Circadian Input Kinases and Their Homologs in Cyanobacteria: Evolutionary Constraints Versus Architectural Diversification

The circadian input kinase A (cikA) gene encodes a protein relaying environmental signal to the central circadian oscillator in cyanobacteria. The CikA protein has a variable architecture and usually consists of four tandemly arrayed domains: GAF, histidine kinase (HisKA), histidine kinase-like ATPase (HATPase_c), and a pseudo-receiver (REC). Among them, HisKA and HATPase_c are the least polymorphic, and REC is not present in heterocystic filamentous cyanobacteria. CikA contains several conserved motifs that are likely important for circadian function. There are at least three types of circadian systems, each of which possesses a different set of circadian genes. The originally described circadian system (kaiABC system) possesses both cikA and kaiA, while the others lack either only cikA (kaiABC ^Δ) or both (kaiBC). The results we obtained allowed us to approximate the time of the cikA origin to be about 2600–2200 MYA and the time of its loss in the species with the kaiABC ^Δ or kaiBC system between 1100 and 600 MYA. Circadian specialization of CikA, as opposed to its non-circadian homologs, is a result of several factors, including the unique conserved domain architecture and high evolutionary constraints of some domains and regions, which were previously identified as critical for the circadian function of the gene.     

Sucrose non‐fermenting kinase 1 (SnRK1) coordinates metabolic and hormonal signals during pea cotyledon growth and differentiation

Seed development passes through developmental phases such as cell division, differentiation and maturation: each have specific metabolic demands. The ubiquitous sucrose non‐fermenting‐like kinase (SnRK1) coordinates and adjusts physiological and metabolic demands with growth. In protoplast assays sucrose deprivation and hormone supplementation, such as with auxin and abscisic acid (ABA), stimulate SnRK1‐promoter activity. This indicates regulation by nutrients: hormonal crosstalk under conditions of nutrient demand and cell proliferation. SnRK1‐repressed pea (Pisum sativum) embryos show lower cytokinin levels and deregulation of cotyledonary establishment and growth, together with downregulated gene expression related to cell proliferation, meristem maintenance and differentiation, leaf formation, and polarity. This suggests that at early stages of seed development SnRK1 regulates coordinated cotyledon emergence and growth via cytokinin‐mediated auxin transport and/or distribution. Decreased ABA levels and reduced gene expression, involved in ABA‐mediated seed maturation and response to sugars, indicate that SnRK1 is required for ABA synthesis and/or signal transduction at an early stage. Metabolic profiling of SnRK1‐repressed embryos revealed lower levels of most organic and amino acids. In contrast, levels of sugars and glycolytic intermediates were higher or unchanged, indicating decreased carbon partitioning into subsequent pathways such as the tricarbonic acid cycle and amino acid biosynthesis. It is hypothesized that SnRK1 mediates the responses to sugar signals required for early cotyledon establishment and patterning. As a result, later maturation and storage activity are strongly impaired. Changes observed in SnRK1‐repressed pea seeds provide a framework for how SnRK1 communicates nutrient and hormonal signals from auxins, cytokinins and ABA to control metabolism and development.     

Temperature increase results in oxidative stress in goldfish tissues. 1. Indices of oxidative stress

Levels of lipid peroxides (LOOH), thiobarbituric-acid reactive substances (TBARS), protein carbonyls and low- and high-molecular weight thiols were measured in brain, liver, kidney, and white muscle of goldfish, Carassius auratus L., over 1-12 h of high temperature (35 degrees C) exposure followed by 4 or 24 h of lower (21 degrees C) temperature recovery. LOOH and TBARS contents increased during heat shock exposure with a maximal rise of 20-fold for liver TBARS, but both mainly reversed at recovery. Protein carbonyl content was unaffected by heat shock but rose in brain, liver, and kidney during recovery. Low-molecular weight thiol concentrations unexpectedly increased up to approximately 4-fold in brain, kidney and muscle under heat shock and remained high during recovery. Protein thiol contents also rose in liver and muscle during high temperature exposure by 2- and 3-fold, respectively, and decreased to control values or below in all tissues at late recovery. Low- and high-molecular weight thiol levels inversely correlated in liver (R2=0.87) suggesting that the former was used to reduce the latter over the experiment. It is concluded that the redox balance in goldfish tissues is strictly maintained probably contributing to the high tolerance of this species to heat shock.     

Proton-powered subunit rotation in single membrane-bound F0F1-ATP synthase

Synthesis of ATP from ADP and phosphate, catalyzed by F(0)F(1)-ATP synthases, is the most abundant physiological reaction in almost any cell. F(0)F(1)-ATP synthases are membrane-bound enzymes that use the energy derived from an electrochemical proton gradient for ATP formation. We incorporated double-labeled F(0)F(1)-ATP synthases from Escherichia coli into liposomes and measured single-molecule fluorescence resonance energy transfer (FRET) during ATP synthesis and hydrolysis. The gamma subunit rotates stepwise during proton transport-powered ATP synthesis, showing three distinct distances to the b subunits in repeating sequences. The average durations of these steps correspond to catalytic turnover times upon ATP synthesis as well as ATP hydrolysis. The direction of rotation during ATP synthesis is opposite to that of ATP hydrolysis.     

Environmental impact on age-related dynamics of karyotypical instability in plants

The dynamics of karyotypical instability of Allium fistulosum L. (Welsh onion) during aging of genetically homogenous seeds from plants grown in three different areas was studied. We analyzed the frequency of anaphase cells with chromosomal aberrations "damage", as a number of chromosomal aberrations per cell with aberrations, and germinating capacity, as an indicator of the 'toxic' influence of age. The seeds' aging was accompanied by an increase in karyotypical instability (increasing frequency of anaphases with aberrations) and with certain changes in the spectrum of chromosome aberrations. The clearest distinctions between old and young seeds were found for the frequency of anaphase cells with chromosome aberrations. The general level of karyotypical instability positively correlates with the age of the seeds. The regression coefficient (b) corresponds to the general tendency of karyotypical instability during seeds' senescence under storage. For 'good' (A), 'normal' (B) and 'bad' (C) conditions, the coefficients (b's) are b(A)=0.22, b(B)=0.46 and b(C)=0.84 (p<0.05 for C, and p<0.001 for A and B). It was found that different ecological conditions of plant vegetation strongly influence age-related dynamics of chromosomal instability in the seeds obtained from these plants. Possible mechanisms of the transgenerational impact of this effect are discussed.     

Modulation of dual fluorescence in a 3-hydroxyquinolone dye by perturbation of its intramolecular proton transfer with solvent polarity and basicity.

A representative of a new class of dyes with dual fluorescence due to an excited state intramolecular proton transfer (ESIPT) reaction, namely 1-methyl-2-(4-methoxy)phenyl-3-hydroxy-4(1H)-quinolone (QMOM), has been studied in a series of solvents covering a large range of polarity and basicity. A linear dependence of the logarithm of its two bands intensity ratio, log(I(N*)/I(T*)), upon the solvent polarity expressed as a function of the dielectric constant, (epsilon- 1)/(2epsilon + 1), is observed for a series of protic solvents. A linear dependence for log(I(N*)/I(T*)) is also found in aprotic solvents after taking into account the solvent basicity. In contrast, the positions of the absorption and the two emission bands of QMOM do not noticeably depend on the solvent polarity and basicity, indicating relatively small changes in the transition moment of QMOM upon excitation and emission. Time-resolved experiments in acetonitrile, ethyl acetate and dimethylformamide suggest an irreversible ESIPT reaction for this dye. According to the time-resolved data, an increase of solvent basicity results in a dramatic decrease of the ESIPT rate constant, probably due to the disruption of the intramolecular H-bond of the dye by the basic solvent. Due to this new sensor property, 3-hydroxyquinolones are promising candidates for the development of a new generation of environment-sensitive fluorescence dyes for probing interactions of biomolecules.