Far-red Wavelengths Research Articles

Noise Reduction for Solar-Induced Fluorescence Retrievals Using Machine Learning and Principal Component Analysis: Simulations and Applications to GOME-2 Satellite Retrievals

Abstract We use a spectral-based approach that employs principal component analysis along with a relatively shallow artificial neural network (NN) to substantially reduce noise and other artifacts in terrestrial chlorophyll solar-induced fluorescence (SIF) retrievals. SIF is a very small emission at red and far-red wavelengths that is difficult to measure and is highly sensitive to random errors and systematic artifacts. Our approach relies upon an assumption that a trained NN can effectively reconstruct the total SIF signal from a relatively small number of leading principal components of the satellite-observed far-red radiance spectra without using information from the trailing modes that contain most of the random errors. We test the approach with simulated reflectance spectra produced with a full atmospheric and surface radiative transfer model using different observing and geophysical parameters and various noise levels. The resulting noisy and noise-reduced retrieved SIF values are compared with true values to assess performance. We then apply our noise reduction approach to SIF derived from two different satellite spectrometers. For evaluation, since the truth in this case is unknown, we compare SIF retrievals from two independent sensors with each other. We also compare the noise-reduced SIF temporal variations with those from an independent gross primary product (GPP) product that should display similar variations. Results show that our noise reduction approach improves the capture of SIF seasonal and interannual variability. Our approach should be applicable to many noisy data products derived from spectral measurements. Our methodology does not replace the original retrieval algorithms; rather, the original noisy retrievals are needed as the target for the NN training process. Significance Statement The purpose of this study is to document and demonstrate a machine learning algorithm that is used to effectively reduce noise and artifacts in a satellite data product, solar-induced fluorescence (SIF) from chlorophyll. This is important because SIF retrievals are typically noisy, and the noise limits their ability to be used for diagnosing plant health and productivity. Our results show substantial improvement in SIF retrievals that may lead to new applications. Our approach can be similarly applied to other noisy satellite data products.

Far-red radiation management for lettuce growth: Physiological and morphological features leading to energy optimization in vertical farming

Recently, far-red wavelengths (FR, 700–750 nm) have been largely investigated in indoor cultivation systems due to their morphological effects on plants (e.g., leaf expansion and stem elongation), resulting also in increasing yield. This work investigated the effect of substituting part of the red (R) and blue (B) radiation with far-red radiation, while keeping constant the photon flux density, in the light spectrum for lettuce grown in a vertical farm. Lettuce (Lactuca sativa var. Canasta) plants were transplanted and grown in an ebb-and-flow system for 29 days. During the cycle, plants were subjected to five different light treatments: a control treatment consisting of an optimized R and B spectrum (ratio of 3; RB3) with a photosynthetic photon flux density of 200 µmol m−2 s−1, and four treatments in which R and B were partially replaced by 10, 30, 50 and 70 µmol m−2 s−1 of FR light, resulting in an increasing FR fraction. Biomass production and most of the morphological parameters were affected from 15 days after transplanting (DAT), while stomatal conductance from 22 DAT. Leaf greenness and specific leaf area values were influenced by the FR radiation starting from 8 DAT. At 29 DAT, substitution of an amount of R and B photons equal to 30 (RB3–30) or 50 (RB3–50) µmol m−2 s−1 with the same amount of FR radiation resulted in increased leaf biomass in both fresh (+49 and +47%, respectively) and dry weight (+45 and +42%, respectively). With RB3–30, the increase was due to leaf area expansion (+103%), whereas stomatal conductance (gs) and quantum efficiency of photosystem II (ΦPSII) did not change compared with the spectrum with only R and B. With RB3–50, gs and ΦPSII decreased compared with RB3 (-27 and -6%, respectively), but the greater biomass accumulation was supported by the greater leaf expansion (+119 %). The adoption of RB3–30 and RB3–50 also promoted light use efficiency (+45 and +42 %, respectively), lighting energy use efficiency (+48 and +53 %, respectively) and therefore the overall energy performance of the system. The adoption of RB3–30 and RB3–50 is a valid strategy to increase yield for lettuce production, but further studies, also in relation to blue radiation intensity, are needed to avoid the negative effect on leaf pigmentation.

Tuning the Shades of Red Emission in InP/ZnSe/ZnS Nanocrystals with Narrow Full Width for Fabrication of Light-Emitting Diodes.

While Cd-based luminescent nanocrystals (NCs) are the most mature NCs for fabricating efficient red light-emitting diodes (LEDs), their toxicity related limitation is inevitable, making it necessary to find a promising alternative. From this point of view, multishell-coated, red-emissive InP-based NCs are excellent luminescent nanomaterials for use as an emissive layer in electroluminescent (EL) devices. However, due to the presence of oxidation states, they suffer from a wide emission spectrum, which limits their performance. This study uses tris(dimethylamino)phosphine (3DMA-P) as a low-cost aminophosphine precursor and a double HF treatment to suggest an upscaled, cost-effective, and one-pot hot-injection synthesis of purely red-emissive InP-based NCs. The InP core structures were coated with thick layers of ZnSe and ZnS shells to prevent charge delocalization and to create a narrow size distribution. The purified NCs showed an intense emission signal as narrow as 43 nm across the entire red wavelength range (626-670 nm) with an emission quantum efficiency of 74% at 632 nm. The purified samples also showed an emission quantum efficiency of 60% for far-red wavelengths of 670 nm with a narrow full width of 50 nm. The samples showed a relatively long average emission lifetime of 50-70 ns with a biexponential decay profile. To demonstrate the practical ability of the prepared NCs in optoelectronics, we fabricated a red-emissive InP-based LEDs. The best-performing device showed an external quantum efficiency (EQE) of 1.16%, a luminance of 1039 cd m-2, and a current efficiency of 0.88 cd A-1.

Leaf morphology, optical characteristics and phytochemical traits of butterhead lettuce affected by increasing the far-red photon flux.

Light and its spectral characteristics are crucial for plant growth and development. The far-red photon flux mediates many plant processes through the action of phytochrome and also accelerates the photosynthetic electron transfer rate. In this study, we assessed the effects of far-red addition on butterhead lettuce morphology, light use efficiency, optical properties, and phytochemical characteristics. Three-week-old lettuce plants (Lactuca sativa L. cv. Alyssa) were grown for up to 28 days under a 10% blue and 90% red light spectrum (200 µmol m-2 s-1, 16h photoperiod) to which five different intensities of far-red light (peak at 735 nm) were added (0-9-18-36-72 µmol m-2 s-1). White light-emitting diodes were included as a proxy for sunlight. Increasing supplemental far-red photon flux from zero to 21% increased the light use efficiency (g per mol) by 37% on day 14; 43% on day 21; and 39% on day 28. Measurements of projected head area suggest that this was associated with an increase in leaf expansion and photon capture and not necessarily a direct effect on photosynthesis. Moreover, vegetation indices based on leaf reflectance showed a decrease in chlorophyll-related indices under a high far-red photon flux. This decrease in pigment content was confirmed by chemical analyses, suggesting that the plants may not reach their full potential in terms of photon capture, limiting the overall photosynthetic performance. Furthermore, the stress-related Carter 1 index increased in plants grown under a high far-red photon flux, indicating early plant stress. Far-red tended to decrease the content of total phenolics and increase soluble sugars. The higher sugar levels can be attributed to an improved photochemical efficiency due to photosystem I excitation by far-red wavelengths, also known as the Emerson Enhancement effect. Despite these higher sugar levels, no effect on foliar nitrate content was observed. Our results show that far-red supplementation has the potential to enhance light interception at the early growth stages, although higher intensities of far-red may cause plant stress.

Deciphering the Effect of Light Wavelengths in Monilinia spp. DHN-Melanin Production and Their Interplay with ROS Metabolism in M. fructicola.

Pathogenic fungi are influenced by many biotic and abiotic factors. Among them, light is a source of information for fungi and also a stress factor that triggers multiple biological responses, including the activation of secondary metabolites, such as the production of melanin pigments. In this study, we analyzed the melanin-like production in in vitro conditions, as well as the expression of all biosynthetic and regulatory genes of the DHN-melanin pathway in the three main Monilinia species upon exposure to light conditions (white, black, blue, red, and far-red wavelengths). On the other hand, we analyzed, for the first time, the metabolism related to ROS in M. fructicola, through the production of hydrogen peroxide (H2O2) and the expression of stress-related genes under different light conditions. In general, the results indicated a clear importance of black light on melanin production and expression in M. laxa and M. fructicola, but not in M. fructigena. Regarding ROS-related metabolism in M. fructicola, blue light highlighted by inhibiting the expression of many antioxidant genes. Overall, it represents a global description of the effect of light on the regulation of two important secondary mechanisms, essential for the adaptation of the fungus to the environment and its survival.

Revealing the tissue-level complexity of endogenous glucagon-like peptide-1 receptor expression and signaling

The glucagon-like peptide-1 receptor (GLP1R) is a class B G protein-coupled receptor (GPCR) involved in glucose homeostasis and food intake. GLP1R agonists (GLP1RA) are widely used in the treatment of diabetes and obesity, yet visualizing the endogenous localization, organization and dynamics of a GPCR has so far remained out of reach. In the present study, we generate mice harboring an enzyme self-label genome-edited into the endogenous Glp1r locus. We also rationally design and test various fluorescent dyes, spanning cyan to far-red wavelengths, for labeling performance in tissue. By combining these technologies, we show that endogenous GLP1R can be specifically and sensitively detected in primary tissue using multiple colors. Longitudinal analysis of GLP1R dynamics reveals heterogeneous recruitment of neighboring cell subpopulations into signaling and trafficking, with differences observed between GLP1RA classes and dual agonists. At the nanoscopic level, GLP1Rs are found to possess higher organization, undergoing GLP1RA-dependent membrane diffusion. Together, these results show the utility of enzyme self-labels for visualization and interrogation of endogenous proteins, and provide insight into the biology of a class B GPCR in primary cells and tissue.

Facing energy limitations - approaches to increase basil (Ocimum basilicum L.) growth and quality by different increasing light intensities emitted by a broadband LED light spectrum (400-780 nm).

Based on the current trend towards broad-bandwidth LED light spectra for basil productions in multi-tiered controlled-environment horticulture, a recently developed white broad-bandwidth LED light spectrum (400-780 nm) including far-red wavelengths with elevated red and blue light fractions was employed to cultivate basil. Four Ocimum basilicum L. cultivars (cv. Anise, cv. Cinnamon, cv. Dark Opal and cv. Thai Magic) were exposed to two different rising light intensity conditions (ILow and IHigh). In dependence of the individual cultivar-specific plant height increase over time, basil cultivars were exposed to light intensities increasing from ~ 100 to ~ 200 µmol m-2 s-1 under ILow, and from 200 to 400 µmol m-2 s-1 under IHigh (due to the exponential light intensity increases with decreasing proximity to the LED light fixtures). Within the first experiment, basils' morphological developments, biomass yields and time to marketability under both light conditions were investigated and the energy consumptions were determined to calculate the basils' light use efficiencies. In detail, cultivar-dependent differences in plant height, leaf and branch pair developments over time are described. In comparison to the ILow light conditions, IHigh resulted in accelerated developments and greater yields of all basil cultivars and expedited their marketability by 3-5 days. However, exposure to light intensities above ~ 300 µmol m-2 s-1 induced light avoidance responses in the green-leafed basil cultivars cv. Anise, cv. Cinnamon and cv. Thai Magic. In contrast, ILow resulted in consumer-preferred visual qualities and greater biomass efficiencies of the green-leafed basil cultivars and are discussed as a result of their ability to adapt well to low light conditions. Contrarily to the green-leafed cultivars, purple-leafed cv. Dark Opal developed insufficiently under ILow, but remained light-tolerant under IHigh, which is related to its high anthocyanin contents. In a second experiment, cultivars' volatile organic compound (VOC) contents and compositions over time were investigated. While VOC contents per gram of leaf dry matter gradually decreased in purple-leafed cv. Dark Opal between seedling stage to marketability, their contents gradually increased in the green cultivars. Regardless of the light treatment applied, cultivar-specific VOC compositions changed tremendously in a developmental stage-dependent manner.

Alteration in Light Spectra Causes Opposite Responses in Volatile Phenylpropanoids and Terpenoids Compared with Phenolic Acids in Sweet Basil (Ocimum basilicum) Leaves.

Basil (Ocimum basilicum, cv. Dolly) grew under three different light spectra (A, B, and C) created by light-emitting diode lamps. The proportions of UV-A, blue, and green-yellow wavelengths decreased linearly from A to C, and the proportions of red and far-red wavelengths increased from A to C. Photosynthetic photon flux density was 300 μmol m–2 s–1 in all spectra. The spectrum C plants had highest concentrations of phenolic acids (main compounds: rosmarinic acid and cichoric acid), lowest concentrations and emissions of phenylpropanoid eugenol and terpenoids (main compounds: linalool and 1,8-cineole), highest dry weight, and lowest water content. Conversely, spectra A and B caused higher terpenoid and eugenol concentrations and emissions and lower concentrations of phenolic acids. High density of peltate glandular trichomes explained high terpenoid and eugenol concentrations and emissions. Basil growth and secondary compounds affecting aroma and taste can be modified by altering light spectra; however, increasing terpenoids and phenylpropanoids decreases phenolic acids and growth and vice versa.

A Light Recipe including Far-Red Wavelength during Healing of Grafted Watermelon Seedlings Enhances the Floral Development and Yield Earliness

Watermelon is widely propagated through grafting, after which seedlings are subjected to healing under controlled conditions including artificial lighting. Light wavelengths, such as blue, red, and far-red, impose considerable effects on seedlings, which possibly carry on to the mature plants. The aim of the present study is to examine whether different light wavelengths during healing of grafted watermelon seedlings impose variable effects during field cultivation. After grafting, seedlings were healed in an environmentally controlled healing chamber under fluorescent (FL) lamps and light-emitting diodes, providing 100% red (R), 100% blue (B), 88/12% R/B (12B), and 12B including 5% far-red (12B + FR). After acclimatization, seedlings were transplanted in the field. Vegetative growth until floral initiation was enhanced by 12B and 12B + FR, as shown by stem diameter and leaf number measurements. Flowering was mainly accelerated by 12B + FR and considerably decelerated by FL and B. The same pattern was followed by fruit yield, which was similar for all treatments at the end of the experiment. Nevertheless, fruit quality was not affected by any of the light treatments. It is concluded that a light recipe, including red, blue and far-red, wavelengths during healing of grafted seedlings enhances the overall growth, and flowering and yield earliness of watermelon crops.

PIF7 controls leaf cell proliferation through an AN3 substitution repression mechanism

Plants are agile, plastic organisms able to adapt to everchanging circumstances. Responding to far-red (FR) wavelengths from nearby vegetation, shade-intolerant species elicit the adaptive shade-avoidance syndrome (SAS), characterized by elongated petioles, leaf hyponasty, and smaller leaves. We utilized end-of-day FR (EODFR) treatments to interrogate molecular processes that underlie the SAS leaf response. Genetic analysis established that PHYTOCHROME-INTERACTING FACTOR 7 (PIF7) is required for EODFR-mediated constraint of leaf blade cell division, while EODFR messenger RNA sequencing data identified ANGUSTIFOLIA3 (AN3) as a potential PIF7 target. We show that PIF7 can suppress AN3 transcription by directly interacting with and sequestering AN3. We also establish that PIF7 and AN3 impose antagonistic control of gene expression via common cis-acting promoter motifs in several cell-cycle regulator genes. EODFR triggers the molecular substitution of AN3 to PIF7 at G-box/PBE-box promoter regions and a switch from promotion to repression of gene expression.

Light Spectrum Variably Affects the Acclimatization of Grafted Watermelon Seedlings While Maintaining Fruit Quality

In many countries of Europe and Eastern Asia, watermelon production is mainly based on the use of grafted seedlings. Upon grafting, seedlings undergo a period of healing where artificial lighting is provided by light-emitting diodes in controlled chambers in order to accelerate and improve the healing process. The objective of our study was to test the effect of light quality on the final product (i.e., seedlings ready for transplanting) in the nursery, as well as to evaluate the possible implications on fruit quality after field cultivation. Narrow-band blue (B) and red (R) wavelengths, 64–36% R-B (36B), 76–24% R-B (24B), 88–12% R-B (12B), and 83–12% R-B plus 5% far-red (12B+FR) wavelengths were tested. 12B+FR enhanced the root dry weight, root architecture, and maximum photosynthetic rate, while RB combinations generally showed better root system development with increased blue portion. R light induced inferior root dry weight and quality indices (root/shoot and shoot–dry–weight/length ratios), lower gas exchange parameters, and chlorophyll content, but high shoot length and leaf area. B light led to inferior root architecture, lower stem diameter, leaf area, and maximum photosynthetic rate. Both R and B wavelengths showed decreased concentration of macronutrients and trace elements. After field cultivation, fruit quality (i.e., morphology and color), and valuable nutritive characteristics (i.e., phenolics, carotenoids, lycopene, antioxidants) maintained high quality irrespective of light treatments. Overall, 12B+FR performed well in almost all qualitative parameters including the morphology, the root development, and photosynthesis, while also maintaining high fruit quality.

Luminescence of Mn4+ in Double Perovskites, Ba2 lnNbO6 (Ln= Y, Gd, La)

The red (600 nm–700 nm) and far-red (FR; 700 nm–750 nm) wavelengths of the electromagnetic spectrum are important for plant growth. Phosphors can be used to down-convert the blue emission of the InGaN LED to red and FR light for use in horticultural lighting. In the archival literature, phosphors activated with tetravalent manganese (Mn4+; 3d3) have been identified as potential generators of red and deep red photons [1-2]. Deep red photons generated by Mn4+ can also be used in lifetime-based luminescence thermometry [3].Compounds with the double perovskite structure have been investigated as generators of deep red photons [4-5]. In this work we provide a systematic and comparative study of the spectroscopic properties of Mn4+ in the double perovskites, Ba2 LnNbO6 (Ln= Y, Gd, La). The Mn4+ energy levels are calculated using the exchange charge model of crystal-field theory and compared with the experimental spectroscopic data. The result of our investigations shows that energy of the 2E→4A2 (R-line) emission transition is determined by octahedral site distortion and polarization of the oxygen electron density within the -Ln-O-Mn-O- linkages. The work provides guidelines for the development of deep red emitting phosphors for horticultural and specialty applications.

Single Wavelengths of LED Light Supplement Promote the Biosynthesis of Major Cyclic Monoterpenes in Japanese Mint.

Environmental light conditions influence the biosynthesis of monoterpenes in the mint plant. Cyclic terpenes, such as menthol, menthone, pulegone, and menthofuran, are major odor components synthesized in mint leaves. However, it is unclear how light for cultivation affects the contents of these compounds. Artificial lighting using light-emitting diodes (LEDs) for plant cultivation has the advantage of preferential wavelength control. Here, we monitored monoterpene contents in hydroponically cultivated Japanese mint leaves under blue, red, or far-red wavelengths of LED light supplements. Volatile cyclic monoterpenes, pulegone, menthone, menthol, and menthofuran were quantified using the head-space solid phase microextraction method. As a result, all light wavelengths promoted the biosynthesis of the compounds. Remarkably, two weeks of blue-light supplement increased all compounds: pulegone (362% increase compared to the control), menthofuran (285%), menthone (223%), and menthol (389%). Red light slightly promoted pulegone (256%), menthofuran (178%), and menthol (197%). Interestingly, the accumulation of menthone (229%) or menthofuran (339%) was observed with far-red light treatment. The quantification of glandular trichomes density revealed that no increase under light supplement was confirmed. Blue light treatment even suppressed the glandular trichome formation. No promotion of photosynthesis was observed by pulse-amplitude-modulation (PAM) fluorometry. The present result indicates that light supplements directly promoted the biosynthetic pathways of cyclic monoterpenes.

A plant parasite uses light cues to detect differences in host-plant proximity and architecture.

Sunlight filtered by green plant tissue becomes diminished in its ratio of red to far-red wavelengths (R:FR). Some parasitic plants exploit this change by growing towards regions of low R:FR to locate host plants. In principle, variation in R:FR can also convey ecologically relevant information about host proximity or architecture. Here, we demonstrate that the parasitic vine Cuscuta epilinum Weihe (Convolvulaceae) can distinguish fine-scale differences in R:FR associated with differences in the proximity and shape of potential host plants. We conducted dual-choice experiments by placing parasite seedlings between targets, including low R:FR fields manipulated via LED lighting and pairs of model plants exhibiting realistic R and FR reflectance but differing in proximity or shape. Seedlings consistently distinguished between low-R:FR fields of differing intensity. Furthermore, they exhibited preferences for nearer plant models versus identical models placed 4 cm further away and between same-sized models exhibiting shape differences. Our results indicate that parasites can discriminate minute differences in R:FR signatures corresponding to host factors (proximity and shape) that impact seedling survival. This keen sensory ability underpins the parasite's sophisticated foraging behaviour and highlights the broader importance of light cues in plant ecology.

(INVITED) Exploring Sm2+ activated phosphors as red-deep red photon generator for horticultural application

The red (600 nm–700 nm) and far-red (FR; 700 nm–750 nm) wavelengths of the electromagnetic spectrum are important for plant growth. Phosphors can be used to down-convert the blue emission of the InGaN LED to red and FR light for use in horticultural lighting. In the archival literature, investigations pertaining to the development of such phosphors are primarily concerned with studies of the photoluminescence of transition metal (Mn4+ and Cr3+) and rare earth (Eu2+) ions. In this work we explore the spectroscopic properties of the divalent samarium (Sm2+) ion for usage in LED based horticultural lighting device. We show that both the inter- and intraconfigurational emission transitions of the Sm2+ ion can provide efficient stimulation of the phytochromes. Factors that determine the nature of emission are discussed as are the general mechanistic aspects of thermal quenching and quantum efficiency of luminescence.

Medicago PHYA promotes flowering, primary stem elongation and expression of flowering time genes in long days

BackgroundFlowering time is an important trait for productivity in legumes, which include many food and fodder plants. Medicago truncatula (Medicago) is a model temperate legume used to study flowering time pathways. Like Arabidopsis thaliana (Arabidopsis), its flowering is promoted by extended periods of cold (vernalization, V), followed by warm long day (LD) photoperiods. However, Arabidopsis flowering-time genes such as the FLOWERING LOCUS C (FLC)/ MADS AFFECTING FLOWERING (MAF) clade are missing and CONSTANS-LIKE (CO-LIKE) genes do not appear to have a role in Medicago or Pisum sativum (pea). Another photoperiodic regulator, the red/far red photoreceptor PHYTOCHROME A (PHYA), promotes Arabidopsis flowering by stabilizing the CO protein in LD. Interestingly, despite the absence of CO-LIKE function in pea, PsPHYA plays a key role in promoting LD photoperiodic flowering and plant architecture. Medicago has one homolog of PHYA, MtPHYA, but its function is not known.ResultsGenetic analysis of two MtPHYA Tnt1 insertion mutant alleles indicates that MtPHYA has an important role in promoting Medicago flowering and primary stem elongation in VLD and LD and in perception of far-red wavelengths in seedlings. MtPHYA positively regulates the expression of MtE1-like (MtE1L), a homologue of an important legume-specific flowering time gene, E1 in soybean and other Medicago LD-regulated flowering-time gene homologues, including the three FLOWERING LOCUS T-LIKE (FT-LIKE) genes, MtFTa1, MtFTb1 and MtFTb2 and the two FRUITFULL-LIKE (FUL-LIKE) genes MtFULa and MtFULb. MtPHYA also modulates the expression of the circadian clock genes, GIGANTEA (GI) and TIMING OF CAB EXPRESSION 1a (TOC1a). Genetic analyses indicate that Mtphya-1 Mte1l double mutants flowered at the same time as the single mutants. However, Mtphya-1 Mtfta1 double mutants had a weak additive effect in delaying flowering and in reduction of primary axis lengths beyond what was conferred by either of the single mutants.ConclusionMtPHYA has an important role in LD photoperiodic control of flowering, plant architecture and seedling de-etiolation under far-red wavelengths in Medicago. It promotes the expression of LD-induced flowering time genes and modulates clock-related genes. In addition to MtFTa1, MtPHYA likely regulates other targets during LD floral induction in Medicago.

Progress of Research on the Regulatory Pathway of the Plant Shade-Avoidance Syndrome.

When subject to vegetational shading, shade-avoiding plants detect neighbors by perceiving reduced light quantity and altered light quality. The former includes decreases in the ratio of red to far-red wavelengths (low R:FR) and low blue light ratio (LBL) predominantly detected by phytochromes and cryptochromes, respectively. By integrating multiple signals, plants generate a suite of responses, such as elongation of a variety of organs, accelerated flowering, and reduced branching, which are collectively termed the shade-avoidance syndrome (SAS). To trigger the SAS, interactions between photoreceptors and phytochrome-interacting factors are the general switch for activation of downstream signaling pathways. A number of transcription factor families and phytohormones, especially auxin, gibberellins, ethylene, and brassinosteroids, are involved in the SAS processes. In this review, shade signals, the major photoreceptors involved, and the phenotypic characteristics of the shade-intolerant plant Arabidopsis thaliana are described in detail. In addition, integration of the signaling mechanisms that link photoreceptors with multiple hormone signaling pathways is presented and future research directions are discussed.

Light and temperature receptors and their convergence in plants

Light and temperature are two essential environmental cues for plants, helping to optimize plant body architecture and physiology. To sense a broad spectrum of sun radiation spanning from UV-B to far-red wavelength, plants are equipped with a sophisticated array of photoreceptors, including phytochromes, cryptochromes, phototropins, Zeitlupes, and UV-B photoreceptor UVR8. On the contrary, since the thermodynamic effects extensively affect the molecular and supramolecular structures, it is difficult to identify the entry point or initial receptor of temperature. Even so, several putative temperature sensors have been proposed, such as calcium ion channels, H2A.Z, and the thermodynamic change of plasma membrane fluidity. Considering that many processes in plant respond to irradiance and temperature, scientists devote to finding out the converge point of these environmental cues. As a typical example, circadian rhythm is such an integration point, which receives the signal input of both irradiance and temperature. The updating evidence shows, as an important photoreceptor, phytochrome B acts as temperature sensors via a thermodynamic active state revision. These findings suggest that the studies on light and temperature receptors in plants should not be separated. Their extensive convergence during signalling provides a new direction for understanding the stimuli perception mechanisms.

Sprout Growth Inhibition and Photomorphogenic Development of Potato Seed Tubers (Solanum tuberosum L.) Under Different LED Light Colours

Green-sprouting potato seed tubers in light and elevated temperatures are vital for production in short-season climates. Using light-emitting diodes (LEDs) to inhibit sprout elongation during pre-sprouting may represent an energy-efficient alternative to traditional indoor light sources. Sprout growth inhibition and some photomorphogenic responses were therefore examined in potato cultivars exposed to LEDs of different wavelength maxima and irradiance rates. Red LED (660 nm) produced the strongest inhibition of sprout elongation at very low irradiances 10–100 nmol m−2 s−1, while far-red LED (735 nm) produced the strongest inhibition at higher irradiances. This inhibitory pattern was similar in all cultivars, although the degree of inhibition varied. The colour of sprouts and tuber skin remained etiolated under far-red LED, in contrast to LEDs between 380 and 660 nm which developed green colour intensity in an irradiance-dependent manner. Mixtures of red and far-red light, and pulses including red/far-red reversals did not produce stronger inhibition, except in some instances where total fluence was increased. Furthermore, green-sprouting under different LED colours did not seem to affect subsequent emergence and growth after planting. The current results suggest an involvement of multiple phytochromes in de-etiolation and sprout growth inhibition in seed potato tubers, which may be selectively utilised in LED-based green-sprouting in red and far-red wavelengths.

Do all chlorophyll fluorescence emission wavelengths capture the spring recovery of photosynthesis in boreal evergreen foliage?

Chlorophyll a fluorescence (ChlF) is closely related to photosynthesis and can be measured remotely using multiple spectral features as solar-induced fluorescence (SIF). In boreal regions, SIF shows particular promise as an indicator of photosynthesis, in part because of the limited variation of seasonal light absorption in these ecosystems. Seasonal spectral changes in ChlF could yield new information on processes such as sustained nonphotochemical quenching (NPQS ) but also disrupt the relationship between SIF and photosynthesis. We followed ChlF and functional and biochemical properties of Pinus sylvestris needles during the photosynthetic spring recovery period to answer the following: (a) How ChlF spectra change over seasonal timescales? (b) How pigments, NPQS , and total photosynthetically active radiation (PAR) absorption drive changes of ChlF spectra? (c) Do all ChlF wavelengths track photosynthetic seasonality? We found seasonal ChlF variation in the red and far-red wavelengths, which was strongly correlated with NPQS , carotenoid content, and photosynthesis (enhanced in the red), but not with PAR absorption. Furthermore, a rapid decrease in red/far-red ChlF ratio occurred in response to a cold spell, potentially relating to the structural reorganization of the photosystems. We conclude that all current SIF retrieval features can track seasonal photosynthetic dynamics in boreal evergreens, but the full SIF spectra provides additional insight.