Hyperspectral imaging for small-scale analysis of Hordeum vulgare L. leaves under the benzo[a]pyrene effect.

Hyperspectral imaging is a newly developed approach to estimate the current state of the plants and to develop the methods of soil and plant ecological state improvement under the effect of different sources. The study was devoted to the novel approach of hyperspectral imaging application in the case of persistent organic pollutants (POP) uptake by plants. Hordeum vulgare L. was used as a test plant and grown on the soil artificially contaminated by benzo[a]pyrene (BaP) in the doses of 20, 100, 200, 400, and 800 ng g-1, which corresponds to 1, 5, 10, 20, and 40 maximum permissible concentrations (MPC) and correlates with the level of soil pollution near industrial facilities in the Rostov Region (Russian Federation). It was analyzed a group of indexes responsible for plants stress, consists of broadband greenness group, narrowband greenness group, light use efficiency group, and leaf pigments group. Benzo[a]pyrene had a stronger effect on the efficiency of the photosynthesis process than on the content of chlorophylls. In the phase of active adaptation to stress in H. vulgare, the content of photosynthetic pigments was increased. The proposed method for selecting spectral profiles by cutting off profiles that do not belong to a plant, based on the NDVI value can be effectively used for the estimation of the plants stress under the BaP contamination and for future perspectives in the most suitable way for the application of the plant's growth stimulants.

Chlorophyll fluorometry in evaluating photosynthetic performance: key limitations, possibilities, perspectives and alternatives.

Non-destructive methods for the assessment of photosynthetic parameters of plants are widely applied to evaluate rapidly the photosynthetic performance, plant health, and shifts in plant productivity induced by environmental and cultivation conditions. Most of these methods are based on measurements of chlorophyll fluorescence kinetics, particularly on pulse modulation (PAM) fluorometry. In this paper, fluorescence methods are critically discussed in regard to some their possibilities and limitations inherent to vascular plants and microalgae. Attention is paid to the potential errors related to the underestimation of thylakoidal cyclic electron transport and anoxygenic photosynthesis. PAM-methods are also observed considering the color-addressed measurements. Photoacoustic methods are discussed as an alternative and supplement to fluorometry. Novel Fourier modifications of PAM-fluorometry and photoacoustics are noted as tools allowing simultaneous application of a dual or multi frequency measuring light for one sample.

Chlorophyll fluorescence kinetics and oxygen evolution in Chlorella vulgaris cells: Blue vs. red light.

Oxygen evolution and chlorophyll fluorescence kinetics in cells of the Chlorella vulgaris strain (Europolytest, Russia) were studied under low, moderate and high photosynthetic photon flux densities (PPFD 40, 130 and 350 µmol photons m-2 s-1) of the red and blue actinic light. A novel method of a pulse amplitude modulated (PAM) Fourier chlorophyll fluorometry was applied to obtain photoinduction curves simultaneously for the red and blue measuring light for one sample. It was found that the red light did not induce oxygen evolution at low and moderate PPFD, whereas at high PPFD it caused a declining oxygen release. There was only a trace fluorescence kinetics at the low PPFD, but noticeable fluorescence kinetics under the red light was observed at the low and moderate PPFD. Particularly, the moderate red illumination of Chlorella cells excited a high chlorophyll fluorescence kinetics along with the absence of oxygen evolution that suggests anoxygenic photosynthesis. In contrast, the blue light induced a significant oxygen evolution as well as fluorescence kinetics already at low PPFD which were both further increased with the PPFD increasing. In addition, a high value of the chromatic divergence of quantum yield of photosystem II was revealed between the red and blue measuring light under high PPFD of the red actinic light.

Recent Development in Micropropagation Techniques for Rare Plant Species.

The current investigation aimed to present an overview of the conservation of biological diversity of rare and endangered plant species. Methods of biodiversity conservation as well as several overview recommendations for the preservation of various rare species have been considered. An overview of the taxa included in the red book has been presented on the example of the Russian Federation. Global and local codes and classifiers of plant rarity were also presented. Future prospects for the conservation of biological diversity and the creation and development of bioresource collections have been considered.

Effective surface conductivity of optical hyperbolic metasurfaces: from far-field characterization to surface wave analysis.

Metasurfaces offer great potential to control near- and far-fields through engineering optical properties of elementary cells or meta-atoms. Such perspective opens a route to efficient manipulation of the optical signals both at nanoscale and in photonics applications. In this paper we show that a local surface conductivity tensor well describes optical properties of a resonant plasmonic hyperbolic metasurface both in the far-field and in the near-field regimes, where spatial dispersion usually plays a crucial role. We retrieve the effective surface conductivity tensor from the comparative analysis of experimental and numerical reflectance spectra of a metasurface composed of elliptical gold nanoparticles. Afterwards, the restored conductivities are validated by semi-analytic parameters obtained with the nonlocal discrete dipole model with and without interaction contribution between meta-atoms. The effective parameters are further used for the dispersion analysis of surface plasmons localized at the metasurface. The obtained effective conductivity describes correctly the dispersion law of both quasi-TE and quasi-TM plasmons in a wide range of optical frequencies as well as the peculiarities of their propagation regimes, in particular, topological transition from the elliptical to hyperbolic regime with eligible accuracy. The analysis in question offers a simple practical way to describe properties of metasurfaces including ones in the near-field zone with effective conductivity tensor extracting from the convenient far-field characterization.

Resonant Nonplasmonic Nanoparticles for Efficient Temperature-Feedback Optical Heating.

We propose a novel photothermal approach based on resonant dielectric nanoparticles, which possess imaginary part of permittivity significantly smaller as compared to metal ones. We show both experimentally and theoretically that a spherical silicon nanoparticle with a magnetic quadrupolar Mie resonance converts light to heat up to 4 times more effectively than similar spherical gold nanoparticle at the same heating conditions. We observe photoinduced temperature raise up to 900 K with the silicon nanoparticle on a glass substrate at moderate intensities (<2 mW/µm2) and typical laser wavelength (633 nm). The advantage of using crystalline silicon is the simplicity of local temperature control by means of Raman spectroscopy working in a broad range of temperatures, that is, up to the melting point of silicon (1690 K) with submicrometer spatial resolution. Our CMOS-compatible heater-thermometer nanoplatform paves the way to novel nonplasmonic photothermal applications, extending the temperature range and simplifying the thermoimaging procedure.

Resonant Raman scattering from silicon nanoparticles enhanced by magnetic response.

Enhancement of optical response with high-index dielectric nanoparticles is attributed to the excitation of their Mie-type magnetic and electric resonances. Here we study Raman scattering from crystalline silicon nanoparticles and reveal that magnetic dipole modes have a much stronger effect on the scattering than electric modes of the same order. We demonstrate experimentally a 140-fold enhancement of the Raman signal from individual silicon spherical nanoparticles at the magnetic dipole resonance. Our results confirm the importance of the optically-induced magnetic response of subwavelength dielectric nanoparticles for enhancing light-matter interactions.