Characterization of a Saccharomyces cerevisiae NADP(H)-dependent alcohol dehydrogenase (ADHVII), a member of the cinnamyl alcohol dehydrogenase family.

A new NADP(H)-dependent alcohol dehydrogenase (the YCR105W gene product, ADHVII) has been identified in Saccharomyces cerevisiae. The enzyme has been purified to homogeneity and found to be a homodimer of 40 kDa subunits and a pI of 6.2-6.4. ADHVII shows a broad substrate specificity similar to the recently characterized ADHVI (64% identity), although they show some differences in kinetic properties. ADHVI and ADHVII are the only members of the cinnamyl alcohol dehydrogenase family in yeast. Simultaneous deletion of ADH6 and ADH7 was not lethal for the yeast. Both enzymes could participate in the synthesis of fusel alcohols, ligninolysis and NADP(H) homeostasis.     

Zinc complexes of 6-methyl-2-pyridinecarboxylic acid. Crystal structure of [Zn(MeC5H3NCOO)2(H2O)] · H2O

Reaction of Zn(AcO)₂ · 2H₂O with 6-methyl-2-pyridinecarboxylic acid (L) yielded a new compound [Zn(MeC₅H₃NCOO)₂(H₂O)] · H₂O. This complex was characterised by elemental analyses, conductivity measurements, infrared, ¹H and ¹³C{¹H} NMR spectroscopies and single-crystal X-ray diffraction. The crystal structure consists of discrete molecules involving a pentacoordinated Zn atom with a geometry intermediate between a trigonal bipyramid and a square pyramid and with the two N_py atoms occupying the apical sites. Treatment of the complex [Zn(MeC₅H₃NCOO)₂(H₂O)] · H₂O with 2,2^′-bipyridine (bpy) produced [Zn(MeC₅H₃NCOO)₂(bpy)]. The metallic atom in this complex displays a distorted octahedral geometry and is coordinated to two ligands (L) via the pyridine nitrogen and the carbonyl oxygen atoms and to one 2,2^′-bypyridine (bpy).     

Novel Approaches to Study Climate Change Effects on Terrestrial Ecosystems in the Field: Drought and Passive Nighttime Warming

This article describes new approaches for manipulation of temperature and water input in the field. Nighttime warming was created by reflection of infrared radiation. Automatically operated reflective curtains covered the vegetation at night to reduce heat loss to the atmosphere. This approach mimicked the way climate change, caused by increased cloudiness and increased greenhouse gas emissions, alters the heat balance of ecosystems. Drought conditions were created by automatically covering the vegetation with transparent curtains during rain events over a 2–5-month period. The experimental approach has been evaluated at four European sites across a climate gradient. All sites were dominated (more than 50%) by shrubs of the ericaceous family. Within each site, replicated 4-m × 5-m plots were established for control, warming, and drought treatments and the effect on climate variables recorded. Results over a two-year period indicate that the warming treatment was successful in achieving an increase of the minimum temperatures by 0.4–1.2°C in the air and soil. The drought treatment resulted in a soil moisture reduction of 33%–82% at the peak of the drought. The data presented demonstrate that the approach minimizes unintended artifacts with respect to water balance, moisture conditions, and light, while causing a small but significant reduction in wind speed by the curtains. Temperature measurements demonstrated that the edge effects associated with the treatments were small. Our method provides a valuable tool for investigating the effects of climate change in remote locations with minimal artifacts.     

Effects of the Argentine ant Linepithema humile on seed dispersal and seedling emergence of Rhamnus alaternus

We studied influence of the Argentine ant's Linepithema humile occurrence on seed dispersal of Rhamnus alaternus (Rhamnaceae). Rhamnus alaternus is a fleshy fruit plant dispersed primarily by birds; the seeds have an elaiosome attractive to ants. The observations were made in two study plots of Mediterranean cork-oak forests (one invaded and the other not invaded by L. humile ) over two years. For R. alaternus , presence of L. humile was associated with of the following: reduction of seed transport to ant nests (80.2% of seed offered were removed in non-invaded vs 7.1% in invaded area), a shorter seed dispersal distance (mean=90.2 cm in non-invaded vs 1.1 cm in invaded area), increase in seed retention time on the soil surface (median time in non-invaded was 50 vs 209.2 min in invaded area) and increased vulnerability to predation. In addition there was lower probability of seedling emergence, due to little elaiosome removal from the seeds (82.0% of emergence for seeds without elaiosome and 57.3% for seeds with elaiosome). These results, similar to findings obtained in South African fynbos, confirm that the Argentine ant invasion can strongly affect ecosystem processes in the Mediterranean biome.     

Ecophysiological responses of two Mediterranean shrubs, Erica multiflora and Globularia alypum, to experimentally drier and warmer conditions

A new approach was used to experimentally dry and warm a Mediterranean shrubland. By means of automatically sliding curtains, the drought period was extended by excluding rain over the two growing seasons (spring and autumn), and passive warming was created by avoiding infra‐red dissipation at night over the whole year. The aim of the study was to test how a future extended drought period and an increase in temperatures could affect the photosynthetic and water use strategies of two co‐occurring Mediterranean shrubs, Erica multiflora and Globularia alypum, which are common species of the dry coastal shrublands. The shoot water potential, leaf gas exchange rates and chlorophyll a fluorescence of plants was monitored seasonally during two years (1999–2001). In addition we measured the photosynthetic response curves to light and CO₂ in autumn 2001 and the foliar N concentration and leaf C and N stable isotopes in summer 1999 and 2000. Droughted plants of both shrub species showed lower shoot water potentials, transpiration rates and stomatal conductances than control plants, although there was a high seasonal variability. Drought treatment reduced significantly the overall leaf net photosynthetic rates of E. multiflora, but not of G. alypum. Droughted plants of E. multiflora also showed lower leaf net photosynthetic rates in response to light and CO₂ and lower carboxylation efficiency than controls, but there was no significant effect of drought on its overall photosystem II (PSII) photochemical efficiency. Although warming treatment did not affect the leaf net photosynthetic rates of the two species overall the study, it increased significantly the carboxylation efficiency and leaf net photosynthetic rates of G. alypum plants in response to CO₂ levels in autumn 2001. In addition, warming treatment increased the potential photochemical efficiency of PSII (F_v/F_m) of both species (but especially of G. alypum) at predawn or midday and mainly in autumn and winter. Thus, the results suggest that drier conditions might decrease the annual productivity of these Mediterranean shrubs, particularly of E. multiflora, and that future warming could alleviate the present low temperature constraints of the photosynthetic performance of the two studied species, but especially of G. alypum, during the colder seasons. Ultimately, drier and warmer conditions in the near future may change the competitive relationship among these species in such Mediterranean ecosystems.     

What controls the length of noncoding DNA?

Several recent studies of genome evolution indicate that the rate of DNA loss exceeds that of DNA gain, leading to an underlying mutational pressure towards collapsing the length of noncoding DNA. That such a collapse is not observed suggests opposing mechanisms favoring longer noncoding regions. The presence of transposable elements alone also does not explain observed features of noncoding DNA. At present, a multidisciplinary approach--using population genetics techniques, large-scale genomic analyses, and in silico evolution--is beginning to provide new and valuable insights into the forces that shape the length of noncoding DNA and, ultimately, genome size. Recombination, in a broad sense, might be the missing key parameter for understanding the observed variation in length of noncoding DNA in eukaryotes.     

Altitudinal differences in UV absorbance,UV reflectance and related morphological traits of Quercus ilex and Rhododendron ferrugineum in the Mediterranean region

We studied the variations in different physiological parameters associated with UV-B radiation defense: UV-B radiation absorbance, UV-visible spectral reflectance, carotenoids concentration, leaf thickness, SLW (specific leaf weigth) and trichome density in Quercus ilex growing at 200 and 1200 m and Rhododendron ferrugineum growing at 2200 m. We examined the role of these parameters as protection mechanisms in an altitudinal gradient of increasing UV radiation in northern Catalonia and in sun and shade leaves. The concentration of UV-B radiation absorbing pigments was 15% higher in sun leaves of Q. ilex at 1200 m than in those from 200 m altitude. Sun leaves of R. ferrugineum presented concentrations three times higher than those of Q. ilex. Reflectance ranged between 5% (in the region 300–400 nm) and 12% (in the region 280–300 nm). The variation of reflectance with altitude followed an inverse trend respect to absorbance in the 280–300 nm region, with higher values the lower the altitude, but in the 300–400 nm region, reflectance of the lower site was the lowest. In both species and altitudes sun leaves presented higher concentrations of UV-B radiation absorbing pigments and UV reflectance than shade leaves. Quercus ilex trees of the higher location presented higher NDPI (Normalized Difference Pigment Reflectance Index) values, indicating higher carotenoids/chlorophyll a ratio. Actual measurements of carotenoid/chlorophyll a ratio confirmed this pattern. The photochemical reflectance index (PRI) presented higher values the higher the location indicating lower photosynthetic radiation-use efficiency. Specific leaf weight (SLW) and leaf thickness were larger in Q. ilex trees of higher location than in those of lower location. In both sites, sun leaves also presented larger SLW values than shade leaves. Adaxial leaf hair density in sun leaves was significantlly higher in the lower location. UV absorption and linked morphological traits (SLW, leaf thickness measured in Q. ilex) presented the larger differences among studied plants at different altitudes and seem to be the dominant UV protecting mechanisms.