova
- Calvin–Benson cycle, chlorophyll a fluorescence induction, discoveries in photosynthesis, modelling, non-photochemical quenching (of the excited state of chlorophyll a), photosynthetic electron transport, state transitions,
- MeSH
- biomasa MeSH
- chlorofyl a * MeSH
- chlorofyl MeSH
- fotosyntéza * MeSH
- fotosystém II (proteinový komplex) MeSH
- kyslík MeSH
- lidé MeSH
- světlo MeSH
- transport elektronů MeSH
- voda MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- přehledy MeSH
- Názvy látek
- chlorofyl a * MeSH
- chlorofyl MeSH
- fotosystém II (proteinový komplex) MeSH
- kyslík MeSH
- voda MeSH
