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Activities of 26 Al and 10 Be in five chert clasts sampled from two beach ridges of late Pleistocene Lake Lisan, precursor of the Dead Sea in southern Israel, indicate low rates of chert bedrock erosion and complex exposure, burial, and by inference, transport histories. The chert clasts were derived from the Senonian Mishash Formation, a chert-bearing chalk, which is widely exposed in the Nahal Zin drainage basin, the drainage system that supplied most of the material to the beach ridges. Simple exposure ages, assuming only exposure at the beach ridge sampling sites, range from 35 to 354 ky; using the ratio 26 Al/ 10 Be, total clast histories range from 0Ð46 to 4Ð3 My, unrelated to the clasts’ current position and exposure period on the late Pleistocene beach ridges, 160–177 m below sea level. Optically stimulated luminescence dating of fine sediments from the same and nearby beach ridges yielded ages of 20Ð0 s 1Ð4 ka and 36Ð1 s 3Ð3 ka. These ages are supported by the degree of soil development on the beach ridges and correspond well with previously determined ages of Lake Lisan, which suggest that the lake reached its highest stand around 27 000 cal. years BP. If the clasts were exposed only once and than buried beyond the range of significant cosmogenic nuclide production, then the minimum initial exposure and the total burial times before delivery to the beach ridge are in the ranges 50–1300 ky and 390–3130 ky respectively. Alternatively, the initial cosmogenic dosing could have occurred during steady erosion of the source bedrock. Back calculating such rates of rock erosion suggests values between 0Ð4 and 12 m My � 1 .T he relatively long burial periods indicate extended sediment storage as colluvium on slopes and/or as alluvial deposits in river terraces. Some clasts may have been stored for long periods in abandoned Pliocene and early Pleistocene routes of Nahal Zin to the Mediterranean before being transported again back into the Nahal Zin drainage system and washed on to the shores of Lake Lisan during the late Pleistocene. Copyright  2003 John Wiley & Sons, Ltd.

Mesas are ubiquitous landforms in arid and semiarid regions and are often characterized by horizontal stratified erodible rocks capped by more resistant strata. The accepted conceptual model for mesa evolution and degradation considers reduction in the width of the mesa flat-top plateau due to cliff retreat but ignores possible denudation of the mesa flat-top and the rates and mechanism of erosion. In this study we examine mesas in the northeastern hyperarid Negev Desert where they appear in various sizes and morphologies and represent different stages of mesa evolution. The variety of mesas within a single climatic zone allows examination of the process of mesa evolution through time. Two of the four sites examined are characterized by a relatively wide (200–230 m) flat-top and a thick caprock whereas the other two are characterized by a much narrower remnant flat-top (several meters) and thinner caprock. We use the concentration of the cosmogenic nuclide 10Be for: (a) determining the chronology of the various geomorphic features associated with the mesa; and (b) understanding geomorphic processes forming the mesa. The 10Be data, combined with field observations, suggest a correlation between the width of flat-top mesa and the denudation and cliff retreat rates. Our results demonstrate that: (a) cliff retreat rates decrease with decreasing width of the flat-top mesa; (b) vertical denudation rates increase with decreasing width of the flat-top mesa below a critical value (~60 m, for the Negev Desert); (c) the reduction in the width of the flat-top mesa is driven mainly by cliff retreat accompanied by extremely slow vertical denudation rate which can persist for a very long time (>106 Ma); and (d) when the width of the mesa decreases below a certain threshold, its rate of denudation increases dramatically and mesa degradation is completed in a short time. Copyright © 2014 John Wiley & Sons, Ltd.

— Photoreactivation in the filamentous soil fungus Trichoderma harzianum is of interest because its blue, UVA photoreceptors (cryptochromes) may share homology with DNA photolyases. Furthermore, this organism antagonizes, by mycoparasitism, a number of soil-borne pathogens. Photoreactivation is thus important as one of the factors that may contribute to survival in the field. Exposure of asexually produced spores (conidia) to UVC inhibits germination. Nongerminating spores either do not swell or are inhibited later in germination, swelling but failing to put out a germ tube. Both types of inhibition can be reversed by photoreactivation with visible and UVA (320-400 nm) light, restoring high germination percentages. Conidia of mutants lacking the normal greenish pigmentation are more sensitive to UVC (200-280 nm) than wild-type conidia but photoreactivation still occurs. The action spectrum for photoreactivation indicates that T. harzianum has a DNA photolyase with a pterin as second chromophore. The most effective wavelengths for photoreactivation correspond to valleys, rather than peaks, in the action spectrum for photoinduction of sporulation. Furthermore, mutants with defects in photoinduction of sporulation (dimY) are not defective in photoreactivation. Induction of sporulation and DNA photorepair, while sharing parts of the blue/UVA spectrum, are different, by spectroscopic, kinetic and genetic criteria.

Gypsum and halite are the most common salts in reg soils developed on alluvial parent material under extremely arid conditions in the Negev Desert, Israel. The aim of this paper is to document the changes in the micromorphology of these salts at different stages of Reg soil development on two alluvial fan chronosequences. The micromorphological analyses included thin section observations and scanning electron microscope and electron microprobe analyses. In this arid soil environment, gypsum and halite possess a variety of crystal forms which may change with depth in a single profile and/or between profiles of different ages. The variety of crystal forms results from changes in the microenvironmental conditions that occur in desert reg soils over time. Poikilitic lenticular gypsum is found in all Reg soils and is distributed throughout the profiles. The conditions needed for such crystals to form are high ionic impurities and deposition in a void system where space is not limiting. Microcrystalline alabastrine gypsum is only found in mature Reg soils and is crystallized when the profile has high amounts of fine material and a well-developed desert pavement. In a well-developed Reg soil, profile indicators, such as a well-developed desert pavement and high amounts of fine earth, limit the leaching depth and cause gypsum deposition from supersaturated soil solutions under high evaporation rates close to the surface. Prismatic and fibrous gypsum are less common. Low amounts of prismatic gypsum are found in young and mature soils while fibrous gypsum is found only in mature soils in re-cemented shattered gravel. The halite crystal form is mainly cubic with low amounts of host material incorporated into the crystal. It occurs predominantly in mature Reg soil profiles through the crystallization from supersaturated soil solutions at the depth of maximum water penetration. Although the alabastrine, prismatic and fibrous gypsum and cubic halite are deposited in a displacive manner, no correlation was found between their occurrence and the distribution of shattered gravel in the soil profile.

The main objective of the present paper is to present an integrated approach to the study of faulting stages in coarse alluvial deposits. The study site is the alluvial fan of Nahal Shehoret, presently under an extremely arid regime. The exposure of fault scarps on the fan surfaces enables the identification of several geomorphic indicators employed in analysing and separating faulting events and periods of quiescence: (a) the nature of fault scarp topography; (b) soil catenary development on fault scarps; (c) buried paleosols in alluvial deposits; (d) colluvial bodies; (e) rotated clasts along fault planes. These indicators enable us to determine, at all sites studied, the total amount of displacement, to separate faulting events and the amount of their displacement per event, and to evaluate scarp stability and the duration of periods of tectonic quiescence.

— Mutants with altered fluorescence are likely to be modified in pigment composition or photochemistry. They can thus help address a variety of problems in photobiology, particularly in the areas of photosynthesis, photomorphogenesis and photobehavior. To aid in the screening for such mutants, we have developed an instrument for detecting fluorescence intensity relative to scattered light intensity. The instrument employs fiber optics for illumination and detection, and an analog electronic circuit to compute the ratio between fluorescence and scattered light. An application of the fluorometer to screen for Arabidopsis mutants altered in chlorophyll accumulation is described.

The presence of herpes simplex virus (HSV) antigens was shown by immunofluorescence staining in 26 of 66 (39.3%) specimens of clinically healthy gingiva, but only one sample contained infectious virus. HSV DNA sequences were clearly identified in intact gingival cells by dot blot hybridization in one specimen, and a weak pattern in a second one. Both specimens harbored viral antigens. These findings of viral genome and protein expression suggest that the virus is present in the latent form in the gingiva. J Periodontol 1992; 63:502–506.