Effects of salt stress on photosynthesis,PSII photochemistry and thermal energy dissipation in leaves of two corn (<Emphasis Type="Italic">Zea mays</Emphasis> L.) varieties

The effect of four different NaCl concentrations (from 0 to 102 mM NaCl) on seedlings leaves of two corn (Zea mays L.) varieties (Aristo and Arper) was investigated through chlorophyll (Chl) a fluorescence parameters, photosynthesis, stomatal conductance, photosynthetic pigments concentration, tissue hydration and ionic accumulation. Salinity treatments showed a decrease in maximal efficiency of PSII photochemistry (F_v/F_m) in dark-adapted leaves. Moreover, the actual PSII efficiency (ϕ_PSII), photochemical quenching coefficient (q_p), proportion of PSII centers effectively reoxidized, and the fraction of light used in PSII photochemistry (%P) were also dropped with increasing salinity in light-adapted leaves. Reductions in these parameters were greater in Aristo than in Arper. The tissue hydration decreased in salt-treated leaves as did the photosynthesis, stomatal conductance (g _s) and photosynthetic pigments concentration essentially at 68 and 102 mM NaCl. In both varieties the reduction of photosynthesis was mainly due to stomatal closure and partially to PSII photoinhibition. The differences between the two varieties indicate that Aristo was more susceptible to salt-stress damage than Arper which revealed a moderate regulation of the leaf ionic accumulation.     

Anatomical changes induced by increasing NaCl salinity in three fodder shrubs, <Emphasis Type="Italic">Nitraria retusa</Emphasis>, <Emphasis Type="Italic">Atriplex halimus</Emphasis> and <Emphasis Type="Italic">Medicago arborea</Emphasis>

Nitraria retusa and Atriplex halimus (xero-halophytes) plants were grown in the range 0–800 mM NaCl while Medicago arborea (glycophyte) in 0–300 mM NaCl. Plants were harvested after 120 days of salt-treatment. The present study was designed to study the effect of salinity on root, stem and leaf anatomy, water relationship, and plant growth in greenhouse conditions. Salinity induced anatomical changes in the roots, stems and leaves. The cuticle and epidermis of N. retusa and A. halimus stems were unaffected by salinity. However, root anatomical parameters (root cross section area, cortex thickness and stele to root area ratio), and stem anatomical parameters (stem cross section area and cortex area) were promoted at 100–200 mM NaCl. Indicating that low to moderate salinity had a stimulating effect on root and stem growth of these xero-halophytic species. At higher salinities, root and stem structures were altered significantly, and their percentages of reduction were higher in A. halimus than in N. retusa whereas, in M. arborea, they were strongly altered as salinity rose. NaCl (100–300 mM) reduced leaf water content by 21.2–56.2% and specific leaf area by 51–88.1%, while increased leaf anatomical parameters in M. arborea (e.g. increased thickness of upper and lower epidermis, palisade and spongy mesophyll, entire lamina, and increased palisade to spongy mesophyll ratio). Similar results were evidenced in A. halimus leaves with salinity exceeding 100 mM NaCl. Leaves of N. retusa were thinner in salt-stressed plants while epidermis thickness and water content was unaffected by salinity. The size of xylem vessel was unchanged under salinity in the leaf’s main vein of the three species while we have increased number in M. arborea leaf main vein in the range of 200–300 mM NaCl. A longer distance between leaf vascular bundle, a reduced size and increased number of xylem vessel especially in stem than in root vascular system was evidenced in M. arborea treated plants and only at (400–800 mM) in the xero-halophytic species. The effects of NaCl toxicity on leaf, stem and root ultrastructure are discussed in relation to the degree of salt resistance of these three species. Our results suggest that both N. retusa and A. halimus show high tolerance to salinity while M. arborea was considered as a salt tolerant species.     

Expression of a ferredoxin-dependent glutamate synthase gene in mesophyll and vascular cells and functions of the enzyme in ammonium assimilation in Nicotiana tabacum (L.)

GLU1 encodes the major ferredoxin-dependent glutamate synthase (Fd-GOGAT, EC 1.4.7.1) in Arabidopsis thaliana (ecotype Columbia). With the aim of providing clues on the role of Fd-GOGAT, we analyzed the expression of Fd-GOGAT in tobacco (Nicotiana tabacum L. cv. Xanthi). The 5′ flanking element of GLU1 directed the expression of the uidA reporter gene in the palisade and spongy parenchyma of mesophyll, in the phloem cells of vascular tissue and in the roots of tobacco. White light, red light or sucrose induced GUS expression in the dark-grown seedlings in a pattern similar to the GLU1 mRNA accumulation in Arabidopsis. The levels of GLU2 mRNA encoding the second Fd-GOGAT and NADH-glutamate synthase (NADH-GOGAT, EC 1.4.1.14) were not affected by light. Both in the light and in darkness, ¹⁵NH₄⁺ was incorporated into [5−¹⁵N]glutamine and [2−¹⁵N]glutamate by glutamine synthetase (GS, EC 6.3.1.2) and Fd-GOGAT in leaf disks of transgenic tobacco expressing antisense Fd-GOGAT mRNA and in wild-type tobacco. In the light, low level of Fd-glutamate synthase limited the [2−¹⁵N]glutamate synthesis in transgenic leaf disks. The efficient dark labeling of [2−¹⁵N]glutamate in the antisense transgenic tobacco leaves indicates that the remaining Fd-GOGAT (15–20% of the wild-type activity) was not the main limiting factor in the dark ammonium assimilation. The antisense tobacco under high CO₂ contained glutamine, glutamate, asparagine and aspartate as the bulk of the nitrogen carriers in leaves (62.5%), roots (69.9%) and phloem exudates (53.2%). The levels of glutamate, asparagine and aspartate in the transgenic phloem exudates were similar to the wild-type levels while the glutamine level increased. The proportion of these amino acids remained unchanged in the roots of the transgenic plants. Expression of GLU1 in mesophyll cells implies that Fd-GOGAT assimilates photorespiratory and primary ammonium. GLU1 expression in vascular cells indicates that Fd-GOGAT provides amino acids for nitrogen translocation. The nucleotide sequence data of the GLU1 gene reported in the present study is available from GenBank with the following accession number: AY189525     

Studies on Manganese uptake in Tilapia mossambica and Salmo gairdnerii

Tilapia mossambica fingerlings, 5 weeks of age, were reared in simulated fresh water medium which was either free of manganese or supplied with manganese at a concentration of 2.5 µg/l. They were fed synthetic diets which were either deficient (2.8 mg Mn/kg dry diet) or supplied with manganese (35.5 mg Mn/kg dry diet). The feeding tests were carried for 10 weeks. Best growth was obtained when the element was supplied in both food and water. When manganese was absent or was supplied only in water or food, the following symptoms were noted: (1) Poor growth, (2) reduced food consumption, (3) loss of equilibrium, and (4) increased mortality. From the results, the daily requirement for manganese by Tilapia for growth and development was calculated to be 1.7 mg/kg live fish.This paper is based on a part of a thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Graduate College of University of Washington, Seattle, Washington.     

A recurrent deletion of DPY19L2 causes infertility in man by blocking sperm head elongation and acrosome formation

An increasing number of couples require medical assistance to achieve a pregnancy, and more than 2% of the births in Western countries now result from assisted reproductive technologies. To identify genetic variants responsible for male infertility, we performed a whole-genome SNP scan on patients presenting with total globozoospermia, a primary infertility phenotype characterized by the presence of 100% round acrosomeless spermatozoa in the ejaculate. This strategy allowed us to identify in most patients (15/20) a 200 kb homozygous deletion encompassing only DPY19L2, which is highly expressed in the testis. Although there was no known function for DPY19L2 in humans, previous work indicated that its ortholog in C. elegans is involved in cell polarity. In man, the DPY19L2 region has been described as a copy-number variant (CNV) found to be duplicated and heterozygously deleted in healthy individuals. We show here that the breakpoints of the deletions are located on a highly homologous 28 kb low copy repeat (LCR) sequence present on each side of DPY19L2, indicating that the identified deletions were probably produced by nonallelic homologous recombination (NAHR) between these two regions. We demonstrate that patients with globozoospermia have a homozygous deletion of DPY19L2, thus indicating that DPY19L2 is necessary in men for sperm head elongation and acrosome formation. A molecular diagnosis can now be proposed to affected men; the presence of the deletion confirms the diagnosis of globozoospermia and assigns a poor prognosis for the success of in vitro fertilization.     

Viral and chloroplastic signals essential for initiation and efficiency of translation in Agrobacterium tumefaciens

The construction of high-level protein expression vectors using the CaMV 35S promoter in concert with highly efficient translation initiation signals for Agrobacterium tumefaciens is a relatively less explored field compared to that of Escherichia coli. In the current study, we experimentally investigated the capacity of the CaMV 35S promoter to direct GFP gene expression in A. tumefaciens in the context of different viral and chloroplastic translation initiation signals. GFP expression and concomitant translational efficiency was monitored by confocal microscopy and Western blot analysis. Among all of the constructs, the highest level of translation was observed for the construct containing the phage T7 translation initiation region followed by the chloroplastic Rubisco Large Subunit (rbcL) 58-nucleotide 5′ leader region including its SD-like sequence (GGGAGGG). Replacing the SD-like (GGGAGGG) with non SD-like (TTTATTT) or replacing the remaining 52 nucleotides of rbcL with nonspecific sequence completely abolished translation. In addition, this 58 nucleotide region of rbcL serves as a translational enhancer in plants when located within the 5′ UTR of mRNA corresponding to GFP. Other constructs, including those containing sequences upstream of the coat proteins of Alfalfa Mosaic Virus, or the GAGG sequence of T4 phage or the chloroplastic atpI and/or PsbA 5′ UTR sequence, supported low levels of GFP expression or none at all. From these studies, we propose that we have created high expression vectors in A. tumefaciens and/or plants which contain the CaMV 35S promoter, followed by the translationally strong T7 SD plus RBS translation initiation region or the rbcL 58-nucleotide 5′ leader region upstream of the gene of interest.     

Effect of acute sleep deprivation and recovery on Insulin-like Growth Factor-I responses and inflammatory gene expression in healthy men

Acute sleep deprivation in humans has been found to increase inflammatory markers and signaling pathways in the periphery through a possible Toll-like receptor 4 (TLR-4). In addition, short duration sleep has been associated with low circulating total Insulin-like Growth Factor-I (IGF-I) concentrations.We aimed to determine whether a total sleep deprivation (TSD) protocol with recovery altered whole-blood gene expression of the proinflammatory cytokines TNF-α and IL-6, as well as TLR-4 expression, and to examine the relationship with circulating concentrations of the IGF-I system. Twelve healthy men participated in a five-day TSD (two control nights followed by one night of sleep deprivation and one night of recovery). Blood was sampled at 0800, before and after sleep deprivation (D2 and D4), and after recovery (D5). It is shown that 25h of sleep deprivation (D4) induced significant increases in mRNA levels of TNF-α and its soluble receptor R1 (P<0.01 respectively), as well as TLR-4 (P<0.05), while IL-6 mRNA levels remained unchanged. Circulating concentrations of free IGF-I were decreased at D4 (P<0.001). One night of recovery was sufficient to restore basal expression levels for TNF-α, sTNF-R1, TLR-4 and circulating IGF-I. Changes in TLR-4 mRNA levels during the protocol correlated positively with those of TNF-α and sTNF-R1 (r = 0.393 and r = 0.490 respectively), and negatively with circulating free IGF-I (r = ?0.494). In conclusion, 25h of sleep deprivation in healthy subjects is sufficient to induce transient and reversible genomic expression of the pro-inflammatory cytokine TNF-α and its R1 receptor, and its mediator TLR-4, with a possible link to IGF-I axis inhibition.     

On the Electroporation Thresholds of Lipid Bilayers: Molecular Dynamics Simulation Investigations

Electroporation relates to the cascade of events that follows the application of high electric fields and that leads to cell membrane permeabilization. Despite a wide range of applications, little is known about the electroporation threshold, which varies with membrane lipid composition. Here, using molecular dynamics simulations, we studied the response of dipalmitoyl-phosphatidylcholine, diphytanoyl-phosphocholine-ester and diphytanoyl-phosphocholine-ether lipid bilayers to an applied electric field. Comparing between lipids with acyl chains and methyl branched chains and between lipids with ether and ester linkages, which change drastically the membrane dipole potential, we found that in both cases the electroporation threshold differed substantially. We show, for the first time, that the electroporation threshold of a lipid bilayer depends not only on the “electrical” properties of the membrane, i.e., its dipole potential, but also on the properties of its component hydrophobic tails.     

Study of a fructose-negative mutant of Rhizobium meliloti

Abstract Rhizobium meliloti grows on fructose as sole carbon source. Following nitrosoguanidine mutagenesis, a mutant of R. meliloti M5N1 was isolated as unable to grow on fructose. Enzyme assays with cell-free extracts showed it to lack significative phosphoglucose isomerase activity. Other enzymes were present at low levels. Both fructose and fructose 6-phosphate were accumulated within this mutant. The in vitro inhibition of fructokinase by fructose 6-phosphate was show. Symbiotic properties remained unaffected in the mutant strain.