Ca(2+)-permeable, outwardly-rectifying K+ channels in mesophyll cells of Arabidopsis thaliana

Advances in cannulation techniques and instruments have helped in difficult bile duct cannulation and thus stone extraction. For small common bile duct (CBD) stones, endoscopic papillary balloon dilatation has been proposed as an alternative to endoscopic papillotomy (EPT). The technique must undergo further evaluation before recommending its routine use. For most patients with bile duct stones, EPT remains the method of choice. Out of 8204 patients treated in three surgical endoscopy centers (Chile, Germany, and India), 86% to 91% of all CBD stones could be extracted subsequently after EPT using a Dormia basket; 4% to 7% required mechanical lithotripsy (ML) before removal and 3% to 10% of the patients needed other sophisticated techniques, such as electrohydraulic lithotripsy (EHL), laser-induced shock-wave lithotripsy (LISL), or extracorporeal shock-wave lithotripsy (ESWL). The local expertise and availability of equipment determines the choice of method used. In general, EHL or LISL is used for impacted CBD stones including stones in Mirizzi syndrome refractory to ML. ESWL is best suited for intrahepatic stones. Permanent stenting can be offered to poor risk patients instead of extensive procedures to clear the bile duct. Using currently available nonsurgical techniques, fewer than 1% of all patients with bile duct stones still require surgical intervention.     

A comparison of gene organization in the zwf region of the genomes of the cyanobacteria Synechococcus sp. PCC 7942 and Anabaena sp. PCC 7120

The region of the genome encoding the glucose-6-phosphate dehydrogenase gene zwf was analysed in a unicellular cyanobacterium, Synechococcus sp. PCC 7942, and a filamentous, heterocystous cyanobacterium, Anabaena sp. PCC 7120. Comparison of cyanobacterial zwf sequences revealed the presence of two absolutely conserved cysteine residues which may be implicated in the light/dark control of enzyme activity. The presence in both strains of a gene fbp, encoding fructose-1,6-bisphosphatase, upstream from zwf strongly suggests that the oxidative pentose phosphate pathway in these organisms may function to completely oxidize glucose 6-phosphate to CO2. The amino acid sequence of fructose-1,6-bisphosphatase does not support the idea of its light activation by a thiol/disulfide exchange mechanism. In the case of Anabaena sp. PCC 7120, the tal gene, encoding transaldolase, lies between zwf and fbp.     

Cotranscription of a GTPase gene from the cyanobacterium Synechocystis PCC 6803 and a P-type Ca(2+)-ATPase gene

Near-infrared spectroscopy is a technique used to monitor cerebral oxygenation. To validate the method, we measured regional oxygen saturation (rSo2) in the brains of 18 dead subjects (mean age, 74.4 +/- 14.6 years) 19.8 +/- 18.2 h (range, 1-73) after cessation of systemic circulation, and in 15 healthy probands (mean age, 34.2 +/- 8.7 years) with an INVOS 3100 cerebral oximeter. The mean (+/-SD) rSo2 in the dead subjects was 51.0 +/- 26.8% [range, 6-88%; left, 48.4 +/- 28.0% (n = 21); right, 54.4 +/- 25.7% (n = 16)]. The mean rSo2 in the control group was 68.4 +/- 5.2% (range, 60-76%; left, 68.1 +/- 5.0%; right, 68.7 +/- 5.6%). After removal of the brain at autopsy in five of the dead subjects, the rSo2 was 73.4 +/- 13.3% (15 measurements). Six of 18 of the dead subjects had values above the lowest values found in the healthy adults (> or = 60%). These findings raise concerns about the validity of cerebral rSo2 data in adults obtained by the INVOS 3100 system.     

Diversity and molecular evolution of the RPS2 resistance gene in Arabidopsis thaliana

The RPS2 gene in Arabidopsis thaliana governs resistance to strains of the bacterial pathogen, Pseudomonas syringae pv. tomato, that express the avrRpt2 gene. The two loci are involved in a gene-for-gene interaction. Seventeen accessions of A. thaliana were sequenced to explore the diversity present in the coding region of the RPS2 locus. An unusually high level of nucleotide polymorphisms was found (1.26%), with nearly half of the observed polymorphisms resulting in amino acid changes in the RPS2 protein. Seven haplotypes (alleles) were identified and their evolutionary relationships deduced. Several of the alleles conferring resistance were found to be closely related, whereas susceptibility to disease was conferred by widely divergent alleles. The possibility of selection at the RPS2 locus is discussed.     

The TERMINAL FLOWER2 (TFL2) gene controls the reproductive transition and meristem identity in Arabidopsis thaliana

A new mutant of Arabidopsis thaliana that initiates flowering early and terminates the inflorescence with floral structures has been identified and named terminal flower2 (tfl2). While these phenotypes are similar to that of the terminal flower1 (tfl1) mutant, tfl2 mutant plants are also dwarfed in appearance, have reduced photoperiod sensitivity and have a more variable terminal flower structure. Under long-day and short-day growth conditions tfl1 tfl2 double mutants terminate the inflorescence without development of lateral flowers; thus, unlike tfl1 single mutants the double mutant inflorescence morphology is not affected by day length. The enhanced phenotype of the double mutant suggests that TFL2 acts in a developmental pathway distinct from TFL1. The complex nature of the tfl2 single mutant phenotype suggests that TFL2 has a regulatory role more global than that of TFL1. Double mutant analysis of tfl2 in combination with mutant alleles of the floral meristem identity genes LEAFY and APETALA1 demonstrates that TFL2 function influences developmental processes controlled by APETALA1, but not those regulated by LEAFY. Thus, the TFL2 gene product appears to have a dual role in regulating meristem activity, one being to regulate the meristem response to light signals affecting the development of the plant and the other being the maintenance of inflorescence meristem identity.     

Effect of aluminum on cytoplasmic Ca2+ homeostasis in root hairs of Arabidopsis thaliana (L.)

Aluminum inhibition of root growth is a major world agricultural problem where the cause of toxicity has been linked to changes in cellular calcium homeostasis. Therefore, the effect of aluminum ions (Al) on changes in cytoplasmic free calcium concentration ([Ca2+]c) was followed in root hairs of wild-type, Al-sensitive and Al-resistant mutants of Arabidopsis thaliana (L.) Heynh. Generally, Al exposure resulted in prolonged elevations in tip-localized [Ca2+]c in both wild-type and Al-sensitive root hairs. However, these Al-induced increases in [Ca2+]c were not tightly correlated with growth inhibition, occurring up to 15 min after Al had induced growth to stop. Also, in 32% of root hairs examined growth stopped without a detectable change in [Ca2+]c. In contrast, Al-resistant mutants showed little growth inhibition in response to AlCl3 exposure and in no case was a change in [Ca2+]c observed. Of the other externally applied stresses tested (oxidative and mechanical stress), both were found to inhibit root hair growth, but only oxidative stress (H2O2, 10 microM) caused a prolonged rise in [Ca2+]c similar to that induced by Al. Again this increase occurred after growth had been inhibited. The lack of a tight correlation between Al exposure, growth inhibition and altered [Ca2+]c dynamics suggests that although exposure of root hairs to toxic levels of Al causes an alteration in cellular Ca2+ homeostasis, this may not be a required event for Al toxicity. The elevation in [Ca2+]c induced by Al also strongly suggests that the phytotoxic action of Al in root hairs is not through blockage of Ca2(+)-permeable channels required for Ca2+ influx into the cytoplasm.     

EIN4 and ERS2 are members of the putative ethylene receptor gene family in Arabidopsis

The Arabidopsis ethylene receptor gene ETR1 and two related genes, ERS1 and ETR2, were identified previously. These three genes encode proteins homologous to the two-component regulators that are widely used for environment sensing in bacteria. Mutations in these genes confer ethylene insensitivity to wild-type plants. Here, we identified two Arabidopsis genes, EIN4 and ERS2, by cross-hybridizing them with ETR2. Sequence analysis showed that they are more closely related to ETR2 than they are to ETR1 or ERS1. EIN4 previously was isolated as a dominant ethylene-insensitive mutant. ERS2 also conferred dominant ethylene insensitivity when certain mutations were introduced into it. Double mutant analysis indicated that ERS2, similar to ETR1, ETR2, ERS1, and EIN4, acts upstream of CTR1. Therefore, EIN4 and ERS2, along with ETR1, ETR2, and ERS1, are members of the ethylene receptor-related gene family of Arabidopsis. RNA expression patterns of members of this gene family suggest that they might have distinct as well as redundant functions in ethylene perception.     

Constitutive non-inducible expression of the Arabidopsis thaliana Nia 2 gene in two nitrate reductase mutants of Nicotiana plumbaginifolia

We have isolated a haploid cell line of N. plumbaginifolia, hNP 588, that is constitutive and not inducible for nitrate reductase. Nitrate reductase mutants were isolated from hNP 588 protoplasts upon UV irradiation. Two of these nitrate reductase-deficient cell lines, nia 3 and nia 25, neither of which contained any detectable nitrate reductase activity, were selected for complementation studies. A cloned Arabidopsis thaliana nitrate reductase gene Nia 2 was introduced into each of the two mutants resulting in 56 independent kanamycin-resistant cell lines. Thirty of the 56 kanamycin-resistant cell lines were able to grow on nitrate as the sole nitrogen source. Eight of these were further analyzed for nitrate reductase enzyme activity and nitrate reductase mRNA production. All eight lines had detectable nitrate reductase activity ranging from 7% to 150% of wild-type hNP 588 callus. The enzyme activity levels were not influenced by the nitrogen source in the medium. The eight lines examined expressed a constitutive, non-inducible 3.2 kb mRNA species that was not present in untransformed controls.     

The role of inorganic phosphate in regulating the kinetics of inositol 1,4,5-trisphosphate-induced Ca2+ release: a putative role for endoplasmic reticulum phosphate transporters

The effects of phosphate and acylphosphonate phosphate transporter inhibitors were investigated on inositol 1,4,5-trisphosphate (InsP3)-induced Ca2+ release from cerebellar microsomes. Although neither changing the phosphate concentration nor adding phosphate transporter inhibitors affected the percentage (extent) of InsP3-induced Ca2+ release, they did, however, affect the transient kinetics of this process. InsP3-induced Ca2+ release is biphasic in nature, arising from two populations of InsP3-sensitive Ca2+ stores which either release Ca2+ in a fast or slow fashion. Altering phosphate concentration or adding phosphate transporter inhibitors appeared to affect only the fast phase component. We therefore suggest that these observations could be explained by the possibility that phosphate transporters only reside in the fast releasing InsP3-sensitive Ca2+ stores.     

Regulation and possible physiological role of the Ca(2+)-dependent K+ channel of cortical collecting ducts of the rat

In the luminal membrane of rat cortical collecting duct (CCD) a big Ca(2+)-dependent and a small Ca(2+)-independent K+ channel have been described. Whereas the latter most likely is responsible for the K+ secretion in this nephron segment, the function of the large-conductance K+ channel is unknown. The regulation of this channel and its possible physiological role were examined with the conventional cell-free and the cell-attached nystatin patch-clamp techniques. Patch-clamp recordings were obtained from the luminal membrane of isolated perfused CCD segments and from freshly isolated CCD cells. Intracellular calcium was measured using the calcium-sensitive dye fura-2. The large-conductance K+ channel was strongly voltage- and calcium-dependent. At 3 mumol/l cytosolic Ca2+ activity it was half-maximally activated. At 1 mmol/l it was neither regulated by cytosolic pH nor by ATP. At 1 mumol/l Ca2+ activity the open probability (Po) of this channel was pH-dependent. At pH 7.0 Po was decreased to 4 +/- 2% (n = 9) and at pH 8.5 it was increased to 425 +/- 52% (n = 9) of the control. At this low Ca2+ activity the Po of the channel was reduced by 1 mmol/l ATP to 8 +/- 4% (n = 6). Cell swelling activated the large-conductance K+ channel (n = 14) and hyperpolarized the membrane potential of the cells by 9 +/- 1 mV (n = 23). Intracellular Ca2+ activity increased after hypotonic stress. This increase depended on the extracellular Ca2+ activity.(ABSTRACT TRUNCATED AT 250 WORDS)