Selection of Arabidopsis cDNAs that partially correct phenotypes of Escherichia coli DNA-damage-sensitive mutants and analysis of two plant cDNAs that appear to express UV-specific dark repari activities

To resist terrestrial UV radiation, plants employ DNA-damage-repair/toleration (DRT) activities, as well as shielding mechanisms. Little is known about the structure and regulation of plant DRT genes. We isolated DRT cDNAs from Arabidopsis thaliana, by selecting for complementation of Escherichia coli mutants lacking all bacterial defenses against UV-light damage to DNA. These mutants are phenotypically deficient in recombinational and mutagenic toleration (RecA^–), excision repair (Uvr^–) and photoreactivation toreactivation (Phr^–). Among 840 survivors of heavily UV-irradiated (10^–7 survival) mutants harboring plasmids derived from an Arabidopsis cDNA library in the vector YES, we identified four unique plant cDNAs, designated DRT100, DRT101, DRT102, and DRT103. Drt101 and Drt102 activity were specific for UV-light damage, and complemented both UvrB^– and UvrC^– phenotypes in the dark. Apparent Uvr^– correction efficiencies were 1 to 40% for Drt101, and 0.2 to 15% for Drt102, depending on the UV fluence. Drt101 and Drt102 showed no extensive amino-acid homology with any known DNA-repair proteins. Drt100 appeared to correct RecA^–, rather than Uvr^–, phenotypes. Although the light dependence of Drt103 activity was consistent with its identification as a photoreactivating enzyme, its predicted amino-acid sequence did not resemble known photolyase sequences. The N-terminal coding sequence of Drt101 suggests that it is targeted to chloroplasts, as reported for Drt100. These cDNAs afforded only modest increases in survival during the original selection procedure. The fact that they were readily isolated nevertheless suggests that selections may be made powerful enough to overcome barriers to expression and function in bacteria, at least for cDNAs of reasonable abundance.     

Investigation of the polymorphic ScaI site by a PCR-based assay at the human atrial natriuretic peptides (hANP) gene locus

The ScaI polymorphic site within the stop codon of the human atrial natriuretic peptides (hANP) gene was investigated in Mauritian Indian, black African and French Caucasian populations. A distinct distribution pattern is observed in these three populations.     

Thiosulfate, polythionates and elemental sulfur assimilation and reduction in the bacterial world

Among sulfur compounds, thiosulfate and polythionates are present at least transiently in many environments. These compounds have a similar chemical structure and their metabolism appears closely related. They are commonly used as energy sources for photoautotrophic or chemolithotrophic microorganisms, but their assimilation has been seldom studied and their importance in bacterial physiology is not well understood. Almost all bacterial strains are able to cleave these compounds since they possess thiosulfate sulfur transferase, thiosulfate reductase or S-sulfocysteine synthase activities. However, the role of these enzymes in the assimilation of thiosulfate or polythionates has not always been clearly established. Elemental sulfur is, on the contrary, very common in the environment. It is an energy source for sulfur-reducing eubacteria and archaebacteria and many sulfur-oxidizing archaebacteria. A phenomenon still not well understood is the 'excessive assimilatory sulfur metabolism' as observed in methanogens which perform a sulfur reduction which exceeds their anabolic needs without any apparent benefit. In heterotrophs, assimilation of elemental sulfur is seldom described and it is uncertain whether this process actually has a physiological significance. Thus, reduction of thiosulfate and elemental sulfur is a common but incompletely understood feature among bacteria. These activities could give bacteria a selective advantage, but further investigations are needed to clarify this possibility. Presence of thiosulfate, polythionates and sulfur reductase activities does not imply obligatorily that these activities play a role in thiosulfate, polythionates or sulfur assimilation as these compounds could be merely intermediates in bacterial metabolism. The possibility also exists that the assimilation of these sulfur compounds is just a side effect of an enzymatic activity with a completely different function. As long as these questions remain unanswered, our understanding of sulfur and thiosulfate metabolism will remain incomplete.     

Influence of soil,plant and meteorological factors on water relations and yield inHevea brasiliensis

Influence of factors governing the soil-plantatmosphere system on components of water relations and yield was studied in two clones of rubber tree,Hevea brasiliensis, viz. RRII 105 and RRII 118. Clonal variations were evident in yield and yield components and associated physiological parameters in response to soil moisture status and meteorological factors. Observations made during different seasons indicatedvariations in yield are attributed to differences in plugging index and initial flow rates, to the major yield components and also variations in components of water relations as influenced by meteorological factors. Among the two clones, RRII 105 was found to be fairly drought tolerant compared to RRII 118. RRII 105 was found to respond well to dry weather through higher stomatal resistances, higher leaf water potentials, lowered transpirational water loss and lower relative transpiration ratios, while RRII 118 was susceptible to stress situations.     

Factors influencing the upper temperature tolerances of three mussel species in a brackish water canal: size, season and laboratory protocols

Mussels are the most problematic organisms encountered in the water intake systems of electrical power plants. Various fouling control measures are adopted, among which heat treatment is considered the relatively more attractive from economic and ecological points of view. Thermal tolerance experiments were carried out to determine the effects of mussel size (2-20 mm shell length), season (breeding vs non-breeding), nutritional status (fed vs non-fed), acclimation temperature (5-25 degrees C) and acclimation salinity (1-35%o) on the mortality pattern of three important mussel species, viz. a freshwater mussel Dreissena polymorpha, a brackish water mussel Mytilopsis leucophaeata and a marine mussel Mytilus edulis under different temperatures (36-41 degrees C). The mussels in the 10 mm size group exposed to 36 degrees C showed 100% mortality after 38 min (D. polymorpha), 84 min (M. edulis) and 213 min (M. leucophaeata). The effect of mussel size on M. edulis and M. leucophaeata mortality at different temperatures was significant, with the largest size group of mussels showing greater resistance, while no significant size-dependence was observed in the case of D. polymorpha. All the three mussel species collected during the non-breeding season (June-October). Nutritional status had no significant influence on the thermal tolerance of the three mussels; fed and non-fed mussels showed 100% mortality at comparable rates. Acclimation temperature had a significant effect on the mortality of all three species. Survival time at any given target temperature increased with increasing acclimation temperature. The acclimation salinity showed no significant effect on the thermal tolerance of the three mussel species. In comparison, M. leucophaeata was more tolerant to high temperature stress than the other two species. The present studies clearly show that various factors can influence the mortality of D. polymorpha, M. edulis and M. leucophaeata to elevated temperatures. The results, therefore, suggest that if heat treatment were to be used as a control measure for these mussels, it has to be employed judiciously, depending on the mussel species, mussel size, breeding season, water temperature and salinity.     

A structural pathway for signaling in the E46Q mutant of photoactive yellow protein

In the bacterial photoreceptor photoactive yellow protein (PYP), absorption of blue light by its chromophore leads to a conformational change in the protein associated with differential signaling activity, as it executes a reversible photocycle. Time-resolved Laue crystallography allows structural snapshots (as short as 150 ps) of high crystallographic resolution (approximately 1.6 A) to be taken of a protein as it functions. Here, we analyze by singular value decomposition a comprehensive time-resolved crystallographic data set of the E46Q mutant of PYP throughout the photocycle spanning 10 ns-100 ms. We identify and refine the structures of five distinct intermediates and provide a plausible chemical kinetic mechanism for their inter conversion. A clear structural progression is visible in these intermediates, in which a signal generated at the chromophore propagates through a distinct structural pathway of conserved residues and results in structural changes near the N terminus, over 20 A distant from the chromophore.     

Metabolism of Indole-3-acetaldehyde

Infiltration of indolcacelaldehyde (IAAId) into living tissues of sonic lower and higher plants gives rise simultaneously to both indoleacetic acid (IAA) and Iryptophol (T-ol). But on a molar basis, there is no correlation between the products indicating a disimitation. Expressed juice of Avena coleoptiles by itself, exhibits only IAA forming activity. Approximately two moles of IAAld are consumed for each mole of IAA formed at pH 4.5, but only if necessary corrections are made for losses of substrate and products. Addition of reduced NAD or NADP readily induces tryptophol formation. But even at pH 4.5, adding reduced NADP causes greater tryptophol formation, leading to a marked divergence in the acid-alcohol ratio. Varying the pH in the presence of reduced coenzymes also alters the ratio, with alcohol formation predominating. NAD and NADP have no influence on the formation of IAA from IAAld by the whole cytoplasm of Avena coleoptiles. Whole cytoplasm of Asparagus shoots forms both IAA and tryptophol from IAAld, but in widely varying amounts, devoid of any suggestive stoichiometry between the products. With the acetone powder of Avena coleoptiles including the first leaf, data indicating an apparent disimitation of IAAld are obtainable only at pH 4.5. On altering the pH however, unequal amounts of the two products, namely IAA and tryptophol, are formed and hence a different ratio results. Acetone powders of wheat coleoptiles and Asparagus shoots do not yield data supporting disimitation either at pH 4.5 or 7.2. IAA formation in Avena is aerobic while tryptophol formation is seemingly independent of oxygen supply. The former activity is selectively abolished by 10^?3M dithionite while the latter activity suffers a similar suppression in the presence of 10^?3M manganese sulphate. Varying the IAAld concentration results in unequal amounts of the two products, revealing the dissimilar affinity of the two activities for the common substrate Saturation to a level of 30 percent with ammonium sulphate throws out most of the acid-forming activity whereas the alcohol-forming system appears mostly in the protein fraction precipitated between 30 and 40 percent saturation. The enzyme system of Avena coleoptiles oxidizing IAAld to IAA can also be easily separated by Sephadex gel filtration and its independent activity demonstrated in the total absence of tryptophol formation. Based on the heterogeneous properties of the two activities, metabolism of IAAld in Avena coleoptiles is believed to be mediated by two independent enzyme systems without the intervention of a mutase or a dismutation mechanism.     

Solution‐Processed Low‐Bandgap CuIn(S,Se)2 Absorbers for High‐Efficiency Single‐Junction and Monolithic Chalcopyrite‐Perovskite Tandem Solar Cells

A novel molecular‐ink deposition route based on thiourea and N,N‐dimethylformamide (DMF) that results in a certified solar cell efficiency world record for non‐vacuum deposited CuIn(S,Se)₂ (CIS) absorbers and non‐vacuum deposited absorbers with a bandgap of 1.0 eV, is presented. It is found that by substituting the widely employed solvent dimethyl sulfoxide with DMF, the coordination chemistry of InCl₃ could be altered, dramatically improving ink stability, enabling up to tenfold increased concentrations, omitting the necessity for elevated ink temperatures, and radically accelerating the deposition process. Furthermore, it is shown that by introducing compositionally graded precursor films, film porosity, compositional gradients, and the surface roughness of the absorbers are effectively reduced and device conversion efficiencies are increased up to 13.8% (13.1% certified, active area). The reduced roughness is also seen as crucial to realize monolithically interconnected CIS‐perovskite tandem devices, where semitransparent MAPbI₃ devices are directly deposited on the CIS bottom cell. Confirming the feasibility of this approach, monolithic devices with near perfect voltage addition between subcells of up to 1.40 V are presented.     

An additional HpaII polymorphism in exon 2 of the human platelet membrane glycoprotein IIIa gene

A novel HpaII polymorphic site caused by a TG transversion at codon 40 of the GP3a locus is described. It was found together with another polymorphic HpaII site at codon 33. Both are associated with the immunologically defined HPA-1b antigen.     

The effect of climatic gradients, topographic variation and species traits on the beta diversity of rain forest trees

Aim  We assessed the rates of turnover of tree species with distance (beta diversity) in wet forests of the Western Ghats (WG) complex of India to see whether climate, topographic variation or species traits influence beta diversity.
Location  The Western Ghats is a chain of mountains about 1600 km in length, running parallel to the western coast of the Indian Peninsula from above 8° N to almost 21° N latitude.
Methods  We used data from 60 small plot inventories concentrated in three regions: the southernmost part of the Western Ghats (SWG) (8°24' to 9°37' N), the Nilgiri Hills (11°12' to 11°14' N), and the central Western Ghats (CWG) (12°32' to 14°51' N). We used Sorensen's index (SI) to estimate the similarity in species composition between two plots and regressed SI against the logarithm of the distance between plots to assess beta diversity. A bootstrapping procedure provided confidence intervals for regression coefficients. To test for the effects of climate, we regressed seasonality differences between plots against SI for low-elevation (< 800 m) plots along the north–south axis, and all plots in the SWG. We assessed the impact of the rainfall gradient in the Kogar region.
Results  Among all three regions, beta diversity was highest along the latitudinal axis, and along the rainfall gradient in the Kogar region. Differences in seasonality between sites were strongly related to beta diversity along the north–south seasonality gradient and within the SWG. Within the three regions, beta diversity was highest in the region with the strongest rainfall gradient and lowest for the topographically heterogeneous SWG. Beta diversity did not differ between forest strata and dispersal modes.
Main conclusions  We conclude that climate, particularly seasonality, is probably the primary driver of beta diversity among rain forest trees of the Western Ghats complex.