Том 63, № 1 (2016)

Depending on the presence or absence of chlorophylls in the embryo, angiosperms are divided into chloroembryophytes and leucoembryophytes. Synthesis of chlorophylls (Chl) in the chloroembryos starts in the globular stage, rises as the embryo is formed, and stops in the late phase of seed maturation. The seeds also contain carotenoids that participate in photosynthesis and act as ABA precursors. The chloroembryos contain photochemically active chloroplasts that contain all the main photosynthetic complexes at a necessary stoichiometric ratio. Dark reactions of photosynthesis in developing seeds are notable for the fact that the main source of carbon therein is sucrose arriving from the maternal plant. Therefore, function of chloroplasts mainly aims at production of NADPH and ATP that are spent on conversion of sucrose into acetyl-CoA and, subsequently, to fatty acids. The CO₂ fixation system involving Rubisco and/or phosphoenolpyruvate carboxylase operates in the chloroembryos. In the course of photosynthesis, oxygen is released, which prevents hypoxia and maintains seed respiration. In late stages of ripening, the seeds enter the state of dormancy, which is associated with dehydration, disintegration of photosynthetic apparatus, Chl breakdown, and transformation of chloroplasts into plastids filled with reserve nutrient substances. At the same time, very often Chl are not destroyed completely and their residues are present in mature seeds of numerous plant species.

Vegetable protein synthesis systems for industry, medicine, and research are becoming increasingly popular. The technology of protein production in plants has certain advantages, compared with the expression systems of bacteria and yeast. The rich variety of promoters, regulatory elements, affinity tags, and fusion partners that are used in molecular biology and plant biotechnology can create hybrid genetic constructs adapted to the solution of various tasks associated with protein synthesis and purification. New methods of modification of plant systems are being developed for the synthesis of functionally active human proteins whose structure is close to the natural analogues. This review shows current approaches to increase the yield of the target protein, facilitating the procedures of its isolation and purification and preventing degradation.

We experimentally tested a possibility that nitrate regulates sucrose synthase (SS) in the roots, vacuolar acid invertase (AcI) in the stems, and alkaline invertase (AlI) in the leaves of garden pea (Pisum sativum L.) where they were predominantly located. In the course of early ontogenesis of the seedlings (0–20 days), NO₃^- stimulated solely SS. We detected three peaks of nitrate-dependent enzyme activity: the greatest peak was observed in the very beginning of germination (48 h from seed imbibition), the intermediate peak corresponded to the most intense utilization of cotyledonal reserves (sixth to eighth day of growth), and the lowest peak coincided with development of autotrophy (tenth to 20th day). In the period of their greatest activity (sixth to 14th day), neither invertases noticeably respond to nitrate. At the first peak, NO₃^- affected SS already at a concentration of 1 mM; this influence was maintained at concentrations rising to 10 mM, which points to a signal nature of the effect. We discuss a functional aspect of the effect of nitrate on SS involved in the system of the enzymes of sucrose dissimilation upon the initiation and development of different physiological processes occurring in this period, as well as its possible applied role in agricultural biotechnologies.

Plants grown in phosphorus-deprived solutions often exhibit disruption of water transport due to reduction in root hydraulic conductivity (Lp_r). To uncover the relationship between root Lp_r and water permeability coefficient (P_f) of plasma membrane and the role of aquaporins, we evaluated P_f of plasma membrane and also PIP-type aquaporin gene expression in tobacco (Nicotiana tabacum L.) plant roots after seven days P-deprivation. The results showed significant reduction in sap flow rate (J_v) and osmotic root hydraulic conductivity (L_pr-o) in P-deprived roots. These effects were reversed 24 h after P-resupplying. Interestingly, the P_f of root protoplasts was 57% lower in P-deprived plants compared with P-sufficient ones. The expression of NtPIP1;1 and NtPIP2;1 aquaporins did not change significantly in P-deprived plants compared with P-sufficient ones, but the copy number of NtAQP1 increased significantly in P-deprived plants. P-deprivation did not change Lpr-o significantly in antisense NtAQP1 plants. Taken together, these findings suggest that P-deprivation may play an important role in modulation of root hydraulic conductivity by affecting P_f in transcellular pathway of water flow across roots and aquaporins. Finally, we concluded that dominant water transport pathway under P-deprivation was transcellular one.

Photosynthetic assimilation of ¹⁴CO₂ was examined in leaves of potato (Solanum tuberosum L.) plants that were grown under direct sunlight and then transferred to 50% irradiance for various periods. The rate of ¹⁴CO₂ assimilation correlated with light intensity: the photosynthetic rate reduced by 52% after 5-day shading and by 70% after 30-min shading. In all shaded and shade-adapted plants, the sucrose/hexose ratio decreased by a factor of 3.5–4.1; furthermore, the radioactivity of glycolate cycle metabolites and the serine/glycine ratio were lowered. In plants shaded for 5 days or 30 min, the radioactivity of aspartate and malate was higher than at continuous high irradiance, especially in plants shaded for 30 min, whereas a sudden illumination of the shaded plants reduced the radioactivity of these substances. We suppose that low irradiance averted the reentry of glycolate path carbon into the Calvin cycle and redirected this carbon source for the production of four-carbon acids that acidified the apoplast. This acidification activated the apoplastic invertase, which enhanced sucrose hydrolysis and hindered the sucrose export from the leaf. Hydrolysis of sucrose promoted the increase in osmolarity of the apoplastic solution, this increase being stronger at close distances to the stomatal pores where water is intensely evaporated. The increase in osmolarity of extracellular medium led to closing of stomata and the suppression of photosynthesis.

We investigated the effects of high pressure treatment on green plant leaves of two species, red rose (Rosa rubiginosa L.) and silver birch male (Betula pendula Roth). Both species were treated with pressure up to 100 bar in order to explore stress reactions, including desirable or undesirable metabolites in plant. When increasing the pressure, chlorophyll (Chl) fluorescence maximum shifts to the wavelength of about 680 nm for both red rose and silver birch, with shift rates–0.062 nm/bar and–0.082 nm/bar, respectively. High pressure induces the changes of the position for the second fluorescence maximum at approximately 730 nm in both species with the same shift rate–0.083 nm/bar. When increasing pressure the change of the photosynthetic apparatus efficiency decreases for both plant species slowly and nonlinearly. High-pressure treatments irreversibly damaged the leaf tissue and at this way induced changes of Chl fluorescence and photosynthetic efficiency.

We applied chlorophyll a fluorescence as a biomarker to assess the growth response and PSII behavior and performance of three pistachio (Pistacia vera) rootstocks to different salt levels after inoculation with arbuscular mycorrhizal fungi Glomus mosseae and compared it with non-mycorrhizal plants (control). Our results confirmed the depressing effect of salt stress on mycorrhization extent and showed that the effect of salinity on colonization rate is completely under the influence of host plant. In this experiment, mycorrhizal symbiosis could enhance plants total dry mass (TDM), electron transfer on the donor and the acceptor side of PSII, decrease the energy dissipation and increase the comprehensive photosynthesis performance under salt stress as well as under normal conditions. We found that both donor and acceptor sides of PSII are the target sides under high salinity in pistachio rootstocks. We also found that performance index is the parameter that better reflects the responses of the studied rootstocks to progressive salt stress. Bane-baqi was less affected by salinity in terms of TDM followed by Sarakhs and Abareqi.

The effects of silicon oxide (SiO₂) nanoparticles at concentrations of 50, 100, 200, 400, and 800 mg/L on Triticum aestivum L. seedlings were investigated. We showed that SiO₂ nanoparticles, at concentrations higher 200 mg/L, had negative impacts on wheat seedlings. At these concentrations, SiO₂ nanoparticles significantly decreased roots and shoots fresh weight, decreased roots and shoots dry weight, decreased amounts of chlorophyll a and b in leaves, decreased amount of carotenoids in leaves, increased proline content in leaves, increased lipid peroxidation in leaves, and increased catalase activity in leaves. Results of this study indicate that at lower concentrations (such as 50 and 100 mg/L), SiO₂ nanoparticles not only have negative effects on wheat seedlings, but can have even some positive effects.

In the present study, the physiological responses of Nitraria tangutorum Bobr. seedlings to NaCl stress and the regulatory function of exogenous application of salicylic acid (SA) were investigated. NaCl in low concentration (100 mM) increased while in higher concentrations (200–400 mM) decreased the individual plant dry weights (wt) of seedlings. Decreased relative water content (RWC) and chlorophyll content were observed in the leaves of seedlings subjected to salinity stress (100–400 mM NaCl). Furthermore, NaCl stress significantly increased electrolyte leakage and malondialdehyde (MDA) content. The levels of osmotic adjustment solutes including proline, soluble sugars, and soluble protein were enhanced under NaCl treatments as compared to the control. In contrast, exogenous application of SA (0.5–1.5 mM) to the roots of seedlings showed notable amelioration effects on the inhibition of individual plant dry wt, RWC, and chlorophyll content. The increases in electrolyte leakage and MDA content in the leaves of NaCl-treated seedlings were markedly inhibited by SA application. The SA application further increased the contents of proline, soluble sugars, and soluble protein. The activities of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) were up-regulated by NaCl stress and the activities of SOD, POD, and CAT were further enhanced by SA treatments. Application of SA in low concentration (0.5 mM) enhanced while in higher concentrations (1.0 and 1.5 mM) inhibited APX activities in leaves of NaCl-treated seedlings. These results indicate that SA effectively alleviated the adverse effects of NaCl stress on N. tangutorum.

The drought is one of the major challenges in rice production in Iran where it is the second most important crop after wheat. Hence, there is an increasing need to develop rice genotypes with drought-tolerant background. Determining drought tolerance mechanisms would be the first priority in order to have a successful rice breeding program. In the present study, three popular rice (Oryza sativa L.) cultivars including Neda, Amol3, and Sang-tarom having contrasting features against drought stress were tested in two water-deficit treatments at both vegetative and reproductive stages. Some important morphological and physiological characteristics related to the drought tolerance mechanism such as ABA content in leaves, size of stomatal apertures, and root length in vegetative phase as well as root volume and weight of panicles in reproductive phase were evaluated. Further, the expression profiles of four important transcription factors involved in drought tolerance regulatory networks, MYB3R-2, ZFP252, AP37, and AP59, were examined by means of quantitative RT-PCR. The data showed that the responses of Neda to drought stress conditions are closer to Amol3 than to Sang-tarom. In Neda, no reduction was observed in stomatal aperture size while the maximum dry and fresh weights of panicles found in Neda under mild drought stress conditions was a remarkable property among the cultivars in long-term drought stress. The genes expression profiles of AP37, AP59, MYB3R-2, and ZFP252 also showed lower levels of increase in Neda compared to Sang-tarom and Amol3.

Phytotoxicity of six polycyclic aromatic hydrocarbons (PAHs) and their 16 oxidized derivatives that may be microbial metabolites arising in the course of PAH degradation was determined using an express test with the seedlings of sorghum (Sorghum bicolor L. Moench) and alfalfa (Medicago sativa L.). It was shown that germinating capacity is the least informative characteristic and the most useful parameter is development of seedlings during 3 days in the presence of compounds under investigation. Among unsubstituted compounds, toxicity in respect to seedlings decreased in the series fluorene > phenanthrene > anthracene. Chrysene, fluoranthene, and pyrene stimulated shoot development. It was found that some of the metabolites produced as a result of microbial degradation of phenanthrene (9,10-phenanthrenequinone, 1-hydroxy-2-naphthoic and benzoic acids) are more toxic for plants than starting PAH molecules. The obtained results are important for understanding rhizosphere processes associated with phytoremediation technique.