Volume 64, Nº 2 (2017)

Energy dynamics of isoprene biosynthesis and the mechanism of isoprene emission are discussed in view of their fundamental role in dissipativity of living cells. The significance of basic principles of colloidal chemistry for biological energy conversion is emphasized. The idea is put forward of the existence in living cells of the universal energy-dynamic structural unit, termed “biological micelle,” that accounts for the transport and distribution of protons over the cell volume. This unit is responsible for the creation and maintenance of physiological pH at any metabolically active site within the cell. Particular attention is paid to the involvement of F-type ATPase in the active proton transport from the thylakoid interior to the F1 domain of ATP-synthase and to recycling of protons from the outer cell surface to the thylakoid lumen due to H+-pumping activity of the thylakoid ATPase. The mechanism responsible for the outflow of entropy deS through the production of isoprene by protonation of dimethylallyl pyrophosphate (DMAPP) has been found. The stable steady-state condition of any thermodynamic system, including the living system, is correlated with the maximum entropy production. The rate of isoprene emission increases with temperature, which compensates for the decrease in outflow of thermal entropy deS. When the ambient temperature is increased, the sum of deS removed as heat and deS removed with isoprene emission remains constant. Thus, photobiosynthesis of isoprene is a special case of the entropy deS dissipation that provides a stable stationary state to the cell.

Changes in fatty acid composition of chloroplast membrane lipids were investigated using tobacco (Nicotiana tabacum L., cv. Samsun) plants subjected to cold hardening for 6 days at 8°C. Under optimal growing temperature (22°C), the lipids of thylakoid membranes were characterized by elevated content of 16:3n-3 and 18:3n-3 fatty acids (FA). Compared to the lipids of chloroplast envelope membranes, the thylakoid lipids were less rich in the content of saturated, mono- and diunsaturated FA. The relative content of unsaturated FA in chloroplast membranes increased substantially during cold hardening, which was mainly due to the accumulation of 18:3n-3 FA. It is concluded that the observed changes in FA composition of chloroplast lipids during cold hardening adjust the fluidity of these membranes to the level sufficient for functioning of tobacco photosynthetic apparatus, which is a prerequisite for accumulation of assimilates and allows the hardened tobacco plants to survive under conditions of hypothermia.

From the roots and root exudates of 3-week-old plants of alfalfa (Medicago sativa L.), anionic and cationic peroxidases differing in principal physicochemical and catalytic properties were isolated and purified. Main features of anionic peroxidases detected in the roots and root exudates were identical. Phenanthrene present in the soil used for alfalfa growing influenced the number of forms and activity of peroxidases in crude enzyme preparations but did not affect the properties of pure enzymes. In the presence of a synthetic mediator, purified peroxidases can oxidize phenanthrene and its derivatives, including potential microbial metabolites of polycyclic aromatic hydrocarbons (PAH). The fact that the enzymes excreted in root exudates in a purified form can oxidase PAH proves their participation in degradation of PAH and their microbial metabolites in alfalfa rhizosphere. These new data indicate that the processes of plant and microbial degradation of pollutants in the rhizosphere are coupled; they are relevant to understanding the molecular mechanisms of degradation of persistent pollutants by plant-microbial complexes.

Kinetics of superoxide anion generation by the isolated plasma membrane was determined by the rate of formazan formation from XTT in the presence of NADPH or NADH. The plasma membrane was prepared from (control) etiolated maize seedlings grown at 25°C and from (cooled) seedlings incubated at 6°C for the last day. Membrane vesicles from the control plants possessed superoxide-producing activity, and the rate of NADH oxidation was markedly higher than that of NADPH. The low-temperature incubation of the seedlings suppressed the NADPH-dependent activity, whereas the NADH-dependent one slightly increased. The solubilized by dodecyl maltoside (DDM) plasma membranes were separated into multiprotein complexes by high-resolution clear native electrophoresis (hrCN-PAGE). The aim was to find complexes exhibiting the superoxide-producing activity sensitive to inhibition by diphenylene iodonium. Several protein complexes from the plasma membrane capable of superoxide producion in the presence of NADPH or NADH were found. The maximum diphenylene iodonium-sensitive activity was found in the high-molecular weight complex, in which proteins reacting with antibodies against C-terminal peptide of phagocytic oxidase (gp91phox) were detectable. The activity of this complex was lower in the cooled than in the control seedlings and displayed higher affinity to NADPH than to NADH. To search for the cooling-induced changes in the polypeptide content of protein complexes, the two-dimensional difference gel electrophoresis (hrCN/SDS-PAGE) was used. Control and cooled samples, whose lysine had been labeled with fluorescent dyes Cy2 and Cy3, respectively, were separated by this method in one gel. Decrease in a temperature of plant growing affected the protein content of the complex so that some new proteins appeared and several polypeptides disappeared as compared with the control. There were no significant differences between the cooled and control counterparts in the content of proteins detectable with gp91phox antibodies. Therefore, the high-molecular complex containing NADPH oxidase looses proteins under low temperature that may decrease its superoxide-producing activity.

The effect of NO donor sodium nitroprusside (SNP) on salt resistance of 4-week-old Arabidopsis thaliana L. wild-type Columbia-0 (Col-0) plants and jin1 mutants defective in the jasmonate signaling have been investigated. As affected by 0.5 mM, SNP salt resistance of wild-type plants rose, which was exhibited in a smaller growth inhibition and preserving the pool of photosynthetic pigments after salt stress (200 mM NaCl). The positive effect of SNP leveled by treatment of plant with NO scavenger: 0.5 mM PTIO (2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide). However, SNP treatment had no significant effect on the salt tolerance of jin1 genotype plants. In the case of wild-type plants but not jin1 mutants, treatment by NO donor increased activity of antioxidant enzymes—superoxide dismutase, guaiacol peroxidase, and catalase—in the leaves, which was especially noticeable in salt stress conditions. In wild-type plants treated by NO donor, proline content in the leaves after salt stress was lower and sugar content was higher than that in the untreated ones. In jin1 mutants, NO donor treatment resulted in a significant increase in proline content in the leaves under salt stress, without changing sugar content. A conclusion was made on the participation of transcript factor JIN1/MYC2 in NO-dependent induction of some plant defense responses to salt stress.

Reactive oxygen species (ROS) play key roles in plants and are regulated by several ROS-scavenging enzymes. Ascorbate peroxidase (APX), which catalyzes the reduction of hydrogen peroxide to water, a vital part of ROS formation, plays a significant role in higher plants. In this study, a cytosolic APX gene from Populus tomentosa, named PcAPX, was identified and characterized. Recombinant PcAPX had a calculated mass of 33.24 kD and showed high activity towards ascorbic acid (ASA) and hydrogen peroxide (H₂O₂). Real-time PCR analysis showed that APX mRNA expression levels were higher in leaves than roots or stems of P. tomentosa. Compared with wild-type, transgenic tobacco plants overexpressing PcAPX showed no significant difference in morphology under normal conditions. However, the transgenic plants were more resistant to drought, salt and oxidative stress conditions, as shown by decreased levels of malondialdehyde and increased levels of chlorophyll. Moreover, decreased H₂O₂ levels, increased ASA consumption, an increase in the NADP to NADPH ratio, and higher APX activity in the transgenic plants suggested an increased ability to eliminate ROS. These data suggest that PcAPX overexpression in transgenic tobacco plants can enhance tolerance to drought, salt and oxidative stress. Therefore, APX has a crucial role in abiotic stress tolerance in plants.

In plants, organ size control is a fundamental process during development. The Arabidopsis ORGAN SIZE RELATED (OSR) gene family plays a key role in organ size regulation. To explore the roles of OSR orthologs in rice, a BLAST search in the rice genome was performed and five putative OSR orthologs were isolated and designated as OsOSR. Constitutive expression of OsOSR1, OsOSR2 and OsOSR4 in Arabidopsis resulted in enlarged organ sizes, as a consequence of enhanced cell number and cell size, while the increase of organ size in the OsOSR3 and OsOSR5-expressing plants was only due to cell enlargement. Our results suggest that the rice OsOSR genes possess the conserved organ growth-promoting function and may be involved in the coordination of cell proliferation and expansion during plant development.

This study aimed to investigate potential pathways associated with arbutin synthesis and potential synthetic routes to 6′-O-caffeoylarbutin (CA) in Vaccinium dunalianum Wight (Ericaceae) via de novo transcriptome sequencing. De novo transcriptome sequencing of leaf buds of V. dunalianum was performed. After quality control and transcriptome assembly, unigenes were predicted and their functions were annotated using Blast2GO. Furthermore, the coding sequences of unigenes were predicted based on NR, SWISS-PROT, KEGG and COG databases. Subsequently, pathways related to arbutin synthesis and potential synthetic routes to CA were analyzed based on KEGG and ExPASy databases. In total, 55537512 clean reads (11.7 G) were generated, and there were 4998376080 nt clean nucleotides. The majority of unigenes were related to the pathways of metabolism, such as carbohydrate and lipid metabolism. Besides, a set of enzymes were related to uridine diphosphate (UDP)-glucose synthesis (e.g. K01784) via some pathways, such as amino sugar and nucleotide sugar metabolism, starch and sucrose metabolism, etc. Some other enzymes were associated with hydroquinone synthesis (e.g. K15849) via tyrosine metabolism. Additionally, chlorogenic acid, caffeoyl-CoA and 1-O-hydroxycinnamoyl-β-D-glucose (HCA-Glc) were predicted to participate in CA synthesis as acyl donors. Some enzymes in pathways related to glycometabolism (e.g. K01784) and tyrosine metabolism (e.g. K15849) may participate in arbutin synthesis. Additionally, chlorogenic acid, caffeoyl-CoA and HCA-Glc may take part in CA synthesis.

MicroRNAs (miRNAs) play key roles in regulating Cd toxicity tolerance in plants. Solanum torvum Sw. is a typical low Cd-accumulating plant that has a high Cd tolerance. Despite its importance, no miRNA has been identified from S. torvum thus far. In this study, high-throughput sequencing of S. torvum small RNAs was used to identify miRNAs that were differentially expressed in response to Cd toxicity. At least 45 miRNA families and 165 individual members within those families were identified in both the control and Cd-treated S. torvum roots. Among these miRNAs, 45 miRNAs from 21 miRNA families were differentially expressed in the control and Cd-treated S. torvum plants. Among these 21 differentially expressed miRNA families, 6 miRNA families were upregulated in the Cd-treated roots, and 15 miRNA families were downregulated in Cd-treated roots. Bioinformatics analysis indicated that these miRNAs were involved in replication, recombination and repair, inorganic ion transport and metabolism, transcription, signal transduction mechanisms, cell cycle control, cell division, chromosome partitioning, RNA processing and modification in S. torvum roots. These results indicated that specific miRNAs are tightly regulated by Cd toxicity in the roots of S. torvum, which may play key roles in the Cd tolerance of S. torvum.