Salicylic acid modulates ozone-induced hypersensitive cell death in tobacco plants

Ozone-tolerant Bel B and ozone-sensitive Bel W3 tobacco cultivars were subjected to acute ozone fumigation (200 p.p.b. for 3 h) and the subcellular localization of H₂O₂ was then studied. H₂O₂ accumulated on the cell walls and plasma membrane of both cultivars but the accumulation pattern differed greatly. H₂O₂ production was high in both cultivars immediately after fumigation, but, in the tolerant Bel B cultivar, after 7 h was only detected in some spongy cells adjacent to epidermal cells. Instead, in the sensitive Bel W3 cultivar, accumulation was still abundant in the cell walls of palisade, spongy and epidermal cells at this time. Significant changes in apoplastic ascorbate pool were noted in both cultivars in the first hours after fumigation. As the reduced ascorbate content remained unchanged, the marked increase in total ascorbate must have originated from the striking increase in dehydroascorbate, particularly in the ozone-sensitive Bel W3. Exposure of plants to ozone resulted in a marked transient increase in both free and conjugated salicylic acid (SA) as well as an increase in the activity of benzoic acid 2-hydroxylase which catalyses SA biosynthesis. SA induction differed greatly in the two cultivars, in that: (1) SA accumulation was far greater in the ozone-sensitive Bel W3 cv. and (2) the maximum SA peak was delayed in Bel W3 and observed only 7 h after fumigation ended. These results suggest that a high SA content, as documented in the ozone-sensitive Bel W3 cultivar, could trigger the production of ROS with subsequent SA-mediated cell-death.     

First report on the presence of Biomphalaria straminea in the municipality of Jaboticatubas,State of Minas Gerais,Brazil

This is the first report on occurrence of Biomphalaria straminea in the district of S?o José de Almeida (municipality of Jaboticatubas) State of Minas Gerais, Brazil. The presence of B. glabrata and B. tenagophila had already been reported in this area. Such municipality is part of the metropolitan region of Belo Horizonte and comprises 60% of the Tourist Complex of Serra do Cipó. Since the 1950s throughout the 1990s, a schistosomiasis prevalence ranging from 15 to 40% has been observed. Although no B. straminea specimen has been found naturally infected in the region, descendants of these snails collected in the area, showed to be experimentally susceptible to Schistosoma mansoni infection reaching rates from 14.6 to 28.6%. Even not being found naturally infected, in the State of Minas Gerais, the possibility that the species B. straminea may keep endemicity foci of schistosomiasis should be regarded, as in the Northeastern region of Brazil where the high density of this planorbid and the social-economic and sanitary conditions enable to the transmission.     

Intestinal NaCl transport in NHE2 and NHE3 knockout mice

Sodium/proton exchangers [Na(+)/H(+) (NHEs)] play an important role in salt and water absorption from the intestinal tract. To investigate the contribution of the apical membrane NHEs, NHE2 and NHE3, to electroneutral NaCl absorption, we measured radioisotopic Na(+) and Cl(-) flux across isolated jejuna from wild-type [NHE(+)], NHE2 knockout [NHE2(-)], and NHE3 knockout [NHE3(-)] mice. Under basal conditions, NHE(+) and NHE2(-) jejuna had similar rates of net Na(+) (approximately 6 microeq/cm(2) x h) and Cl(-) (approximately 3 microeq/cm(2) x h) absorption. In contrast, NHE3(-) jejuna had reduced net Na(+) absorption (approximately 2 microeq/cm(2) x h) but absorbed Cl(-) at rates similar to NHE(+) and NHE2(-) jejuna. Treatment with 100 microM 5-(N-ethyl-N-isopropyl) amiloride (EIPA) completely inhibited net Na(+) and Cl(-) absorption in all genotypes. Studies of the Na(+) absorptive flux (J) indicated that J in NHE(+) jejunum was not sensitive to 1 microM EIPA, whereas J in NHE3(-) jejunum was equally sensitive to 1 and 100 microM EIPA. Treatment with forskolin/IBMX to increase intracellular cAMP (cAMP(i)) abolished net NaCl absorption and stimulated electrogenic Cl(-) secretion in all three genotypes. Quantitative RT-PCR of epithelia from NHE2(-) and NHE3(-) jejuna did not reveal differences in mRNA expression of NHE3 and NHE2, respectively, when compared with jejunal epithelia from NHE(+) siblings. We conclude that 1) NHE3 is the dominant NHE involved in small intestinal Na(+) absorption; 2) an amiloride-sensitive Na(+) transporter partially compensates for Na(+) absorption in NHE3(-) jejunum; 3) cAMP(i) stimulation abolishes net Na(+) absorption in NHE(+), NHE2(-), and NHE3(-) jejunum; and 4) electroneutral Cl(-) absorption is not directly dependent on either NHE2 or NHE3.     

Guanosine enhances glutamate uptake in brain cortical slices at normal and excitotoxic conditions

1. The effect of guanosine on L-[2,3-³H]glutamate uptake was investigated in brain cortical slices under normal or oxygen–glucose deprivation (OGD) conditions.2. In slices exposed to physiological conditions, guanosine (1–100 M) stimulated glutamate uptake (up to 100%) in a concentration-dependent manner when a high (100 M) but not a low (1 M) concentration of glutamate was used.3. In slices submitted to OGD, guanosine 1 and 100 M also increased 100 M glutamate uptake (38 and 70%, respectively).4. The increasing of glutamate and taurine released to the incubation medium in cortical slices submitted to OGD were significantly attenuated by the presence of guanosine in the incubation medium.5. Guanosine prevented the increase in propidium iodide incorporation into cortical slices induced by OGD, indicating a protective role against ischemic injury.6. These results support the hypothesis of a protective role for guanosine during brain ischemia, possibly by activating glutamate uptake into neural cells.     

Two-level evolution of foraging agent communities

This paper presents simulation results of artificial foraging agent communities. The goal of each agent in the community is to find food. Once a food source is found, agents eat portions of it and carry some other portions to the nest (in a manner similar to ants) until the food is depleted. Agents may also communicate food positions when they are near each other. They are given a set of genes that control several characteristics, such as their activity, memory, scepticism, lying, etc. These genes are recombined and propagated by means of sexual reproduction. When one nest is superpopulated with agents, it can break in two nests. Agents can communicate only with those belonging to the same nest, which gives rise to emergent situations of competition and cooperation between the agents in the same nest, as well as competition between different nests. Other emergent phenomena such as the propagation of rumours are also studied.     

Linking cranial kinematics,buccal pressure,and suction feeding performance in largemouth bass

The rate and magnitude of buccal expansion are thought to determine the pattern of water flow and the change in buccal pressure during suction feeding. Feeding events that generate higher flow rates should induce stronger suction pressure and allow predators to draw prey from further away. We tested these expectations by measuring the effects of prey capture kinematics on suction pressure and the effects of the latter on the distance from which prey were drawn-termed suction distance. We simultaneously, but not synchronously, recorded 500-Hz video and buccal pressure from 199 sequences of four largemouth bass, Micropterus salmoides, feeding on goldfish. From the video, we quantified several kinematic variables associated with the head and jaws of the feeding bass that were hypothesized to affect pressure. In a multiple regression, kinematic data accounted for 79.7% of the variation among strikes in minimum pressure. Faster mouth opening and hyoid depression were correlated with lower pressures, a larger area under the pressure curve, and a faster rate of pressure reduction. In contrast, buccal pressure variables explained only 16.5% of the variation in suction distance, and no single pressure variable had a significant relationship with suction distance. Thus, although expected relationships between head kinematics and buccal pressure were confirmed, suction distance was only weakly related to buccal pressure. Three explanations are considered. First, bass may not attempt to maximize the distance from which prey are drawn. Second, the response of prey items to suction-induced flow depends on prey behavior and orientation and is, therefore, subject to considerable variation. Third, previous theoretical work indicates that water velocity decays exponentially with distance from the predator's mouth, indicating that variation among strikes in flow at the mouth opening is compressed away from the mouth. These findings are consistent with other recent data and suggest that suction distance is a poor metric of suction feeding performance.