Dina V. Kazantseva

In this work, we investigated the effect of photoconversion covers based on ruby (chromium-doped alumina (Al₂O₃:Cr³⁺)) particles (PCC-R) on the growth and development of lettuce (Lactuca sativa) plants. Ruby particles (from 100 nm to 2 μm) were obtained by the sequential application of spall laser ablation and further laser fragmentation. The content of chromium ions relative to aluminum ions in the nanoparticles was 3.3 × 10⁻³. The covers with different densities of applied ruby particles (2 × 10⁷ m⁻² (PCC-R7), 2 × 10⁸ m⁻² (PCC-R8), 2 × 10⁹ m⁻² (PCC-R9)) were studied in the present work. The PCC-Rs had two wide bands of luminescence excitation. The first one was from 350 nm to 450 nm with a maximum at 405 nm, and the second one was from 500 nm to 600 nm with a peak at 550 nm. Synthesized covers emitted in the range of 650 nm to 750 nm, with a peak at 695 nm. It has been shown that PCC-R8, in contrast to PCC-R7 and PCC-R9, provided an increase in yield by 40% and was characterized by increased water use efficiency during dark respiration and assimilation of carbon dioxide in plants. It is assumed that the observed positive effect of PCC-R8 photoconversion covers is associated with the activation of regulatory mechanisms due to a qualitative change in the light spectrum.

The effect of osmolytes (trehalose, sucrose, betaine, D-glucose and hydroxyectoine) on the photoassembly of the functionally active inorganic core of the water-oxidizing complex (Mn₄CaO₅ cluster) in Mn-depleted PSII preparations (apo-WOC-PSII) was investigated. It was revealed that the efficiency of the photoassembly of the Mn₄CaO₅ cluster was considerably (three times) increased in the presence of 1 M disaccharides (trehalose or sucrose) in contrast to other osmolytes. It was found that the osmolytes (especially trehalose or sucrose) improved the redox interaction of exogenous Mn²⁺ with apo-WOC-PSII, enhanced the protective effect of Mn²⁺ against the photoinhibition of apo-WOC-PSII, protected CaCl₂-treated PSII preparations against thermoinactivation, and stabilized the water-oxidizing complex and electron transport from Q_A to Q_B in native PSII preparations during heat treatment. It is suggested that the ability of osmolytes to enhance the efficiency of the photoassembly of a Mn₄CaO₅ cluster depends on their effect on the following key processes: the redox interaction of Mn²⁺ with apo-WOC-PSII; the stability of apo-WOC-PSII to photoinhibition during the photoactivation procedure; and the stabilization of both the newly assembled functionally active Mn₄CaO₅ cluster and the electron transfer from Q_A to Q_B.

The effect of graphene oxide-based photoconversion covers on the growth and photosynthesis of tomatoes (Solanum lycopersicum) was investigated. Two types of photoconversion composite for covers were produced. In the first, only graphene oxide nanoparticles were used as a phosphor, and in the second, the graphene oxide nanoparticles were used jointly with europium oxide nanoparticles. The freshly prepared composites for covers had almost identical photoluminescence spectra: an intense peak in the red region and a minor peak in the blue region. It was revealed that during operation, luminescence in the red region decreased, while in the blue region it increased, probably due to the photothermal reduction of graphene oxide. It was shown that the photoconversion covers increased productivity (25%) and intensified photosynthesis (30–35%) in the tomato plants. It is suggested that the stimulation of plant growth is caused by changes in the light spectrum induced by the photoconversion covers.

A method for stimulating the growth of spruce and strawberry in the early phases of development is proposed. A technology for obtaining plasma-activated water (PAW) with the help of a glow discharge plasma generator was developed. The method is proposed for increasing the shelf life of PAW by adding an aqueous colloid of polyvinylpyrralidone (PVP) polymer. It is shown that after treatment with a PAW + PVP mixture, the seeds have a higher percentage of germination, the plants develop faster in the early stages, and they are more viable. At the physicochemical level, after seed treatment with PAW + PVP, higher rates of metabolite outflow from seeds are observed. At the biological level, seed treatment with PAW + PVP leads to a slight decrease in the activity of antioxidant enzymes and a higher content of chlorophylls in the leaves, and a slightly higher assimilation rate is observed. In the leaves, there is higher content of the growth hormone indole-3-acetic acid (IAA), whereas the content of the growth-inhibiting hormone abscisic acid decreases. The use of a stimulating drug based on the composition of an aqueous solution activated by plasma and polyvinylpyrrolidone (PAW + PVP) polymer can be an effective means of a single pre-sowing treatment of spruce seeds in solving the problem of reforestation and strawberry during plant propagation.

In the present work, we investigated the effect of light conversion using europium (Eu(III))-based photoconversion covers on the cultivation of agricultural plants and their resistance to stress conditions. Two types of europium nanoparticles were used. The first one was obtained from europium oxide (Eu₂O₃) by laser fragmentation. The second one was Eu³⁺:LaF₃ nanocrystals obtained by hydrothermal-microwave treatment, the content of europium ions in which was 50% of the total amount of cations. Tomatoes (Solanum lycopersicum) and cucumbers (Cucumis sativus) were used as model plants. It was shown that plants grown under cover with Eu₂O₃ (PCC-Eu₂O₃) were 30–40% larger, gave a higher yield, and the activation of gas exchange processes and the light phase of photosynthesis in the leaves in response to the lighting was faster. On the contrary, plants grown under cover with Eu³⁺:LaF₃ (PCC-Eu³⁺:LaF₃) tended to slow down the rate of biomass accumulation and decrease the rate of gas exchange activation. It was shown that photoconversion covers change the resistance of plants to stress conditions: if plants grown under PCC-Eu₂O₃ became more sensitive to heat (+40 °C) and cold (+4 °C) treatment, then plants grown under PCC-Eu³⁺:LaF₃ became more resistant to high and low temperatures. It was found that PCC-Eu₂O₃ inhibited the development of the phytopathogen Phytophthora infestans on tomato plants. It was assumed that changes in the illumination spectrum by the photoconversion covers cause both the activation of plant growth in the case of Eu₂O₃ and an increase in plant resistance in the case of Eu³⁺:LaF₃ applications.