Biogenesis of chlorophyll-binding proteins under iron stress in <Emphasis Type="Italic">Synechocystis</Emphasis> sp. PCC 6803

The biogenesis of chlorophyll-binding proteins under iron stress has been investigated in vivo in a chlN deletion mutant of Synechocystis sp. PCC 6803. The chlN gene encodes one subunit of the light-independent protochlorophyllide reductase. The mutant is unable to synthesize chlorophyll in darkness, causing chlorophyll biosynthesis to become light dependent. When the mutant was propagated in darkness, essentially no chlorophyll and photosystems were detected. Upon return of the chlN deletion mutant to light, 77 K fluorescence emission spectra and oxygen evolution of greening cells under iron-sufficient or-deficient conditions were measured. The gradual blue shift of the photosystem I (PS I) peak upon greening under iron stress suggested the structural alteration of newly synthesized PS I. Furthermore, the rate of biogenesis of PS II was delayed under iron stress, which might be due to the presence of IsiA.     

Kinetic modeling of electron transfer reactions in photosystem I complexes of various structures with substituted quinone acceptors

The reduction kinetics of the photo-oxidized primary electron donor P₇₀₀ in photosystem I (PS I) complexes from cyanobacteria Synechocystis sp. PCC 6803 were analyzed within the kinetic model, which considers electron transfer (ET) reactions between P₇₀₀, secondary quinone acceptor A₁, iron-sulfur clusters and external electron donor and acceptors – methylviologen (MV), 2,3-dichloro-naphthoquinone (Cl₂NQ) and oxygen. PS I complexes containing various quinones in the A₁-binding site (phylloquinone PhQ, plastoquinone-9 PQ and Cl₂NQ) as well as F _X-core complexes, depleted of terminal iron–sulfur F _A/F _B clusters, were studied. The acceleration of charge recombination in F _X-core complexes by PhQ/PQ substitution indicates that backward ET from the iron–sulfur clusters involves quinone in the A₁-binding site. The kinetic parameters of ET reactions were obtained by global fitting of the P₇₀₀ ⁺ reduction with the kinetic model. The free energy gap ΔG ₀ between F _X and F _A/F _B clusters was estimated as ?130 meV. The driving force of ET from A₁ to F _X was determined as ?50 and ?220 meV for PhQ in the A and B cofactor branches, respectively. For PQ in A_1A-site, this reaction was found to be endergonic (ΔG ₀?=?+75 meV). The interaction of PS I with external acceptors was quantitatively described in terms of Michaelis–Menten kinetics. The second-order rate constants of ET from F _A/F _B, F _X and Cl₂NQ in the A₁-site of PS I to external acceptors were estimated. The side production of superoxide radical in the A₁-site by oxygen reduction via the Mehler reaction might comprise ≥0.3% of the total electron flow in PS I.     

Mutational spectrum of the gene for 21-hydroxylase in the patients with congenital adrenal hyperplasia from Bashkortostan

Molecular genetic analysis of congenital adrenal hyperplasia (CAH) was carried out in 59 patients from the Republic of Baskortostan, which belonged to two main groups. The first group was represented by 35 patients with salt wasting form of the disease, and the second group was comprised of 24 patients with simple virilizing form. Analysis of the CYP21A2 gene in the patients with congenital adrenal hyperplasia from the Republic of Bashkortostan revealed seven different mutations on 81.58% chromosomes, including deletion/conversion delA2 or LGC gene, R356W, I2splice, I172N, Q318X, V281L, and P30L. The mutations were present on 89.71% of chromosomes from the patients with salt wasting form, and in 69.5% of chromosomes from the patients with simple virilizing form. The most frequent mutation was gene deletion/conversion, delA2 or LGC, which was found with the frequency of 30.83%. In six CAH patients the presence of three different mutation clusters on one chromosome was demonstrated: Q318X + R356W, I172N + Q318X, and delA2 or LGC + V281L. For the mutations leading to partial loss of 21-hydroxylase activity and simple virilizing form, 100% conformity of the phenotype to genotype was established.     

Interaction of various types of photosystem I complexes with exogenous electron acceptors

Interaction of photosystem I (PS I) complexes from cyanobacteria Synechocystis sp. PCC 6803 containing various quinones in the A₁-site (phylloquinone PhQ in the wild-type strain (WT), and plastoquinone PQ or 2,3-dichloronaphthoquinone Cl ₂ NQ in the menB deletion strain) and different numbers of Fe₄S₄ clusters (intact WT and F_X-core complexes depleted of F_A/F_B centers) with external acceptors has been studied. The efficiency of interaction was estimated by measuring the light-induced absorption changes at 820 nm due to the reduction of the special pair of chlorophylls (P₇₀₀ ⁺) by an external acceptor(s). It was shown that externally added Cl ₂ NQ is able to effectively accept electrons from the terminal iron-sulfur clusters of PS I. Moreover, the efficiency of Cl ₂ NQ as external acceptor was higher than the efficiency of the commonly used artificial electron acceptor, methylviologen (MV) for both the intact WT PS I and for the F_X-core complexes. The comparison of the efficiency of MV interaction with different types of PS I complexes revealed gradual decrease in the following order: intact WT?>?menB?>?F_X-core. The effect of MV on the recombination kinetics in menB complexes of PS I with Cl ₂ NQ in the A₁-site differed significantly from all other PS I samples. The obtained effects are considered in terms of kinetic efficiency of electron acceptors in relation to thermodynamic and structural characteristics of PS I complexes.     

Photoinhibition of photosystem I in <Emphasis Type="Italic">Nephrolepis falciformis</Emphasis> depends on reactive oxygen species generated in the chloroplast stroma

We studied how high light causes photoinhibition of photosystem I (PSI) in the shade-demanding fern Nephrolepis falciformis, in an attempt to understand the mechanism of PSI photoinhibition under natural field conditions. Intact leaves were treated with constant high light and fluctuating light. Detached leaves were treated with constant high light in the presence and absence of methyl viologen (MV). Chlorophyll fluorescence and P700 signal were determined to estimate photoinhibition. PSI was highly oxidized under high light before treatments. N. falciformis showed significantly stronger photoinhibition of PSI and PSII under constant high light than fluctuating light. These results suggest that high levels of P700 oxidation ratio cannot prevent PSI photoinhibition under high light in N. falciformis. Furthermore, photoinhibition of PSI in N. falciformis was largely accelerated in the presence of MV that promotes the production of superoxide anion radicals in the chloroplast stroma by accepting electrons from PSI. From these results, we propose that photoinhibition of PSI in N. falciformis is mainly caused by superoxide radicals generated in the chloroplast stroma, which is different from the mechanism of PSI photoinhibition in Arabidopsis thaliana and spinach. Here, we provide some new insights into the PSI photoinhibition under natural field conditions.     

Salinity induced changes in the chloroplast proteome of the aquatic pteridophyte <Emphasis Type="Italic">Azolla microphylla</Emphasis>

The growth of the nitrogen fixing aquatic pteridophyte Azolla microphylla is severely affected by salinity. Salinity exposure (0.5%) resulted in significant reduction in chlorophyll a and b content, altered chl a/b ratio and photosynthetic efficiency (Fv/Fm). Chloroplasts maintain photosynthesis but are highly sensitive to salinity stress. Chloroplast proteins extracted from A. microphylla was separated by two-dimensional electrophoresis (2DE) and approximately 200 proteins were observed on each gel. Forty two differentially expressed protein spots were detected and out of this 17 could be identified through MALDI-TOF-MS/MS analysis. Out of the 17 identified proteins, 15 were found to be down regulated and 2 proteins were up regulated. Most of the down regulated proteins were associated with Calvin cycle, ATP synthesis, oxygen evolution, photosystem I and ROS scavenging. The results show changes in proteome dynamics of the chloroplasts of A. microphylla and such changes may lead to reduction in growth and metabolism. The primary target of salinity in A. microphylla is photosynthesis and the changes in the proteome dynamics of the chloroplasts lead to reduced growth.     

Glutathione reductase gene expression depends on chloroplast signals in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Glutathione reductase (EC 1.6.4.2) is one of the main antioxidant enzymes of the plant cell. In Arabidopsis thaliana, glutathione reductase is encoded by two genes: the gr1 gene encodes the cytosolic-peroxisomal form, and the gr2 gene encodes the chloroplast-mitochondrial form. Little is known about the regulation of expression of plant glutathione reductase genes. In the present work, we have demonstrated that gr2 (but not gr1) gene expression in Arabidopsis leaves changes depending on changes in redox state of the photosynthetic electron transport chain. Expression of both the gr1 and gr2 genes was induced by reactive oxygen species. In heterotrophic suspension cell culture of Arabidopsis, expression of both studied genes did not depend on H₂O₂ level or on changes in the redox state of the mitochondrial electron transport chain. Our data indicate that chloroplasts are involved in the regulation of the glutathione reductase gene expression in Arabidopsis.     

Nutrient allocation and photochemical responses of <Emphasis Type="Italic">Populus</Emphasis> × <Emphasis Type="Italic">canadensis</Emphasis> ‘Neva’ to nitrogen fertilization and exogenous <Emphasis Type="Italic">Rhizophagus irregularis</Emphasis> inoculation

Arbuscular mycorrhizal fungi (AMF) can promote plant growth performance, but their effectiveness varies depending on soil nitrogen (N) availability. To clarify the effectiveness of exogenous AMF along an N-fertilization gradient (0, 2, 10, 20, and 30 mM), the impacts of exogenous Rhizophagus irregularis and N on the growth, photochemical activity, and nutritional status of Populus?×?canadensis ‘Neva’ in natural soil were evaluated in a pot experiment. The results showed that the 10 mM N level was the optimal fertilization regime with the highest promotion effect on plant growth and the maximum quantum yield of photosystem II (PSII) (F_v/F_m). Excess N (20 and 30 mM) fertilization reduced the actual quantum yield of PSII (ФPSII) and the F_v/F_m of the plants. Regardless of the N availability, inoculated plants exhibited greater F_v/F_m values than did non-inoculated plants. The biomass of inoculated plants was significantly higher compared with the control under low N levels (0 and 2 mM). Under high N levels, inoculated plants showed significant increases in ФPSII. Moreover, the nutrient imbalance of plants inoculated with exogenous R. irregularis was eased by increasing P, Fe, Mn and Cu uptake in roots and higher P, Ca, Mg, Fe, Mn and Zn concentrations in leaves. Moreover, the F_v/F_m and ФPSII exhibited positive correlations with P, Ca, Mg and Zn concentrations in leaves. In conclusion, inoculation with exogenous R. irregularis can benefit plant fitness by improving the photochemical capacity and nutrient composition of poplar under different N levels.     

The involvement of TsFtsH8 in <Emphasis Type="Italic">Thellungiella salsuginea</Emphasis> tolerance to cold and high light stresses

Thellungiella salsuginea is a plant that commonly grows in harsh environments of salinity and low temperature. Although the molecular mechanism underlying salt tolerance in T. salsuginea has been extensively explored, our understanding of how this species tolerates cold stress is limited. In a previous study, Wong et al. (2006) identified a cold-inducible TsFtsH8 gene in T. salsuginea. Based on the role of AtFtsH in D1 protein turnover and in maintaining the normal function of photosystem II, we hypothesized that TsFtsH8 might be related to cold tolerance in T. salsuginea. In the present study, RNAi lines of TsFtsH8 were generated and its tolerance to cold was evaluated. The results showed that in early spring, TsFtsH8-RNAi lines underwent leaf variegation, severe chlorophyll decomposition, organelle deterioration, decrease in the maximum photochemical efficiency of photosystem II (F _v /F _m) and in the proportion of open photosystem II reaction centers (qP), and incomplete degradation of the 23 kDa fragment of the D1 protein. These findings suggest that TsFtsH8 is involved in the development of T. salsuginea in the early spring.     

Overexpression of plastidic maize NADP-malate dehydrogenase (<Emphasis Type="Italic">ZmNADP-MDH</Emphasis>) in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> confers tolerance to salt stress

The plastidic C4 Zea mays NADP-malate dehydrogenase (ZmNADP-MDH), responsible for catalysis of oxaloacetate to malate, was overexpressed in Arabidopsis thaliana to assess its impact on photosynthesis and tolerance to salinity stress. Different transgenic lines were produced having ~3–6-fold higher MDH protein abundance and NADP-MDH enzyme activity than vector control. The overexpressors had similar chlorophyll, carotenoid, and protein content as that of vector control. Their photosynthetic electron transport rates, carbon assimilation rate, and consequently fresh weight and dry weight were almost similar. However, these overexpressors were tolerant to salt stress (150 mM NaCl). In saline environment, the Fv/Fm ratio, yield of photosystem II, chlorophyll, and protein content were higher in ZmNADP-MDH overexpressor than vector control. Under identical conditions, the generation of reactive oxygen species (H₂O₂) and production of malondialdehyde, a membrane lipid peroxidation product, were lower in overexpressors. In stress environment, the structural distortion of granal organization and swelling of thylakoids were less pronounced in ZmNADP-MDH overexpressing plants as compared to the vector control. Chloroplastic NADP-MDH in consort with cytosolic and mitochondrial NAD-MDH plays an important role in exporting reducing power (NADPH) and exchange of metabolites between different cellular compartments that maintain the redox homeostasis of the cell via malate valve present in chloroplast envelope membrane. The tolerance of NADP-MDH overexpressors to salt stress could be due to operation of an efficient malate valve that plays a major role in maintaining the cellular redox environment.     

Effects of ALA on Photosynthesis,Antioxidant Enzyme Activity,and Gene Expression,and Regulation of Proline Accumulation in Tomato Seedlings Under NaCl Stress

This study examined the effects of 5-aminolevulinic acid (ALA) application on photosynthesis, activity and gene expression of key antioxidant enzymes, and on proline accumulation in tomato (Lycopersicon esculentum Mill. ‘Hezuo 903’) seedlings under NaCl stress. NaCl stress significantly decreased the net photosynthetic rates and inhibited the activity of photosystem II, whereas exogenous ALA application significantly restored the net photosynthetic rates, quantum yield of electron transport, and energy conversion efficiency of photosystem II of tomato under NaCl stress. Production of superoxide, hydrogen peroxide, and malondialdehyde strongly increased in response to NaCl stress, and these increases were significantly counteracted by ALA. ALA increased the activity of reactive oxygen species (ROS) scavenging antioxidant enzymes, including superoxide dismutase, catalase, ascorbate peroxidase, and peroxidase, and upregulated the expression of SOD, APX, and POD, genes that encode these enzymes in NaCl-treated plants. ALA simultaneously increased proline accumulation in tomato seedlings under NaCl stress by regulating the expression of genes that encode ALA biosynthetic enzymes and that control proline biosynthesis and metabolism, for example, expression of GluRS and GluTR was downregulated, accompanied by a significant increase in the expression of P5CS and decline in the expression of ProDH. ALA provided protection against NaCl stress by increasing photosynthetic capacity, regulating antioxidant enzyme gene expression and proline accumulation, and decreasing ROS accumulation and lipid peroxidation in tomato.     

Heat and hypoxia give a global invader, <Emphasis Type="Italic">Gambusia holbrooki,</Emphasis> the edge over a threatened endemic fish on Australian floodplains

Deciphering the mechanisms by which climate change interacts with invasive species to affect biodiversity is a major challenge of global change biology. We conducted experiments to determine whether the global invader, Gambusia holbrooki, was more resistant to high water temperature (heat) and low dissolved oxygen (hypoxia) than a threatened native fish, Nannoperca australis. Metabolic experiments conducted at 25 and 29 °C showed that G. holbrooki had at least four times the capacity for metabolic depression during hypoxia than N. australis. An increase in environmental temperature from 25 to 29 °C had no significant impact on the critical oxygen tension, P _crit, of G. holbrooki, but significantly and strongly increased P _crit of N. australis. Gambusia holbrooki also had a lower Q ₁₀ of standard metabolic rate than N. australis. Our results indicate that G. holbrooki have physiological traits conferring greater resistance to hypoxia than N. australis, and as temperature increases, the resistance of N. australis to hypoxia was more eroded than that of G. holbrooki. Intensive monitoring of the temperature and dissolved oxygen dynamics of wetlands showed that contemporary heat waves are already causing conditions that might give G. holbrooki the edge over N. australis on Australian floodplains. Our study adds weight to recent anecdotal reports of drought and heat waves causing localised extinction of N. australis, but the proliferation of G. holbrooki.     

Nitrogen-induced variations in leaf gas exchange of spring triticale under field conditions

Nitrogen (N) is the key factor limiting photosynthetic processes and crop yield. Little is known about the response of leaf gas exchange of spring triticale (Triticosecale Wittm.) to N supply. The effect of N fertilizers on different gas exchange variables, i.e., photosynthetic rate (A), transpiration rate (E), stomatal conductance (g _s), instantaneous water use efficiency (WUE) and maximum quantum yield of photosystem II (PSII) (F _v/F _m), chlorophyll index (SPAD, soil–plant analysis development), and the relationship of these variables with yield were studied in spring triticale grown under field conditions. Six treatments of N—0, 90, 180, 90 + 30, 90 + 30 + 30 kg ha^?1 (applied as ammonium nitrate, AN) and one treatment of N 90 + 30 + 30 kg ha^?1 (applied as urea ammonium nitrate solution, UAN) were compared. The analysis of variance showed that throughout the triticale growing season, N fertilization had significant effects on A, WUE, g _s and SPAD. On average, N fertilizer application increased A values by 14–70%. E and F _v/F _m values were not influenced by N fertilization levels. The effect of growth stage and year on gas exchange variables and F _v/F _m and SPAD was found to be significant. At different growth stages, A values varied and maximum ones were reached at BBCH 31–33 (decimal code system of growth stages) and BBCH 59. With aging, values of A decreased independently of N fertilization level. The gas exchange variables were equally affected by both fertilizer forms. The interplay among grain yield, leaf gas exchange variables, F _v/F _m and SPAD of spring triticale was estimated. The statistical analysis showed that grain yield positively and significantly correlated with A and SPAD values throughout the growing season.     

Regional-scale patterns of δ<Superscript>13</Superscript>C and δ<Superscript>15</Superscript>N associated with multiple ecosystem functions along an aridity gradient in grassland ecosystems

Background and aims

Nitrogen (N) deficiency and drought are two key limiting factors for rice production worldwide, but the relationship of drought stress with N homeostasis in rice is rarely advanced. The aim of this study was to dissect the physiological effects of drought stress on rice growth that coupled unbalanced N metabolism.

Results

Water-deficient stress (WD) limited stomatal aperture function and activity of Rubisco carboxylase to photosynthesis. The rate of total electron transport (J_t) and the electron to carboxylation (J_c) were considerably decreased, whereas the proportion of e^? flow to photorespiration was stimulated by WD, especially at 1600 μmol m^?2 s^?1 PPFD. Concurrently, the expressions of glycolate oxidase genes (GOX1, GOX5) and glycine decarboxylase complex (GDCH, GDCP and GDCT) were significantly induced in leaves of WD treatment, which led to the accumulation of reactive oxygen species in leaves. With the photosynthetic change, nitrate uptake and reduction were suppressed. Moreover, the enhanced photorespiration generated excess NH₃ accumulation in leaves and stimulated the expressions of GS1;1, GS1;2 and GS2, which were tightly coupled with the expressions of PEPC1 and PEPC2 under WD stress.

Conclusions

Our results suggest that the inhibited nitrate reduction associated with diminished electron transport rate, and the photorespiration-associated accumulation of hydrogen peroxide and NH₃ were critical in the drought-induced rice growth inhibition.

     

Physiological and biochemical responses of photomorphogenic tomato mutants (cv. Micro-Tom) under water withholding

In addition to mediating photomorphogenesis, phytochromes are responsible for many abiotic stress responses, acting upon biochemical and molecular mechanisms of cell signaling. In this work, we measured the physiological and biochemical responses of phytochrome-mutant plants under water stress. In tomato (Solanum lycopersicum L.), the aurea mutant (au) is phytochrome-deficient and the high-pigment-1 mutant (hp1) has exaggerated light responses. We examined the effects of water withholding on water potential, leaf gas exchange, chlorophyll fluorescence, chloroplast pigment content and antioxidant enzyme activity in au and hp1 and their wild-type cultivar Micro-Tom (MT). Initial fluorescence and potential quantum efficiency of photosystem II (PSII) photochemistry were not affected by the treatment, but effective quantum yield of PSII, electron transport rate decreased and non-photochemical quenching increased significantly in MT. Under water withholding conditions, MT had higher malondialdehyde concentration than the mutants, but au had higher activities of catalase and ascorbate peroxidase compared to the other genotypes. The tolerance of mutants to the effects of water withholding may be explained by the higher activity of antioxidant enzymes in au and by a higher concentration of antioxidant compounds, such as carotenoids, in hp1.     

Behavior of sex chromosomes at early meiosis stages in three wood mice species of the genus <Emphasis Type="Italic">Apodemus</Emphasis> (Rodentia,Muridae)

The prophase of the first meiotic division was studied in field mice of the species Apodemus (Sylvaemus) flavicollis, A. (S.) ponticus, and A. (S.) uralensis by light and electron microscopy. The karyotypes of three species were described on the base of electron microscopy of synaptonemal complexes in spermatocytes I. The axial elements of the sex chromosomes at early-middle pachytene synapse along the major portion of the Y axis; at late pachytene-early diplotene, the synapsis region shrinks; and at diakinesis-metaphase I, X and Y chromosomes associate end-to-end in all species studied. The behavior of sex chromosomes in the synapsis in the species studied was quite uniform. The results are discussed in the context of earlier data on the behavior of sex chromosomes in various rodent species in meiosis prophase I and their banding.     

Diagnoses of and illustrated key to the species of <Emphasis Type="Italic">Ixodes</Emphasis> Latreille, 1795 (Acari: Ixodidae) from Brazil

The current Brazilian Ixodes fauna is composed of the following eight species: I. amarali Fonseca, 1935; I. aragaoi Fonseca, 1935; I. auritulus Neumann, 1904; I. fuscipes Koch, 1844; I. loricatus Neumann, 1899; I. luciae Sénevet, 1940; I. paranaensis Barros-Battesti, Arzua, Pichorim &; Keirans, 2003; and I. schulzei Aragão &; Fonseca, 1951. Further studies are needed to establish the taxonomic status of I. serrafreirei Amorim, Gazeta, Bossi &; Linhares, 2003, a recently proposed species based solely on the nymphal stage. We present an up-to-date key to adults of the currently valid Brazilian species of Ixodes based on scanning electron microscopy. The relationships between Brazilian and other Neotropical Ixodes are also discussed.     

Distribution of representatives of the genus <Emphasis Type="Italic">Neoabbottiella</Emphasis> (Rhodophyta: Halymeniales) in the Russian Far Eastern Seas and taxonomic status of <Emphasis Type="Italic">N. valentinae</Emphasis> N. Klochkova et Pisareva, 2013

The new information on distribution of the red algae Neoabbottiella in the Russian Far East changes the concept of the areal of these algae and their preferred temperatures. A comparison of N. valentinae N. Klochkova et Pisareva with Schizymenia dubyi f. palmata Yamada collected by Y. Yamada from Urup Island and stored with its type and paratypes in the collection of Hokkaido University Museum (Sapporo, Japan) showed their conspecificity. Based on the data, N. valentinae was recognized as a synonym of Schizymenia dubyi f. palmata. Since this form does not possess the main generic feature of the genus Schizymenia and at the same time has well-expressed generic features of Neoabbottiella, the form S. dubyi f. palmata is transferred to this genus with the name N. palmata (Yamada) N. Klochkova et Pisareva.     

Photoreduction and Photophosphorylation with Tris-Washed Chloroplasts

The artificial electron donor compounds p-phenylenediamine (PD), N, N, N′, N′-tetramethyl-p-phenylenediamine (TMPD), and 2,6-dichlorophenol-indophenol (DCPIP) restored the Hill reaction and photophosphorylation in chloroplasts that had been inhibited by washing with 0.8 m tris (hydroxymethyl) aminomethane (tris) buffer, pH 8.0. The tris-wash treatment inhibited the electron transport chain between water and photosystem II and electron donation occurred between the site of inhibition and photosystem II. Photoreduction of nicotinamide adenine dinucleotide phosphate (NADP) supported by 33 μm PD plus 330 μm ascorbate was largely inhibited by 1 μm 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) while that supported by 33 μm TMPD or DCPIP plus ascorbate was relatively insensitive to DCMU. Experiments with the tris-washed chloroplasts indicated that electron donors preferentially donate electrons to photosystem II but in the presence of DCMU the donors (with the exception of PD at low concentrations) could also supply electrons after the DCMU block. The PD-supported photoreduction of NADP showed the relative inefficiency in far-red light characteristic of chloroplast reactions requiring photosystem II. With phosphorylating systems involving electron donors at low concentrations (33 μm donor plus 330 μm ascorbate) photophosphorylation, which occurred with P/e₂ ratios approaching unity, was completely inhibited by DCMU but with higher concentrations of the donor systems, photophosphorylation was only partially inhibited.     

Drug resistance mutations and susceptibility phenotypes of <Emphasis Type="Italic">Neisseria gonorrhoeae</Emphasis> isolates in Russia

Steady growth in the degree of antimicrobial resistance in Neisseria gonorrhoeae calls for the control of the spreading of resistance mutations. Here we present the data describing drug resistance mutations, the results of antimicrobial susceptibility tests, and molecular genotypes of 128 recent N. gonorrhoeae isolates collected across 9 regions of the Russian Federation. The mutations in chromosome genes penA, ponA, rpsJ, gyrA, parC, which determine the susceptibility of N. gonorrhoeae to penicillins, tetracyclines, and fluoroquinolones were detected by multiplex amplification followed by hybridization on a hydrogel microarray. The most frequent mutation was an insertion of an aspartate at position 345 of penA gene (76.6%), whereas mutations Leu421Pro in ponA gene, Val57Met in rpsJ gene, Ser91Phe in gyrA gene, Asp95Gly in gyrA gene, and Ser87Arg in parC gene were detected in 32.8–36.7% of strains. One third of studied N. gonorrhoeae isolates harbored multiple drug resistance mutations in bacterial chromosome, resulting in the bimodal distribution of mutation profiles and related patterns of antimicrobial susceptibility. The spread of multiple resistance could be explained by the vertical transfer of the mutations resulting in the clonality of the N. gonorrhoeae population.