Salinity tolerance in different cultivars of barley (Hordeum vulgare L.)

Seven barley(Hordeum vulgäre L.) cultivars tested varied greatly in their responses to root medium salinity (electrical conductivity of 3, 5, 10, 15 and 20 dS nr^-1)-lant growth was relatively more adversely affected than seed germination. Dry/fresh mass ratio increased at higher salinity levels in all barley cultivars indicating reduced water uptake. Higher K/Na ratio in plant shoots compared to that in the root medium solution indicated selective uptake of K that seems to be among processes involved in tolerance of cultivars to salinity stress.     

Targeting Homologous Recombination in Notch-Driven C. elegans Stem Cell and Human Tumors

Mammalian NOTCH1-4 receptors are all associated with human malignancy, although exact roles remain enigmatic. Here we employ glp-1(ar202), a temperature-sensitive gain-of-function C. elegans NOTCH mutant, to delineate NOTCH-driven tumor responses to radiotherapy. At ≤20°C, glp-1(ar202) is wild-type, whereas at 25°C it forms a germline stem cell⁄progenitor cell tumor reminiscent of human cancer. We identify a NOTCH tumor phenotype in which all tumor cells traffic rapidly to G2⁄M post-irradiation, attempt to repair DNA strand breaks exclusively via homology-driven repair, and when this fails die by mitotic death. Homology-driven repair inactivation is dramatically radiosensitizing. We show that these concepts translate directly to human cancer models.     

Lipid composition of thylakoid membranes of cadmium treated wheat seedlings.

Cadmium (200 ppm) applied through the rooting medium to 30-day-old wheat plants decreased chlorophyll content, net CO2 exchanges and PSII activity by 34, 54 and 43% respectively. Thylakoid total lipids, total glycolipids, total phospholipids and total neutral lipids decreased by 22, 23, 12 and 25%, respectively, under cadmium treatment. Thylakoid membrane glycolipids had three major constituents, viz. monogalactosyl diacylglycerol, digalactosyl diacylglycerol and sulphoquinovosyl diacylglycerol. Monogalactosyl diacylglycerol and digalactosyl diacylglycerol contents decreased by 32 and 27%, respectively, under cadmium. Cadmium application also decreased the concentration of phosphatidyl glycerol and phosphatidyl choline to the extent of about 57 and 31%, respectively. On the other hand, phosphatidic acid and free fatty acids content showed an increase. These compositional changes in thylakoid membranes might be responsible for reduced PSII activity and rate of photosynthesis as observed under cadmium treatment.     

Dual role of osteoblastic proenkephalin derived peptides in skeletal tissues

Proenkephalin encodes a group of small peptides with opiate-like activity, the endogenous opioids, known to function as neurohormones, neuromodulators, and neurotransmitters. Recently, we have demonstrated that in addition to its abundance in fetal brain tissue, proenkephalin is highly expressed in nondifferentiated mesodermal cells of developing fetuses. We identified the skeletal tissues, bone, and cartilage as major sites of proenkephalin expression. To examine the possibility that proenkephalin is involved in bone development we have studied the expression of this gene in bone-derived cells, its modulation by bone active hormones, and the effects of enkephalin-derived peptides on osteoblastic phenotype. Our studies revealed that osteoblastic cells synthesize high levels of proenkephalin mRNA which are translated, and the derived peptides are secreted. Reciprocal interrelationships between osteoblast maturation and proenkephalin expression were established. These results together with our observations demonstrating inhibitory effects of proenkephalin-derived peptides on osteoblastic alkaline phosphatase activity, strongly support the notion that proenkephalin is involved in bone development. A different direction of research by other investigators has established the capability of the opioid system in the periphery to participate in the control of pain. On the basis of these two lines of observation, we would like to present the following hypothesis: The potential of embryonic skeletal tissue to synthesize proenkephalin-derived peptides is retained in the adult in small defined undifferentiated cell populations. This potential is realized in certain situations requiring rapid growth, such as remodeling or fracture repair. We suggest that in these processes, similarly to the situation in the embryo, the undifferentiated dividing cells produce the endogenous opioids. In the adult these peptides may have a dual function, namely participating in the control of tissue regeneration and in the control of pain. © 1994 Wiley-Liss, Inc.     

Effects of membrane physical parameters on hematoporphyrin-derivative binding to liposomes: A spectroscopic study

Summary Physical parameters of membrane bilayers were studied for their effect on the binding of hematoporphyrin derivative (Hpd), which is used as a sensitizer in photodynamic therapy of cancerous tissues. The purpose of this study was to clarify which parameters were relevant, under physiological conditions, to the selectivity of Hpd binding to cancer cells. Fluorescence spectroscopy was used to measure the relative partitioning of the dye between the lipid and aqueous media. Increasing the microviscosity of the liposomes' membranes by various bilayer additives results in a strong reduction of Hpd binding, to an extent independent of the specific additive. The effect of temperature near the physiological value as well as the effect of cross membrane potential are small. Surface potential does not affect the binding constant, indicating that the binding species does not carry a net electric charge.     

Transposon Mutants of Bradyrhizobium japonicum Altered in Attachment to Host Roots

Transposon mutants of Bradyrhizobium japonicum 110 ARS were produced and screened for changes in attachment ability. Mutant CFK4 produced twice as many piliated cells, attached in 2.5-fold-higher numbers to soybean root segments, and colonized roots in about 2-fold-higher numbers than did the parental strain, 110 ARS. Mutants CFK35 and CFK38 were reduced in their attachment about 2-fold and 3.5-fold, respectively. This corresponded to reductions in piliated cells in their populations, reduced reaction with anti-pilus antiserum, and reduced hydrophobic attachment. Mutants CFK4 and CFK38 nodulated soybeans at about the same level as the parent strain, but CFK35 induced only pseudonodules. Two-dimensional gel analyses of the proteins from the mutants showed relatively few changes in proteins.     

Interactions of troponin subunits: free energy of binary and ternary complexes

We have determined the free energy of formation of the binary complexes formed between skeletal troponin C and troponin T (TnC.TnT) and between troponin T and troponin I (TnT.TnI). This was accomplished by using TnC fluorescently modified at Cys-98 with N-(iodoacetyl)-N'-(5-sulfo-1-naphthyl)ethylenediamine for the first complex and TnI labeled at Cys-133 with the same probe for the other complex. The free energy of the ternary complex formed between troponin C and the binary complex TnT.TnI [TnC.(TnT.TnI)] was also measured by monitoring the emission of 5-(iodoacetamido)eosin attached to Cys-133 of the troponin I in TnT.TnI. The free energies were -9.0 kcal.mol-1 for TnC.TnT, -9.2 kcal.mol-1 for TnT.TnI, and -8.7 kcal.mol-1 for TnC.(TnT.TnI). In the presence of Mg2+ the free energies of TnC.TnT and TnC.(TnT.TnI) were -10.3 and -10.9 kcal.mol-1, respectively; in the presence of Ca2+ the corresponding free energies were -10.6 and -13.5 kcal.mol-1. Mg2+ and Ca2+ had negligible effect on the free energy of TnT.TnI. From these results the free energies of the formation of troponin from the three subunits were found to be -16.8 kcal.mol-1, -18.9 kcal.mol-1, and -21.6 kcal.mol-1 in the presence of EGTA, Mg2+, and Ca2+, respectively. Most of the free energy decrease caused by Ca2+ binding to the Ca2+-specific sites is derived from stabilization of the TnI-TnC linkage.(ABSTRACT TRUNCATED AT 250 WORDS)     

Studies on N2-fixing bacteria associated with the salt-tolerant grass,Leptochloa fusca (L.) Kunth

Summary N₂-fixing bacteria were isolated from the rhizosphere of naturally grown salt tolerant grass (Leptochloa fusca). A broad spectrum of diazotrophs was found to be associated with the roots ofL. fusca. the systematic position of the three isolates, NIAB-1, C-2 and Iso-2 was determined by morphological, biochemical and mol % (G+C) DNA contents. Two isolates were identified asKlebsiella pneumoniae (NIAB-1) andBeijerinckia sp. (Iso-2).¹⁵N enrichment studies confirmed the nitrogen fixing ability of the isolates. The effects of different levels of combined nitrogen (NO ₃ ^– & NH ₄ ⁺ ), pH (5.5–9.0) and salt (NaCl) on nitrogenase activity of the isolates were determined at various time intervals. All isolates exhibited nitrogenase activity even in the presence of 5 mmol/l NO ₃ ^– or NH ₄ ⁺ in a semi-solid medium after 24 h of growth. Maximum nitrogenase activity was observed at alkaline pH and all isolates were able to tolerate up to 3% NaCl in the medium.

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Resumen Se han aíslado bacterias fijadoras de N₂ en la rizosfera del hábitat natural de la graminea halófilaLeptochloa fusca. Un amplio espectro de diazotrofos se encontró asociado con las raíces deL. fusca. La posición sistemática de tres aíslados: NIAB-1, C-2 y Iso-2 se determinó utilizando sus características morfológicas, bioquímicas y el % (G+C) molar del ADN. El aíslado NIAB-1 se identificó comoKlebsiella pneumoniae y el aíslado Iso-2 comoBeijerinckia. sp. Estudios mediante¹⁵N confirmaron la habilidad fijadora de N₂ de los aíslados. Se determinaron periodicamente los efectos de distintos niveles de nitrógeno combinado (NO₃ ^– y NH₄ ⁺), pH (5.5–9.0) y sal (NaCl) en la actividad nitrogenásica de los aíslados. Todas las cepas aísladas mostraron actividad nitrogenásica incluso en presencia de 5mmol/l de NO₃ ^– y NH₄ ⁺ en un medio semisólido desqués de 24 h. de crecimiento. La actividad nitrogenásica máxima se observó a pH alcalino y todos loa aíslados eran capaces de tolerar hasta 3% de NaCl en el medio.

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Résumé Des bactéries fixatrices de l'azote ont été isolées à partir de la rhizosphère de l'herbe halotoléranteLeptochloa fusca développée dans les conditions naturelles. Il a été constaté qu'un large spectre de diazotrophes est associé aux racines de la plante. La position taxonomique de 3 souches isolées, NIAB-1, C-2 et Iso-2, a été déterminée par des critères morphologiques et biochimiques et par le pourcentage de (G+C) de l'ADN. Deux souches on été identifiées commeKlebsiella pneumoniae (NIAB-1) etBeijerinckia sp. (Iso-2). Les études d'enrichissement en¹⁵N ont confirmé l'aptitude des souches à fixer l'azote. les effets de différents niveaux d'azote combiné (NO₃ ^– et NH₄ ⁺), de pH (5.5–9.0) et de sel (NaCl) sur l'activité nitrogénasique des souches ont été déterminés à divers intervalles de temps. Toutes les souches présentent une activité nitrogènase après 24 h de croissance en milieu semi-solide, et cela même en présence de 5 mmol/l de NO₃ ^– ou NH₄ ⁺. L'activité nitrogènase maximum est observée à pH alcalin, et toutes les souches tolèrent jusqu'à 3% de NaCl dans le milieu.