Isolation and sequence analysis of mutations inCEN5 DNA of yeast

We used a positive selection scheme involving a minichromosome maintenance mutantmcm2 to isolate mutations in centromeric DNA of the yeastSaccharomyces cerevisiae. Two mutations inCEN5 DNA were isolated. One of these mutations is a change from C:G to T: A at the 14th base pair of the CDEIII box, while the second is a complete deletion of all the CDE elements of this centromere. This work underscores the importance of the 14th base pair of CDEIII inCEN5 function.     

Respiration rhythms and heartbeats of diapausing Colorado potato beetles, Leptinotarsa decemlineata, at low temperatures

Discontinuous gas exchange cycles (DGCs), active muscular ventilation, microcycles of repetitive openings, and heartbeats of diapausing adult Colorado potato beetle, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), were studied at low temperatures (0, 5, and 10 °C) using an electrolytic respirometer combined with an infrared actograph. The DGC of the adult constriction-flutter-open type was the main respiration mode in fully quiescent beetles at temperatures from 5 to 10 °C. The CO₂ bursts were actively ventilated at temperatures above 5 °C. During the flutter period, a series of microcycles appeared, but no muscular contractions associated with the microcycles were detected. We identified this respiration mode as discontinuous suction ventilation.
The hydration condition of the beetles did not influence the frequency of the gas exchange cycles, but dehydrated beetles showed significantly longer flutter periods and shorter ventilation periods than hydrated beetles. The heartbeat frequencies were influenced by both temperature and hydration status.
We conclude from the results that DGCs are used at rest in adult L. decemlineata under various environmental conditions and also at low temperatures. Our results showed that DGCs are the main respiration mode of resting adult Colorado potato beetle irrespective of its hydration state and temperature. Our method resolves O₂ uptake and subsequent CO₂ release in flutter and ventilation periods and shows that diffusion is replaced by convection to reduce water loss in adult beetles.     

Maintenance of larval color polymorphism in Orgyia antiqua (Lepidoptera: Lymantriidae): evaluating the role of thermal adaptation

Intraspecific color polymorphism is widespread in insects, and various mechanisms have been proposed to explain its maintenance. Some explanations rely on the effect of body color on the organism's thermal physiology. Darker individuals accumulate solar energy more efficiently, and therefore, dark body coloration in insects is frequently presumed to be an adaptation to low temperature conditions. However, it is largely unclear what is the importance of the thermal biology in comparison to other potential selective forces on body coloration. In this study, we evaluated the role of temperature as a potential selective factor maintaining color polymorphism in aposematic larvae of the moth Orgyia antiqua L. It was found that darker, and thus less aposematic, larvae accumulated solar energy more efficiently. However, in a set of laboratory and outdoor experiments, we found no evidence of temperature-dependent performance of different color morphs or in development of different morphs induced by rearing temperature. We conclude that the effects related to thermal physiology are not likely important determinants of optimal coloration in O. antiqua. The reasons may lie in high mobility of the larvae, which allows for effective behavioral thermoregulation, which is also shown in this study. Our results caution against an uncritical extrapolation of results obtained for model organisms and indicate the need for giving more attention to the species-specific ecological background in ecophysiological studies.     

Droughts,hydraulic redistribution,and their impact on vegetation composition in the Amazon forest

Hydraulic redistribution (HR), the nocturnal transport of moisture by plant roots from wetter to drier portions of the root zone, in general can buffer plants against seasonal water deficits. However, its role in longer droughts and its long-term ecological impact are not well understood. Based on numerical model experiments for the Amazon forest, this modeling study indicates that the impact of HR on plant growth differs between droughts of different time scales. While HR increases transpiration and plant growth during regular dry seasons, it reduces dry season transpiration and net primary productivity (NPP) under extreme droughts such as those during El Niño years in the Amazon forest. This occurs because, in places where soil water storage is not able to sustain the ecosystem through the dry season, the HR-induced acceleration of moisture depletion in the early stage of the dry season reduces water availability for the rest of the dry season and causes soil moisture to reach the wilting point earlier. This gets exacerbated during extreme droughts, which jeopardizes the growth of trees that are not in dry season dormancy, i.e., evergreen trees. As a result, the combination of drought and HR increases the percentage of drought deciduous trees at the expense of evergreen trees, and the fractional coverage of forest canopy is characterized by sudden drops following extreme droughts and slow recovery afterwards. The shift of the tropical forest towards more drought deciduous trees as a result of the combined effects of extreme drought and HR has important implications for how vegetation will respond to future climate changes.     

ESKIMO1 disruption in Arabidopsis alters vascular tissue and impairs water transport

Water economy in agricultural practices is an issue that is being addressed through studies aimed at understanding both plant water-use efficiency (WUE), i.e. biomass produced per water consumed, and responses to water shortage. In the model species Arabidopsis thaliana, the ESKIMO1 (ESK1) gene has been described as involved in freezing, cold and salt tolerance as well as in water economy: esk1 mutants have very low evapo-transpiration rates and high water-use efficiency. In order to establish ESK1 function, detailed characterization of esk1 mutants has been carried out. The stress hormone ABA (abscisic acid) was present at high levels in esk1 compared to wild type, nevertheless, the weak water loss of esk1 was independent of stomata closure through ABA biosynthesis, as combining mutant in this pathway with esk1 led to additive phenotypes. Measurement of root hydraulic conductivity suggests that the esk1 vegetative apparatus suffers water deficit due to a defect in water transport. ESK1 promoter-driven reporter gene expression was observed in xylem and fibers, the vascular tissue responsible for the transport of water and mineral nutrients from the soil to the shoots, via the roots. Moreover, in cross sections of hypocotyls, roots and stems, esk1 xylem vessels were collapsed. Finally, using Fourier-Transform Infrared (FTIR) spectroscopy, severe chemical modifications of xylem cell wall composition were highlighted in the esk1 mutants. Taken together our findings show that ESK1 is necessary for the production of functional xylem vessels, through its implication in the laying down of secondary cell wall components.     

Tel1p preferentially associates with short telomeres to stimulate their elongation

In many organisms, telomeric DNA consists of long tracts of short repeats. Shorter tracts are preferentially lengthened by telomerase, suggesting a conserved mechanism that recognizes and elongates short telomeres. Tel1p, an ATM family checkpoint kinase, plays an important role in telomere elongation, as cells lacking Tel1p have short telomeres and show reduced recruitment of telomerase components to telomeres. We show that Tel1p association increased as telomeres shortened in vivo in the presence or absence of telomerase and that Tel1p preferentially associated with the shortest telomeres. Tel1p association was independent of Tel1p kinase activity and enhanced by Mre11p. Tel1p overexpression simultaneously stimulated telomerase-mediated elongation and Tel1p association with all telomeres. Thus, Tel1p preferentially associates with the shortest telomeres and stimulates their elongation by telomerase.     

Morphology and monoaminergic modulation of Crustacean Hyperglycemic Hormone-like immunoreactive neurons in the lobster nervous system

Neuronal somata located near branch points in the second thoracic nerve roots of the lobster are immunoreactive for Crustacean Hyperglycemic Hormone (CHH)-like peptides, a family of putative stress hormones. We have employed intracellular dye injection, immunostaining, and confocal imaging to observe the anatomy of these root neurons, which are morphologically diverse and dye coupled. Some root neurons contribute to neurosecretory structures at the points of exit of the root from the nerve cord. Other CNS-projecting root neurons send projections into the T5-A1 interganglionic connectives. Neurosecretory elements of the serotonin (5HT) and octopamine (OCT) systems, implicated in postural control and aggression, terminate densely in the vicinity of the second thoracic root neurons. We have confirmed by double immunostaining for 5HT and CHH-like peptides that the endings of the 5HT neurons are in close apposition to root neurons in the superficial regions of the root. We have also extended previous studies documenting electrophysiological responses of the root neurons to 5HT or OCT. Bath-applied 5HT and OCT inhibit the spontaneous bursting activity of root neurons at concentrations higher than 100 nM. The root neurons desensitize to the persistent presence of high concentrations of 5HT, but not OCT, in the bath. Nanomolar concentrations of OCT, but not 5HT have an excitatory effect on the spontaneous bursting activity of root neurons. This region of the lobster nervous system is of continuing interest, as identified neurons of three neuromodulatory systems implicated in stress and aggression converge and interact at the level of identified neurons.