Two molecular species of phytochrome A with distinct modes of action

2019 ◽  
Vol 46 (2) ◽  
pp. 118 ◽  
Author(s):  
V. Sineshchekov
Keyword(s):  
Molecular Species ◽  
High Irradiance ◽  
Fine Tuning ◽  
Light Conditions ◽  
Functional Heterogeneity ◽  
Serine Residue ◽  
Environmental Light ◽  
Adiantum Capillus Veneris ◽  
Phytochrome System ◽  
Cellular Context

Adaptation of plants to environmental light conditions is achieved via operation of a highly complex photoreceptor apparatus. It includes the phytochrome system comprising phytochromes A and B (phyA and phyB) as the major components. phyA differs from phyB by several properties, including its ability to mediate all three photoresponse modes – the very low and low fluence responses (VLFR and LFR respectively) and the high irradiance responses (HIR), whereas phyB is responsible for LFR. This review discusses the uniqueness of phyA in terms of its structural and functional heterogeneity. The photoreceptor is presented in monocots and dicots by two native molecular species, phyAʹ and phyAʹʹ, differing by spectroscopic, photochemical and phenomenological properties. phyA differentiation into substates includes post-translational phosphorylation of a serine residue(s) at the N-terminal extension of the molecule with phyAʹ being the phosphorylated species and phyAʹʹ, dephosphorylated. They differ also by their mode of action, which depends on the cellular context. The current working hypothesis is that phyAʹ mediates VLFR and phyAʹʹ, HIR and LFR. The content and functional activity of the two pools are regulated by light and by phosphatase/kinase equilibrium and pH in darkness, what contributes to the fine-tuning of the phytochrome system. Detection of the native pools of the cryptogamic plant fern Adiantum capillus-veneris phy1 (phy1ʹ and phy1ʹʹ) similar to those of phyA suggests that the structural and functional heterogeneity of phyA is not a unique phenomenon and may have arisen earlier in the molecular evolution of the phytochrome system than the appearance of the angiosperm phytochromes.

scholarly journals A chloroplast thylakoid lumen protein is required for proper photosynthetic acclimation of plants under fluctuating light environments

2017 ◽  
Vol 114 (38) ◽  
pp. E8110-E8117 ◽  
Author(s):  
Jun Liu ◽  
Robert L. Last
Keyword(s):  
Photosystem Ii ◽  
Light Stress ◽  
High Irradiance ◽  
Light Conditions ◽  
Agricultural Plant ◽  
Photosynthetic Organisms ◽  
Fluctuating Light ◽  
Stress Susceptibility ◽  
Efficiency And Productivity ◽  
Photosynthetic Adaptation

Despite our increasingly sophisticated understanding of mechanisms ensuring efficient photosynthesis under laboratory-controlled light conditions, less is known about the regulation of photosynthesis under fluctuating light. This is important because—in nature—photosynthetic organisms experience rapid and extreme changes in sunlight, potentially causing deleterious effects on photosynthetic efficiency and productivity. Here we report that the chloroplast thylakoid lumenal protein MAINTENANCE OF PHOTOSYSTEM II UNDER HIGH LIGHT 2 (MPH2; encoded byAt4g02530) is required for growth acclimation ofArabidopsis thalianaplants under controlled photoinhibitory light and fluctuating light environments. Evidence is presented thatmph2mutant light stress susceptibility results from a defect in photosystem II (PSII) repair, and our results are consistent with the hypothesis that MPH2 is involved in disassembling monomeric complexes during regeneration of dimeric functional PSII supercomplexes. Moreover,mph2—and previously characterized PSII repair-defective mutants—exhibited reduced growth under fluctuating light conditions, while PSII photoprotection-impaired mutants did not. These findings suggest that repair is not only required for PSII maintenance under static high-irradiance light conditions but is also a regulatory mechanism facilitating photosynthetic adaptation under fluctuating light environments. This work has implications for improvement of agricultural plant productivity through engineering PSII repair.

Assimilate Movement in Lolium and Sorghum Leaves. II. Irradiance Effects on the Products of Photosynthesis

1976 ◽  
Vol 3 (3) ◽  
pp. 389 ◽  
Author(s):  
IF Wardlaw ◽  
C Marshall
Keyword(s):  
Amino Acids ◽  
Species Differences ◽  
High Irradiance ◽  
High Light ◽  
Light Conditions ◽  
Primary Metabolites ◽  
Lolium Temulentum ◽  
C4 Species ◽  
Sorghum Sudanense ◽  
Storage Starch

The rate of export and longitudinal movement of 14C-labelled assimilates in the phloem was found to be greater in Sorghum sudanense than in Lolium temulentum. Sucrose was the predominant metabolite translocated from the leaf in both species in both low and high light conditions. The effect of irradiance on the rate of formation and nature of the products of photosynthesis was examined using 14CO2 pulse-chase techniques and the differences in the primary metabolites closely followed those expected for a C3 and a C4 species. Reduction in irradiance reduced the rate of incorporation of 14C into sucrose, especially in Sorghum, and led to the accumulation of amino acids in both species. Although species differences in export of 14C-labelled assimilate were not apparently related to the rate of 14C incorporation into sucrose, this could account for the delay in export of 14C-labelled assimilates associated with reduced irradiance. There was a rapid initial labelling of starch and the proportion of *14C incorporated as starch was enhanced at high irradiance, particularly in Sorghum. Overall, the results support the view that there is a greater partitioning of assimilate into storage (starch) at high irradiance relative to assimilate moving into the phloem and that irradiance (in the range 20-96 W m-2) did not directly influence vein loading.

scholarly journals Isomeric composition of bacteriorhodopsin under different environmental light conditions

FEBS Letters ◽  
1979 ◽  
Vol 97 (1) ◽  
pp. 129-132 ◽  
Author(s):  
Walter Sperling ◽  
Charles N. Rafferty ◽  
Klaus-Dieter Kohl ◽  
Norbert A. Dencher
Keyword(s):  
Isomeric Composition ◽  
Light Conditions ◽  
Environmental Light

scholarly journals Polyamine Metabolism under Different Light Regimes in Wheat

2021 ◽  
Vol 22 (21) ◽  
pp. 11717
Author(s):  
Orsolya Kinga Gondor ◽  
Judit Tajti ◽  
Kamirán Áron Hamow ◽  
Imre Majláth ◽  
Gabriella Szalai ◽  
...  
Keyword(s):  
Gene Expression ◽  
Fine Tuning ◽  
Polyamine Metabolism ◽  
Light Conditions ◽  
Light Regimes ◽  
Test Light ◽  
Lower Light ◽  
The Relationship ◽  
Back Conversion ◽  
Gene Expression Levels

Although the relationship between polyamines and photosynthesis has been investigated at several levels, the main aim of this experiment was to test light-intensity-dependent influence of polyamine metabolism with or without exogenous polyamines. First, the effect of the duration of the daily illumination, then the effects of different light intensities (50, 250, and 500 μmol m–2 s–1) on the polyamine metabolism at metabolite and gene expression levels were investigated. In the second experiment, polyamine treatments, namely putrescine, spermidine and spermine, were also applied. The different light quantities induced different changes in the polyamine metabolism. In the leaves, light distinctly induced the putrescine level and reduced the 1,3-diaminopropane content. Leaves and roots responded differently to the polyamine treatments. Polyamines improved photosynthesis under lower light conditions. Exogenous polyamine treatments influenced the polyamine metabolism differently under individual light regimes. The fine-tuning of the synthesis, back-conversion and terminal catabolism could be responsible for the observed different polyamine metabolism-modulating strategies, leading to successful adaptation to different light conditions.

scholarly journals Aging Affects the Capacity of Photoperiodic Adaptation Downstream from the Central Molecular Clock

2020 ◽  
Vol 35 (2) ◽  
pp. 167-179 ◽  
Author(s):  
M. Renate Buijink ◽  
Anneke H. O. Olde Engberink ◽  
Charlotte B. Wit ◽  
Assaf Almog ◽  
Johanna H. Meijer ◽  
...  
Keyword(s):  
Molecular Clock ◽  
The Elderly ◽  
Light Conditions ◽  
Targeted Interventions ◽  
The Core ◽  
Environmental Light ◽  
Age Related ◽  
Wake Patterns ◽  
Central Clock ◽  
Membrane Components

Aging impairs circadian clock function, leading to disrupted sleep-wake patterns and a reduced capability to adapt to changes in environmental light conditions. This makes shift work or the changing of time zones challenging for the elderly and, importantly, is associated with the development of age-related diseases. However, it is unclear what levels of the clock machinery are affected by aging, which is relevant for the development of targeted interventions. We found that naturally aged mice of >24 months had a reduced rhythm amplitude in behavior compared with young controls (3-6 months). Moreover, the old animals had a strongly reduced ability to adapt to short photoperiods. Recording PER2::LUC protein expression in the suprachiasmatic nucleus revealed no impairment of the rhythms in PER2 protein under the 3 different photoperiods tested (LD: 8:16, 12:12, and 16:8). Thus, we observed a discrepancy between the behavioral phenotype and the molecular clock, and we conclude that the aging-related deficits emerge downstream of the core molecular clock. Since it is known that aging affects several intracellular and membrane components of the central clock cells, it is likely that an impairment of the interaction between the molecular clock and these components is contributing to the deficits in photoperiod adaptation.

Influence of Emission Spectrum and Irradiance on Light Curing of Resin-Based Composites

2017 ◽  
Vol 42 (5) ◽  
pp. 537-547 ◽  
Author(s):  
CAK Shimokawa ◽  
B Sullivan ◽  
ML Turbino ◽  
CJ Soares ◽  
RB Price
Keyword(s):  
Emission Spectrum ◽  
Broad Spectrum ◽  
Light Transmission ◽  
High Irradiance ◽  
Degree Of Conversion ◽  
Single Peak ◽  
Bottom Surface ◽  
Light Conditions ◽  
Violet Light ◽  
Light Curing

SUMMARY Purpose: This study examined the influence of different emission spectra (single-peak and broad-spectrum) light-curing units (LCUs) delivering the same radiant exposures at irradiance values of 1200 or 3600 mW/cm2 on the polymerization and light transmission of four resin-based composites (RBCs). Methods and Materials: Two prototype LCUs that used the same light tip, but were either a single-peak blue or a broad-spectrum LED, were used to deliver the same radiant exposures to the top surfaces of the RBCs using either standard (1200 mW/cm2) or high irradiance (3600 mW/cm2) settings. The emission spectrum and radiant power from the LCUs were measured with a laboratory-grade integrating sphere coupled to a spectrometer, and the light beam was assessed with a beam profiler camera. Four RBCs (Filtek Supreme Ultra A2, Tetric EvoCeram A2, Tetric EvoCeram T, and TPH Spectra High Viscosity A2) were photoactivated using four different light conditions: single-peak blue/standard irradiance, single-peak blue/high irradiance, broad-spectrum/standard irradiance, and broad-spectrum/high irradiance. The degree of conversion (N=5) and microhardness at the top and bottom of 2.3-mm-diameter by 2.5-mm-thick specimens (N=5) were analyzed with analysis of variance and Tukey tests. The real-time light transmission through the RBCs was also measured. Results: For all light conditions, the 2.3-mm-diameter specimens received a homogeneous irradiance and spectral distribution. Although similar radiant exposures were delivered to the top surfaces of the RBCs, the amount of light energy emitted from the bottom surfaces was different among the four RBCs, and was also greater for the single-peak lights. Very little violet light (wavelengths below 420 nm) reached the bottom of the 2.5-mm-thick specimens. The degree of conversion and microhardness results varied according to the RBC (p<0.05). The RBCs that included alternative photoinitiators had greater microhardness values at the top when cured with broad-spectrum lights, while at the bottom, where little violet light was observed, the results were equal or higher when they were photoactivated with single-peak blue lights. With the exception of the microhardness at the top of TPH, equivalent or higher microhardness and degree-of-conversion values were achieved at the bottom surface when the standard (1200 mW/cm2) irradiance levels were used compared to when high irradiance levels were used. Conclusions: Considering the different behaviors of the tested RBCs, the emission spectrum and irradiance level influenced the polymerization of some RBCs. The RBCs that included alternative photoinitiators produced greater values at the top when cured with broad-spectrum lights, while at the bottom, results were equal or higher for the RBCs photoactivated with single-peak blue lights.

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