Otolith resorption induced by anaerobic stress in the goldfish, Carassius auratus

To examine otolith resorption induced by anaerobic stress, ⁴⁵Ca-prelabelled goldfish, Carassius auratus , were kept in oxygen-deficient ambient water (O₂ < 0.5 .1 1⁻¹, 26° C) for 2 days and otoliths (asterisci) were analysed for ⁴⁵Ca retention. In a second experiment, fish were anaerobically stressed for 2 days, and then received a single intraperitoneal injection of ⁴⁵Ca. They were maintained under stress for one more day and killed to examine ⁴⁵Ca deposition in otoliths. Plasma was analysed for total and radioactive calcium. Otoliths (lapilli) were examined for stress-induced check formation by scanning electron microscopy (SEM).
Stress significantly reduced plasma calcium levels and the rate of calcium retention in otoliths, which was calculated from the ⁴⁵Ca specific activity of the plasma. On the other hand, the rate of calcium deposition in otoliths was the same in the stressed as in the control fish. SEM observation revealed that the applied stress resulted in a check formation in otoliths. These results indicate that a 48-h stress of oxygen deficiency induces calcium resorption in otoliths.     

The effect of water status and season on the incorporation of 14CO2 and [14C]-acetate into resin and rubber fractions in guayule

The effects of drought stress and season on both allocation of photosynthates to stems and leaves and potential for stem rubber synthesis were studied in guayule ( Parthenium argentatum Gray USDA line 11604). Two-year-old plants grown under field conditions in the Negev desert of Israel were subjected to different irrigation regimes, and water status was assessed by measuring the relative water content (RWC). Undetached plant tips were exposed to a 1 h pulse of ¹⁴CO₂, followed by a 24 h chase. ¹⁴C fixed and translocated to different plants parts and notably ¹⁴C incorporation into rubber and resin fractions was determined. The potential of detached branch slices to incorporate [¹⁴C]-acetate into rubber was also studied. A higher percentage of fixed ¹⁴C was translocated from shoot tips in winter (28–30%) than in summer (15–18%). The percentage of [¹⁴C]-acctate incorporated into the rubber fraction by stem slices was maximal in winter (20%) and minimal in summer (3–5%) in both cases in the absence of drought stress. In summer the translocation of photosynthates into stems was inversely related to plant RWC, dropping from 18% three days after irrigation to 3% 14 days later, and the potential of stems to synthesise rubber was high under drought conditions and low in well irrigated plants.     

Tansley Review No. 95: 15N natural abundance in soil–plant systems

The following citations were erroneously omitted from the 'References':
Groffman PM, Zak DR, Christensen S, Mosier A, Tiedje JM. 1993. Early spring nitrogen dynamics in a temperate forest landscape. Ecology 74 : 1579–1585.
Handley LL, Brendel O, Scrimgeour CM, Schmidt S, Raven JA, Turnbull MH, Stewart GR. 1996. The ¹⁵N natural abundance patterns of field-collected fungi from three kinds of ecosystems. Rapid Communications in Mass Spectrometry 10 : 974–978.
Handley LL, Daft MJ, Wilson J, Scrimgeour CM, Ingleby K, Sattar, MA. 1993. Effects of the ecto- and VA-mycorrhizal fungi Hydnagium carneum and Glomus clarum on the δ¹⁵N and δ¹³C values of Eucalyptus globulus and Ricinus communis. Plant, Cell and Environment 16 : 375–382.
Handley LL, Odee D, Scrimgeour CM. 1994. δ¹⁵N and δ¹³C patterns in savanna vegetation: dependence on water availability and disturbance. Functional Ecology 8 : 306–314.
Handley LL, Raven JH. 1992. The use of natural abundance of nitrogen isotopes in plant physiology and ecology: commissioned review. Plant, Cell and Environment 15 : 965–985.
Handley LL, Scrimgeour CM. 1997. Terrestrial plant ecology and ¹⁵N natural abundance: the present limits to interpretation for uncultivated systems with original data from a Scottish old field. Advances in Ecological Research 27 : 133–212.
Hansen AP, Pate JS. 1987. Evaluation of the ¹⁵N natural abundance method and xylem sap analysis for assessing N₂ fixation of understorey legumes in jarrah ( Eucalyptus marginata Donn ex Sm.) forest in S.W. Australia. Journal of Experimental Botany 38 : 1446–1458.
New Phytologist apologizes unreservedly to all authors of the above papers for this error.     

Population Dynamics of Pseudomonas syringae pv. tomato Strains on Tomato Cultivars Rio Grande and Rio Grande-Pto under Field Conditions

We examined the effects of the Pto resistance locus on the population dynamics of Pseudomonas syringae pv. tomato (Pst) strains in field experiments with the nearly isogenic tomato lines Rio Grande (RG, susceptible to Pst races 0 and 1) and Rio Grande-Pto (RG-Pto, resistant to Pst race 0, susceptible to Pst race 1). Pst strain SM78-1Sm^r (race 0) grew well under field conditions and caused ample bacterial speck disease on susceptible RG plants. In contrast, strain DC3000 failed to establish large populations when inoculated onto field grown RG plants. Mean population sizes of SM78-1Sm^r were 4–5 orders of magnitude larger on RG than RG-Pto plants indicating that RG-Pto plants were highly effective in attenuating pathogen population development. Most of the sampled leaflets from RG-Pto field plots harboured small numbers of SM78-1Sm^r. However, population sizes SM78-1Sm^r as large as 10⁵–10⁶ CFU were found on a few leaflets. Bacteria isolated from these leaflets had phenotypes characteristic of Pst race 1 strains. In growth chamber plant assays, the bacterial strains grew well and caused typical speck lesions on RG-Pto plants. The strains appeared to be race-shift mutants of SM SM78-1Sm^r. Interestingly, results from DNA hybridization experiments demonstrated that the race-shift mutants were deleted for the avirulence gene, avrPto but not for avrPtoB.     

Novel role of Wag31 in protection of mycobacteria under oxidative stress

Wag31 of Mycobacterium tuberculosis belongs to the DivIVA family of proteins known to regulate cell morphology in Gram-positive bacteria. Here we demonstrate an unrecognized, novel role of Wag31 in oxidatively stressed mycobacteria. We report the cleavage of penicillin-binding protein 3 (PBP3) by the intramembrane metalloprotease Rv2869c (MSMEG_2579) in oxidatively stressed cells. Amino acids ¹⁰²A and ¹⁰³A of PBP3 are required for Rv2869c-mediated cleavage. Wag31_MTB, by virtue of its interaction with PBP3 through amino acid residues ⁴⁶NSD⁴⁸, protects it from oxidative stress-induced cleavage. PBP3 undergoes cleavage in Mycobacterium smegmatis (strain PM2) harbouring wag31 (Δ⁴⁶NSD⁴⁸) instead of the wild type, with concomitant reduction in ability to withstand oxidative stress. Overexpression of Wag31(Δ⁴⁶NSD⁴⁸) attenuates the survival of M. tuberculosis in macrophages with concomitant cleavage of PBP3, and renders the organism more susceptible towards hydrogen peroxide as well as drugs which generate reactive oxygen species, namely isoniazid and ofloxacin. We propose that targeting Wag31 could enhance the activity of mycobactericidal drugs which are known to generate reactive oxygen species.     

Changes in free amino acids and osmotic adjustment in leaves of water-stressed bean

Bean ( Phaseolus vulgaris L. cv. Topcrop) plants were raised in a growth chamber in small pots or flower boxes and kept at full water regime until the full development of primary leaves (14–16 days). Both potted and flower box-grown plants were subjected to a gradually increased water stress of about 60–70 kPa day⁻¹ leaf water potential (stressed plants) or full water regime (control). The water potential, osmotic potential and turgor pressure in freshly detached primary leaves and osmotic potential at zero turgor were calculated using pressure/volume curves. Changes in free amino acids and amides were also measured in parallel trials. Water relation parameters documented that in the stressed leaves there was moderate osmotic adjustment, which was more evident in the potted plants. If considered 0% ionised, the accumulation of free amino acids and amides (μmol g⁻¹ H₂O) accounts for a van't Hoff's value of about 10.2 kPa in the small pot-grown and 5.5 kPa in the box-grown plants. The values are twice as high if considered 100% ionised. Proline accumulation accounted for about 6.4% of the pool enlargement in the potted plants and 22.3% in the flower box plants.     

Homologous Mammalian Brain Cell Lysate System for the Initiation and Translation of Exogenous mRNAs

Abstract: The rate of protein synthesis in mammalian brain tissue is affected by a variety of physiological conditions, both natural and induced. The process of initiation may be involved in some of the observed changes, although as yet the actual rates of initiation of natural mRNAs have not been directly measured in these circumstances. One approach to studying the regulation of protein synthesis in brain tissue would be to utilize a homologous cell-free system to examine in vitro the translation of various added mRNAs. The present report describes a micrococcal nuclease-treated cell-free lysate system derived from fetal mouse brain tissue which is capable of actively initiating and translating exogenously added mRNA. Sodium dodecyl sulfate-polyacrylamide slab gel electrophoretic analysis of the specific protein products of the reaction mixture allowed a qualitative and quantitative assessment of the translational process under a variety of experimental conditions. Optimal conditions for mRNA-dependent protein synthesis were the following: 30°C incubation temperature; 80–100 mM-KCl; 2.1 mM-Mg²⁺; 50 μM-spermhe; and 10 μg/ml poly A(+) mRNA. Incorporation of L-[³⁵S]methionine into proteins required ATP, GTP, and an energy regenerating system. The addition of saturating amounts of a homologous "initiation factors" fraction stimulated incorporation twofold during the first 20 min of incubation, while the patterns of inhibition observed upon the addition of 5 × 10^-5 M-aurin tricarboxylic acid at various periods during incubation demonstrated the occurrence of multiple rounds of initiation.