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.     

Mec1p associates with functionally compromised telomeres

In many organisms, telomere DNA consists of simple sequence repeat tracts that are required to protect the chromosome end. In the yeast Saccharomyces cerevisiae, tract maintenance requires two checkpoint kinases of the ATM family, Tel1p and Mec1p. Previous work has shown that Tel1p is recruited to functional telomeres with shorter repeat tracts to promote telomerase-mediated repeat addition, but the role of Mec1p is unknown. We found that Mec1p telomere association was detected as cells senesced when telomere function was compromised by extreme shortening due to either the loss of telomerase or the double-strand break binding protein Ku. Exonuclease I effects the removal of the 5' telomeric strand, and eliminating it prevented both senescence and Mec1p telomere association. Thus, in contrast to Tel1p, Mec1p associates with short, functionally compromised telomeres.     

Richness and diversity of sand flies (Diptera,Psychodidae) in an Atlantic rainforest reserve in southeastern Brazil

Our objective was to study and evaluate the richness and diversity of Phlebotominae fauna in the Duas Bocas Biological Reserve (DBBR) in the state of Espírito Santo, in southeastern Brazil. Sand fly collections were carried out during four consecutive nights each month between August 2007 and July 2008 at DBBR by using CDC automatic light traps and an illuminated Shannon trap. Specific richness (S) and Shannon diversity index (H) was calculated for each trap. We collected 18,868 sand flies belonging to 29 species and 13 genera. Nyssomyia yuilli yuilli was the most abundant species followed by Psychodopygus ayrozai, Ps. hirsutus, Psathyromyia pascalei, and Ps. matosi. We recorded Brumptomyia cardosoi, Br. troglodytes, and Ps. geniculatus for the first time in the state of Espírito Santo. We discuss the differences in diversity and richness of the sand flies in both traps and in relation to other Brazilian localities and biomes. We also discuss the possibility of wild transmission of Leishmania in the DBBR and the influence of the sand fly species in leishmaniasis transmission to the adjacent areas of the reserve.     

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.     

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.     

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.