Showing papers in "Russian Journal of Plant Physiology in 2016"

Variable chlorophyll fluorescence and its use for assessing physiological condition of plant photosynthetic apparatus

Abstract: Analysis of plant behavior under diverse environmental conditions would be impossible without the methods for adequate assessment of the processes occurring in plants. The photosynthetic apparatus and its reaction to stress factors provide a reliable source of information on plant condition. One of the most informative methods based on monitoring the plant biophysical characteristics consists in detection and analysis of chlorophyll a fluorescence. Fluorescence is mainly emitted by chlorophyll a from the antenna complexes of photosystem II (PSII). However, fluorescence depends not only on the processes in the pigment matrix or PSII reaction centers but also on the redox reactions at the PSII donor and acceptor sides and even in the entire electron transport chain. Presently, a large variety of fluorometers from various manufacturers are available. Although application of such fluorometers does not require specialized training, the correct interpretation of the results would need sufficient knowledge for converting the instrumental data into the information on the condition of analyzed plants. This review is intended for a wide range of specialists employing fluorescence techniques for monitoring the physiological plant condition. It describes in a comprehensible way the theoretical basis of light emission by chlorophyll molecules, the origin of variable fluorescence, as well as relations between the fluorescence parameters, the redox state of electron carriers, and the light reactions of photosynthesis. Approaches to processing and analyzing the fluorescence induction curves are considered in detail on the basis of energy flux theory in the photosynthetic apparatus developed by Prof. Reto J. Strasser and known as a “JIP-test.” The physical meaning and relation of each calculated parameter to certain photosynthetic characteristics are presented, and examples of using these parameters for the assessment of plant physiological condition are outlined.

Effects of silicon oxide nanoparticles on growth and physiology of wheat seedlings

Abstract: 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.

Exogenous salicylic acid improves salinity tolerance of Nitraria tangutorum

Abstract: 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.

Effects of exogenous spermidine on antioxidant system of tomato seedlings exposed to high temperature stress

Abstract: The effects of foliar spraying with spermidine (Spd) on antioxidant system in tomato (Lycopersicon esculentum Mill.) seedlings were investigated under high temperature stress. The high temperature stress significantly inhibited plant growth and reduced chlorophyll (Chl) content. Application of exogenous 1 mM Spd alleviated the inhibition of growth induced by the high temperature stress. Malondialdehyde (MDA), hydrogen peroxide (H2O2) content and superoxide anion (O2) generation rate were significantly increased by the high temperature stress, but Spd significantly reduced the accumulation of reactive oxygen species (ROS) and MDA content under the stress. The high temperature stress significantly decreased glutathione (GSH) content and activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR), but increased contents of dehydroascorbic acid (DHA), ascorbic acid (AsA), and oxidized glutathione (GSSG) in tomato leaves. However, Spd significantly increased the activities of antioxidant enzymes, levels of antioxidants and endogenous polyamines in tomato leaves under the high temperature stress. In addition, to varying degrees, Spd regulated expression of MnSOD, POD, APX2, APX6, GR, MDHAR, DHAR1, and DHAR2 genes in tomato leaves exposed to the high temperature stress. These results suggest that Spd could change endogenous polyamine levels and alleviate the damage by oxidative stress enhancing the non-enzymatic and enzymatic antioxidant system and the related gene expression.

Physiological and biochemical adaptations in lentil genotypes under drought stress

Abstract: Drought is a major restrictive factor for declining grain yield in lentil globally. Present investigation was conducted by taking microsperma (HUL-57) and macrosperma (IPL-406) genotypes of lentil (Lens culinaris Medik.) as information regarding physiological and biochemical basis of differences in drought resistance in macrosperma (bold-seeded) and microsperma (small-seeded) are not well understood. Pot grown plants were exposed to drought stress at specific phenophase viz. mid-vegetative, flower initiation and pod formation stage by withholding irrigation till the plants experienced one cycle of permanent wilting (PWP). Genotypes exhibited substantial differences for most of the measured traits under drought irrespective of the phenophase of stress imposed. Under drought HUL-57 had lower CMI, higher CSI, lower values of Δ13C, maintained higher SLN, accumulated more N and efficiently remobilized accumulated N to developing seeds. Higher chlorophyll content, increased accumulation of osmotically active solutes viz. soluble sugars and proline under drought stress was evident in HUL-57. Drought induced H2O2 accumulation and lipid peroxidation in both genotypes, but increments were of lesser magnitudes in HUL-57. Drought stress of pod formation stage followed by flower initiation stage was most damaging than the stress imposed at mid-vegetative stage in both genotypes. HUL-57 showed a better drought resistance capacity than IPL-406. Drought indices viz. DSI, STI and MP are proposed as criterion to identify and breed lentil genotypes for drought conditions.

Hydrolytic enzymes and their proteinaceous inhibitors in regulation of plant–pathogen interactions

Abstract: This review considers the main groups of hydrolytic enzymes associated with plant pathogens, as well as proteinaceous inhibitors of these enzymes, acting as the components of plant defense system. The role of hydrolases is described in the development of a pathological process in plant tissues. Significance of hydrolase inhibitors in the development of plant resistance to pathogens is analyzed. It is proposed that specific interactions in the “host plant–pathogen” system, involving hydrolytic enzymes and their proteinaceous inhibitors, depend on the nutritional specialization of fungi.

Constitutive and cold-induced resistance of rye and wheat seedlings to oxidative stress

Abstract: The influence of cold hardening of rye (Secale cereale L.) and wheat (Triticum aestivum L.) seedlings on their resistance to the oxidative stress (OS) agents, namely, 50 mM hydrogen peroxide or 5 mM iron (II) sulfate was studied. Unhardened rye seedlings were more resistant to hydrogen peroxide than those of wheat, since their growth was less inhibited, and they accumulated lesser amounts of lipid peroxidation products after a treatment with H2O2. The interspecific differences in responses to FeSO4 were less significant. The unhardened seedlings of rye, in comparison with those of wheat, possessed more active guaiacol peroxidase (GPO) and more levels of anthocyanins and proline. In response to the OS agents, the unhardened rye seedlings enhanced activities of superoxide dismutase and catalase, whereas the wheat seedlings enhanced GPO activity and proline content. The cold hardening (6 days at 2°C) increased activities of antioxidant (AO) enzymes, contents of proline, sugars, and anthocyanins in seedlings of both species, and made the seedlings more resistant to the OS agents. After the cold hardening, rye seedlings were more resistant to OS than wheat seedlings. The hardened seedlings of both species activated the AO enzymes in response to H2O2 or FeSO4 greater than the unhardened ones. However, the hardened wheat seedlings, in contrast to the unhardened ones, did not augment the proline content in contact with the OS agents. The conclusion was drawn on different contributions of AO enzymes and low-molecular weight compounds to the basal and induced by the cold—hardening resistances of rye and wheat seedlings to OS.

Photosynthesis in the seeds of chloroembryophytes

Abstract: 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.

Quantify the response of purslane plant growth, photosynthesis pigments and photosystem II photochemistry to cadmium concentration gradients in the soil

Abstract: The cadmium (Cd), being a widespread soils pollutant and one of the most toxic heavy metals in the environment, adversely affects sustainable crop production and food safety. Pot experiment was conducted to quantify and simulate the response of purslane (Portulaca oleracea L.) plants to Cd toxicity. The purslane germinated seeds were cultivated in twelve Cd concentrations (from 0 to 300 mg/kg of Cd in soil) for six weeks and then some growth characteristics, photosynthesis pigments, and chlorophyll a fluorescence parameters were measured. The influence of Cd gradients in the soil on all growth parameters, photosynthesis pigments and chlorophyll a fluorescence parameters (except F m and carotenoid content) were described by a segmented model. Furthermore, F m and carotenoid contents were fitted to a linear model. The growth characteristics, chlorophyll content, photosynthetic pigments and some parameters of chlorophyll a fluorescence such as F v, F v/F m, Y(II) and ETR decreased when Cd concentration increased. In contrast, F 0, Y(NPQ) and Y(NO) increased and F m was not significantly affected. In general, most variations in the studied parameters were recorded with low concentrations of cadmium, which ranged from 0 to 125 mg/kg. Also, the growth characteristics (especially stem, leaf, and shoot dry weights) were more sensitive to Cd contamination than other parameters. Moreover, among chlorophyll fluorescence parameters, Y(NPQ) was the most sensitive to Cd concentration gradients in the soil that can be due to disturbances of antennae complex of PSII.

Transgenic sorghum with improved digestibility of storage proteins obtained by Agrobacterium -mediated transformation

Abstract: Development of transgenic plants with modified seed storage protein composition and increased nutritive value is one of the most promising areas of genetic engineering. This task is especially important for sorghum—a unique drought tolerant cereal crop that is characterized, however, by a relatively poor nutritive value in comparison with other cereals. It is considered that one of the reasons of the low nutritive value of the sorghum grain is the resistance of one of its seed storage proteins, γ-kafirin, located in the outer layer of endosperm protein bodies, to protease digestion. Using Agrobacterium-mediated genetic transformation, we obtained transgenic sorghum plants (Sorghum bicolor (L.) Moench) harboring a genetic construct for RNAi silencing of the γ-kafirin gene. In the T1 generation, the plants with almost floury or modified endosperm texture of kernels were found. In these kernels, the vitreous endosperm layer has been reduced and/or covered by a thin layer of floury endosperm. In vitro protein digestibility (IVPD) analysis showed that the amount of undigested protein in transgenic plants from the T3 generation was reduced by 2.9–3.2 times, in comparison with the original non-transgenic line, and the digestibility index reached 85–88% (in comparison with 59% in the original line). In T2 families, the plants combining high IVPD with vitreous endosperm type were found. In the electrophoretic spectra of endosperm proteins of transgenic plants with increased digestibility, the proportion of 20 kD protein that is encoded by the γ-kafirin gene, was significantly reduced, in comparison with the original non-transgenic line. HPLC analysis showed total amino acid content in two out of the three studied transgenic plants from the T2 generation was reduced in comparison with the original non-transgenic line, while the lysine proportion increased by 1.6–1.7 times. The mechanisms conditioning improved digestibility of storage proteins in transgenic plants are discussed. The results of experiments demonstrate that it is feasible to develop sorghum lines combining high protein digestibility and vitreous endosperm that has a high breeding value.

Cell ultrastructure and fatty acid composition of lipids in vegetative organs of Chenopodium album L. under salt stress conditions

Abstract: White goosefoot plants (Chenopodium album L. of the family Chenopodiaceae) grown at various NaCl concentrations (3–350 mM) in the nutrient solution were used to study the cell ultrastructure as well as the qualitative and quantitative composition of fatty acids in the lipids of vegetative organs. In addition, the biomass of Ch. album vegetative organs, the water content, and the concentrations of K+, Na+, and Cl– were determined. The growth rates of plants raised at NaCl concentrations up to 200–250 mM were the same as for the control plants grown at 3 mM NaCl; the growth parameters remained rather high even at NaCl concentrations of 300–350 mM. The water content in Ch. album organs remained high at all NaCl concentrations tested. Analysis of the ionic status of Ch. album revealed a comparatively high K+ content in plant organs. At low NaCl concentrations in the nutrient solution, K+ ions were the dominant contributors to the osmolarity (the total concentration of osmotically active substances) and, consequently, to the lowered cell water potential in leaves and roots. As the concentration of NaCl was increased, the plant organs accumulated larger amounts of Na+ and Cl–, and the contribution of these ion species to osmolarity became increasingly noticeable. At 300–350 mM NaCl the contribution of Na+ and Cl– to osmolarity was comparable to that of K+. An electron microscopy study of Ch. album cells revealed that, apart from the usual response to salinity manifested in typical ultrastructural changes of chloroplasts, mitochondria, and the cytosol, the salinity response comprised the enhanced formation of endocytic structures and exosomes and stimulation of autophagy. It is supposed that activation of these processes is related to the removal from the cytoplasm of toxic substances and the cell structures impaired by salt stress conditions. The qualitative and quantitative composition of fatty acids in the lipids of Ch. album organs was hardly affected by NaCl level. These findings are consistent with the high salt tolerance of Ch. album, manifested specifically in retention of growth functions under wide-range variations of NaCl concentration in the nutrient solution and in maintenance of K+, Na+, and Cl– content in organs at a constant level characteristic of untreated plants.

Adaptive changes in pigment complex of Pinus sylvestris needles upon cold acclimation

Abstract: We studied seasonal changes in the content and ratio between photosynthetic pigments in one-yearold needles of Scotch pine (Pinus sylvestris L.) growing in Central Yakutia. Maximum accumulation of chlorophylls in developed young needles occurred in July when light and temperature conditions were favorable. In this period, the needles were notable for a relatively high level of β-carotene and neoxanthin and a reduced content of lutein and the pigments of violaxanthin cycle (VXC). In the course of autumn hardening, the content of chlorophylls decreased two times. Total content of carotenoids remained the same, but pigment composition considerably changed when plants progressed from a vegetating to frost-resistant state. We revealed time and temperature ranges of variation for individual carotenoids. In the beginning of hardening at reduced and low abovezero temperatures, the content of β-carotene in the needles decreased, the pigment-protein complexes (PPC) became enriched in lutein, the pigment pool of VXC gradually increased, and the content of neoxanthin transiently rose. When average daily air temperature further decreased to near- zero values, the content of zeaxanthin sharply rose. In winter, high levels of lutein and zeaxanthin were maintained. Main changes in pigment complex of the needles of P. sylvestris were completed before the coming of steady below-zero temperatures. The obtained data suggested that, upon seasonal decrease in temperature in early stages of hardening, a decrease in the level of chlorophyll promotes a reduction in the quantity of absorbed radiant energy. Apparently, this is accompanied by activation of the role of lutein and neoxanthin that perform specific photoprotective functions in antenna PPC associated with a gradual decrease in plants’ ability to quench singlet energy of excited chlorophyll. Accumulation of zeaxanthin as a result of inhibition of back reaction of epoxidation at near-zero temperatures creates necessary prerequisites for turning on the mechanisms of steady dissipation of absorbed light energy, which do not depend on transmembrane proton gradient of thylakoids. At the same time, zeaxanthin can perform antioxidant functions both in PPC and in the lipid phase of thylakoid membranes. The obtained data point to an adaptive nature of the observed reactions and a specific role of individual pigments in structural and functional reorganization of photosynthetic machinery in the course of development of frost-resistance in the needles.

Cyclic electron flow plays an important role in protection of spinach leaves under high temperature stress

Abstract: Heat stress is one of the major abiotic stresses and affects plant productivity in a negative manner. Photosynthetic processes are largely influenced by heat stress. In spinach (Spinacia oleracea L.) leaves at 40°C the decrease in PSII activity was mainly due to the decreased efficiency to capture excitation energy, increased yield of regulatory energy dissipation mechanism Y(NPQ), and decreased quantum yield Y(II). According to the results below 45°C PSI is stable and protected while at a higher temperature stability of PSI was reduced and protection was not sufficient. Therefore, we conclude that cyclic electron flow plays an important role in protecting PSI from heat stress.

Effects of arbuscular mycorrhizal fungi on photosystem II activity of three pistachio rootstocks under salt stress as probed by the OJIP-test

Abstract: 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.

Mitochondrial respiration of the photosynthesizing cell

Abstract: Current notions on respiration of photosynthesizing cells are reviewed. Over the past three decades, the modern methods based on isotope techniques and reverse and molecular genetics provided convincing evidence that mitochondrial respiration is functional in the light and contributes to the creation of optimal conditions for photosynthesis and for protection of cells from photodegradation. Novel data are presented on the substrates that are used for respiration in the light. Individual respiration steps are considered in the context of their possible role in photosynthesizing cells. The mechanisms and carriers mediating the export of reducing equivalents from chloroplasts for their subsequent oxidation in the mitochondrial electron-transport chain are discussed. The regulation of nonphosphorylating (unrelated to energy generation) electron transport pathways mediated by alternative oxidase and alternative type II NADPH-dehydrogenases, as well as the role of uncoupling proteins in plant mitochondria, are analyzed. These components were shown to play a significant role in NAD(P)H oxidation for maintaining the redox balance in mitochondria and whole green cells. A generalized scheme of biochemical interactions between organelles—chloroplasts, mitochondria, and peroxisomes—is presented. The directions for future research are outlined.

pH and CO2 effects on Coelastrella (Scotiellopsis) rubescens growth and metabolism

Abstract: We studied effects of рН and СО2 enrichment on the physiological condition and biochemical composition of a carotenogenic microalga Coelastrella (Scotiellopsis Vinatzer) rubescens Kaufnerova et Elias (Scenedesmaceae, Sphaeropleales, Chlorophyceae), a promising source of natural astaxanthin. The microalga was grown at a constant pH (5, 6, 7 or 8) maintained by direct СО2 injection. The air-sparged culture served as the control. Cell division rate and size, dry biomass productivity, the rates of nitrogen and phosphorus uptake as well as photosynthetic pigment and total lipid content and fatty acid composition were followed. С. rubescens possessed a narrow-range рН tolerance (the optimum рН 6–7). Under these conditions, the highest values of the maximum (1.0–1.1 1/day) and average (0.3–0.35 1/day) specific growth rate, chlorophyll а (4.8–4.9%) and total carotenoid dry weight percentages (1.7–1.8%) were recorded. Cell lipid fatty acid unsaturation index (1.851) and polyunsaturated fatty acid percentage (36–39%) and С18:3 ω3/С18:1 ω9 ratio (3.8–4.5) were also the highest under these conditions. A decline of рН to 5 brought about severe stress manifesting itself as a cell division cessation, photosynthetic apparatus reduction, two-fold increase in cell volume, accumulation of dry weight and lipids and a considerable decline in fatty acid unsaturation. Cultivation of С. rubescens without СО2 enrichment resulted in a rapid alkalization of the medium to рН 9.5–10.5 impairing the physiological condition of the cells. Reasons of the deteriorative effects of suboptimal pH values on the physiological condition of C. rubescens are discussed.

Changes in phytotoxicity of polycyclic aromatic hydrocarbons in the course of microbial degradation

Abstract: 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.

Validation of reliability for reference genes under various abiotic stresses in tea plant

Abstract: Reference genes are frequently used as a normalization standard to obtain reliable data during quantitative real-time polymerase chain reaction (qRT-PCR). However, recent studies showed that most traditional reference genes were not stable under different treatments or environmental stresses, which may lead to misinterpret expression of the target genes. In this study, 7 candidate reference genes in tea plant (Camellia sinensis (L.) Kuntze cv. Yingshuang) were selected and their expression stability under different abiotic stresses was analyzed using geNorm, NormFinder, and BestKeeper methods. Our results suggest that TUA1 (alpha-1 tubulin) has the most stable expression under damage stresses according to 3 methods of analysis. For drought stresses, 18S rRNA, and GAPDH (glyceraldehyde-3-phosphate dehydrogenase) were the most stable genes. For cold, Al, and NaCl stresses, GAPDH and TUA1 may be the alternative options. Our results may provide an insight for identification of the optimal reference genes for tea plants under various treatments.

Phosphofructokinase and glucose-6-phosphate dehydrogenase in response to drought and bicarbonate stress at transcriptional and functional levels in mulberry

Abstract: Drought and bicarbonate stress are the most common abiotic stresses limiting plant growth and crop production all over the world. Glycolytic and pentose phosphate pathways have important effects on the resistance response of plants to abiotic stress. Phosphofructokinase (PFK) and glucose-6-phosphate dehydrogenase (G6PDH) are the rate limiting enzymes of the two pathways which control carbon flow through the two pathways, respectively. In Morus alba L. leaves, the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and the proline content increased under drought and bicarbonate stress at first, and then decreased. At the functional level, drought and bicarbonate stress exert an activating effect on the G6PDH activity and an inhibitory effect on the PFK activity in M. alba leaves. At the transcriptional level ATP-PFK, PPi-PFK and G6PDH genes showed no significant change under 80 g/L PEG 6000 treatment. The changes were observed at the ATP-PFK, PPi-PFK and G6PDH mRNA levels under 30 mM NaHCO3 treatment. Although M. alba stopped growing under two different treatments and the changes of G6PDH and PFK are different suggesting that may be additional factors playing important roles in glucose and energy metabolism in plant responses to stresses.

Induction of heat resistance in wheat seedlings by exogenous calcium, hydrogen peroxide, and nitric oxide donor: functional interaction of signal mediators

Abstract: Functional interactions of calcium ions, hydrogen peroxide, and nitric oxide as signal mediators in root cells of wheat (Triticum aestivum L.) seedlings upon induction of their heat resistance was studied with use of inhibitor-based analysis. Treatment of the seedlings with hydrogen peroxide or a combination of calcium chloride with ionophore A23187 significantly increased their content of nitric oxide, which peaked 0.5–1 h after the start of the treatment. CaCl2 or exogenous NO donor (sodium nitroprusside, SNP) transitorily increased the hydrogen peroxide level in the roots. Seedlings pretreatments with calcium chelator (EGTA), blocker of Ca2+ channels (LaCl3), inhibitor of phospholipase C (neomycin), or antagonist of cyclic adenosine-5'-diphosphatribose formation (nicotinamide) more or less prevented the rise in the nitric oxide content in roots caused by exogenous H2O2; the SNP-induced rise in hydrogen peroxide was also damped down. However, the seedlings pretreatment with antioxidants ionol or dimethylthiourea did not hinder the increase in the NO level, which was caused by exogenous Ca2+. The inhibitors of NO synthase (NG-nitro-L-arginine methyl ester, L-NAME) or nitrate reductase (sodium tungstate) did not interfere in the accumulation of H2O2 in root tissues stimulated by exogenous calcium. Calcium antagonists diminished the seedlings heat resistance increased by hydrogen peroxide or SNP. Antioxidants and inhibitors of NO synthase or nitrate reductase weakened the calcium-stimulated enhancement in the seedlings heat resistance. It was concluded that calcium may activate NO- and H2O2-generating enzymatic systems as well as participate in the transduction of signals of these mediators into genetic apparatus and in the formation of physiological reactions underlying the enhanced heat resistance.

Involvement of phosphoenolpyruvate carboxylase and antioxydants enzymes in nitrogen nutrition tolerance in Sorghum bicolor plants

Abstract: Plants of Sorghum bicolor (C4 species) were grown at different nitrate or ammonium concentrations (0.5, 5, 20 and 50 mM) in order to examine the effect of nitrogen nutrition on growth, phosphoenolpyruvate carboxylase (PEPC) and antioxidant enzymes activities in both roots and leaves of 30-day-old plants. At high NO3− levels (20 and 50 mM) the fresh weight was significantly higher. When the nitrogen source was in ammonium form, the leaf and root mass increased drastically at low concentration 5 mM and significantly at 20 mM, however similar fresh weight was found at high level of ammonium (50 mM). The leaves catalase (CAT), guaiacol peroxidase (POD), glutathione reductase (GR), and glutathione S-transferase (GST) activities and the roots glutathione reductase and glutathione S-transferase activities were significantly higher in the NH4+-fed plants than those grown in the nitrate medium. Activity and proteins levels of phosphoenolpyruvate carboxylase in both leaves and roots of sorghum plants were increased progressively with increasing external nitrogen concentration. This increase was more pronounced at high level of ammonium (50 mM), being 2-fold at 50 mM of NO3− and 3-fold at 50 mM of NH4+. Our results suggested that antioxidant enzymes activities and PEPC play a key role in ammonium detoxification and tolerance in sorghum plants.

Roles of ethylene and cytokinins in development of defense responses in Triticum aestivum plants infected with Septoria nodorum

Abstract: Effects of ethephon (2-chloroethylphosphonic acid, ET), which is a producer of ethylene, and 1-methylcyclopropene (1-MCP), which inhibits ethylene binding with the corresponding receptors, on defense responses caused by the causal agent of leaf blotch (Septoria nodorum Berk.) in leaves of soft spring wheat (Triticum aestivum L.) of cultivars contrast in the resistance to the pathogen were studied. After treatment with 1-MCP, an induction of wheat resistance to the disease, more prominent in the susceptible cv. Kazakhstanskaya 10 than in the resistant cv. Omskaya 35, was found. The rise in the resistance was accompanied by rise in zeatin content in leaves, enhanced generation of hydrogen peroxide (most likely, due to the decreased catalase activity and increased peroxidase activity), and accumulation of transcripts of marker genes of the salicylate signaling pathway (PR-1 and PR-2). On the contrary, in ET-treated plants, all the studied defense responses were inhibited, and the pathogen developed more intensively. The effect of ethylene on zeatin distribution in infected wheat leaves of the susceptible cv. Kazakhstanskaya 10 was also found. In the 1-MCP-treated wheat leaves, cytokinins were localized in mesophyll cells and cell walls. In the ET-treated leaves, cell walls were free of zeatin, and the hormone concentrated in developing hyphae of the pathogen. The results allow for the hypothesis that wheat plant resistance is controlled by antagonistic interaction of signaling pathways of salicylic acid and ethylene with participation of cytokinins.

Genome-wide identification and analysis of the U-box family of E3 ligases in grapevine

Abstract: E3 ubiquitin ligases play essential roles in determining the specificity of ubiquitination and subsequent protein degradation. The plant U-box (PUB) family of E3 ligases has been implicated in biotic and abiotic stress signaling and developmental events in various species. A comprehensive bioinformatics analysis identified 56 PUB genes in the grapevine (Vitis vinifera L.) genome. Based on conserved motifs, the VvPUB family was classified into seven subclasses. Expansion of this family was driven by chromosomal, segmental, and tandem duplications. Microarray expression profiling revealed that three PUB genes were preferentially expressed in pollen, four in leaf, and five in root. Moreover, a large number of PUB genes were differentially expressed under abiotic stresses and eight PUB genes likely participated in defense against powdery mildew. The microarray expression data were verified by RT-qPCR. Genome-wide identification of VvPUB genes and examination of their expression will give insights into the functions of U-box genes in grapevine.

Effects of exogenous polyamines on nitrate tolerance in cucumber

Abstract: Putrescine (Put), spermidine (Spd), and spermine (Spm) are the major polyamines (PAs) in plant, which are not only involved in the regulation of plant developmental and physiological processes, but also play key roles in modulating the defense response of plants to diverse environmental stresses. In this study, Cucumis sativus L. seedlings were cultivated in nutrient solution and sprayed with three kinds of PAs (Put, Spd, and Spm). The effects of PAs were investigated on excess nitrate stress tolerance of C. sativus by measuring growth and nitrogen (N) metabolism parameters. The contents of NO 3- − N, NH 4- + N, proline and soluble protein in leaves were increased; while plant height, leaf area, shoot fresh and dry weight, root fresh weight were decreased under 140 mM NO 3 − treatment for 7 d. In addition, the activities of nitrate reductase (NR), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH) were significantly inhibited under 140 mM NO 3 − treatment for 7 d. With foliar treatment by 1 mM Spd or Spm under stress treatment, the contents of Spm, Put, and Spd in leaves increased significantly, except that Spm content decreased under Spd treatment. The activities of NR, glutamine synthetase (GS), GOGAT and GDH and plant height, leaf area, shoot fresh and dry weights were significantly increased. The contents of proline and soluble protein in leaves were significantly enhanced. In contrast, the accumulation of NO 3- − N and NH 4- + N were significantly decreased. However, there were minor differences in activities of N metabolism enzymes and the content of osmotic adjustment substances under 1 mM Put treatment. These findings suggest that 1 mM exogenous Spm or Spd could enhance the capacity of N metabolism, promote growth and increase resistance to high concentrations of NO 3 − . The ameliorating effect of Spd was the best, and that of Put the worst.

Molecular and physiological responses of Arabidopsis thaliana plants deficient in the genes responsible for ABA and cytokinin reception and metabolism to heat shock

Abstract: Using mutant plants of Arabidopsis thaliana, participation of the genes involved in abscisic acid (ABA) and cytokinins (CKs) metabolism and signaling in plant defense responses to heat shock (HS) was investigated The magnitude of the stress action was assessed with biochemical indicators, such as accumulation of proline and malonic dialdehyde (MDA) and changes in the content of gene transcripts of heat shock proteins (HSPs) (HSP901 and HSP905) and transcription factor of HS (HSFA2) as well as stress-inducible genes, markers of oxidative stress (AOX1a, RD29, PRODH1, and P5CS1) Mutants with inactivated genes of ABA synthesis and, especially, signal perception exhibited lower thermo-resistance and accumulated elevated amounts of CK metabolism and signal transduction genes In contrast, plants with inactivated components of CK synthesis and signal perception displayed increased tolerance to high temperatures and reduced levels of mRNA of oxidative stress genes as compared to wild type (WT) plants However, enhancement of HS contributed to decrease of thermo-resistance of CKs receptor mutants up to the level of WT plants Under hyperthermia, the stimulation of the plant defense mechanisms was accompanied by downregulation of the expression of CK metabolism and signal transduction genes (IPT3, CKX1, ARR5, AHK2, and AHK4) and ABA catabolism gene (CYP707A1) and upregulation of the expression of ABA synthesis and signal perception genes (ABA3 and ABI2) In the mutants insensitive to ABA, CYP707A1 gene was upregulated under the HS, while the expression of CK receptor gene expression did not reliably change The results indicate that the response of the plants to elevated temperatures was determined not only by strength and the duration of the stress but the state of their ABA and CK metabolic and signaling systems as well

Characteristics of photosynthesis in maize leaves (С4 plants) upon changes in the level of illuminance and nitrate nutrition

Abstract: We studied assimilation of 14СО2 and distribution of 14С among the products of 3-min-long photosynthesis of maize (Zea mays L.) leaves. The day before the experiment, half of the plants were fertilized with Ca(NO3)2 (1 g/L of water) at a rate of 6 L/m2. Five days before the experiment, some plants were shaded for adaptation (illuminance was reduced by 50%). On the day of the experiment (before the application of 14СО2), several shaded plants were exposed to direct sunlight for 3 min, and some plants grown at full light (light plants) were shaded for 3 min (illuminance of 50%). Unfertilized plants adapted for 5 days to shading showed photosynthesis of 75.9% of control level (full light). If light plants were transferred to shading for 3 min, their photosynthesis decreased to 42.1%. In plants shaded for 5 days and then transferred to full light, photosynthesis in 3 min was 96.3% of control level. At full light, fertilization with nitrate boosted photosynthesis to 132.6% as compared with control material, but photosynthesis decreased to 43.5 and 65.4% of control level in plants shaded for 5 days and those shaded for 3 min, respectively. At the same time, the plants shaded for 5 days and then exposed for 3 min to full light restored photosynthesis to almost control level (95.5%). Analysis of 14С distribution among the products of 3-min-long photosynthesis showed that, the same as in C3 plants, a decrease in illuminance (especially a sudden one) in maize reduced the ratio between labeled sucrose and hexoses and elevates incorporation of 14С into malate, which indicated that its consumption in bundle sheath cells was suppressed. A decrease in the ratio between labeled sucrose and hexoses became more pronounced under the influence of nitrates with this effect also occurring in transport products of photosynthesis (20 cm below 14С-providing leaf area). In plants fertilized with nitrates, radioactivity of sucrose (% of radioactivity of soluble compounds) decreased in all the types of illumination. When illuminance was suddenly reduced for 3 min, incorporation of 14С into sucrose was 21.5 against 51.2% in light plants, and radioactivity of aspartate and malate sharply rose to 13.7 and 26.1% (against 2.1 and 8.9% in control material). Incorporation of 14С into compounds of glycolate pathway was low (less than 2.5%), but it was somewhat greater in nitrate plants. We concluded that the same mechanism of interaction between stomatal apparatus of leaf epidermis, invertase of mesophyll apoplast, and photosynthetic metabolism of carbon with electron flux via electron transport chain in chloroplasts of bundle sheath cells, which governs the rate of photosynthesis and assimilate export from the leaf but is triggered by the extent of consumption in the bundle sheath cells of C4 acids produced in the mesophyll operates in C4 plants (the same as in C3 plants).

Epigenetic variability in plants: Heritability, adaptability, evolutionary significance

Abstract: DNA methylation is the most stable epigenetic modification with a well studied maintenance mechanism in the mitotically dividing cell generations. The plant DNA is methylated at sites of three types, CG, CHG and CHH. The methylation mechanisms of these sites are different and involve functional activity of various DNA methyltransferases and their accessory factors, that largely define the genome locus specificity of methylation. The genome methylation pattern, DNA methylome, in plants is inheritable not only in the dividing cell generations but also to a considerable extent in generations of the whole plants. A great number of spontaneous epimutations, both natural and experimental ones, are known, that have discernible phenotypic manifestations and are stably inheritable in the plant generations as Mendelian traits. A fundamental distinction of such epimutations from classical mutations is their reversibility. The higher plants epigenome is much more flexible compared with their genome. The single-nucleotide epimutation frequency is hundredfolds higher than the mutation frequency. This variability is probably a main source of the plant phenotypic plasticity, that enables them to adapt to changing environment on the time scales too short for adaptive mutations to occur. A dramatic increase in the plant population epigenetic variability on a practically unchanged genetic context is observed when the essential environmental factors are rapidly changing. Being flexible enough for such adaptive changes, on the other hand, epigenome is stable enough for these adaptive variations to be inheritable between the plant generations. Obviously, the epigenetic variations, that enable plants to adapt to the fast changing environmental factors, serve as material for natural selection and other evolutionary processes on the respective time scales. A still another aspect of evolutionary significance is a capability of epigenetic mechanisms to induce transient bursts of genetic variability by transposon mobilization.

Overexpression of the Arabidopsis DREB1A gene enhances potato drought-resistance

Abstract: Drought is a major environmental stress that limits potato (Solanum tuberosum L.) production worldwide. The transcription factor DREB1A/CBF3 specifically interacts with the dehydration responsive element (DRE/CRT) and induces expression of genes involved in environmental stress tolerance in Arabidopsis thaliana. In this study, DREB1A of A. thaliana was overexpressed in a potato cultivar Longshu 3 (L3) through Agrobacterium tumefaciens-mediated transformation. The transformation and overexpression of DREB1A were assessed using PCR, Southern blotting and semi-quantitative RT-PCR analysis. The results clearly confirmed that the DREB1A gene was successfully integrated into the genome and expressed. When pot-grown plants with 15–16 leaves were subjected to drought stress treatments by withholding water for 8 days, the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), the MDA content and electrolyte leakage in leaves from both non-transgenic and transgenic L3 plants leaves increased. The average activities of SOD, CAT, and POD in transgenic plant leaves, respectively showed 69.77, 60.78, and 24.60% increase than those of non-transgenic L3. The MDA content and electrolyte leakage in non-transgenic L3 plant leaves, respectively increased 59.09 and 37.63% relative to those of transgenic plant leaves. When water was withheld for 14 days control plants exhibited severe wilting and transgenic plants only partially wilting. These results demonstrated that overexpression of DREB1A resulted in improved drought stress tolerance in S. tuberosum plants.

Protective effect of wheat germ agglutinin on the course of mitosis in the roots of Triticum aestivum seedlings exposed to cadmium

Abstract: Effect of pretreatment with 28 nM wheat germ agglutinin (WGA) on cell divisions in the root apical meristem of 4-day-old seedlings of wheat (Triticum aestivum L), distribution of cells among mitotic phases, cadmium-induced disruptions of normal progression through mitosis, and activity of nucleolar organizer regions (NOR) of the chromosomes was studied after 7-h-long exposure to 1 mM cadmium acetate Pretreatment with WGA has a pronounced protective effect on divisions of root meristem cells exposed to cadmium Progression of the cells through mitotic phases was normalized, abnormal mitoses became much less numerous, and the share of binuclear cells decreased Activity of NOR remained at the control level that much depended on the ability of WGA to prevent reduction in cytokinin content under cadmium stress

Increasing Triticum aestivum tolerance to cadmium stress through endophytic strains of Bacillus subtilis

Abstract: Impact of inoculation of wheat seeds with endophytic strains of B. subtilis bacterium on revealing cadmium phytotoxicity of the plants was investigated. It was shown that, in the presence of Cd in the plants whose seeds were inoculated with the above bacteria, the activities of catalase and peroxidase and the content of nonprotein thiols were increased, while an intensity of lipid peroxidation decreased. Moreover, inoculation of plant seeds with the bacteria contributed to lowering the metal content in plant shoots.