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Greenhouse crop production in northern countries often relies heavily on supplemental lighting for year-round yield and product quality. Among the different spectra used in supplemental lighting, red is often considered the most efficient, but plants do not develop normally when grown solely under monochromatic red light (\"red light syndrome\"). Addition of blue light has been shown to aid normal development, and typical lighting spectra in greenhouse production include a mixture of red and blue light. However, it is unclear whether sunlight, as part of the light available to plants in the greenhouse, may be sufficient as a source of blue light. In a greenhouse high-wire tomato ( ), we varied the percentage of blue supplemental light (in a red background) as 0, 6, 12, and 24%, while keeping total photosynthetically active radiation constant. Light was supplied as a mixture of overhead (99 μmol m s ) and intracanopy (48 μmol m s ) LEDs, together with sunlight. Averaged over the whole experiment (111 days), sunlight comprised 58% of total light incident onto the crop. Total biomass, yield and number of fruits increased with the addition of blue light to an optimum, suggesting that both low (0%) and high (24%) blue light intensities were suboptimal for growth. Stem and internode lengths, as well as leaf area, decreased with increases in blue light percentage. While photosynthetic capacity increased linearly with increases in blue light percentage, photosynthesis in the low blue light treatment (0%) was not low enough to suggest the occurrence of the red light syndrome. Decreased biomass at low (0%) blue light was likely caused by decreased photosynthetic light use efficiency. Conversely, decreased biomass at high (24%) blue light was likely caused by reductions in canopy light interception. We conclude that while it is not strictly necessary to add blue light to greenhouse supplemental red light to obtain a functional crop, adding some (6-12%) blue light is advantageous for growth and yield while adding 24% blue light is suboptimal for growth.

Allophycocyanins are phycobiliproteins that absorb red light and transfer the energy to the reaction centers of oxygenic photosynthesis in cyanobacteria and red algae. Recently, it was shown that some allophycocyanins absorb far-red light and that one subset of these allophycocyanins, comprising subunits from the ApcD4 and ApcB3 subfamilies (FRL-AP), form helical nanotubes. The lowest energy absorbance maximum of the oligomeric ApcD4-ApcB3 complexes occurs at 709 nm, which is unlike allophycocyanin (AP; ApcA-ApcB) and allophycocyanin B (AP-B; ApcD-ApcB) trimers that absorb maximally at ~ 650 nm and ~ 670 nm, respectively. The molecular bases of the different spectra of AP variants are presently unclear. To address this, we structurally compared FRL-AP with AP and AP-B, performed spectroscopic analyses on FRL-AP, and leveraged computational approaches. We show that among AP variants, the α-subunit constrains pyrrole ring A of its phycocyanobilin chromophore to different extents, and the coplanarity of ring A with rings B and C sets a baseline for the absorbance maximum of the chromophore. Upon oligomerization, the α-chromophores of all AP variants exhibit a red shift of the absorbance maximum of ~ 25 to 30 nm and band narrowing. We exclude excitonic coupling in FRL-AP as the basis for this red shift and extend the results to discuss AP and AP-B. Instead, we attribute these spectral changes to a conformational alteration of pyrrole ring D, which becomes more coplanar with rings B and C upon oligomerization. This study expands the molecular understanding of light-harvesting attributes of phycobiliproteins and will aid in designing phycobiliproteins for biotechnological applications.

Phycobilisomes (PBS), the major light-harvesting antenna in cyanobacteria, are supramolecular complexes of colorless linkers and heterodimeric, pigment-binding phycobiliproteins. Phycocyanin and phycoerythrin commonly comprise peripheral rods, and a multi-cylindrical core is principally assembled from allophycocyanin (AP). Each AP subunit binds one phycocyanobilin (PCB) chromophore, a linear tetrapyrrole that predominantly absorbs in the orange-red region of the visible spectrum (600–700 nm). AP facilitates excitation energy transfer from PBS peripheral rods or from directly absorbed red light to accessory chlorophylls in the photosystems. Paralogous forms of AP that bind PCB and are capable of absorbing far-red light (FRL; 700–800 nm) have recently been identified in organisms performing two types of photoacclimation: FRL photoacclimation (FaRLiP) and low-light photoacclimation (LoLiP). The FRL-absorbing AP (FRL-AP) from the thermophilic LoLiP strain Synechococcus sp. A1463 was chosen as a platform for site-specific mutagenesis to probe the structural differences between APs that absorb in the visible region and FRL-APs and to identify residues essential for the FRL absorbance phenotype. Conversely, red light-absorbing allophycocyanin-B (AP-B; ~ 670 nm) from the same organism was used as a platform for creating a FRL-AP. We demonstrate that the protein environment immediately surrounding pyrrole ring A of PCB on the alpha subunit is mostly responsible for the FRL absorbance of FRL-APs. We also show that interactions between PCBs bound to alpha and beta subunits of adjacent protomers in trimeric AP complexes are responsible for a large bathochromic shift of about ~ 20 nm and notable sharpening of the long-wavelength absorbance band.

Perovskite‐based light‐emitting diodes (PeLEDs) are now approaching the upper limits of external quantum efficiency (EQE); however, their application is currently limited by reliance on lead and by inadequate color purity. The Rec. 2020 requires Commission Internationale de l'Eclairage coordinates of (0.708, 0.292) for red emitters, but present‐day perovskite devices only achieve (0.71, 0.28). Here, lead‐free PeLEDs are reported with color coordinates of (0.706, 0.294)—the highest purity reported among red PeLEDs. The variation of the emission spectrum is also evaluated as a function of temperature and applied potential, finding that emission redshifts by <3 nm under low temperature and by <0.3 nm V−1 with operating voltage. The prominent oxidation pathway of Sn is identified and this is suppressed with the aid of H3PO2. This strategy prevents the oxidation of the constituent precursors, through both its moderate reducing properties and through its forming complexes with the perovskite that increase the energetic barrier toward Sn oxidation. The H3PO2 additionally seeds crystal growth during film formation, improving film quality. PeLEDs are reported with an EQE of 0.3% and a brightness of 70 cd m−2; this is the record among reported red‐emitting, lead‐free PeLEDs. Sn‐based perovskite light‐emitting diodes with ultra‐high red color purity, a brightness of 70 cd m−2, and 24 nm linewidth are prepared. The devices show excellent color stability under different temperatures, power, and operating voltage. Based on the oxidation pathway of Sn, H3PO2 is chosen to suppress the oxidation of Sn2+ and slow down the crystal growth, simultaneously.

Light passing through or reflected from adjacent foliage provides a developing plant with information that is used to guide specific genetic and physiological processes. Changes in gene expression underlie adaptation to, or avoidance of, the light-compromised environment. These changes have been well described and are mostly attributed to a decrease in the red light to far-red light ratio and/or a reduction in blue light fluence rate. In most cases, these changes rely on the integration of red/far-red/blue light signals, leading to changes in phytohormone levels. Studies over the last decade have described distinct responses to green light and/or a shift of the blue-green, or red-green ratio. Responses to green light are typically low-light responses, suggesting that they may contribute to the adaptation to growth under foliage or within close proximity to other plants. This review summarizes the growth responses in artificially manipulated light environments with an emphasis on the roles of green wavebands. The information may be extended to understanding the influence of green light in shade avoidance responses as well as other plant developmental and physiological processes.

Sensory photoreceptors elicit vital physiological adaptations in response to incident light. As light-regulated actuators, photoreceptors underpin optogenetics, which denotes the noninvasive, reversible, and spatiotemporally precise perturbation by light of living cells and organisms. Of particular versatility, naturally occurring photoactivated adenylate cyclases promote the synthesis of the second messenger cAMP under blue light. Here, we have engineered a light-activated phosphodiesterase (LAPD) with complementary light sensitivity and catalytic activity by recombining the photosensor module of Deinococcus radiodurans bacterial phytochrome with the effector module of Homo sapiens phosphodiesterase 2A. Upon red-light absorption, LAPD up-regulates hydrolysis of cAMP and cGMP by up to sixfold, whereas far-red light can be used to down-regulate activity. LAPD also mediates light-activated cAMP and cGMP hydrolysis in eukaryotic cell cultures and in zebrafish embryos; crucially, the biliverdin chromophore of LAPD is available endogenously and does not need to be provided exogenously. LAPD thus establishes a new optogenetic modality that permits light control over diverse cAMP/cGMP-mediated physiological processes. Because red light penetrates tissue more deeply than light of shorter wavelengths, LAPD appears particularly attractive for studies in living organisms.

Plants monitor their surrounding ambient light environment by specialized photoreceptor proteins. Among them, phytochromes monitor red and far-red light. These molecules perceive photons, undergo a conformational change, and regulate diverse light signaling pathways, resulting in the mediation of key developmental and growth responses throughout the whole life of plants. Posttranslational modifications of the photoreceptors and their signaling partners may modify their function. For example, the regulatory role of phosphorylation has been investigated for decades by using different methodological approaches. In the past few years, a set of studies revealed that ubiquitin-like short protein molecules, called small ubiquitin-like modifiers (SUMOs) are attached reversibly to different members of phytochrome signaling pathways, including phytochrome B, the dominant receptor of red light signaling. Furthermore, SUMO attachment modifies the action of the target proteins, leading to altered light signaling and photomorphogenesis. This review summarizes recent results regarding SUMOylation of various target proteins, the regulation of their SUMOylation level, and the physiological consequences of SUMO attachment. Potential future research directions are also discussed.

Phytochromes are dimeric proteins that function as red and far-red light sensors influencing nearly every phase of the plant life cycle. Of the three major phytochrome families found in flowering plants, PHYTOCHROME C (PHYC) is the least understood. In Arabidopsis and rice, PHYC is unstable and functionally inactive unless it heterodimerizes with another phytochrome. However, when expressed in an Arabidopsis phy- null mutant, wheat PHYC forms signaling active homodimers that translocate into the nucleus in red light to mediate photomorphogenic responses. Tetraploid wheat plants homozygous for loss-of-function mutations in all PHYC copies (phyC ᴬᴮ) flower on average 108 d later than wild-type plants under long days but only 19 d later under short days, indicating a strong interaction between PHYC and photoperiod. This interaction is further supported by the drastic down-regulation in the phyC ᴬᴮ mutant of the central photoperiod gene PHOTOPERIOD 1 (PPD1) and its downstream target FLOWERING LOCUS T1 , which are required for the promotion of flowering under long days. These results implicate light-dependent, PHYC-mediated activation of PPD1 expression in the acceleration of wheat flowering under inductive long days. Plants homozygous for the phyC ᴬᴮ mutations also show altered profiles of circadian clock and clock-output genes, which may also contribute to the observed differences in heading time. Our results highlight important differences in the photoperiod pathways of the temperate grasses with those of well-studied model plant species.

The impact of red and blue light-emitting diodes (LEDs) irradiation on the sugar metabolism and γ-aminobutyric acid in postharvest table grapes stored at 4 °C for 21 days after harvest were explored. Grape clusters were exposed to red and blue light irradiation at the same intensity (500 lx). The findings revealed that red and blue light treatments enhanced total soluble solids (TSS) and total acidity (TA) content. Furthermore, red-light irradiation retained higher phenolic compound during storage than blue light and control. Red-light radiation sustained higher levels of phenolic biosynthesis-related enzymes, including phenylalanine ammonia-lyase (PAL), tyrosine ammonia-lyase (TAL), cinnamate 4-hydroxylase (C4H), and p -coumarate ligase (4CL), than blue light irradiation and control. The results showed that red light increased glucose, fructose, and sucrose levels, which were 32.19, 33.18, and 2.95 mg g −1 , compared with those in blue light and control at the end of storage and enhancing the sucrose synthase synthesis (SS-synthesis) and acid invertase (AI), while blue light enhanced sucrose synthase cleavage (SS-cleavage). In addition, red light irradiation increased glutamic acid decarboxylase (GAD) activity while red and blue light irradiation inhibited γ-aminobutyric acid transaminase (GABA-T) activity by 22.14 and 20.71 U g −1 at 21 days of storage, compared to control, leading to γ-aminobutyric acid (GABA) accumulation. These findings suggest that red and blue light will help in maintaining the quality of grape during postharvest storage.

Alkut Elham,1,2 Xiangjun Meng1 1Department of Ophthalmology, Affiliated Zhongshan Hospital of Dalian University, Dalian, Liaoning, People’s Republic of China; 2Dalian Medical University, Dalian, Liaoning, People’s Republic of ChinaCorrespondence: Xiangjun Meng, Department of Ophthalmology, Affiliated Zhongshan Hospital of Dalian University, Dalian, Liaoning, People’s Republic of China, Email mengxiangjunsci@sina.comPurpose: To evaluate the efficacy and safety of combining repeated low-level red light (RLRL) therapy with orthokeratology (OK) in slowing axial elongation in children with rapid myopia progression.Patients and Methods: This retrospective cohort included 72 children aged 8– 14 years (RLRL+OK, n=36; OK-only, n=36) meeting the rapid-progressor definition (> 0.40 mm/year axial elongation. One eye per child was randomly selected. Axial length (AL) was measured at baseline and at 3, 6, and 12 months. Inverse probability of treatment weighting (IPTW) based on age, sex, and baseline AL achieved good balance between groups. The primary outcome was the 12-month AL change, assessed using IPTW-weighted linear mixed-effects models adjusted for covariates. Prespecified subgroup analyses were stratified by age (< 10 vs ≥ 10 years). Sensitivity analyses included propensity score matching (PSM), per-protocol analysis (PP; adherence ≥ 80%), and dose–response evaluation. Safety was assessed using slit-lamp biomicroscopy and macular OCT imaging.Results: At 12 months, the RLRL+OK group had significantly less elongation than OK-only (mean difference − 0.298 mm; 95% CI − 0.388 to − 0.209; p< 0.001), with significant group×time interactions from 3 months. Benefits were consistent across age subgroups without effect modification. Sensitivity analyses confirmed robustness: PSM (− 0.255 mm; p< 0.001) and PP (− 0.298 mm; p< 0.001). Dose–response showed each 10% higher adherence reduced elongation by − 0.148 mm (p< 0.001). No clinically significant adverse events were detected.Conclusion: RLRL combined with OK significantly reduced axial elongation in rapid-progressing children compared with OK alone, with a clear adherence-dependent effect and reassuring short-term safety profile.Keywords: Myopia control, Orthokeratology, Repeated low-level red light, Children and adolescents