Regulation of tomato fruit pericarp development by an interplay between CDKB and CDKA1 cell cycle genes

Growth of tomato fruits is determined by cell division and cell expansion, which are tightly controlled by factors that drive the core cell cycle. The cyclin-dependent kinases (CDKs) and their interacting partners, the cyclins, play a key role in the progression of the cell cycle. In this study the role of CDKA1, CDKB1, and CDKB2 in fruit development was characterized by fruit-specific overexpression and down-regulation. CDKA1 is expressed in the pericarp throughout development, but is strongly up-regulated in the outer pericarp cell layers at the end of the growth period, when CDKB gene expression has ceased. Overexpression of the CDKB genes at later stages of development and the down-regulation of CDKA1 result in a very similar fruit phenotype, showing a reduction in the number of cell layers in the pericarp and alterations in the desiccation of the fruits. Expression studies revealed that CDKA1 is down-regulated by the expression of CDKB1/2 in CDKB1 and CDKB2 overexpression mutants, suggesting opposite roles for these types of CDK proteins in tomato pericarp development.     

The endogenous circadian pacemaker imparts a scale-invariant pattern of heart rate fluctuations across time scales spanning minutes to 24 hours

Heartbeat fluctuations in mammals display a robust temporal structure characterized by scale-invariant/fractal patterns. These scale-invariant patterns likely confer physiological advantage because they change with cardiovascular disease and these changes are associated with reduced survival. Models of physical systems imply that to produce scale-invariant patterns, factors influencing the system at different time scales must be coupled via a network of feedback interactions. A similar cardiac control network is hypothesized to be responsible for the scale-invariant pattern in heartbeat dynamics, although the essential network components have not been determined. Here is shown that scale-invariant cardiac control occurs across time scales from minutes to approximately 24 h, and that lesioning the mammalian circadian pacemaker (suprachiasmatic nucleus; SCN) completely abolishes the scale-invariant pattern at time scales>or approximately 4 h. At time scales相似文献   

Molecular sieves provoke multiple substitutions in the enzymatic synthesis of fructose oligosaccharide–lauryl esters

The cause of discrepancies in the literature regarding the specificity of immobilized Candida antarctica lipase B in the acylation of oligosaccharides was examined. Molecular sieves, generally used to control the water content during acylation reactions, turned out to have an important role in this. It was proven that molecular sieves alone can catalyze the acylation of fructose oligomers using vinyl laurate, leading to multiple substitution of the oligomers. This effect was the most profound at conditions unfavorable for the enzyme, because this resulted in a relatively high concentration of the chemically produced adducts. The enzyme alone catalyzed the formation of monosubstituted oligomers. It was proven that even solvent pre-drying by molecular sieves already causes the release of catalyzing compounds to the liquid, leading to subsequent catalysis. These findings should be taken into account when applying molecular sieves in this type of reactions in the future. Molecular sieves could, moreover, be used as a catalyst when multiple substitution is desired.     

The biological clock: the bodyguard of temporal homeostasis

In order for any organism to function properly, it is crucial that it be table to control the timing of its biological functions. An internal biological clock, located, in mammals, in the suprachiasmatic nucleus of the hypothalamus (SCN), therefore carefully guards this temporal homeostasis by delivering its message of time throughout the body. In view of the large variety of body functions (behavioral, physiological, and endocrine) as well as the large variety in their preferred time of main activity along the light:dark cycle, it seems logical to envision different means of time distribution by the SCN. In the present review, we propose that even though it presents a unimodal circadian rhythm of general electrical and metabolic activity, the SCN seems to use several sorts of output connections that are active at different times along the light: dark cycle to control the rhythmic expression of different body functions. Although the SCN is suggested to use diffusion of synchronizing factors in the rhythmic control of behavioral functions, it also needs neuronal connections for the control of endocrine functions. The distribution of the time-of-day message to neuroendocrine systems is either directly onto endocrine neurons or via intermediate neurons located in specific SCN targets. In addition, the SCN uses its connections with the autonomic nervous system for spreading its time-of-day message, either by setting the sensitivity of endocrine glands (i.e., thyroid, adrenal, ovary) or by directly controlling an endocrine output (i.e., melatonin synthesis). Moreover, the SCN seems to use different neurotransmitters released at different times along the light: dark cycle for each of the different connection types presented. Clearly, the temporal homeostasis of endocrine functions results from a diverse set of biological clock outputs.     

A putative consensus sequence for the nucleotide-binding site of annexin A6

Reaction-induced infrared difference spectroscopy (RIDS) has been used to investigate the nature of interactions of human annexin A6 (ANXA6) with nucleotides. RIDS results for ANXA6, obtained after the photorelease of GTP-gamma-S, ATP, or P(i) from the respective caged compounds, were identical, suggesting that the interactions between the nucleotide and ANXA6 were dominated by the phosphate groups. Phosphate-induced structural changes in ANXA6 were small and affected only seven or eight amino acid residues. The GTP fluorescent analogue, 2'(3')-O-(2,4,6-trinitrophenyl)guanosine 5'-triphosphate (TNP-GTP), quenched tryptophan fluorescence of ANXA6 when bound to the protein. A binding stoichiometry of 1 mol of nucleotide/mol ANXA6 was established with a K(D) value of 2.8 microM for TNP-GTP. The bands observed on RIDS of ANXA6 halves (e.g., N-terminal half, ANXA6a, and C-terminal half, ANXA6b) were similar to those of the whole molecule. However, their amplitudes were smaller by a factor of 2 compared to those of whole ANXA6. TNP-GTP bound to both fragments of ANXA6 with a stoichiometry of 0.5 mol/mol. However, the binding affinities of ANXA6a and ANXA6b differed from that of ANXA6. Simulated molecular modeling revealed a nucleotide-binding site which was distributed in two distinct domains. Residues K296, Y297, K598, and K644 of ANXA6 were less than 3 A from the bound phosphate groups of either GTP or ATP. The presence of two identical sequences in ANXA6 with the F-X-X-K-Y-D/E-K-S-L motif, located in the middle of ANXA6, at residues 293-301 (within ANXA6a) and at 641-649 (within ANXA6b), suggested that the F-X-X-K-Y-D/E-K-S-L motif was the putative sequence in ANXA6 for nucleotide binding.     

Is it possible to replace stimulus animals by scent-filled cups in the social discrimination test?

A study in which the rat social discrimination test was refined is described. This test measures social memory by using, in general, juvenile rats as stimulus animals. Rats are offered a first juvenile to investigate (learning trial), and after a specified interval, the rats are offered the same rat and a second juvenile rat to investigate again (retrieval trial). When the rats sniff the second juvenile in the retrieval trial more than the first, social memory for the second juvenile is said to be present. This test is mainly based on scents from the juvenile. Attempts were made to refine the test to reduce the number of animals used, to enhance the scope of the test, and to improve its validity. Firstly, the stimulus animals were replaced by the scent of juveniles, in the form of cups filled with sawdust taken from cages of juvenile rats. Similar results to those in the original test were obtained when using these scents. Furthermore, male and female scents were tested, and showed the same results as for the juvenile scents. Secondly, rats were also given two cups (one scent-filled and one filled with plain sawdust) in the learning trial, to determine which allowed a more-precise delineation of motivational, discriminatory and memory components. Overall, it is possible to replace stimulus animals by scent-filled cups in the social discrimination test, to enhance the scope of the test, and to draw more-valid conclusions with respect to social memory.     

Phytoseiid predators suppress populations of Bemisia tabaci on cucumber plants with alternative food

Phytoseiids are known to attack whiteflies, but it is an open question whether they can be used for biological control of these pest insects. Preselection experiments in the laboratory showed that two out of five phytoseiid species tested, Euseius scutalis and Typhlodromips swirskii, stood out in terms of their ability to develop and reproduce on a diet of Bemisia tabaci immatures. In this paper, we show that both predators are able to suppress whitefly populations on isolated cucumber plants in a greenhouse. Predatory mites were released 2 weeks in advance of the release of B. tabaci. To enable their survival and promote their population growth, they were provided weekly with alternative food, that is, Typha sp. pollen. A few weeks after whitefly introduction, the numbers of adult whiteflies on plants with predators were consistently lower than on plants without predators, where B. tabaci populations grew exponentially. After 9 weeks, this amounted to a 16- to 21-fold difference in adult whitefly population size. This shows that the two phytoseiid species are promising biocontrol agents of B. tabaci on greenhouse cucumber. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tackling speciose genera: species composition and phylogenetic position of Senecio sect. Jacobaea (Asteraceae) based onplastid and nrDNA sequences

The molecular phylogeny of Senecio sect. Jacobaea (Asteraceae; Senecioneae) was studied to clarify species composition and interspecific relationships of Senecio sect. Jacobaea. This information is necessary for studies seeking explanations of the evolutionary success of Senecio, in terms of high species numbers and the evolution of chemical defense mechanisms. Parsimony analyses with 60 species of the tribe Senecioneae, representing 23 genera and 11 sections of Senecio, based on DNA sequence data of the plastid genome (the trnT-L intergenic spacer, the trnL intron, and two parts of the trnK intron, flanking both sides of the matK gene) and nuclear genome (ITS1, 5.8S, and ITS2 gene and spacers) show that sect. Jacobaea is a strongly supported monophyletic group. Fifteen species have been identified as members of section Jacobaea, including three species that have been consistently ascribed to this section in taxonomic literature and 12 species that were either placed in other sections of Senecio or not exclusively ascribed to sect. Jacobaea. This section was traditionally circumscribed as a group of European, biennial, or perennial herbs with pinnately incised leaves, but the results of this study show that one annual species, a species from northeastern Asia, and a species growing in the Himalayas are members of sect. Jacobaea as well. Furthermore, not all species in the section have pinnately incised leaves. The genera Emilia, Packera, and Pseudogynoxys form the sister clade of sect. Jacobaea, but this relationship lacks strong bootstrap support and thus remains provisional.     

Effects of surfactant distribution and ventilation strategies on efficacy of exogenous surfactant

The effectsof both surfactant distribution patterns and ventilation strategiesutilized after surfactant administration were assessed in lung-injuredadult rabbits. Animals received 50 mg/kg surfactant via intratrachealinstillation in volumes of either 4 or 2 ml/kg. A subset ofanimals from each treatment group was euthanized for evaluation of theexogenous surfactant distribution. The remaining animals wererandomized into one of three ventilatory groups: group1 [tidal volume(VT) of 10 ml/kg with 5 cmH₂O positive end-expiratorypressure (PEEP)]; group 2 (VT of 5 ml/kg with 5 cmH₂O PEEP); orgroup 3 (VT of 5 ml/kg with 9 cmH₂O PEEP). Animals wereventilated and monitored for 3 h. Distribution of the surfactant wasmore uniform when it was delivered in the 4 ml/kg volume. When thedistribution of surfactant was less uniform, arterial PO₂ values were greater ingroups 2 and3 compared with group1. Oxygenation differences among the differentventilation strategies were less marked in animals with the moreuniform distribution pattern of surfactant (4 ml/kg). In bothsurfactant treatment groups, a high mortality was observed with theventilation strategy used for group 3.We conclude that the distribution of exogenous surfactant affects theresponse to different ventilatory strategies in this model of acutelung injury.