Tagesschwankungen der UV-Strahlenresistenz beiAllium cepa L.

Zusammenfassung Die UV-Resistenz von Zwiebelschuppen-Epidermen vonAllium cepa zeigt einen circadianen Rhythmus mit 2 Maxima (etwa um 12 und um 24 Uhr) und 2 Minima (zwischen 18 und 21 Uhr bzw. zwischen 3 und 6 Uhr). Zur Zeit hoher bzw. geringer Strahlenempfindlichkeit mit gleichen Dosen bestrahlte Epidermen zeigen verschiedene Öberlebenskurven, die am 19. Tag nach der Bestrahlung auf 10% bzw. 40% überlebender Zellen absinken. Beziehungen zwischen den Tagesschwankungen der Strahlenresistenz, Tagesschwankungen verschiedener Plasmazustände und Tagesschwankungen der Kerngröße werden diskutiert.

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The circadian rhythm of UV-resistance ofAllium cepa L.

Summary UV-resistance ofAllium cepa scale epidermis cells shows a circadian rhythm with two maxima (at about 12 hours and 24 hours) and two minima (between 18–21 hours and 3–6 hours). 19 days after irradiation, about 10% of the cells irradiated during the maximal sensitivity period are alive, whereas about 40% survive in preparations irradiated during the period of maximal resistance. Correlations between diurnal changes in radiation resistance, different plasmatic properties, and diurnal changes in nuclear size are discussed.

     

Seasonal changes in stomatal responses of sweet cherry and plum to water status in detached leaves

Seasonal changes in the relationship between stomatal responses and water potential components in detached leaves of sweet cherry ( Prunus avium L. cv. Bigarreau Morreau) and plum ( Prunus domestica L. cv. Queen Victoria) were examined by the simultaneous measurement of stomatal conductance and water relation parameters derived from pressure-volume curves. The water potential threshold for stomatal closure in sweet cherry leaves throughout the season and in plum leaves until mid-July varied nearly in parallel with changes in the osmotic potential at the turgor loss point. From August onward, closing reactions of plum stomata had no relationship to the turgor loss point. Stomata of sweet cherry leaves opened more widely and showed slower reactions to dehydration early in the season than later. Seasonal changes of stomatal conductance and stomatal responses to dehydration in both species seem thus to be influenced by fruit development and ripening.     

Stk33 is required for spermatid differentiation and male fertility in mice

Spermiogenesis is the final phase during sperm cell development in which round spermatids undergo dramatic morphological changes to generate spermatozoa. Here we report that the serine/threonine kinase Stk33 is essential for the differentiation of round spermatids into functional sperm cells and male fertility. Constitutive Stk33 deletion in mice results in severely malformed and immotile spermatozoa that are particularly characterized by disordered structural tail elements. Stk33 expression first appears in primary spermatocytes, and targeted deletion of Stk33 in these cells recapitulates the defects observed in constitutive knockout mice, confirming a germ cell-intrinsic function. Stk33 protein resides in the cytoplasm and partially co-localizes with the caudal end of the manchette, a transient structure that guides tail elongation, in elongating spermatids, and loss of Stk33 leads to the appearance of a tight, straight and elongated manchette. Together, these results identify Stk33 as an essential regulator of spermatid differentiation and male fertility.     

Real-time definition of non-randomness in the distribution of genomic events

Features such as mutations or structural characteristics can be non-randomly or non-uniformly distributed within a genome. So far, computer simulations were required for statistical inferences on the distribution of sequence motifs. Here, we show that these analyses are possible using an analytical, mathematical approach. For the assessment of non-randomness, our calculations only require information including genome size, number of (sampled) sequence motifs and distance parameters. We have developed computer programs evaluating our analytical formulas for the real-time determination of expected values and p-values. This approach permits a flexible cluster definition that can be applied to most effectively identify non-random or non-uniform sequence motif distribution. As an example, we show the effectivity and reliability of our mathematical approach in clinical retroviral vector integration site distribution.     

Dynamics of seedling growth acclimation towards altered light conditions can be quantified via GROWSCREEN: a setup and procedure designed for rapid optical phenotyping of different plant species

Using a novel setup, we assessed how fast growth of Nicotiana tabacum seedlings responds to alterations in the light regime and investigated whether starch-free mutants of Arabidopsis thaliana show decreased growth potential at an early developmental stage. Leaf area and relative growth rate were measured based on pictures from a camera automatically placed above an array of 120 seedlings. Detection of total seedling leaf area was performed via global segmentation of colour images for preset thresholds of the parameters hue, saturation and value. Dynamic acclimation of relative growth rate towards altered light conditions occurred within 1 d in N. tabacum exposed to high nutrient availability, but not in plants exposed to low nutrient availability. Increased leaf area was correlated with an increase in shoot fresh and dry weight as well as root growth in N. tabacum. Relative growth rate was shown to be a more appropriate parameter than leaf area for detection of dynamic growth acclimation. Clear differences in leaf growth activity were also observed for A. thaliana. As growth responses are generally most flexible in early developmental stages, the procedure described here is an important step towards standardized protocols for rapid detection of the effects of changes in internal (genetic) and external (environmental) parameters regulating plant growth.     

Chronic PYY3-36 treatment promotes fat oxidation and ameliorates insulin resistance in C57BL6 mice

PYY(3-36) is a gut-derived hormone acting on hypothalamic nuclei to inhibit food intake. We recently showed that PYY(3-36) acutely reinforces insulin action on glucose disposal in mice. We aimed to evaluate effects of PYY(3-36) on energy metabolism and the impact of chronic PYY(3-36) treatment on insulin sensitivity. Mice received a single injection of PYY(3-36) or were injected once daily for 7 days, and energy metabolism was subsequently measured in a metabolic cage. Furthermore, the effects of chronic PYY(3-36) administration (continuous and intermittent) on glucose turnover were determined during a hyperinsulinemic-euglycemic clamp. PYY(3-36) inhibited cumulative food intake for 30 min of refeeding after an overnight fast (0.29 +/- 0.04 vs. 0.56 +/- 0.12 g, P = 0.036) in an acute setting, but not after 7 days of daily dosing. Body weight, total energy expenditure, and physical activity were not affected by PYY(3-36). However, it significantly decreased the respiratory quotient. Both continuous and intermittent PYY(3-36) treatment significantly enhanced insulin-mediated whole body glucose disposal compared with vehicle treatment (81.2 +/- 6.2 vs. 77.1 +/- 5.2 vs. 63.4 +/- 5.5 micromol.min(-1).kg(-1), respectively). In particular, PYY(3-36) treatment increased glucose uptake in adipose tissue, whereas its impact on glucose disposal in muscle did not attain statistical significance. PYY(3-36) treatment shifts the balance of fuel use in favor of fatty acids and enhances insulin sensitivity in mice, where it particularly promotes insulin-mediated glucose disposal. Notably, these metabolic effects of PYY(3-36) remain unabated after chronic administration, in contrast to its anorexic effects.     

Oral glucose intake inhibits hypothalamic neuronal activity more effectively than glucose infusion

We previously showed that hypothalamic neuronal activity, as measured by the blood oxygen level-dependent (BOLD) functional MRI signal, declines in response to oral glucose intake. To further explore the mechanism driving changes in hypothalamic neuronal activity in response to an oral glucose load, we here compare hypothalamic BOLD signal changes subsequent to an oral vs. an intravenous (iv) glucose challenge in healthy humans. Seven healthy, normal-weight men received four interventions in random order after an overnight fast: 1) ingestion of glucose solution (75 g in 300 ml) or 2) water (300 ml), and 3) iv infusion of 40% glucose solution (0.5 g/kg body wt, maximum 35 g) or 4) infusion of saline (0.9% NaCl, equal volume). The BOLD signal was recorded as of 8 min prior to intervention (baseline) until 30 min after. Glucose infusion was associated with a modest and transient signal decline in the hypothalamus. In contrast, glucose ingestion was followed by a profound and persistent signal decrease despite the fact that plasma glucose levels were almost threefold lower than in response to iv administration. Accordingly, glucose ingestion tended to suppress hunger more than iv infusion (P < 0.1). We infer that neural and endocrine signals emanating from the gastrointestinal tract are critical for the hypothalamic response to nutrient ingestion.     

Catheter based simultaneous mapping of cardiac activation and motion: a review

Heart failure as a result of a variety of cardiac diseases is an ever growing, challenging condition that demands profound insight in the electrical and mechanical state of the myocardium. Assessment of cardiac function has largely relied on evaluation of cardiac motion by multiple imaging techniques. In recent years electrical properties have gained attention as heart failure could be improved by biventricular resynchronization therapy. In contrast to early belief, QRS widening as a result of left bundle branch block could not be identified as a surrogate for asynchronous contraction. The combined analysis of electrical and mechanical function is yet a largely experimental approach. Several mapping system are principally capable for this analysis, the most prominent being the NOGA-XP system. Electromechanical maps have concentrated on the local shortening of the reconstructed endocardial surface from end-diastole to end-systole. Temporal analysis of motion propagation, however, is a new aspect. The fundamental principles of percutaneous catheter based activation and motion assessment are reviewed. Related experimental setups are presented and their main findings discussed.