Silicified structures affect leaf optical properties in grasses and sedge

Evapotranspiration-linked silica deposition in a basal tracheophyte plant (Lycopodiaceae: Lycopodiella alopecuroides): implications for the evolutionary origins of phytoliths

Phytoliths, microscopic deposits of hydrated silica within plants, play a myriad of functional roles in extant tracheophytes - yet their evolutionary origins and the original selective pressures leading to their deposition remain poorly understood. To gain new insights into the ancestral condition of tracheophyte phytolith production and function, phytolith content was intensively assayed in a basal, morphologically conserved tracheophyte: the foxtail clubmoss Lycopodiella alopecuroides. Wet ashing was employed to perform phytolith extractions from every major anatomical region of L. alopecuroides. Phytolith occurrence was recorded, alongside abundance, morphometric information, and morphological descriptions. Phytoliths were recovered exclusively from the microphylls, which were apicodistally silicified into multiphytolith aggregates. Phytolith aggregates were larger and more numerous in anatomical regions engaging in greater evapotranspirational activity. The tissue distribution of L. alopecuroides phytoliths is inconsistent with the expectations of proposed adaptive hypotheses of phytolith evolutionary origin. Instead, it is hypothesized that phytoliths may have arisen incidentally in the L. alopecuroides-like ancestral plant, polymerizing from intraplant silicon accumulations arising via bulk flow and 'leaky' cellular micronutrient channels. This basal, nonadaptive phytolith formation model would provide the evolutionary 'raw material' for later modification into the useful, adaptative, phytolith deposits seen in later-diverging plant clades.

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.

Selenium Regulates Antioxidant, Photosynthesis, and Cell Permeability in Plants under Various Abiotic Stresses: A Review

Plant growth is affected by various abiotic stresses, including water, temperature, light, salt, and heavy metals. Selenium (Se) is not an essential nutrient for plants but plays important roles in alleviating the abiotic stresses suffered by plants. This article summarizes the Se uptake and metabolic processes in plants and the functions of Se in response to water, temperature, light, salt, and heavy metal stresses in plants. Se promotes the uptake of beneficial substances, maintains the stability of plasma membranes, and enhances the activity of various antioxidant enzymes, thus alleviating adverse effects in plants under abiotic stresses. Future research directions on the relationship between Se and abiotic stresses in plants are proposed. This article will further deepen our understanding of the relationship between Se and plants.

Size always matters, shape matters only for the big: potential optical effects of silica bodies in Selaginella

Silica bodies are commonly found in Selaginella , but their function is unclear. Lens-like appearance and location in many species above giant chloroplasts of dorsal epidermal cells suggest optical functions. Silica body morphology in three Selaginella species was studied by microscopy. Optical effects were assessed by wave-optic simulations. Large convex, approximately hemispherical (papillose) and small approximately conical (concave–convex) silica bodies were found in different species. Both types lead to a concentrated spot of light high in the dorsal epidermal cell. Large convex bodies concentrate light 10–25 times in a shape-dependent manner by refraction, and small silica bodies concentrate light in a shape-insensitive, but wavelength-dependent, manner by diffraction (red light: approx. 2.3 times; blue light: approx. 1.5 times). Due to chloroplast movement, this concentrated light is above the chloroplast under high light, but within it under low light. Beyond the spot of concentration, light is dispersed into the chloroplast. Thin Selaginella leaves mean these effects may enhance light capture and minimize photodamage, but other effects such as inhibition of herbivory, mechanical support, and immune responses need to be considered. Silica bodies undoubtedly have optical effects, but their significance to the functioning of the plant requires direct studies of ecophysiological performance.

Different Concentrations of Potassium Silicate in Nutrient Solution Affects Selected Growth Characteristics and Mineral Composition of Barley (Hordeum vulgare L.)

This study was undertaken to determine the effect of potassium silicate (K₂SiO₃) on the physiological and growth characteristics and elemental composition of barley plants. Hydroponically grown barley (Hordeum vulgare L.) var. Wilma was exposed to four different levels of Si in the form of K₂SiO₃ at concentrations of 0 (Si₀), 0.5 (Si_0.5), 1 (Si₁) or 1.5 (Si_1.5) mM Si. Plants were analyzed for root length, number of dry leaves, number of trichomes, electron transport system activity in mitochondria (ETS), leaf pigment content and elemental composition of roots and leaves. Treatment with Si_0.5 significantly increased the concentration of total chlorophylls, root length and ETS activity in barley. Plants with no Si added to the nutrient solution had significantly more dry leaves than plants from all Si-treated groups. Necrosis was observed in Si₀ plants, while leaf damage was not visible in treated plants. According to the results of the study, we evidenced that plants were stressed due to Si deficiency. The addition of K₂SiO₃ significantly affected the concentration of Si, K, Ca, Cl, S, Mn, Fe and Zn in roots and leaves of barley. In barley treated with Si_0.5, plants showed the best performance in terms of their physiological characteristics and growth.

Comparative Study of Temporal Changes in Pigments and Optical Properties in Sepals of Helleborus odorus and H. niger from Prebloom to Seed Production

Helleborus niger is an evergreen species, while H. odorus is an herbaceous understorey species. They both develop flowers before the forest canopy layer closes. Their sepals remain after flowering and have multiple biological functions. To further elucidate the functions of sepals during flower development, we examined their optical and chemical properties, and the photochemical efficiency of photosystem II in the developing, flowering, and fruiting flowers. Sepals of the two species differed significantly in the contents of photosynthetic pigments and anthocyanins, but less in the UV-absorbing substances’ contents. Significant differences in photosynthetic pigment contents were also revealed within different developmental phases. The sepal potential photochemical efficiency of photosystem II was high in all developmental phases in H. odorus, whereas in H. niger, it was initially low and later increased. In the green H. odorus sepals, we obtained typical green leaf spectra with peaks in the green and NIR regions, and a low reflectance and transmittance in the UV region. On the other hand, in the white H. niger sepals in the developing and flowering phases, the response was relatively constant along the visible and NIR regions. Pigment profiles, especially chlorophylls, were shown to be important in shaping sepal optical properties, which confirms their role in light harvesting. All significant parameters together accounted for 44% and 34% of the reflectance and transmittance spectra variability, respectively. These results may contribute to the selection of Helleborus species and to a greater understanding of the ecological diversity of understorey plants in the forests.

The Optical Properties of Leaf Structural Elements and Their Contribution to Photosynthetic Performance and Photoprotection

Leaves have evolved to effectively harvest light, and, in parallel, to balance photosynthetic CO2 assimilation with water losses. At times, leaves must operate under light limiting conditions while at other instances (temporally distant or even within seconds), the same leaves must modulate light capture to avoid photoinhibition and achieve a uniform internal light gradient. The light-harvesting capacity and the photosynthetic performance of a given leaf are both determined by the organization and the properties of its structural elements, with some of these having evolved as adaptations to stressful environments. In this respect, the present review focuses on the optical roles of particular leaf structural elements (the light capture module) while integrating their involvement in other important functional modules. Superficial leaf tissues (epidermis including cuticle) and structures (epidermal appendages such as trichomes) play a crucial role against light interception. The epidermis, together with the cuticle, behaves as a reflector, as a selective UV filter and, in some cases, each epidermal cell acts as a lens focusing light to the interior. Non glandular trichomes reflect a considerable part of the solar radiation and absorb mainly in the UV spectral band. Mesophyll photosynthetic tissues and biominerals are involved in the efficient propagation of light within the mesophyll. Bundle sheath extensions and sclereids transfer light to internal layers of the mesophyll, particularly important in thick and compact leaves or in leaves with a flutter habit. All of the aforementioned structural elements have been typically optimized during evolution for multiple functions, thus offering adaptive advantages in challenging environments. Hence, each particular leaf design incorporates suitable optical traits advantageously and cost-effectively with the other fundamental functions of the leaf.

Endopolyploidy is a common response to UV-B stress in natural plant populations, but its magnitude may be affected by chromosome type

BACKGROUND AND AIMS

Ultraviolet-B radiation (UV-B) radiation damages the DNA, cells and photosynthetic apparatus of plants. Plants commonly prevent this damage by synthetizing UV-B-protective compounds. Recent laboratory experiments in Arabidopsis and cucumber have indicated that plants can also respond to UV-B stress with endopolyploidy. Here we test the generality of this response in natural plant populations, considering their monocentric or holocentric chromosomal structure.

METHODS

We measured the endopolyploidy index (flow cytometry) and the concentration of UV-B-protective compounds in leaves of 12 herbaceous species (1007 individuals) from forest interiors and neighbouring clearings where they were exposed to increased UV-B radiation (103 forest + clearing populations). We then analysed the data using phylogenetic mixed models.

KEY RESULTS

The concentration of UV-B protectives increased with UV-B doses estimated from hemispheric photographs of the sky above sample collection sites, but the increase was more rapid in species with monocentric chromosomes. Endopolyploidy index increased with UV-B doses and with concentrations of UV-B-absorbing compounds only in species with monocentric chromosomes, while holocentric species responded negligibly.

CONCLUSIONS

Endopolyploidy seems to be a common response to increased UV-B in monocentric plants. Low sensitivity to UV-B in holocentric species might relate to their success in high-UV-stressed habitats and corroborates the hypothesized role of holocentric chromosomes in plant terrestrialization.

Frond Optical Properties of the Fern Phyllitis scolopendrium Depend on Light Conditions in the Habitat

Ferns display an elevated degree of phenotypic plasticity to changes in irradiance levels; however, only a few reports deal with their response to different light conditions. To get an insight into the extent of phenotypic plasticity of the fern Phyllitis scolopendrium, thriving in a forested area along a radiation gradient at the entrance of a cave, we examined selected biochemical, morphological, and physiological frond traits of the ferns from three different habitats. Sampling was performed two times during the vegetation season, in April and June. We also measured frond optical properties to point out the differences in leaf/light interactions between different plant samples. According to frond size, the middle habitat, receiving 125 µmol m−2s−1 of photosynthetically active radiation at both sampling times, appeared to be the most favourable. The production of UV-absorbing substances was highest in the habitat with the lowest radiation level. At the beginning of the season, the level of photosynthetic pigments in this habitat was the same as in the other habitats, while it was significantly lower in June when the tree canopy was closed. Frond reflectance was similar when comparing habitats and different sampling times. The most significant differences were obtained in the UV-A and near-infrared regions. The reflectance spectra depended mainly on frond biochemical properties, which altogether explained 54% (p ≤ 0.05) of the spectra variability. Frond transmittance depended on both, morphological parameters, explaining 51% (p ≤ 0.05), and frond biochemistry, explaining 73% (p ≤ 0.05) of the spectra variability. P. scolopendrium was revealed to be highly plastic regarding light conditions. The shapes of the frond reflectance and transmittance optical curves were similar to those typical of leaves of seed plants. The fronds exhibited high morphological plasticity when comparing different habitats. However, their biochemical and optical traits differed more between the two sampling times than between the habitats.

Water Shortage Strongly Alters Formation of Calcium Oxalate Druse Crystals and Leaf Traits in Fagopyrum esculentum

Common buckwheat (Fagopyrum esculentum Moench) is a robust plant with high resistance to different environmental constraints. It contains high levels of calcium oxalate (CaOx) druse crystals, although their role remains obscure. The objective was to examine the effects of water shortage on plant biomass partition and leaf traits and formation of CaOx druse crystals in common buckwheat. Buckwheat plants were exposed to favorable and reduced water availability for 28 days. The element composition and morphological, biochemical, physiological and optical traits of the leaves, and the plant biomass were investigated under these conditions. Measurements of photochemical efficiency of photosystem II showed undisturbed functioning for buckwheat exposed to water shortage, apparently due to partially closed stomata and more efficient water regulation. Strong relationships were seen between water-related parameters and Ca, Mn and S content, and size and density of CaOx druse crystals. Redundancy analysis revealed the importance of the size of CaOx druse crystals to explain reflection in the UV range. Water shortage resulted in shorter plants with the same leaf mass (i.e., increased mass:height ratio), which, together with denser leaf tissue and higher content of photosynthetic pigments and protective substances, provides an advantage under extreme weather conditions.

Silicon Effects on Biomass Carbon and Phytolith-Occluded Carbon in Grasslands Under High-Salinity Conditions

Changes in climate and land use are causing grasslands to suffer increasingly from abiotic stresses, including soil salinization. Silicon (Si) amendment has been frequently proposed to improve plant resistance to multiple biotic and abiotic stresses and increase ecosystem productivity while controlling the biogeochemical carbon (C) cycle. However, the effects of Si on plant C distribution and accumulation in salt-suffering grasslands are still unclear. In this study, we investigated how salt ions affected major elemental composition in plants and whether Si enhanced biomass C accumulation in grassland species in situ. In samples from the margins of salt lakes, our results showed that the differing distance away from the shore resulted in distinctive phytocoenosis, including halophytes and moderately salt-tolerant grasses, which are closely related to changing soil properties. Different salinity (Na+/K+, ranging from 0.02 to 11.8) in plants caused negative effects on plant C content that decreased from 53.9 to 29.2% with the increase in salinity. Plant Si storage [0.02-2.29 g Si m-2 dry weight (dw)] and plant Si content (0.53 to 2.58%) were positively correlated with bioavailable Si in soils (ranging from 94.4 to 192 mg kg-1). Although C contents in plants and phytoliths were negatively correlated with plant Si content, biomass C accumulation (1.90-83.5 g C m-2 dw) increased due to the increase of Si storage in plants. Plant phytolith-occluded carbon (PhytOC) increased from 0.07 to 0.28‰ of dry mass with the increase of Si content in moderately salt-tolerant grasses. This study demonstrates the potential of Si in mediating plant salinity and C assimilation, providing a reference for potential manipulation of long-term C sequestration via PhytOC production and biomass C accumulation in Si-accumulator dominated grasslands.

Visualising Silicon in Plants: Histochemistry, Silica Sculptures and Elemental Imaging

Silicon is a non-essential element for plants and is available in biota as silicic acid. Its presence has been associated with a general improvement of plant vigour and response to exogenous stresses. Plants accumulate silicon in their tissues as amorphous silica and cell walls are preferential sites. While several papers have been published on the mitigatory effects that silicon has on plants under stress, there has been less research on imaging silicon in plant tissues. Imaging offers important complementary results to molecular data, since it provides spatial information. Herein, the focus is on histochemistry coupled to optical microscopy, fluorescence and scanning electron microscopy of microwave acid extracted plant silica, techniques based on particle-induced X-ray emission, X-ray fluorescence spectrometry and mass spectrometry imaging (NanoSIMS). Sample preparation procedures will not be discussed in detail, as several reviews have already treated this subject extensively. We focus instead on the information that each technique provides by offering, for each imaging approach, examples from both silicifiers (giant horsetail and rice) and non-accumulators (Cannabis sativa L.).

Arabidopsis halleri shows hyperbioindicator behaviour for Pb and leaf Pb accumulation spatially separated from Zn

Lead (Pb) ranks among the most problematic environmental pollutants. Background contamination of soils is nearly ubiquitous, yet plant Pb accumulation is barely understood. In a survey covering 165 European populations of the metallophyte Arabidopsis halleri, several field samples had indicated Pb hyperaccumulation, offering a chance to dissect plant Pb accumulation. Accumulation of Pb was analysed in A. halleri individuals from contrasting habitats under controlled conditions to rule out aerial deposition as a source of apparent Pb accumulation. Several elemental imaging techniques were employed to study the spatial distribution and ligand environment of Pb. Regardless of genetic background, A. halleri individuals showed higher shoot Pb accumulation than A. thaliana. However, dose-response curves revealed indicator rather than hyperaccumulator behaviour. Xylem sap data and elemental imaging unequivocally demonstrated the in planta mobility of Pb. Highest Pb concentrations were found in epidermal and vascular tissues. Distribution of Pb was distinct from that of the hyperaccumulated metal zinc. Most Pb was bound by oxygen ligands in bidentate coordination. A. halleri accumulates Pb whenever soil conditions render Pb phytoavailable. Considerable Pb accumulation under such circumstances, even in leaves of A. thaliana, strongly suggests that Pb can enter food webs and may pose a food safety risk.

Effect of UV radiation and altitude characteristics on the functional traits and leaf optical properties in Saxifraga hostii at the alpine and montane sites in the Slovenian Alps

UV radiation affects the biochemical, physiological and morphological responses of plants. The effect is most pronounced at high altitude, such as alpine regions, and low latitude environments. The effect of UV radiation is impacted by different environmental conditions including temperature. We examined the response of the alpine plant Saxifraga hostii Tausch subsp. hostii growing at two altitudes (montane, 1100 m a.s.l. and alpine, 1500 m a.s.l.) in the Slovenian Alps. Selected ecophysiological, anatomical and pigment analyses along with measurements of the leaf optical properties were carried out during the growing season from July to September. Plants were grown under two different UV levels, near-ambient UV (UV) and reduced UV (UV-) radiation, and temperature conditions were monitored at both altitudes. Saxifraga hostii exhibited high photochemical efficiency of photosystem II and stomatal conductance under near-ambient UV radiation in August, which indicates that it is a well-acclimated plant. In September, photochemical efficiency was higher under reduced UV at the alpine altitude which together with a lower photosynthetic pigment content indicate delayed senescence for plants growing under reduced UV. Most leaf tissue thicknesses were not affected by UV radiation and altitude difference. There was a trend of increased stomatal density and reduced stomatal length on both leaf surfaces under near-ambient UV in August. However, there was no effect of UV attenuation or location at the alpine or montane site on the content of UV-B absorbing compounds, which implies the plant's tolerance of UV-B radiation. Saxifraga hostii leaves showed high absorption in the UV spectrum at higher altitudes, as shown by their optical properties. This study shows that Saxifraga hostii is well-acclimated to ambient UV radiation and to the environmental conditions at both altitudes. The effect of UV radiation is impacted by site conditions and this produces diverse plant responses, which contribute to the specific functional traits of Saxifraga hostii in the high-altitude environment.

Severe Water Deficiency during the Mid-Vegetative and Reproductive Phase has Little Effect on Proso Millet Performance

Climate change can result in extreme droughts, significantly affecting crop production. C4 crop proso millet (Panicum miliaceum L.) has the lowest water consumption among all of the cereal crops. Understanding its survival mechanisms is thus crucial for agriculture. Furthermore, yield reduction does not only occur directly due to water shortage, but is also a consequence of an impaired element uptake during drought. This study aimed to examine the effect of water deficiency on proso millet leaf traits, plant biomass partition, and yield. In addition, leaf element contents were analysed, including silicon, which is an important multifunctional element for grasses. The majority of the measured parameters showed little change from the control to the moderate and severe water shortage treatments, even though the soil moisture levels differed significantly. The most pronounced reduction in comparison to the control was for leaf biomass, leaf stomatal conductance, and leaf silicon, phosphorus, calcium, and sulphur contents. Conversely, an increase was obtained for leaf potassium and chlorine contents. Panicle biomass was the same for all plant groups. Leaf silicon was positively correlated to reflectance in the UV region, while leaf calcium was negatively correlated to reflectance in the visible regions, which might prevent damage due to short-wave UV radiation and provide sufficient visible light for photosynthesis. The efficient light and water management, reduction of leaf biomass, and same-sized root system may be the mechanisms that mitigate the negative effects of water shortage in proso millet.

Effects of water availability and UV radiation on silicon accumulation in the C4 crop proso millet

In proso millet, water shortage reduced leaf silicon, calcium, phosphorus, and sulphur levels, and ambient ultraviolet radiation reinforced this effect.

Plants and Light Manipulation: The Integrated Mineral System in Okra Leaves

Calcium oxalate and silica minerals are common components of a variety of plant leaves. These minerals are found at different locations within the leaf, and there is little conclusive evidence about the functions they perform. Here tools are used from the fields of biology, optics, and imaging to investigate the distributions of calcium oxalate, silica minerals, and chloroplasts in okra leaves, in relation to their functions. A correlative approach is developed to simultaneously visualize calcium oxalates, silica minerals, chloroplasts, and leaf soft tissue in 3D without affecting the minerals or the organic components. This method shows that in okra leaves silica and calcium oxalates, together with chloroplasts, form a complex system with a highly regulated relative distribution. This distribution points to a significant role of oxalate and silica minerals to synergistically optimize the light regime in the leaf. The authors also show directly that the light scattered by the calcium oxalate crystals is utilized for photosynthesis, and that the ultraviolet component of light passing through silica bodies, is absorbed. This study thus demonstrates that calcium oxalates increase the illumination level into the underlying tissue by scattering the incoming light, and silica reduces the amount of UV radiation entering the tissue.

The effect of selenium and UV radiation on leaf traits and biomass production in Triticum aestivum L

UV radiation as an evolutionarily important environmental factor, significantly affects plants traits and alters the effects of other environmental factors. Single and combined effects of ambient UV radiation, its exclusion, and Se foliar treatments on Si concentrations and production of Si phytoliths in wheat (Triticum aestivum L.) cv. 'Reska' were studied. The effects of these treatments on growth parameters of the plants, structural and biochemical traits of the leaves, and interactions of the leaves with light, as Si incrustation is the first barrier to light at the leaf surface were also examined. Under ambient UV radiation and foliar treatment with 10mgL^-1 sodium selenate solution, there was a trade-off between the plant investment in primary and secondary metabolism, as the production of UV-absorbing compounds was enhanced while photosynthetic pigment levels were reduced. Independent of Se treatment, ambient UV radiation lowered respiratory potential, Ca concentration, and leaf thickness, and increased Si concentration, Si phytoliths formation, and cuticle thickness. The Se treatment has little effect on plant traits and biomass production but it increased Se concentrations in the plants by >100-fold, independent of UV radiation. In combination with UV radiation Se strengthen the protection of plants against stress by increasing the amount of UV absorbing compounds, light reflectance and transmittance.

New method for visualization of silica phytoliths in Sorghum bicolor roots by fluorescence microscopy revealed silicate concentration-dependent phytolith formation

Silica phytoliths are microscopic structures of amorphous hydrated silica (SiO2 · nH2O) formed by specialized plant cells. Besides their biological roles, physical, chemical, and structural properties of biogenic silica offer a wide spectrum of applications in many fields of industry and technology. Therefore, processes involved in their formation recently become a very interesting topic to study. However, optical transparency and microscopic sizes of silica phytoliths do not allow their visualization and localization by classical light microscopy methods. Their observation thus requires phytolith isolation, technically difficult or lengthy sample preparation procedures, or a work with toxic chemicals. In this paper we are proposing a novel method for visualization of silica phytoliths in Sorghum bicolor root endodermal cells by fluorescence microscopy using alkali mounting solution (pH 12). This method offers an easy and quick preparation of the samples and high contrast imaging. Based on our results we can assume that the proposed fluorescent method for silica phytolith investigation allows observation of multiple samples in relatively short time period and thus might be applicable also for high-throughput screenings. Using this method we found out that after a 3-day cultivation of sorghum plants the minimal needed concentration of sodium silicate, limiting the formation of silica phytoliths in the root endodermis, was 25 µmol dm(-3). The positive correlation of sodium silicate concentration in the substrate with the phytolith diameter was also observed.

Phytoliths in taxonomy of phylogenetic domains of plants

We discuss, from the aspect of phylogeny, the interrelationships of the phytolith types in plants from the main taxonomical groups (algae, lichens, horsetails, gymnosperms, and floral plants) with homologues of known proteins of biomineralization. Phytolith morphotypes in various phylogenetic plant domains have different shapes. We found that, in ancient types of plants (algae, horsetails, and gymnosperms), there are fewer different phytolith morphotypes compared to more modern plants (floral plants). The phytolith morphotypes in primitive plants are generally larger than the morphotypes in more highly organized plants. We found that the irregular ruminate and irregular smooth morphotypes are the two most frequently encountered phytolith morphotypes in the tested plants (from algae to floral plants). These two morphotypes probably have a universal role. Silacidins, silicon transporters, silicateins, silaffins, and silicase homologues are often found in the major taxonomic groups of plants. Red algae had the smallest number of homologues of the biomineralization proteins (70-80), Monocotyledonous: 142, Coniferous: 166, Mosses: 227, and Dicotyledones: 336.

Leaf optical properties are affected by the location and type of deposited biominerals

This study aimed to relate the properties of incrusted plant tissues and structures as well as biomineral concentrations and localization with leaf reflectance and transmittance spectra from 280nm to 880nm in the grasses Phragmites australis, Phalaris arundinacea, Molinia caerulea and Deschampsia cespitosa, and the sedge Carex elata. Redundancy analysis revealed that prickle-hair length on adaxial surface and thickness of lower epidermis exerted significant effects in P. australis; prickle-hair density at abaxial leaf surface and thickness of epidermis on adaxial leaf surface in P. arundinacea; thickness of epidermis on adaxial leaf in D. cespitosa; prickle-hair density on adaxial leaf surface and thickness of cuticle in M. caerulea; and prickle-hair density on adaxial leaf surface and cuticle thickness of the lower side in C. elata. Micro-PIXE and LEXRF elemental localization analysis show that all of these structures and tissues are encrusted by Si and/or by Ca. Reflectance spectra were significantly affected by the Ca concentrations, while Si and Mg concentrations and the Ca concentrations significantly affected transmittance spectra. High concentrations of Mg were detected in epidermal vacuoles of P. arundinacea, M. caerulea and D. cespitosa. Al co-localises with Si in the cuticle, epidermis and/or prickle hairs.