Effect of 4-week preoperative prism adaptation in preventing postoperative residual esotropia.

BACKGROUND: Preoperative prism adaptation (PPA) simulates postoperative status and possibly can predict postoperative undercorrection before surgery in esotropia. The present study aimed to assess the effect of 4-week PPA in preventing postoperative residual esotropia. METHODS: Seventy-five (75) esotropes who had undergone surgery at a single strabismus center were retrospectively enrolled. They included 25 basic, 31 acute comitant, 10 partially accommodative, and 9 recurrent esotropia patients. The preoperative deviation angle, which had been determined using the alternating prism and cover test, was fully corrected with press-on prisms 4 weeks before surgery. If there was an increase of 5 PD or more of esodeviation, the prisms were changed accordingly at 2 weeks. The deviation angle measured at 4 weeks was determined as the surgical target angle. Patients were then divided into increase (≥ 5 PD increase of angle during 4-week PPA) and non-increase groups. Success was defined as either esodeviation of 8 PD or under or exodeviation of 5 PD or under at distance at postoperative 6 months. RESULTS: The increase group included 44 patients (58.7%). The mean deviation angle before PPA was 27.4 PD, and after the 4-week PPA, there was an average increase of 9.4 PD. The success rate was 90.9% in the increase group and 96.8% in the non-increase group (p = 0.316). There were no intergroup differences in preoperative clinical characteristics, esotropia types, postoperative deviation angle or postoperative near stereopsis (p > 0.05). CONCLUSIONS: The results of this study indicated a beneficial effect of 4-week PPA in esotropia of various types, specifically by uncovering the hidden esodeviation in the increase group and simulating the postoperative alignment in both the increase and the non-increase groups.

Long-term light adaptation of light-harvesting and energy-transfer processes in the glaucophyte Cyanophora paradoxa under different light conditions.

In response to fluctuation in light intensity and quality, oxygenic photosynthetic organisms modify their light-harvesting and excitation energy-transfer processes to maintain optimal photosynthetic activity. Glaucophytes, which are a group of primary symbiotic algae, possess light-harvesting antennas called phycobilisomes (PBSs) consistent with cyanobacteria and red algae. However, compared with cyanobacteria and red algae, glaucophytes are poorly studied and there are few reports on the regulation of photosynthesis in the group. In this study, we examined the long-term light adaptation of light-harvesting functions in a glaucophyte, Cyanophora paradoxa, grown under different light conditions. Compared with cells grown under white light, the relative number of PBSs to photosystems (PSs) increased in blue-light-grown cells and decreased in green-, yellow-, and red-light-grown cells. Moreover, the PBS number increased with increment in the monochromatic light intensity. More energy was transferred from PBSs to PSII than to PSI under blue light, whereas energy transfer from PBSs to PSII was reduced under green and yellow lights, and energy transfer from the PBSs to both PSs decreased under red light. Decoupling of PBSs was induced by intense green, yellow, and red lights. Energy transfer from PSII to PSI (spillover) was observed, but the contribution of the spillover did not distinctly change depending on the culture light intensity and quality. These results suggest that the glaucophyte C. paradoxa modifies the light-harvesting abilities of both PSs and excitation energy-transfer processes between the light-harvesting antennas and both PSs during long-term light adaption.

Coherent feedback leads to robust background compensation in oscillatory and non-oscillatory homeostats.

When in a reaction kinetic integral controller a step perturbation is applied besides a constant background, the concentration of a controlled variable (described as A) will generally respond with decreased response amplitudes ΔA as backgrounds increase. The controller variable E will at the same time provide the necessary compensatory flux to move A back to its set-point. A typical example of decreased response amplitudes at increased backgrounds is found in retinal light adaptation. Due to remarks in the literature that retinal light adaptation would also involve a compensation of backgrounds we became interested in conditions how background compensation could occur. In this paper we describe novel findings how background influences can be robustly eliminated. When such a background compensation is active, oscillatory controllers will respond to a defined perturbation with always the same (damped or undamped) frequency profile, or in the non-oscillatory case, with the same response amplitude ΔA, irrespective of the background level. To achieve background compensation we found that two conditions need to apply: (i) an additional set of integral controllers (here described as I1 and I2) have to be employed to keep the manipulated variable E at a defined set-point, and (ii), I1 and I2 need to feed back to the A-E signaling axis directly through the controlled variable A. In analogy to a similar feedback applied in quantum control theory, we term these feedback conditions as 'coherent feedback'. When analyzing retinal light adaptations in more detail, we find no evidence of the presence of background compensation mechanisms. Although robust background compensation, as described theoretically here, appears to be an interesting regulatory property, relevant biological or biochemical examples still need to be identified.

Weighted Geometric Mean (WGM) method: A new chromatic adaptation model.

The human visual system has undergone evolutionary changes to develop sophisticated mechanisms that enable stable color perception under varying illumination. These mechanisms are known as chromatic adaptation, a fundamental aspect of color vision. Chromatic adaptation can be divided into two categories: sensory adaptation, which involves automatic adjustments in the visual system, such as retinal gain control, in response to changes in the stimulus, and cognitive adaptation, which depends on the observer's knowledge of the scene and context. The geometric mean has been suggested to be the fundamental mathematical relationship that governs peripheral sensory adaptation. This paper proposes the WGM model, an advanced chromatic adaptation model based on a weighted geometric mean approach that can anticipate incomplete adaptation as it moves along the Planckian or Daylight locus. Compared with two other chromatic adaptation models (CAT16 and vK20), the WGM model is tested with different corresponding color data sets and found to be a significantly improvement while also predicting degree of adaptation (sensory and cognitive adaptation) in a physiologically plausible manner.

Light Adaptation of Retinal Rod Bipolar Cells.

The sensitivity of retinal cells is altered in background light to optimize the detection of contrast. For scotopic (rod) vision, substantial adaptation occurs in the first two cells, the rods and rod bipolar cells (RBCs), through sensitivity adjustments in rods and postsynaptic modulation of the transduction cascade in RBCs. To study the mechanisms mediating these components of adaptation, we made whole-cell, voltage-clamp recordings from retinal slices of mice from both sexes. Adaptation was assessed by fitting the Hill equation to response-intensity relationships with the parameters of half-maximal response (I1/2 ), Hill coefficient (n), and maximum response amplitude (Rmax ). We show that rod sensitivity decreases in backgrounds according to the Weber-Fechner relation with an I1/2 of ∼50 R* s-1 The sensitivity of RBCs follows a near-identical function, indicating that changes in RBC sensitivity in backgrounds bright enough to adapt the rods are mostly derived from the rods themselves. Backgrounds too dim to adapt the rods can however alter n, relieving a synaptic nonlinearity likely through entry of Ca2+ into the RBCs. There is also a surprising decrease of Rmax , indicating that a step in RBC synaptic transduction is desensitized or that the transduction channels became reluctant to open. This effect is greatly reduced after dialysis of BAPTA at a membrane potential of +50 mV to impede Ca2+ entry. Thus the effects of background illumination in RBCs are in part the result of processes intrinsic to the photoreceptors and in part derive from additional Ca2+-dependent processes at the first synapse of vision.SIGNIFICANCE STATEMENT Light adaptation adjusts the sensitivity of vision as ambient illumination changes. Adaptation for scotopic (rod) vision is known to occur partly in the rods and partly in the rest of the retina from presynaptic and postsynaptic mechanisms. We recorded light responses of rods and rod bipolar cells to identify different components of adaptation and study their mechanisms. We show that bipolar-cell sensitivity largely follows adaptation of the rods but that light too dim to adapt the rods produces a linearization of the bipolar-cell response and a surprising decrease in maximum response amplitude, both mediated by a change in intracellular Ca2+ These findings provide a new understanding of how the retina responds to changing illumination.

Single-cell profiling reveals Müller glia coordinate retinal intercellular communication during light/dark adaptation via thyroid hormone signaling.

Light adaptation enables the vertebrate visual system to operate over a wide range of ambient illumination. Regulation of phototransduction in photoreceptors is considered a major mechanism underlying light adaptation. However, various types of neurons and glial cells exist in the retina, and whether and how all retinal cells interact to adapt to light/dark conditions at the cellular and molecular levels requires systematic investigation. Therefore, we utilized single-cell RNA sequencing to dissect retinal cell-type-specific transcriptomes during light/dark adaptation in mice. The results demonstrated that, in addition to photoreceptors, other retinal cell types also showed dynamic molecular changes and specifically enriched signaling pathways under light/dark adaptation. Importantly, Müller glial cells (MGs) were identified as hub cells for intercellular interactions, displaying complex cell‒cell communication with other retinal cells. Furthermore, light increased the transcription of the deiodinase Dio2 in MGs, which converted thyroxine (T4) to active triiodothyronine (T3). Subsequently, light increased T3 levels and regulated mitochondrial respiration in retinal cells in response to light conditions. As cones specifically express the thyroid hormone receptor Thrb, they responded to the increase in T3 by adjusting light responsiveness. Loss of the expression of Dio2 specifically in MGs decreased the light responsive ability of cones. These results suggest that retinal cells display global transcriptional changes under light/dark adaptation and that MGs coordinate intercellular communication during light/dark adaptation via thyroid hormone signaling.

Acute hyperglycemia compromises the responses of choroidal vessels using swept-source optical coherence tomography during dark and light adaptations.

Purpose: To clarify the effects of acute hyperglycemia on the responses of choroidal structural components and vascularity index during light modulation in healthy participants using techniques including image binarization and artificial intelligence (AI) segmentation based on swept-source optical coherence tomography (SS-OCT). Methods: Twenty-four eyes of 24 healthy participants were imaged at different stages after ambient light, 40 min of dark adaptation, and 5 min of light adaptation in two imaging sessions: control and after receiving 75 g of oral glucose solution. The choroidal structural parameters, including luminal volume (LV), stromal volume (SV), total choroidal volume (TCV), and choroidal vascularity index (CVI) within a 6 mm area were determined using a custom algorithm based on image binarization and AI segmentation of SS-OCT. These measurements were compared among the conditions after adjusting for axial length, age to identify the differences. Results: In the dark, CVI decreased (-0.36 ± 0.09%) significantly in acute hyperglycemia compared to the control condition. During the transition to ambient light, there was an increasing trend in the choroidal parameters compared with the control experiment. However, only TCV (0.38 ± 0.17 mm3) and LV (0.27 ± 0.10 mm3) showed a significant increase at the time point of 5 min after ambient light. Conclusion: Analysis of choroidal structural parameters and CVI based on SS-OCT images is a potentially powerful method to objectively reflect subtle changes in neurovascular coupling between the choroid and photoreceptor during dark adaptation.

Single-cell profiling reveals Müller glia coordinate retinal intercellular communication during light/dark adaptation via thyroid hormone signaling

Light adaptation enables the vertebrate visual system to operate over a wide range of ambient illumination. Regulation of phototransduction in photoreceptors is considered a major mechanism underlying light adaptation. However, various types of neurons and glial cells exist in the retina, and whether and how all retinal cells interact to adapt to light/dark conditions at the cellular and molecular levels requires systematic investigation. Therefore, we utilized single-cell RNA sequencing to dissect retinal cell-type-specific transcriptomes during light/dark adaptation in mice. The results demonstrated that, in addition to photoreceptors, other retinal cell types also showed dynamic molecular changes and specifically enriched signaling pathways under light/dark adaptation. Importantly, Müller glial cells (MGs) were identified as hub cells for intercellular interactions, displaying complex cell‒cell communication with other retinal cells. Furthermore, light increased the transcription of the deiodinase Dio2 in MGs, which converted thyroxine (T4) to active triiodothyronine (T3). Subsequently, light increased T3 levels and regulated mitochondrial respiration in retinal cells in response to light conditions. As cones specifically express the thyroid hormone receptor Thrb, they responded to the increase in T3 by adjusting light responsiveness. Loss of the expression of Dio2 specifically in MGs decreased the light responsive ability of cones. These results suggest that retinal cells display global transcriptional changes under light/dark adaptation and that MGs coordinate intercellular communication during light/dark adaptation via thyroid hormone signaling.

Phosphatic metabolism in dark- and light-adapted rat retinas.

This study defines retinal phosphatic metabolites and their adjustment to illumination in rat retinas under conditions that preserve retinal function. Metabolic data are measured using high-performance liquid chromatography (HPLC) and 31P nuclear magnetic resonance (31P NMR) spectroscopy after 10 min of light exposure in vivo compared with retinas from dark-adapted rats. Multiple high-energy and low-energy phosphatic metabolites of intermediary metabolism were quantified. The concentration of the high-energy phosphate adenosine triphosphate (ATP) remained unchanged from dark- to light-adaptation. Under the same conditions the concentrations of the high-energy phosphates guanosine triphosphate (GTP) and creatine phosphate increased, whereas the inorganic phosphate decreased. Comparing dark-adapted controls with retinas light-adapted either in vitro or in vivo, the evidence is consistent with a light-dependent increase in GTP and a decrease in cyclic guanosine monophosphate. Although cyclic adenosine monophosphate (cAMP) levels were lower in retinas light-adapted in vivo than in the dark-adapted controls, this did not seem to be an effect of light, as cAMP levels decreased similarly after 10 min incubation in dark or light in parallel with recovery of ATP/adenosine diphosphate ratios. This study: (1) reports on retinal metabolic changes with adjustment in illumination, (2) provides baseline measurements of retinal phosphatic metabolites in whole retinas, and (3) reports on the validity of chromatographic and spectroscopic methods used for studying retinal metabolism establishing a high correlation among measurements made using HPLC and 31P NMR.

Distinct mechanisms of light adaptation of elementary responses in photoreceptors of dipteran flies and American cockroach.

Of many light adaptation mechanisms optimizing photoreceptor functioning in the compound eyes of insects, those modifying the single-photon response, the quantum bump (QB), remain least studied. Here, by recording from photoreceptors of the blow fly Protophormia terraenovae, the hover fly Volucella pellucens, and the cockroach Periplaneta americana, we investigated mechanisms of rapid light adaptation by examining how properties of QBs change after light stimulation and multiquantal impulse responses during repetitive stimulation. In P. terraenovae, light stimulation reduced latencies, characteristic durations, and amplitudes of QBs in an intensity- and duration-dependent manner. In P. americana, only QB amplitudes decreased consistently. In both species, time constants of QB parameters' recovery increased with the strength and duration of stimulation, reaching ∼30 s after bright prolonged 10-s pulses. In the blow fly, changes in QB amplitudes during recovery correlated with changes in half-widths but not latencies, suggesting at least two separate mechanisms of light adaptation: acceleration of QB onset by sensitizing transduction channels and acceleration of transduction channel inactivation causing QB shortening and decrease. In the cockroach, light adaptation reduced QB amplitude by apparently lowering the transduction channel availability. Impulse response data in the blow fly and cockroach were consistent with the inferences from the QB recovery experiments. However, in the hover fly V. pellucens, impulse response latencies and durations decreased simultaneously, whereas amplitudes decreased little, even when bright flashes were applied at high frequencies. These findings indicate the existence of dissimilar mechanisms of light adaptation in the microvilli of different species.NEW & NOTEWORTHY By studying light adaptation of elementary responses in photoreceptors of the blow fly and the cockroach we found three distinct mechanisms. In the blow fly, one mechanism speeds quantum bump onset and another accelerates quantum bump inactivation, decreasing its size. In the cockroach, quantum bump amplitude decreases without changes in kinetics, indicating decreased availability of transduction channels. The findings can be explained by expression of different transduction channels in the flies and cockroaches.

The Use of Optical Coherence Tomography to Demonstrate Dark and Light Adaptation in a Live Moth.

To work effectively, the eyes of nocturnal insects have a problem they must overcome. During the night, the light levels are low, so their eyes need to be very sensitive; but they also need a way of adapting to environmental light conditions, and protecting those sensitive organs, if a bright light is encountered. Human eyes have a pupil that changes size to regulate light input to the eye. Moths (Lepidoptera) use a light absorbing pigment that moves position to limit the light within the eye. This pigment migration is difficult to record because it is a dynamic process and will only occur in a live moth. This paper presents the first use of Ocular Coherence Tomography as a method of viewing anatomical detail in a compound eye. This is noninvasive and does not harm the insect. To demonstrate the effectiveness, this article documents the dynamic process of light adaptation within a moth's eye.

Variation in terpenoids in leaves of Artemisia annua grown under different LED spectra resulting in diverse antimalarial activities against Plasmodium falciparum.

BACKGROUND: Productivities of bioactive compounds in high-value herbs and medicinal plants are often compromised by uncontrollable environmental parameters. Recent advances in the development of plant factories with artificial lighting (PFAL) have led to improved qualitative and/or quantitative production of bioactive compounds in several medicinal plants. However, information concerning the effect of light qualities on plant pharmaceutical properties is limited. The influence of three different light-emitting diode (LED) spectra on leaf fresh weight (FW), bioactive compound production and bioactivity of Artemisia annua L. against the malarial parasite Plasmodium falciparum NF54 was investigated. Correlation between the A. annua metabolites and antimalarial activity of light-treated plant extracts were also determined. RESULTS: Artemisia annua plants grown under white and blue spectra that intersected at 445 nm exhibited higher leaf FW and increased amounts of artemisinin and artemisinic acid, with enhanced production of several terpenoids displaying a variety of pharmacological activities. Conversely, the red spectrum led to diminished production of bioactive compounds and a distinct metabolite profile compared with other wavelengths. Crude extracts obtained from white and blue spectral treatments exhibited 2 times higher anti-Plasmodium falciparum activity than those subjected to the red treatment. Highest bioactivity was 4 times greater than those obtained from greenhouse-grown plants. Hierarchical cluster analysis (HCA) revealed a strong correlation between levels of several terpenoids and antimalarial activity, suggesting that these compounds might be involved in increasing antimalarial activity. CONCLUSIONS: Results demonstrated a strategy to overcome the limitation of A. annua cultivation in Bangkok, Thailand. A specific LED spectrum that operated in a PFAL system promoted the accumulation of some useful phytochemicals in A. annua, leading to increased antimalarial activity. Therefore, the application of PFAL with appropriate light spectra showed promise as an alternative method for industrial production of A. annua or other useful medicinal plants with minimal environmental influence.

Prism adaptation test before strabismus surgery in patients with decompensated esophoria and decompensated microesotropia.

PURPOSE: To evaluate the effect of Prism adaptation test (PAT) on the angle of squint in decompensated esophoria (decEPH) and decompensated microesotropia (decMET). METHODS: In this single-center retrospective study we reviewed the medical records of patients with the diagnosis of decEPH or decMET, aged at least 12 years, who were treated by strabismus surgery for the first time. The maximum Angle of squint (AOS) for far (F) and near (N) fixation and PAT results before surgery, as well as AOS (F) and AOS (N) after surgery and results of binocular function tests were considered. PAT included wearing a prism based on the largest angle for over 60 min. RESULTS: 100 patients (mean age 37 ± 17 years) were included in the decEPH group, 82 patients (mean age 30 ± 13 years) in the decMET group. For decEPH, before surgery AOS was 25.5 ± 8.8 pdpt (F) and 23.5 ± 9.8 pdpt (N). During PAT the AOS increased significantly by 2.7 ± 4.3 to 28.2 ± 8.6 pdpt (F) and by 4.9 ± 4.5 to 28.3 ± 9.5 pdpt (N). Altogether, in 82% of decEPH patients AOS (F) and/ or AOS (N) in- or decreased by at least 3 pdpt. For decMET, before surgery AOS was 28.6 ± 10.8 pdpt for far (F) and 30.9 ± 11.8 pdpt for near fixation (N). During PAT the AOS increased significantly by 4.2 ± 5.8 to 32.5 ± 9.5 pdpt (F) and by 3.7 ± 6.1 to 34.4 ± 9.5 pdpt (N). Altogether, in 51% of decMET patients, AOS (F) and/ or AOS (N) increased by at least 10 pdpt, therefore more than 5° which would have been maximally expected from mictrotropia, or decreased by at least 3 pdpt. CONCLUSIONS: The Prism adaptation test (PAT) showed remarkable changes in AOS in both decEPH and decMET. In patients with decEPH, the preoperative assessment of the "true AOS" under PAT reflects a pivotal requirement for successful strabismus surgery, as 82% had dose relevant angle changes ≥ 3 pdpt. For patients with decMET the preoperative prism adaptation test is especially of diagnostic value, but also 51% of decMET patients had changes in AOS beyond the expected microtropic angle (≥ 10 pdpt) or even a dose relevant angle decrease (≥ 3pdpt).

Protection of photosystem I during sudden light stress depends on ferredoxin:NADP(H) reductase abundance and interactions.

Plant tolerance to high light and oxidative stress is increased by overexpression of the photosynthetic enzyme Ferredoxin:NADP(H) reductase (FNR), but the specific mechanism of FNR-mediated protection remains enigmatic. It has also been reported that the localization of this enzyme within the chloroplast is related to its role in stress tolerance. Here, we dissected the impact of FNR content and location on photoinactivation of photosystem I (PSI) and photosystem II (PSII) during high light stress of Arabidopsis (Arabidopsis thaliana). The reaction center of PSII is efficiently turned over during light stress, while damage to PSI takes much longer to repair. Our results indicate a PSI sepcific effect, where efficient oxidation of the PSI primary donor (P700) upon transition from darkness to light, depends on FNR recruitment to the thylakoid membrane tether proteins: thylakoid rhodanase-like protein (TROL) and translocon at the inner envelope of chloroplasts 62 (Tic62). When these interactions were disrupted, PSI photoinactivation occurred. In contrast, there was a moderate delay in the onset of PSII damage. Based on measurements of ΔpH formation and cyclic electron flow, we propose that FNR location influences the speed at which photosynthetic control is induced, resulting in specific impact on PSI damage. Membrane tethering of FNR therefore plays a role in alleviating high light stress, by regulating electron distribution during short-term responses to light.

Impaired Light Adaptation of ON-Sustained Ganglion Cells in Early Diabetes Is Attributable to Diminished Response to Dopamine D4 Receptor Activation.

Purpose: Retinal neuronal signaling is disrupted early in diabetes, before the onset of the vascular pathologies associated with diabetic retinopathy. There is also growing evidence that retinal dopamine, a neuromodulator that mediates light adaptation, is reduced in early diabetes. Previously, we have shown that after 6 weeks of diabetes, light adaptation is impaired in ON-sustained (ON-s) ganglion cells in the mouse retina. The purpose of this study was to determine whether changes in the response to dopamine receptor activation contribute to this dysfunction. Methods: Single-cell retinal patch-clamp recordings from the mouse retina were used to determine how activating dopamine type D4 receptors (D4Rs) changes the light-evoked and spontaneous excitatory inputs to ON-s ganglion cells, in both control and 6-week diabetic (STZ-injected) animals. Fluorescence in situ hybridization was also used to assess whether D4R expression was affected by diabetes. Results: D4R activation decreased light-evoked and spontaneous inputs to ON-s ganglion cells in control and diabetic retinas. However, D4R activation caused a smaller reduction in light-evoked excitatory inputs to ON-s ganglion cells in diabetic retinas compared to controls. This impaired D4R signaling is not attributable to a decline in D4R expression, as there was no change in D4R mRNA density in the diabetic retinas. Conclusions: These results suggest that the cellular response to dopamine signaling is disrupted in early diabetes and may be amenable to chronic dopamine supplementation therapy.

Physiological mechanism of strigolactone enhancing tolerance to low light stress in cucumber seedlings.

Strigolactone is a newly discovered type of plant hormone that has multiple roles in modulating plant responses to abiotic stress. Herein, we aimed to investigate the effects of exogenous GR24 (a synthetic analogue of strigolactone) on plant growth, photosynthetic characteristics, carbohydrate levels, endogenous strigolactone content and antioxidant metabolism in cucumber seedlings under low light stress. The results showed that the application of 10 µM GR24 can increase the photosynthetic efficiency and plant biomass of low light-stressed cucumber seedlings. GR24 increased the accumulation of carbohydrates and the synthesis of sucrose-related enzyme activities, enhanced antioxidant enzyme activities and antioxidant substance contents, and reduced the levels of H2O2 and MDA in cucumber seedlings under low light stress. These results indicate that exogenous GR24 might alleviate low light stress-induced growth inhibition by regulating the assimilation of carbon and antioxidants and endogenous strigolactone contents, thereby enhancing the tolerance of cucumber seedlings to low light stress.

High-Light-Induced Stress Activates Lipid Deacylation at the Sn-2 Position in the Cyanobacterium Synechocystis Sp. PCC 6803.

Cyanobacterial mutants defective in acyl-acyl carrier protein synthetase (Aas) produce free fatty acids (FFAs) because the FFAs generated by deacylation of membrane lipids cannot be recycled. An engineered Aas-deficient mutant of Synechocystis sp. PCC 6803 grew normally under low-light (LL) conditions (50 µmol photons m-2 s-1) but was unable to sustain growth under high-light (HL) conditions (400 µmol photons m-2 s-1), revealing a crucial role of Aas in survival under the HL conditions. Several-times larger amounts of FFAs were produced by HL-exposed cultures than LL-grown cultures. Palmitic acid accounted for ∼85% of total FFAs in HL-exposed cultures, while C18 fatty acids (FAs) constituted ∼80% of the FFAs in LL-grown cultures. Since C16 FAs are esterified to the sn-2 position of lipids in the Synechocystis species, it was deduced that HL irradiation activated deacylation of lipids at the sn-2 position. Heterologous expression of FarB, the FFA exporter protein of Neisseria lactamica, prevented intracellular FFA accumulation and rescued the growth defect of the mutant under HL, indicating that intracellular FFA was the cause of growth inhibition. FarB expression also decreased the 'per-cell' yield of FFA under HL by 90% and decreased the proportion of palmitic acid to ∼15% of total FFA. These results indicated that the HL-induced lipid deacylation is triggered not by strong light per se but by HL-induced damage to the cells. It was deduced that there is a positive feedback loop between HL-induced damage and lipid deacylation, which is lethal unless FFA accumulation is prevented by Aas.

Maintaining the Chloroplast Redox Balance through the PGR5-Dependent Pathway and the Trx System Is Required for Light-Dependent Activation of Photosynthetic Reactions.

Light-dependent activation of chloroplast enzymes is required for the rapid induction of photosynthesis after a shift from dark to light. The thioredoxin (Trx) system plays a central role in this process. In chloroplasts, the Trx system consists of two pathways: the ferredoxin (Fd)/Trx pathway and the nicotinamide adenine dinucleotide phosphate (NADPH)-Trx reductase C (NTRC) pathway. In Arabidopsis (Arabidopsis thaliana) mutants defective in either pathway, the photoreduction of thiol enzymes was impaired, resulting in decreased carbon fixation. The close relationship between the Fd/Trx pathway and proton gradient regulation 5 (PGR5)-dependent photosystem I cyclic electron transport (PSI CET) in the induction of photosynthesis was recently elucidated. However, how the PGR5-dependent pathway is involved in the NTRC pathway is unclear, although NTRC has been suggested to physically interact with PGR5. In this study, we analyzed Arabidopsis mutants lacking either the PGR5 or the chloroplast NADH dehydrogenase-like complex (NDH)-dependent PSI CET pathway in the ntrc mutant background. The ntrc pgr5 double mutant suppressed both the growth defects and the high non-photochemical quenching phenotype of the ntrc mutant when grown under long-day conditions. By contrast, the inactivation of NDH activity with the chlororespiratory reduction 2-2 mutant failed to suppress either phenotype. We discovered that the phenotypic rescue of ntrc by pgr5 is caused by the partial restoration of Trx-dependent reduction of thiol enzymes. These results suggest that electron partitioning to the PGR5-dependent pathway and the Trx system needs to be properly regulated for the activation of the Calvin-Benson-Bassham cycle enzymes during the induction of photosynthesis.

Toward predicting photosynthetic efficiency and biomass gain in crop genotypes over a field season.

Photosynthesis acclimates quickly to the fluctuating environment in order to optimize the absorption of sunlight energy, specifically the photosynthetic photon fluence rate (PPFR), to fuel plant growth. The conversion efficiency of intercepted PPFR to photochemical energy (ɛe) and to biomass (ɛc) are critical parameters to describe plant productivity over time. However, they mask the link of instantaneous photochemical energy uptake under specific conditions, that is, the operating efficiency of photosystem II (Fq'/Fm'), and biomass accumulation. Therefore, the identification of energy- and thus resource-efficient genotypes under changing environmental conditions is impeded. We long-term monitored Fq'/Fm' at the canopy level for 21 soybean (Glycine max (L.) Merr.) and maize (Zea mays) genotypes under greenhouse and field conditions using automated chlorophyll fluorescence and spectral scans. Fq'/Fm' derived under incident sunlight during the entire growing season was modeled based on genotypic interactions with different environmental variables. This allowed us to cumulate the photochemical energy uptake and thus estimate ɛe noninvasively. ɛe ranged from 48% to 62%, depending on the genotype, and up to 9% of photochemical energy was transduced into biomass in the most efficient C4 maize genotype. Most strikingly, ɛe correlated with shoot biomass in seven independent experiments under varying conditions with up to r = 0.68. Thus, we estimated biomass production by integrating photosynthetic response to environmental stresses over the growing season and identified energy-efficient genotypes. This has great potential to improve crop growth models and to estimate the productivity of breeding lines or whole ecosystems at any time point using autonomous measuring systems.