Photonic multilayer structure of Begonia chloroplasts enhances photosynthetic efficiency

Structural color in the bacterial domain: The ecogenomics of a 2-dimensional optical phenotype

Structural color is an optical phenomenon resulting from light interacting with nanostructured materials. Although structural color (SC) is widespread in the tree of life, the underlying genetics and genomics are not well understood. Here, we collected and sequenced a set of 87 structurally colored bacterial isolates and 30 related strains lacking SC. Optical analysis of colonies indicated that diverse bacteria from at least two different phyla (Bacteroidetes and Proteobacteria) can create two-dimensional packing of cells capable of producing SC. A pan-genome-wide association approach was used to identify genes associated with SC. The biosynthesis of uroporphyrin and pterins, as well as carbohydrate utilization and metabolism, was found to be involved. Using this information, we constructed a classifier to predict SC directly from bacterial genome sequences and validated it by cultivating and scoring 100 strains that were not part of the training set. We predicted that SCr is widely distributed within gram-negative bacteria. Analysis of over 13,000 assembled metagenomes suggested that SC is nearly absent from most habitats associated with multicellular organisms except macroalgae and is abundant in marine waters and surface/air interfaces. This work provides a large-scale ecogenomics view of SC in bacteria and identifies microbial pathways and evolutionary relationships that underlie this optical phenomenon.

Living jewels: iterative evolution of iridescent blue leaves from helicoidal cell walls

BACKGROUND AND AIMS

Structural colour is responsible for the remarkable metallic blue colour seen in the leaves of several plants. Species belonging to only ten genera have been investigated to date, revealing four photonic structures responsible for structurally coloured leaves. One of these is the helicoidal cell wall, known to create structural colour in the leaf cells of five taxa. Here we investigate a broad selection of land plants to understand the phylogenetic distribution of this photonic structure in leaves.

METHODS

We identified helicoidal structures in the leaf epidermal cells of 19 species using transmission electron microscopy. Pitch measurements of the helicoids were compared with the reflectance spectra of circularly polarized light from the cells to confirm the structure-colour relationship.

RESULTS

By incorporating species examined with a polarizing filter, our results increase the number of taxa with photonic helicoidal cell walls to species belonging to at least 35 genera. These include 19 monocot genera, from the orders Asparagales (Orchidaceae) and Poales (Cyperaceae, Eriocaulaceae, Rapateaceae) and 16 fern genera, from the orders Marattiales (Marattiaceae), Schizaeales (Anemiaceae) and Polypodiales (Blechnaceae, Dryopteridaceae, Lomariopsidaceae, Polypodiaceae, Pteridaceae, Tectariaceae).

CONCLUSIONS

Our investigation adds considerably to the recorded diversity of plants with structurally coloured leaves. The iterative evolution of photonic helicoidal walls has resulted in a broad phylogenetic distribution, centred on ferns and monocots. We speculate that the primary function of the helicoidal wall is to provide strength and support, so structural colour could have evolved as a potentially beneficial chance function of this structure.

Multiple-pathways light modulation in Pleurosigma strigosum bi-raphid diatom

Ordered, quasi-ordered, and even disordered nanostructures can be identified as constituent components of several protists, plants and animals, making possible an efficient manipulation of light for intra- and inter- species communication, camouflage, or for the enhancement of primary production. Diatoms are ubiquitous unicellular microalgae inhabiting all the aquatic environments on Earth. They developed, through tens of millions of years of evolution, ultrastructured silica cell walls, the frustules, able to handle optical radiation through multiple diffractive, refractive, and wave-guiding processes, possibly at the basis of their high photosynthetic efficiency. In this study, we employed a range of imaging, spectroscopic and numerical techniques (including transmission imaging, digital holography, photoluminescence spectroscopy, and numerical simulations based on wide-angle beam propagation method) to identify and describe different mechanisms by which Pleurosigma strigosum frustules can modulate optical radiation of different spectral content. Finally, we correlated the optical response of the frustule to the interaction with light in living, individual cells within their aquatic environment following various irradiation treatments. The obtained results demonstrate the favorable transmission of photosynthetic active radiation inside the cell compared to potentially detrimental ultraviolet radiation.

Hyperreflective photonic crystals created by shearing colloidal dispersions at ultrahigh volume fraction

Colloidal crystallization serves as one of the most economic and scalable production methods for photonic crystals. However, insufficient optical performance, nonuniformity and low reproducibility remain challenges for advanced high-value applications. In this study, we optimally formulate a photocurable dispersion of silica particles and apply shear flow to unify the orientation of the colloidal crystals, ensuring high optical performance and uniformity. The silica particles experience strong repulsion at ultrahigh volume fractions of 50% but demonstrate low mobility, leading to polycrystalline structures. Applying shear flow to the dispersions allows the silica particles to rearrange into larger crystalline domains with a unidirectional orientation along the flow. This shear-induced structural change produces absolute reflectivity at the stopband as high as 90% and a high transparency of 90% at off-resonant wavelengths with minimal diffusive scattering. Furthermore, the strong interparticle repulsion ensures a uniform volume fraction of particles throughout the dispersion, reducing deviations in the optical properties. We intricately micropattern the photocurable dispersions using photolithography. Additionally, the photonic films and patterns can be stacked to form multiple layers, displaying mixed structural colors and multiple reflectance peaks without sacrificing reflectivity. These superior photonic materials hold promise for various optical applications, including optical components and anticounterfeiting patches.

Diversification of Plastid Structure and Function in Land Plants

Plastids represent a largely diverse group of organelles in plant and algal cells that have several common features but also a broad spectrum of morphological, ultrastructural, biochemical, and physiological differences. Plastids and their structural and metabolic diversity significantly contribute to the functionality and developmental flexibility of the plant body throughout its lifetime. In addition to the multiple roles of given plastid types, this diversity is accomplished in some cases by interconversions between different plastids as a consequence of developmental and environmental signals that regulate plastid differentiation and specialization. In addition to basic plastid structural features, the most important plastid types, the newly characterized peculiar plastids, and future perspectives in plastid biology are also provided in this chapter.

Co-modulation of structural and pigmentary coloration in Lyropteryx apollonia butterfly

Nature produces some of the most striking optical effects through the combination of structural and chemical principles to give rise to a wide range of colors. However, creating non-spectral colors that extend beyond the color spectrum is a challenging task, as it requires meeting the requirements of both structural and pigmentary coloration. In this study, we investigate the magenta non-spectral color found in the scales of the ventral spots of the Lyropteryx apollonia butterfly. By employing correlated optical and electron microscopy, as well as pigment extraction techniques, we reveal how this color arises from the co-modulation of pigmentary and structural coloration. Specifically, the angle-dependent blue coloration results from the interference of visible light with chitin-based nanostructures, while the diffused red coloration is generated by an ommochrome pigment. The ability to produce such highly conspicuous non-spectral colors provides insights for the development of hierarchical structures with precise control over their optical response. These structures can be used to create hierarchically-arranged systems with a broadened color palette.

Increased ascorbic acid synthesis by overexpression of AcGGP3 ameliorates copper toxicity in kiwifruit

The widespread application of copper (Cu) -based fertilizers and pesticides could increase the accumulation of Cu in kiwifruit. According to a global survey, red- and yellow-fleshed kiwifruit contained more elevated amounts of Cu than green-fleshed kiwifruit due to weaker disease resistance and higher use of Cu pesticides. Intriguingly, our research revealed that external and endogenous ascorbic acid (AsA) reduced the phenotypic and physiological injury of Cu toxicity in kiwifruit. Cu stress assays and transcriptional analysis have shown that Cu treatment for 12 h significantly increased the AsA content in kiwifruit leaves and up-regulated key genes involved in AsA biosynthesis, such as GDP-L-galactose phosphorylase3 (GGP3) and GDP-mannose-3',5'-epimerase (GME). Overexpressing GGP3 in transgenic kiwifruit significantly increased the endogenous AsA content of kiwifruit, which was beneficial in mitigating Cu toxicity by decreasing levels of reactive oxygen species, malondialdehyde, and electrolyte leakage, as well as reducing damage to the chloroplast structure and photosystem II. This study presented a novel strategy to ameliorate plant Cu stress by increasing the endogenous antioxidant (AsA) content through transgenesis.

Interactions between color and gloss in iridescent camouflage

Iridescence is a taxonomically widespread form of structural coloration that produces often intense hues that change with the angle of viewing. Its role as a signal has been investigated in multiple species, but recently, and counter-intuitively, it has been shown that it can function as camouflage. However, the property of iridescence that reduces detectability is, as yet, unclear. As viewing angle changes, iridescent objects change not only in hue but also in intensity, and many iridescent animals are also shiny or glossy; these "specular reflections," both from the target and background, have been implicated in crypsis. Here, we present a field experiment with natural avian predators that separate the relative contributions of color and gloss to the "survival" of iridescent and non-iridescent beetle-like targets. Consistent with previous research, we found that iridescent coloration, and high gloss of the leaves on which targets were placed, enhance survival. However, glossy targets survived less well than matt. We interpret the results in terms of signal-to-noise ratio: specular reflections from the background reduce detectability by increasing visual noise. While a specular reflection from the target attracts attention, a changeable color reduces the signal because, we suggest, normally, the color of an object is a stable feature for detection and identification.

Organellomic gradients in the fourth dimension

Organelles function as hubs of cellular metabolism and elements of cellular architecture. In addition to 3 spatial dimensions that describe the morphology and localization of each organelle, the time dimension describes complexity of the organelle life cycle, comprising formation, maturation, functioning, decay, and degradation. Thus, structurally identical organelles could be biochemically different. All organelles present in a biological system at a given moment of time constitute the organellome. The homeostasis of the organellome is maintained by complex feedback and feedforward interactions between cellular chemical reactions and by the energy demands. Synchronized changes of organelle structure, activity, and abundance in response to environmental cues generate the fourth dimension of plant polarity. Temporal variability of the organellome highlights the importance of organellomic parameters for understanding plant phenotypic plasticity and environmental resiliency. Organellomics involves experimental approaches for characterizing structural diversity and quantifying the abundance of organelles in individual cells, tissues, or organs. Expanding the arsenal of appropriate organellomics tools and determining parameters of the organellome complexity would complement existing -omics approaches in comprehending the phenomenon of plant polarity. To highlight the importance of the fourth dimension, this review provides examples of organellome plasticity during different developmental or environmental situations.

Plastids: diving into their diversity, their functions, and their role in plant development

Plastids are a group of essential, heterogenous semi-autonomous organelles characteristic of plants that perform photosynthesis and a diversity of metabolic pathways that impact growth and development. Plastids are remarkably dynamic and can interconvert in response to specific developmental and environmental cues, functioning as a central metabolic hub in plant cells. By far the best studied plastid is the chloroplast, but in recent years the combination of modern techniques and genetic analyses has expanded our current understanding of plastid morphological and functional diversity in both model and non-model plants. These studies have provided evidence of an unexpected diversity of plastid subtypes with specific characteristics. In this review, we describe recent findings that provide insights into the characteristics of these specialized plastids and their functions. We concentrate on the emerging evidence that supports the model that signals derived from particular plastid types play pivotal roles in plant development, environmental, and defense responses. Furthermore, we provide examples of how new technologies are illuminating the functions of these specialized plastids and the overall complexity of their differentiation processes. Finally, we discuss future research directions such as the use of ectopic plastid differentiation as a valuable tool to characterize factors involved in plastid differentiation. Collectively, we highlight important advances in the field that can also impact future agricultural and biotechnological improvement in plants.

The Plant Leaf: A Biomimetic Resource for Multifunctional and Economic Design

As organs of photosynthesis, leaves are of vital importance for plants and a source of inspiration for biomimetic developments. Leaves are composed of interconnected functional elements that evolved in concert under high selective pressure, directed toward strategies for improving productivity with limited resources. In this paper, selected basic components of the leaf are described together with biomimetic examples derived from them. The epidermis (the "skin" of leaves) protects the leaf from uncontrolled desiccation and carries functional surface structures such as wax crystals and hairs. The epidermis is pierced by micropore apparatuses, stomata, which allow for regulated gas exchange. Photosynthesis takes place in the internal leaf tissue, while the venation system supplies the leaf with water and nutrients and exports the products of photosynthesis. Identifying the selective forces as well as functional limitations of the single components requires understanding the leaf as an integrated system that was shaped by evolution to maximize carbon gain from limited resource availability. These economic aspects of leaf function manifest themselves as trade-off solutions. Biomimetics is expected to benefit from a more holistic perspective on adaptive strategies and functional contexts of leaf structures.

Different photoprotective strategies for white leaves between two co-occurring Actinidia species

At the outer canopy, the white leaves of Actinidia kolomikta can turn pink but they stay white in A. polygama. We hypothesized that the different leaf colors in the two Actinidia species may represent different photoprotection strategies. To test the hypothesis, leaf optical spectra, anatomy, chlorophyll a fluorescence, superoxide (O₂ ˙^- ) concentration, photosystem II photo-susceptibility, and expression of anthocyanin-related genes were investigated. On the adaxial side, light reflectance was the highest for white leaves of A. kolomikta, followed by its pink leaves and white leaves of A. polygama, and the absorptance for white leaves of A. kolomikta was the lowest. Chlorophyll and carotenoid content of white and pink leaves in A. kolomikta were significantly lower than those of A. polygama, while the relative anthocyanin content of pink leaves was the highest. Chloroplasts of palisade cells of white leaves in A. kolomikta were not well developed with a lower maximum quantum efficiency of PSII than the other types of leaves (pink leaves of A. kolomikta and white leaves of A. Polygama at the inner/outer canopy). After high light treatment from the abaxial surface, F_v /F_m decreased to a larger extent for white leaves of A. kolomikta than pink leaf and white leaves of A. polygama, and its non-photochemical quenching was also the lowest. White leaves of A. kolomikta showed higher O₂ ˙^- concentration compared to pink leaves under the same strong irradiance. The expression levels of anthocyanin biosynthetic genes in pink leaves were higher than in white leaves. These results indicate that white leaves of A. kolomikta apply a reflection strategy for photoprotection, while pink leaves resist photoinhibition via anthocyanin accumulation.

Centrifugation-Assisted Growth of Single-Crystalline Grains in Microcapsules

Colloidal crystals have been tailored in a format of microspheres to use them as a building block to construct macroscopic photonic surfaces. However, the polycrystalline grains grown from the spherical surface usually exhibit low reflectivity. Although single-crystalline microspheres have been produced, it is difficult to control the crystal orientation. Here, we design spherical microcapsules with density anisotropy that contain single-crystalline grains along the heavy side. The microcapsules spontaneously align to have a heavy side down under the action of gravity and display a bright and uniform reflection color from the entire surface of the grains. Key to the success is the use of gentle centrifugal force to initiate nucleation and grow single-crystalline grains from the heavy side through depletion attraction. The microcapsules have density anisotropy due to the heterogeneity of the shell thickness, which causes them to self-align under centrifugation. At the same time, particles are accumulated on the heavy side, which produces many tiny grains on the heavy side immediately after the centrifugation. With controlled depletion attraction among particles, only a few grains survive during postincubation through Ostwald ripening, and one or a few giant single-crystalline grains are finally produced along the heavy side of each microcapsule.

Multiple origins of lipid-based structural colors contribute to a gradient of fruit colors in Viburnum (Adoxaceae)

Structural color is poorly known in plants relative to animals. In fruits, only a handful of cases have been described, including in Viburnum tinus where the blue color results from a disordered multilayered reflector made of lipid droplets. Here, we examine the broader evolutionary context of fruit structural color across the genus Viburnum. We obtained fresh and herbarium fruit material from 30 Viburnum species spanning the phylogeny and used transmission electron microscopy, optical simulations, and ancestral state reconstruction to identify the presence/absence of photonic structures in each species, understand the mechanism producing structural color in newly identified species, relate the development of cell wall structure to reflectance in Viburnum dentatum, and describe the evolution of cell wall architecture across Viburnum. We identify at least two (possibly three) origins of blue fruit color in Viburnum in species which produce large photonic structures made of lipid droplets embedded in the cell wall and which reflect blue light. Examining the full spectrum of mechanisms producing color in pl, including structural color as well as pigments, will yield further insights into the diversity, ecology, and evolution of fruit color.

Begonia-Inspired Slow Photon Effect of a Photonic Crystal for Augmenting Algae Photosynthesis

Plant photosynthesis is considered to be an environmentally friendly and effective measure for reducing carbon dioxide levels to meet the global objective of carbon neutrality. However, the light energy utilization of photosynthetic pigments is insufficient. Begonia pavonine (B. pavonina) with blue leaves exhibits a photosynthetic quantum yield 10% higher than those of other plants by virtue of their photonic crystal (PC) thylakoids. Inspired by this property, we prepared non-angle-dependent PC hydrogels and assembled them with algae Chlorella pyrenoidosa (C. pyre). The band edge of PC hydrogels matched the absorption peaks of C. pyre, and the resulting slow photon effect increased the interaction time between incident light and photosynthetic pigments, which in turn induced the expression of light-harvesting proteins and the synthesis of pigments, thereby improving the light energy utilization. Further, we introduced an artificial antenna into the assembly, which assisted the slow photon effect in increasing the oxygen evolution and carbon sequestration rate by more than 200%. This method avoids the photobleaching problems faced by methods of synthesizing artificial antenna pigments and the biosafety problems faced by genetically engineered methods of editing pigments or proteins.

Improving Plant Photosynthesis through Light-Harvesting Upconversion Nanoparticles

Nanotechnology is considered as an emerging effective means to augment plant photosynthesis. However, there is still a lot of work to be done in this field. Here, we applied the upconversion nanoparticles (UCNPs) on lettuce leaves and found that the UCNPs were able to transport into the lettuce body and colocalize with the chloroplasts. It was proved that UCNPs could harvest the near-infrared light of sunlight and increase the electron transfer rate in the photosynthesis process, thus increasing the photosynthesis rate. The gene expression analysis showed that more than 90% of gene expression in photosynthesis was upregulated. After spraying the UCNP solution on the leaves of lettuce and placing the lettuce under sunlight for 1 week, the wet/dry weight of the leaves increased by 53.33% and 45.71%, respectively. This nanoengineering of light-harvesting UCNPs may have great potential for applications in agriculture.

Designing photonic microparticles with droplet microfluidics

Photonic materials with a periodic change of refractive index show unique optical properties through wavelength-selective diffraction and modulation of the optical density of state, which is promising for various optical applications. In particular, photonic structures have been produced in the format of microparticles using emulsion templates to achieve advanced properties and applications beyond those of a conventional film format. Photonic microparticles can be used as a building block to construct macroscopic photonic materials, and the individual microparticles can serve as miniaturized photonic devices. Droplet microfluidics enables the production of emulsion drops with a controlled size, composition, and configuration that serve as the optimal confining geometry for designing photonic microparticles. This feature article reviews the recent progress and current state of the art in the field of photonic microparticles, covering all aspects of microfluidic production methods, microparticle geometries, optical properties, and applications. Two distinct bottom-up approaches based on colloidal assembly and liquid crystals are, respectively, discussed and compared.

Measuring Photonics in Photosynthesis: Combined Micro-Fourier Image Spectroscopy and Pulse Amplitude Modulated Chlorophyll Fluorimetry at the Micrometre-Scale

Natural photonic structures are common across the biological kingdoms, serving a diversity of functionalities. The study of implications of photonic structures in plants and other phototrophic organisms is still hampered by missing methodologies for determining in situ photonic properties, particularly in the context of constantly adapting photosynthetic systems controlled by acclimation mechanisms on the cellular scale. We describe an innovative approach to determining spatial and spectral photonic properties and photosynthesis activity, employing micro-Fourier Image Spectroscopy and Pulse Amplitude Modulated Chlorophyll Fluorimetry in a combined microscope setup. Using two examples from the photosynthetic realm, the dynamic Bragg-stack-like thylakoid structures of Begonia sp. and complex 2.5 D photonic crystal slabs from the diatom Coscinodiscus granii, we demonstrate how the setup can be used for measuring self-adapting photonic-photosynthetic systems and photonic properties on single-cell scales. We suggest that the setup is well-suited for the determination of photonic–photosynthetic systems in a diversity of organisms, facilitating the cellular, temporal, spectral and angular resolution of both light distribution and combined chlorophyll fluorescence determination. As the catalogue of photonic structure from photosynthetic organisms is rich and diverse in examples, a deepened study could inspire the design of novel optical- and light-harvesting technologies.

Convergent evolution of disordered lipidic structural colour in the fruits of Lantana strigocamara (syn. L. camara hybrid cultivar)

The majority of plant colours are produced by anthocyanin and carotenoid pigments, but colouration obtained by nanostructured materials (i.e. structural colours) is increasingly reported in plants. Here, we identify a multilayer photonic structure in the fruits of Lantana strigocamara and compare it with a similar structure in Viburnum tinus fruits. We used a combination of transmission electron microscopy (EM), serial EM tomography, scanning force microscopy and optical simulations to characterise the photonic structure in L. strigocamara. We also examine the development of the structure during maturation. We found that the structural colour derives from a disordered, multilayered reflector consisting of lipid droplets of c.105 nm that form a plate-like structure in 3D. This structure begins to form early in development and reflects blue wavelengths of light with increasing intensity over time as the structure develops. The materials used are likely to be lipid polymers. Lantana strigocamara is the second origin of a lipid-based photonic structure, convergently evolved with the structure in Viburnum tinus. Chemical differences between the lipids in L. strigocamara and those of V. tinus suggest a distinct evolutionary trajectory with implications for the signalling function of structural colours in fruits.

Chloroplastic photoprotective strategies differ between bundle sheath and mesophyll cells in maize (Zea mays L.) Under drought

Bundle sheath cells play a crucial role in photosynthesis in C4 plants, but the structure and function of photosystem II (PSII) in these cells is still controversial. Photoprotective roles of bundle sheath chloroplasts at the occurrence of environmental stresses have not been investigated so far. Non-photochemical quenching (NPQ) of chlorophyll a fluorescence is the photoprotective mechanism that responds to a changing energy balance in chloroplasts. In the present study, we found a much higher NPQ in bundle sheath chloroplasts than in mesophyll chloroplasts under a drought stress. This change was accompanied by a more rapid dephosphorylation of light-harvesting complex II (LHCII) subunits and a greater increase in PSII subunit S (PsbS) protein abundance than in mesophyll cell chloroplasts. Histochemical staining of reactive oxygen species (ROS) suggested that the high NPQ may be one of the main reasons for the lower accumulation of ROS in bundle sheath chloroplasts. This may maintain the stable functioning of bundle sheath cells under drought condition. These results indicate that the superior capacity for dissipation of excitation energy in bundle sheath chloroplasts may be an environmental adaptation unique to C4 plants.

Mechanism underlying the carotenoid accumulation in shaded tea leaves

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Long-term shading treatment (14 days) increased carotenoid content in tea leaves.

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Long-term darkness (14 days) decreased carotenoid content in tea leaves.

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Long-term shading treatment increased carotenoid biosynthetic gene expression levels.

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Long-term darkness decreased carotenoid biosynthetic gene expression levels.

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The functions of CsDXS1, CsDXS3, CsPSY, CsLCYB and CsLCYE genes have been verified.

Carotenoids contribute to tea leaf coloration and are the precursors of important aromatic compounds. Shading can promote the accumulation of carotenoids in tea leaves, but the underlying mechanism remains unknown. In the study, we analyzed the content and composition of carotenoids, and transcript levels and functions of related genes in carotenoid biosynthesis using HPLC, qRT-PCR, and heterologous expression system. It was found that long-term shading (14 days, 90% shading) significantly increased the total carotenoid content in tea leaves, and increased the expression of non-mevalonate pathway (MEP) genes (CsDXS1 and CsDXS3) and key genes in carotenoid synthesis pathway (CsPSY, CsLCYB, and CsLCYE). Long-term exposure to darkness (14 days, 0 lx) decreased the transcription of most carotenoid biosynthetic genes and adversely affected carotenoid accumulation. Furthermore, CsDXS1, CsDXS3, CsPSY, CsLCYB, and CsLCYE were functionally identified and contributed to the enhanced accumulation of carotenoids in tea leaves in response to long-term shading.

Enhancement of Photosynthetic Capacity in Spongy Mesophyll Cells in White Leaves of Actinidia kolomikta

Considering that Actinidia kolomikta bears abundant white leaves on reproductive branches during blossoming, we hypothesized that the white leaves may maintain photosynthetic capacity by adjustments of leaf anatomy and physiological regulation. To test this hypothesis, leaf anatomy, gas exchange, chlorophyll a fluorescence, and the transcriptome were examined in white leaves of A. kolomikta during flowering. The palisade and spongy mesophyll in the white leaves were thicker than those in green ones. Chloroplast development in palisade parenchyma of white leaves was abnormal, whereas spongy parenchyma of white leaves contained functional chloroplasts. The highest photosynthetic rate of white leaves was ~82% of that of green leaves over the course of the day. In addition, the maximum quantum yield of PSII (F _v/F _m) of the palisade mesophyll in white leaves was significantly lower than those of green ones, whereas F _v/F _m and quantum yield for electron transport were significantly higher in the spongy mesophyll of white leaves. Photosynthetic capacity regulation of white leaf also was attributed to upregulation or downregulation of some key genes involving in photosynthesis. Particularly, upregulation of sucrose phosphate synthase (SPS), glyeraldehyde-3-phosphate dehydrogenase (GAPDH) and RuBisCO activase (RCA) in white leaf suggested that they might be involved in regulation of sugar synthesis and Rubisco activase in maintaining photosynthetic capacity of white leaf. Conclusions: white leaves contained a thicker mesophyll layer and higher photosynthetic activity in spongy parenchyma cells than those of palisade parenchyma cells. This may compensate for the lowered photosynthetic capacity of the palisade mesophyll. Consequently, white leaves maintain a relatively high photosynthetic capacity in the field.

Recent Progress in Responsive Structural Color

Structural color has been regarded as an ideal alternative to pigments because of the advantages of environmental friendliness, resistance to fading, and dynamic regulation. Responsive structural color can give real-time visible feedback to external stimuli and thus has great prospects in many applications, such as displays, sensing, anticounterfeiting, information storage, and healthcare monitoring. In this Perspective, we elucidate basic concepts, controllable fabrications, and promising applications of responsive structural colors. In particular, we systematically summarize the general regulation mode of all kinds of responsive structural color systems. First, we introduce the basic chromogenic structures as well as the regulation modes of responsive structural color. Second, we present the fabrication methods of patterned structural color. Then, the promising applications of responsive structural color systems are highlighted in detail. Finally, we present the existing challenges and future perspectives on responsive structural colors.

Mechanism Underlying the Shading-Induced Chlorophyll Accumulation in Tea Leaves

Besides aroma and taste, the color of dry tea leaves, tea infusion, and infused tea leaves is also an important index for tea quality. Shading can significantly increase the chlorophyll content of tea leaves, leading to enhanced tea leaf coloration. However, the underlying regulatory mechanism remains unclear. In this study, we revealed that the expressions of chlorophyll synthesis genes were significantly induced by shading, specially, the gene encoding protochlorophyllide oxidoreductase (CsPOR). Indoor control experiment showed that decreased light intensity could significantly induce the expression of CsPOR, and thus cause the increase of chlorophyll content. Subsequently, we explored the light signaling pathway transcription factors regulating chlorophyll synthesis, including CsPIFs and CsHY5. Through expression level and subcellular localization analysis, we found that CsPIF3-2, CsPIF7-1, and CsHY5 may be candidate transcriptional regulators. Transcriptional activation experiments proved that CsHY5 inhibits CsPORL-2 transcription. In summary, we concluded that shading might promote the expression of CsPORL-2 by inhibiting the expression of CsHY5, leading to high accumulation of chlorophyll in tea leaves. The results of this study provide insights into the mechanism regulating the improvements to tea plant quality caused by shading.

Janus Photonic Microspheres with Bridged Lamellar Structures via Droplet-Confined Block Copolymer Co-Assembly

Artificial self-assembly systems typically exhibit limited capability in creating nature-inspired complex materials with advanced functionalities. Here, an effective co-assembly strategy is demonstrated for the facile creation of complex photonic structures with intriguing light reflections. Two different lipophilic and amphiphilic bottlebrush block copolymers (BCPs) are placed within shrinking droplets to enable a cooperative working mechanism of microphase segregation and organized spontaneous emulsification, respectively. Layer assemblies of the lipophilic BCP and uniform water nanodroplets stabilized by the bottlebrush surfactant are both generated, and co-assembled into a bridged lamellar structure with the alternating arrangement of layers and closely packed nanodroplet arrays. Janus microspheres with diverse dual optical characteristics are successfully fabricated, and reflected wavelengths of light are highly tunable simply by changing the formulation or molecular weight of BCP.

Direct writing of customized structural-color graphics with colloidal photonic inks

Colloidal crystals and glasses have been designed to develop structural colors that are tunable, iridescent, nonfading, and nontoxic. However, the low printability and poor printing quality have restricted their uses. Here, we report the direct writing of structural-color graphics with high brightness and saturation using colloidal inks. The inks are prepared by dispersing silica particles in acrylate-based resins, where the volume fraction is optimized to simultaneously provide pronounced coloration and satisfactory printing rheology. With the inks, any macroscopic design of lines and faces can be directly written on various substrates, where the microscopic colloidal arrangement is set to be either crystalline or amorphous depending on the resin viscosity to control the iridescence of the colors. In addition, the high mechanical stability and controlled modulus enable the graphics to be surface-transferred, origami-folded, or elastically stretched. This direct-writing approach provides unprecedented levels of controllability and versatility for pragmatic uses of structural colors.

Finite-difference Time-domain (FDTD) Optical Simulations: A Primer for the Life Sciences and Bio-Inspired Engineering

Light influences most ecosystems on earth, from sun-dappled forests to bioluminescent creatures in the ocean deep. Biologists have long studied nano- and micro-scale organismal adaptations to manipulate light using ever-more sophisticated microscopy, spectroscopy, and other analytical equipment. In combination with experimental tools, simulations of light interacting with objects can help researchers determine the impact of observed structures and explore how variations affect optical function. In particular, the finite-difference time-domain (FDTD) method is widely used throughout the nanophotonics community to efficiently simulate light interacting with a variety of materials and optical devices. More recently, FDTD has been used to characterize optical adaptations in nature, such as camouflage in fish and other organisms, colors in sexually-selected birds and spiders, and photosynthetic efficiency in plants. FDTD is also common in bioengineering, as the design of biologically-inspired engineered structures can be guided and optimized through FDTD simulations. Parameter sweeps are a particularly useful application of FDTD, which allows researchers to explore a range of variables and modifications in natural and synthetic systems (e.g., to investigate the optical effects of changing the sizes, shape, or refractive indices of a structure). Here, we review the use of FDTD simulations in biology and present a brief methods primer tailored for life scientists, with a focus on the commercially available software Lumerical FDTD. We give special attention to whether FDTD is the right tool to use, how experimental techniques are used to acquire and import the structures of interest, and how their optical properties such as refractive index and absorption are obtained. This primer is intended to help researchers understand FDTD, implement the method to model optical effects, and learn about the benefits and limitations of this tool. Altogether, FDTD is well-suited to (i) characterize optical adaptations and (ii) provide mechanistic explanations; by doing so, it helps (iii) make conclusions about evolutionary theory and (iv) inspire new technologies based on natural structures.

The Role of Periodic Structures in Light Harvesting

The features of light propagation in plant leaves depend on the long-period ordering in chloroplasts and the spectral characteristics of pigments. This work demonstrates a method of determining the hidden ordered structure. Transmission spectra have been determined using transfer matrix method. A band gap was found in the visible spectral range. The effective refractive index and dispersion in the absorption spectrum area of chlorophyll were taken into account to show that the density of photon states increases, while the spectrum shifts towards the wavelength range of effective photosynthesis.

Overexpression of FaHSP17.8-CII improves cadmium accumulation and tolerance in tall fescue shoots by promoting chloroplast stability and photosynthetic electron transfer of PSII

Genetic improvement could play a significant role in enhancing the Cd accumulation, translocation and tolerance in plants. In this study, for the first time, we constructed transgenic tall fescue overexpressing a class II (CII) sHSP gene FaHSP17.8-CII, which enhanced Cd tolerance and the root-to-shoot Cd translocation. After exposed to 400 μM CdCl₂, two FaHSP17.8-CII overexpressing lines (OE#3 and OE#7) exhibited 30% and 40% more shoot fresh weight, respectively, relative to the wild-type (WT). Both transgenic lines showed higher tolerance to Cd, as evidenced by lower levels of electrolyte leakage and malondialdehyde compared to the WT plants under Cd stress. FaHSP17.8-CII overexpression increased shoot Cd contents 49-59% over the WT plants. The Cd translocation factor of root-to-shoot in OE grasses was 69-85% greater than WT under Cd stress. Furthermore, overexpression of FaHSP17.8-CII reduced Cd-induced damages of chloroplast ultra-structure and chlorophyll synthesis, and then improved photosystem II (PSII) function under Cd stress, which resulted in less reactive oxygen species (ROS) accumulation in OE grasses than that in WT exposed to Cd stress. The study suggests a novel FaHSP17.8-CII-PSII-ROS module to understand the mechanisms of Cd detoxification and tolerance, which provides a new strategy to improve phytoremediation efficiency in Cd-stressed grasses.

Photoresponsive and Polarization-Sensitive Structural Colors from Cellulose/Liquid Crystal Nanophotonic Structures

Cellulose nanocrystals (CNCs) possess the ability to form helical periodic structures that generate structural colors. Due to the helicity, such self-assembled cellulose structures preferentially reflect left-handed circularly polarized light of certain colors, while they remain transparent to right-handed circularly polarized light. This study shows that combination with a liquid crystal enables modulation of the optical response to obtain light reflection of both handedness but with reversed spectral profiles. As a result, the nanophotonic systems provide vibrant structural colors that are tunable via the incident light polarization. The results are attributed to the liquid crystal aligning on the CNC/glucose film, to form a birefringent layer that twists the incident light polarization before interaction with the chiral cellulose nanocomposite. Using a photoresponsive liquid crystal, this effect can further be turned off by exposure to UV light, which switches the nematic liquid crystal into a nonbirefringent isotropic phase. The study highlights the potential of hybrid cellulose systems to create self-assembled yet advanced photoresponsive and polarization-tunable nanophotonics.

Using structural colour to track length scale of cell-wall layers in developing Pollia japonica fruits

Helicoidally arranged layers of cellulose microfibrils in plant cell walls can produce strong and vivid coloration in a wide range of species. Despite its significance, the morphogenesis of cell walls, whether reflective or not, is not fully understood. Here we show that by optically monitoring the reflectance of Pollia japonica fruits during development we can directly map structural changes of the cell wall on a scale of tens of nanometres. Visible-light reflectance spectra from individual living cells were measured throughout the fruit maturation process and compared with numerical models. Our analysis reveals that periodic spacing of the helicoidal architecture remains unchanged throughout fruit development, suggesting that interactions in the cell-wall polysaccharides lead to a fixed twisting angle of cellulose helicoids in the cell wall. By contrast with conventional electron microscopy, which requires analysis of different fixed specimens at different stages of development, the noninvasive optical technique we present allowed us to directly monitor live structural changes in biological photonic systems as they develop. This method therefore is applicable to investigations of photonic tissues in other organisms.

Fruit Coloration: Attractive, Fatty Blue Colours?

The use of visible colours as honest signals to attract seed-dispersers is a well-known property of fruits. While most of these colours are due to pigments, it has now been discovered that the evergreen Viburnum tinus shrubs display their edible and nutritious fruit with a blue structural colour based on lipid inclusions in the epidermal cells.

Lighting system bioinspired by Haworthia obtusa

Electricity plays an important role in modern societies, with lighting and illumination accounting for approximately one-fifth of the global demand for electricity. Haworthia obtusa has the remarkable ability to collect solar light through a so-called ‘window’ which allows it to photosynthesise in the dark. Inspired by this unique characteristic, we developed a novel lighting system that does not use electricity. The ‘window’ of H. obtusa is replicated using a scattering medium that collects solar light and guides it to an optical fibre. The optical fibre then carries the light indoors, where illumination is needed. The efficacy of this unique lighting system was confirmed both numerically and experimentally. The developed system should help in lowering energy consumption.

Photonic paper: Multiscale assembly of reflective cellulose sheets in Lunaria annua

Bright, iridescent colors observed in nature are often caused by light interference within nanoscale periodic lattices, inspiring numerous strategies for coloration devoid of inorganic pigments. Here, we describe and characterize the septum of the Lunaria annua plant that generates large (multicentimeter), freestanding iridescent sheets, with distinctive silvery-white reflective appearance. This originates from the thin-film assembly of cellulose fibers in the cells of the septum that induce thin-film interference-like colors at the microscale, thus accounting for the structure's overall silvery-white reflectance at the macroscale. These cells further assemble into two thin layers, resulting in a mechanically robust, iridescent septum, which is also significantly light due to its high air porosity (>70%) arising from the cells' hollow-core structure. This combination of hierarchical structure comprising mechanical and optical function can inspire technological classes of devices and interfaces based on robust, light, and spectrally responsive natural substrates.

Influence of Surface Structure, Pigmentation and Particulate Matter on Plant Reflectance and Fluorescence

Optical properties of plant leaves are relevant to evaluate their physiological state and stress effect. The main objective of this work was to study how variegation, pigment composition or reflective features modifies leaves' photophysical behavior. For this purpose, green leaves (Ficus benjamina), purple leaves (Tradescantia pallida), green leaves covered by white trichomes (Cineraria maritima) and variegated leaves (Codiaeum aucubifolium) were analyzed. Firstly, foliar surface morphology was evaluated by scanning electron microscopy. UV-vis and near-IR reflectance and transmittance spectra were obtained to calculate absorption (k) and scattering (s) coefficients. The theoretical approaches of Pile of Plates and Kubelka-Munk's theory resulted still valid for nonstandard leaves with differing surface conditions. However, frequently used spectral indices were not reliable for predicting water content, when leaves differed from conventional ones. The proportionality between the absorption factor and chromophore/pigment concentration was also lost for hairy leaves. A simplified model to describe these facts was presented here. Fluorescence spectra were recorded and corrected, due to light re-absorption. Water-optical parameter connection and pigment-optical parameter connection were thoroughly discussed. Leaf surface morphology and pigmentation have not only influenced the optical features of leaves but also played a role in the effect that particulate matter could cause on leaf photosynthesis.

Highly Reproducible, Bio-Based Slab Photonic Crystals Grown by Diatoms

Slab photonic crystals (PhCs) are photonic structures used in many modern optical technologies. Fabrication of these components is costly and usually involves eco-unfriendly methods, requiring modern nanofabrication techniques and cleanroom facilities. This work describes that diatom microalgae evolved elaborate and highly reproducible slab PhCs in the girdle, a part of their silicon dioxide exoskeletons. Under natural conditions in water, the girdle of the centric diatom Coscinodiscus granii shows a well-defined optical pseudogap for modes in the near-infrared (NIR). This pseudogap shows dispersion toward the visible spectral range when light is incident at larger angles, eventually facilitating in-plane propagation for modes in the green spectral range. The optical features can be modulated with refractive index contrast. The unit cell period, a critical factor controlling the pseudogap, is highly preserved within individuals of a long-term cultivated inbred line and between at least four different C. granii cell culture strains tested in this study. Other diatoms present similar unit cell morphologies with various periods. Diatoms thereby offer a wide range of PhC structures, reproducible and equipped with well-defined properties, possibly covering the entire UV-vis-NIR spectral range. Diatoms therefore offer an alternative as cost-effective and environmentally friendly produced photonic materials.

3D structured materials and devices for artificial photosynthesis

Artificial photosynthesis is an effective way to convert solar energy into fuels, which is of great significance to energy production and reduction of atmospheric CO₂ content. In recent years, 3D structured artificial photosynthetic system has made great progress as an effective design strategy. This review first highlights several typical mechanisms for improved artificial photosynthesis with 3D structures: improved light harvesting, mass transfer and charge separation. Then, we summarize typical examples of 3D structured artificial photosynthetic systems, including bioinspired structures, photonic crystals (PC), designed photonic structures (PC coupling structure, plasmon resonance structure, optical resonance structure, metamaterials), 3D-printed systems, nanowire integrated systems and hierarchical 3D structures. Finally, we discuss the problems and challenges to the application and development of 3D artificial photosynthetic system and the possible trends of future development. We hope this review can inspire more progress in the field of artificial photosynthesis.

Mechanical Ecology-Taking Biomechanics to the Field

Synopsis Interdisciplinary research can have strong and surprising synergistic effects, leading to rapid knowledge gains. Equally important, it can help to reintegrate fragmented fields across increasingly isolated specialist sub-disciplines. However, the lack of a common identifier for research "in between fields" can make it difficult to find relevant research outputs and network effectively. We illustrate and address this issue for the emerging interdisciplinary hotspot of "mechanical ecology," which we define here as the intersection of quantitative biomechanics and field ecology at the organism level. We show that an integrative approach crucially advances our understanding in both disciplines by (1) putting biomechanical mechanisms into a biologically meaningful ecological context and (2) addressing the largely neglected influence of mechanical factors in organismal and behavioral ecology. We call for the foundation of knowledge exchange platforms such as meeting symposia, special issues in journals, and focus groups dedicated to mechanical ecology.

Gigantic chloroplasts, including bizonoplasts, are common in shade-adapted species of the ancient vascular plant family Selaginellaceae

PREMISE

Unique among vascular plants, some species of Selaginella have single giant chloroplasts in their epidermal or upper mesophyll cells (monoplastidy, M), varying in structure between species. Structural variants include several forms of bizonoplast with unique dimorphic ultrastructure. Better understanding of these structural variants, their prevalence, environmental correlates and phylogenetic association, has the potential to shed new light on chloroplast biology unavailable from any other plant group.

METHODS

The chloroplast ultrastructure of 76 Selaginella species was studied with various microscopic techniques. Environmental data for selected species and subgeneric relationships were compared against chloroplast traits.

RESULTS

We delineated five chloroplast categories: ME (monoplastidy in a dorsal epidermal cell), MM (monoplastidy in a mesophyll cell), OL (oligoplastidy), Mu (multiplastidy, present in the most basal species), and RC (reduced or vestigial chloroplasts). Of 44 ME species, 11 have bizonoplasts, cup-shaped (concave upper zone) or bilobed (basal hinge, a new discovery), with upper zones of parallel thylakoid membranes varying subtly between species. Monoplastidy, found in 49 species, is strongly shade associated. Bizonoplasts are only known in deep-shade species (<2.1% full sunlight) of subgenus Stachygynandrum but in both the Old and New Worlds.

CONCLUSIONS

Multiplastidic chloroplasts are most likely basal, implying that monoplastidy and bizonoplasts are derived traits, with monoplastidy evolving at least twice, potentially as an adaptation to low light. Although there is insufficient information to understand the adaptive significance of the numerous structural variants, they are unmatched in the vascular plants, suggesting unusual evolutionary flexibility in this ancient plant genus.

Disordered wax platelets on Tradescantia pallida leaves create golden shine

Disordered arrangement of wax platelets on Tradescantia leaves increase long wavelength reflectance, contrary to the commonly observed UV-protection mechanism.

Interfacial Assembly of Amphiphilic Tiles for Reconfigurable Photonic Surfaces

Nature has created photonic structures in cells and assembled them to make photonic layers for a living. Inspired from nature, we design amphiphilic photonic tiles and assemble them at air-water interface to compose highly reconfigurable photonic layers. The photonic tiles are prepared by photolithographically defining the shape of the disc using a photocurable dispersion of repulsive particles. The tiles are further treated by directional dry etching to selectively render top and side surfaces of the discs hydrophobic. The amphiphilic photonic tiles deform the air-water interface by gravity, which causes a strong attractive force driven by capillarity. Therefore, the tiles form two-dimensional (2D) dense-packing, which rapidly adapts dynamic fluctuation and shape change of the interface, providing highly reconfigurable photonic layers. In addition, the assembly can be transferred into target solid surfaces through the Langmuir-Blodgett method to make photonic coatings. Moreover, the amphiphilic tiles can be assembled on the surface of water drops, forming a photonic shell on liquid marbles which resembles photonic structures in nature. We believe that our strategy based on a 2D tile assembly at the free interface will provide a simple yet useful means to create photonic layers on various purposes.

Nature-Inspired Design and Application of Lipidic Lyotropic Liquid Crystals

Amphiphilic lipids aggregate in aqueous solution into a variety of structural arrangements. Among the plethora of ordered structures that have been reported, many have also been observed in nature. In addition, due to their unique morphologies, the hydrophilic and hydrophobic domains, very high internal interfacial surface area, and the multitude of possible order-order transitions depending on environmental changes, very promising applications have been developed for these systems in recent years. These include crystallization in inverse bicontinuous cubic phases for membrane protein structure determination, generation of advanced materials, sustained release of bioactive molecules, and control of chemical reactions. The outstanding diverse functionalities of lyotropic liquid crystalline phases found in nature and industry are closely related to the topology, including how their nanoscopic domains are organized. This leads to notable examples of correlation between structure and macroscopic properties, which is itself central to the performance of materials in general. The physical origin of the formation of the known classes of lipidic lyotropic liquid crystalline phases, their structure, and their occurrence in nature are described, and their application in materials science and engineering, biology, medical, and pharmaceutical products, and food science and technology are exemplified.

Using natural variation to understand the evolutionary pressures on plant photosynthesis

Photosynthesis is the gateway of the Sun's energy into the biosphere and the source of the ozone layer; thus it is both provider and protector of life as we know it. Despite its pivotal role we know surprisingly little about the genetic basis of variation in photosynthesis and the selective pressures giving rise to or maintaining this variation. In this review, I will briefly summarise our current knowledge of intraspecific and interspecific variation in photosynthesis to understand the main selective constraints on photosynthesis and what this means for the future of nature and agriculture in a changing world.

Information Needs of Next-Generation Forest Carbon Models: Opportunities for Remote Sensing Science

Forests are integral to the global carbon cycle, and as a result, the accurate estimation of forest structure, biomass, and carbon are key research priorities for remote sensing science. However, estimating and understanding forest carbon and its spatiotemporal variations requires diverse knowledge from multiple research domains, none of which currently offer a complete understanding of forest carbon dynamics. New large-area forest information products derived from remotely sensed data provide unprecedented spatial and temporal information about our forests, which is information that is currently underutilized in forest carbon models. Our goal in this communication is to articulate the information needs of next-generation forest carbon models in order to enable the remote sensing community to realize the best and most useful application of its science, and perhaps also inspire increased collaboration across these research fields. While remote sensing science currently provides important contributions to large-scale forest carbon models, more coordinated efforts to integrate remotely sensed data into carbon models can aid in alleviating some of the main limitations of these models; namely, low sample sizes and poor spatial representation of field data, incomplete population sampling (i.e., managed forests exclusively), and an inadequate understanding of the processes that influence forest carbon accumulation and fluxes across spatiotemporal scales. By articulating the information needs of next-generation forest carbon models, we hope to bridge the knowledge gap between remote sensing experts and forest carbon modelers, and enable advances in large-area forest carbon modeling that will ultimately improve estimates of carbon stocks and fluxes.

Functional nanomaterials to augment photosynthesis: evidence and considerations for their responsible use in agricultural applications

At the current population growth rate, we will soon be unable to meet increasing food demands. As a consequence of this potential problem, considerable efforts have been made to enhance crop productivity by breeding, genetics and improving agricultural practices. While these techniques have traditionally been successful, their efficacy since the 'green revolution' has begun to significantly plateau. This stagnation of gains combined with the negative effects of climate change on crop yields has prompted researchers to develop novel and radical methods to increase crop productivity. Recent work has begun exploring the use of nanomaterials as synthetic probes to augment how plants use light. Photosynthesis in crops is often limited by their ability to absorb and exploit solar energy for photochemistry. The capacity to interact with and optimize how plants use light has the potential to increase the productivity of crops and enable the tailoring of crops for different environments and to compensate for predicted climate changes. Advances in the synthesis and surface modification of nanomaterials have overcome previous drawbacks and renewed their potential use as synthetic probes to enhance crop yields. Here, we review the current applications of functional nanomaterials in plants and will make an argument for the continued development of promising new nanomaterials and future applications in agriculture. This will highlight that functional nanomaterials have the clear potential to provide a much-needed route to enhanced future food security. In addition, we will discuss the often-ignored current evidence of nanoparticles present in the environment as well as inform and encourage caution on the regulation of nanomaterials in agriculture.

Structural colours in the frond of Microsorum thailandicum

Blue and near-ultraviolet structural colours have often been reported in understorey plants living in deep shade. While this intense blue coloration is very catchy to the eye of a human observer, there are cases in which structural colours can be hidden either by the scattered light interacting with pigments or because they are found in unexpected positions in the plants. Here, we show that the fronds of Microsorum thailandicum produce structural coloration on both the adaxial and abaxial epidermal surface. While cellulose helicoidal structures are responsible for this coloration in both epidermal layers, the reflected colours are consistently different: an intense blue reflection is found in the adaxial epidermis while red-shifted and less intense colours are observed in the abaxial epidermis, possibly suggesting photo-adaptation of the plant to the light environment. By comparing the optical properties of the fern with its anatomy we computed the theoretical reflection accounting for the presence of disorder in the cellulose helicoidal architecture.

The cellular and genetic basis of structural colour in plants

While the pathways that produce plant pigments have been well studied for decades, the use by plants of nanoscale structures to produce colour effects has only recently begun to be studied. A variety of plants from across the plant kingdom have been shown to use different mechanism to generate structural colours in tissues as diverse as leaves, flowers and fruits. In this review we explore the cellular mechanisms by which these nanoscale structures are built and discuss the first insights that have been published into the genetic pathways underpinning these traits.

Nanophotonics of higher-plant photosynthetic membranes

The thylakoid membrane inside chloroplasts hosts the light-dependent reactions of photosynthesis. Its embedded protein complexes are responsible for light harvesting, excitation energy transfer, charge separation, and transport. In higher plants, when the illumination conditions vary, the membrane adapts its composition and nanoscale morphology, which is characterized by appressed and non-appressed regions known as grana and stroma lamellae, respectively. Here we investigate the nanophotonic regime of light propagation in chloroplasts of higher plants and identify novel mechanisms in the optical response of the thylakoid membrane. Our results indicate that the relative contributions of light scattering and absorption to the overall optical response of grana strongly depend on the concentration of the light-harvesting complexes. For the pigment concentrations typically found in chloroplasts, the two mechanisms have comparable strengths, and their relative value can be tuned by variations in the protein composition or in the granal diameter. Furthermore, we find that collective modes in ensembles of grana significantly increase light absorption at selected wavelengths, even in the presence of moderate biological disorder. Small variations in the granal separation or a large disorder can dismantle this collective response. We propose that chloroplasts use this mechanism as a strategy against dangerously high illumination conditions, triggering a transition to low-absorbing states. We conclude that the morphological separation of the thylakoid membrane in higher plants supports strong nanophotonic effects, which may be used by chloroplasts to regulate light absorption. This adaptive self-organization capability is of interest as a model for novel bioinspired optical materials for artificial photosynthesis, imaging, and sensing.